WATER POLLUTION CONTROL RESEARCH SERIES
14010 DEE 12/70
Treatment of Acid Mine Drainage
U.S. DEPARTMENT OF THE INTERIOR FEDERAL WATER QUALITY ADMINISTRATION
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Reports describe
the results and progress in the control and abatement
of pollution in our Nation's waters» They provide a
central source of information on the research, develop-
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Treatment of Acid Mine Drainage
by
Horizons Incorporated
23800 Mercantile Road
Cleveland, Ohio 44122
for
Federal Water Quality Administration
Department of the Interior
Program No. 14010 DEE
Contract No. 14-12-496
December, 1970
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, IXC. 20402 - Price SI
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FWQA Review Notice
This report has been reviewed by the Federal Water Quality
Administration and approved for publication. Approval does
not signify that the contents necessarily reflect the views
and policies of the Federal Water Quality Administration,
nor does mention of trade names or commercial products con-
stitute endorsement or recommendation for use.
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ABSTRACT
Basic experiments were conducted to establish the feasibility
of foam fractionation in the treatment of acid coal mine
drainage for the removal of the metal ions iron, calcium, man-
ganese and magnesium. The independent variables controlling
foam separation of metal ions were determined to be the concen-
tration ratio of surfactant to iron, the air volume throughput,
the foam drainage time, the total dissolved salt content and
the type of surfactant used.
The major part of iron, calcium, manganese and magnesium
can be foam separated from acid solution by proper control of
the independent variables. Reductipn of residual surfactant
concentration in the treated water and reduction of water en-
trained with the foam are two areas in need of further investi-
gation.
Foam separation was tested on acid drainage, partially
lime neutralized drainage and complete limestone neutralized
drainage. Tests on model solutions indicate that treatment
of raw acid drainage is most feasible at present.
Operating and capital costs are estimated for 0.1 and 1.0 MGD
batch treatment plants. Reduction of chemical costs through
recovery and regeneration of surfactant is the major means for
total cost reduction. Further investigation of methods for sur-
factant reuse are required. Significant capital cost reduction
on a volume basis is estimated for 1.0 MGD in contrast to 0.1
MGD operation.
This report was submitted in fulfillment of Project
14010 DEE, Contract 14-12-496, under the sponsorship of the
Federal Water Quality Administration.
Key Words:
Foam separation, acid coal mine drainage, metal ion re-
moval, iron, calcium, manganese, magnesium, surfactant,
treatment costs.
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CONTENTS
Section Page
I Conclusions 1
II Recommendations 3
III Introduction 4
IV Experimental 12
1. Apparatus - Foam Tower 12
2. Procedure - Operation of Foam Tower 14
3. Analytical Methods 16
V Results and Discussion 18
1. Surfactant Screening Tests 18
2. Foam Separation Tests 21
(1) Foam Separation of Iron from Partially
Neutralized Solutions 22
(2) Foam Separation of Iron and Calcium
from Partially Neutralized Solutions 33
(3) Foam Separation of Iron and Calcium
after Limestone Neutralization 35
(4) Foam Separation of Manganese and
Iron from Acid Solution 37
(5) Foam Separation of Iron, Calcium and
Magnesium from Synthetic and Real
Acid Mine Drainage 38
VI Economic Evaluation and Summary 40
VII Acknowledgments 52
VIII References 53
IX Appendices 55
ii
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FIGURES
No.
1 Cross Section through Three Foam Bubbles in Contact
2 Experimental Foam Tanks
3 Beaker Foaming Apparatus
4 Effect of Surfactant:Iron Ratio on Foam
Separation of Iron 25
5 Effect of pH on Iron Removal 27
6 Effect of Surfactant Concentration on Surfactant
Removal Rate 28
7 Effect of Drainage Time and Initial Surfactant:Iron
Ratio on Volume Raduction Factor 30
8 Rate of Iron Removal as a Function of the Surfactant:
Iron Ratio 32
9 Conceptual Design of a Feasible Foam Separation Plant
for Batch Treatment of Acid Mine Water 45
10 Schematic Diagram for Batch Foam Fractionation
Removal of Iron 47
iii
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TABLES
Number Page
I Surfactant Screening Tests 19
II Experiments 1-9 23
III Experiments 10 - 17 24
IV Experiment 18 31
V Comparison of Foam Separation in Sulfuric
Acid and Gypsum Solutions 34
VI Material Balance for Batch Foam Separation 41
VII Chemical Cost Estimate 43
VIII Estimate of Delivered Equipment Costs 46
IX Estimation of Power Costs for Process
Equipment 48
X Capital Costs Estimate - 0.1 MOD 49
XI Capital Costs Estimate - 1.0 MGD 50
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SECTION I
CONCLUSIONS
The significant conclusions reached are as follows:
1. Iron, calcium, manganese, and magnesium can be
accumulated in and removed from solution by the
foams of selected surfactants under controlled
conditions.
2. The independent variables controlling efficient
batch operated foam separation of metal ions are:
a. the concentration ratio of surfactant to
metal
b. the air sparging rate as related to the
total air volume throughput and the bubble
residence time in the liquid phase
c. the foam drainage time
d. the total dissolved solids in the liquid
phase
e. the chemical nature of the surfactant
3. The major parts of iron, calcium, manganese and mag-
nesium can be removed from acid drainage accompanied
by a significant residual surfactant concentration
left in the treated solution and by a significant
water loss from the solution to the foam.
4. Temperature in the range from 1 - 25°C has no apparent
effect on the efficiency of foam separation of metal
ions.
5. Anionic surfactants are more efficient for foam
separation of metal ions.
r
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6. Of the surfactants tested, ring substituted and un-
substituted aliphatic sulfonates have shown most
promise for foam separation in acidic solution.
7. An increase in total dissolved solids, particularly
calcium, tends to reduce the foam drainage time or
foam persistence, thus reducing separation efficiency.
8. The particular surfactant can have a significant
effect on the rate of foam drainage and, thus, on
the amount of water loss and the efficiency of
foam separation.
9. The effect of pH on foam separation of metal ions
is not completely clear, except that a high enough
pH to promote precipitation of ferric hydroxide
results in decreased foam separation efficiency.
10. The surfactant concentration has two restraints for
efficient foam separation: (1) it must be large
enough to promote persistent foam formation, (2)
it must be large enough to provide an adequate
surfactant to metal ion concentration ratio.
11. Analysis of capital and operating cost estimates
indicates that surfactant costs are significant for
the batch process.
12. Methods to improve surfactant recovery, regeneration
and reuse would significantly reduce process costs.
13. Methods to improve foam drainage would significantly
improve treatment efficiency.
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SECTION II
RECOMMENDATIONS
1. Methods to increase foam drainage efficiency should be
investigated in order to reduce liquid entrainment in
the foam. Design of special drainage apparatus and
further screening for surfactants with efficient
drainage characteristics are two such areas for investi-
gation.
2. The present research on batch foam fractionation should
be extended to potentially more efficient continuous
flow operation with systematic evaluation of the control-
ling independent variables determined to date.
3. Methods to recover and regenerate surfactant should be
further investigated. If surfactant consumption (loss)
can be effectively reduced, then operational costs for
the process would be reduced and the cost restriction on
surfactants could be reduced. Surfactants specific to
particular metal ion could be developed and cost-effectively
applied.
4. The few tests conducted on synthetic and natural acid mine
drainage should be extended since the effects of these
complex solutions on foam separation are not completely
clear.
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SECTION III
INTRODUCTION
The problem is the economic treatment of mine drainage
for the production of water meeting the quality standards as
established by the states under the Federal Water Pollution
Control Act. The treatment of mine drainage requires the re-
moval of metal and nonmetal ions and the neutralization of
sulfuric acid; the extent of treatment will depend on the end
use of the purified water. Progressively greater purification
will be required for water meeting the standards of industrial
use, domestic use and the most stringent interstate stream
water quality criteria, respectively.
Coal and coal wastes often contain pyritic minerals which
through wet oxidation produce ferrous sulfate and sulfuric
acid.
FeS2 + H2O + 3.5O2 * FeSO4 + H2SO4
By further reaction with surrounding minerals, the solution
can increase in chemical complexity. A typical mine drainage
may contain calcium,manganese, magnesium, aluminum, silicon
chloride, and sodium in addition to iron, sulfate and free acid.
Obviously, the most objectionable constituents ought to be
removed from the mine drainage before it is permitted to mix
with ground and surface waters. Several methods of purification
have been used. They need not be discussed here. It is suf-
ficient to state that none of these processes are considered
perfect and that the need for a better treatment method still
exists.
In the present work foam fractionation was the method
selected to treat mine drainage. Foam fractionation has several
inherent features which make it attractive for the treatment
of mine drainage, namely, simplicity and economy combined with
operation at ambient temperature and pressure. The foam frac-
tionation process is based on the chemical composition of the
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surface layer of a solution being different from that of the
bulk. For instance, the concentration of a component in the
surface layer may be much greater than in the bulk of the
liquid. If this layer is removed, the residual solution will
contain less of the component.
The investigator is confronted with two problems: (1)
how to accumulate the unwanted material in the surface layer,
and (2) how to remove this layer.
(1) Surface tension differences are a common cause of
the above accumulation. Let y denote the surface
tension, and c the concentration of a solution.
If d f'/dc is negative, that is, if surface ten-
sion decreases when concentration increases,
then it is energetically advantageous for the
system to accumulate the solute near the surface.
Hence, the surface energy (and the total free
energy) of the system is lowered when segregation
takes place; thus, accumulation of the "surface-
active" solute next to the surface is a spontaneous
process. The thermodynamic basis for surface ad-
sorption is given approximately by the simplified
form of the Gibbs equation
_ d_£ _ RT p (1)
dc ~ c. ' l J
where' is the surface excess (g-cm~2) of a com-
ponent with concentration c (g-cm~3) in the bulk
liquid. R is the gas constant, and T is the absolute
temperature.
In aqueous solutions of inorganic salts, such as
ferrous sulfate, water is the surface-active ingredient,
This means that the surface tension of these solu-
tions increases when the salt concentration increases
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so that the surface layer contains less salt
than an equal volume of the bulk liquid. How-
ever, if the liquid contains, in addition to
the salt, a surfactant, the surfactant may trans-
fer the inorganic ingredient into the surface
layer. Suppose, for instance, that sodium dodecyl
sulfate is the surfactant and FeS04 is the in-
organic salt. The chemical reaction
2C,i H23-CH2 -O'SOg -ONa + FeSO4 5
(C,, H23 *CH2 «O'SO2 -O)2Fe + Na2SO4
is probable and the resulting ferrous dodecyl sul-
fate accumulates in the surface because it lowers
the surface tension of the solution in the same
manner as does sodium dodecyl sulfate.
The accumulation of surfactant and salt in the
surface layer can be expressed quantitatively.
Let P , measured in g-cm~2, be the surface excess
of a component. Hence, the amount of this com-
ponent present in a layer 0cvi thick and of area
A cm2, is A / c + A P, where c is the concentra-
tion of the component in g*cm 3. If there were no
segregation at the surface, this amount would have
been A /c. The ratio of the two concentrations
is given by
R = AQ /c + A0P)/Ao/c = 1 + (T/^c). (2)
In many instances of equilibrium adsorption, " is
0 _ *
of the order of 10~ g-mol-cm"2. If I is 10~ cm
and c is 10 g-mol-cm"3, then the above ratio is
as high as 1001. This ratio is usually denoted as
the accumulation ratio R.
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(2) The surface layer of a liquid can be removed by
mechanical skimming but foaming is a much simpler
and more efficient method for separating the sur-
face active component from the bulk liquid. As
gas is bubbled through the liquid, adsorption of
surfactant occurs at the liquid-gas interface.
If the bubbles remain intact as they pass out of
the bulk liquid, and if the foam remains stable
without bursting or coalescing for at least
several minutes, then physical separation of
the component enriched foam provides an effective
separation process. Thus it is obvious that since
bubbles provide the surfaces for adsorption, more
efficient separation would be achieved by maximizing
the total bubble surface area passing through the
bulk liquid.
Foam bubbles are usually distorted pentagonal
dodecahedrons. To simplify the discussion of
foams, assume them to be cubes with linear edges
of Jt . If^is the thickness of the liquid film
surrounding the gas phase, then the bubble surface
area is 6j£2 and the liquid volume in the bubble
is approximately &JLza. Foam films may be pictured
as sandwiches in which a solution (whose composi-
tion is almost identical with that of the bulk
solution) is confined between two (usually uni-
molecular) layers of surfactant. Let ^be the
thickness of each surfactant layer and J the
thickness of the liquid interlayer, so that
a = 2 <^ + J' . Assuming that the density of
all materials involved is equal to that of water,
the amount of the surfactant pertaining to one
bubble is 6j£2 (2 ^ + c fQ) . The concentration
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(g'CirT3) of the surfactant in the foam lamellae
is (2^ + cyo)/(2^ + /" Q) . The ratio of this
concentration to that (c) in the bulk solution
is another expression of the accumulation ratio R.
+ c/
The purpose of deriving equation (3) is to show
the dependence of efficient foam separation on
the thickness J of the liquid interlayer in a
foam film. If £ Q is large, then relatively more
liquid with essentially the concentration of the
bulk solution is contained within the film. This
reduces the efficiency of surfactant separation.
When d is very small, the surfactant concentration
o '
in the film is almost equal to 1, and almost the
whole film consists of surfactant. For example,
if c = 10~4 g-crn"3, then R = 104 - In contrast, if
is much greater than ^ , then surfactant con-
centrations in the foam and in the bulk are almost
equal, and R = 1.0.
The above considerations are only approximate because the
thickness of the liquid surrounding a gas bubble in a foam is
not constant. At the cross- line between three bubbles, a thicker
liquid vein (now known as Plateau's border) exists, and a con-
siderable fraction of the solution present in the foam is found
in these veins. The semi-quantitative conclusions that R greatly
depends on g are not invalidated by this refinement.
Both effects considered above, that is the accumulation
of a component in the surface layer and the spatial separation
of this layer in a foam, are time -de pen dent.
When a bubble forms in a surfactant solution, surfactant
molecules (or ions) have to diffuse to the air-liquid inter-
face before they can coat this boundary with an oriented
8
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unimolecular layer. If the bubble is released right under the
horizontal surface of the bulk liquid, the time of ascent
through the bulk liquid may be too short to achieve equilibrium
adsorption at the bubble surface as described by the Gibbs
equation (1). However, in the experiments reported here, no
effect was noticed which could be attributed to an incomplete
adsorption. Consequently, this complication is not considered
further in the present report.
When a foam rises in a vertical tube a simultaneous liquid
flow in the opposite direction takes place. This flow is
known as foam drainage and is an important factor controlling
the efficiency of foam separation. Foam drainage has two causes
and two paths. One obvious cause is gravitation; the liquid is
denser than air and, consequently, drains down. The other cause
is related to surface tension. Figure 1 schematically represents
a cross-section through three foam bubbles in contact.
c
Cross-Section through Three Foam Bubbles in Contact
FIGURE 1
A, B, and C are the gas volumes. The liquid films between them
form three angles of 120° each. At the spots indicated by the
arrows, the gas-liquid interfaces are concave to the gas phase.
Consequently, the pressure in the liquid between the arrows
(this space is a Plateau border) is less than elsewhere in
the bubble wall. This pressure difference drives liquid toward
and into Plateau's borders, in which downward flow then occurs.
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Thus, a part of the liquid drains through Plateau borders.
Another part flows in the lamellae between the relatively flat
bubble walls. The relative importance of the two paths depends
on the ratio of the lamellae thickness to the average diameter
of the Plateau border. In many systems the lamellae are so
thin that the Plateau borders are the main drainage channels.
The Plateau borders, as seen in Figure 1, are not of circular
cross-section, but an average radius r may be attributed to
each. The volume rate (cm3 -sec"1 ) of drainage is proportional
to r4 , and thus is greatly dependent on the dimension of the
liquid veins.
When the drainage times of two different surfactant solu-
tions are compared, the difference may be due to the different
values of the radii r. There is also another cause of difference
When the external layers of each foam film (whose thickness was
denoted with Jt above) are nearly solid, the drainage takes more
time than if the layers are more liquid-like. At given external
conditions, the rate of drainage greatly depends on the proper-
ties of the surfactant used.
The volume rate of drainage decreases in time because the
effective radius r of Plateau borders and the thickness of
the liquid interlayer gradually decrease. In some instances it
seems to stop when
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If considerable bursting starts when the bubbles are * seconds
old, then the drainage should not be continued longer than C
or even 0.5 ^ seconds. Thus, the persistence (or lifetime)
of the foam bubbles determines the duration of the drainage
and, consequently, the highest accumulation ratio which can be
achieved. Different surfactants produce foams with varying
persistences. A high value of £ is a requisite property for
a surfactant suitable for foam fractionation.
A complete discussion of the structure and drainage of
foams is given by Bikerman (1).
11
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SECTION IV
EXPERIMENTAL
1. Apparatus - Foam Tower
Compressed air from a cylinder was forced through a
metering valve into a 20 liter glass jar, then through a purifi-
cation and humidification system (sulfuric acid, sodium hy-
droxide, and water), a stopcock, a flowmeter, and a gas dis-
persing tube. The dispersing tube (Figure 2) usually was of
"extra coarse" fritted glass with a nominal pore size of
about 0.2 mm.
Figure 2 illustrates two types of foaming tower used in
the experiments. A three-neck 2.5 liter flask (1) contained
the solution to be foamed. Compressed air was introduced
through one of the side tubes through the air dispersing
device (2). The foam rose in the glass tower (3) which was
graduated in 100 cm3 intervals. The internal diameters of the
tubes ranged from 30 to 114 mm. The lower part of each tube
was narrow so that it could be inserted into the central opening
of the flask (1). The vertical length of the tube was usually
50 cm. In early experiments, the foam tower was open at the
(4)
(3)
(1
FIGURE 2 : Experimental Foam Tanks
12
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upper end, and the foam rising above this end -vas ci^ off with
a spatula and transferred to a container. In later tests, an
inverted glass U-tube was mounted on the tower, and the foam
flowed into the receptable (5).
The duration of drainage, the importance of which was em-
phasized in the Introduction, can be calculated from the flow-
meter readings. The flowmeters used were calibrated for the
experimental conditions and the readings translated into volume
rates of air V cm3-sec"' . If S is the cross section (cm2) of
the foam tower, then V/S cm-sec" is the linear ascent rate
of air. If the height of the tower is h cm, then hS/V sec is
the time during which the bubbles exist and drain. Hence, the
duration of drainage is hS/V.
Another simple way to measure the duration of drainage is
direct observation of the ascent of selected bubbles visible
through the glass tower. If 4h/4 t is the linear rate of
bubble ascent and h is the total height of tl tower, then the
duration of drainage is hAt/^lh sec. It is tssamed in both
methods that no significant bursting or coal3. cin^ of bubbles
takes place.
The first method also implies that the a i.r pressure in the
bubble is identical with atmospheric pressure for which the
flowmeter was calibrated. This assumption car,not b? exact
because the bubble walls usually are curved, and capillary
pressure would increase the pressure in eac.i bubole, A simple
calculation shows, however, that this complication 13 negligible.
The equation for the change in capillary pr s&ui A o is
^ p = 2 >*/r
where 1C is the surface tension of the sol'- tion srd r is the radius
of curvature of the bubble walls. The radius r is much greater
than the length Jt of a simplified cubical bubble a.^ .1.?fined in
the Introduction. In the experiments being reported, JL rarely
13
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fj -2
was shorter than 0.1 cm. Since e usually was near 30 g-sec ,
A I
p generally was less than 600 g-cm sec 2.
Since the average atmospheric pressure is 10 g-cm sec2, the
pressure inside a bubble was at most only 0.06% greater than
outside.
2. Procedure - Operation of Foam Tower
The solution to be foamed was prepared and placed in the
foaming flask. The dissolution of the inorganic salts in water
offered no difficulty but it was necessary to stir the foaming
agent for several minutes to obtain a dispersion which appeared
uniform. It appears that the surfactant concentrations used
in this study were generally above the critical micells con-
centrations so that colloidal particles were present. An ali-
quot of the initial solution was withdrawn for analyses. The
flask and remaining solution was weighed and the total weight
W recorded.
o
The 20-liter jar was filled with air at a pressure of
4-8 psi. The stopcock between the jar and the flowmeter
was opened to a predetermined reading. The gas dispersing
tube was immersed in the flask. Conspicuous foam bubbles were
selected in the rising foam and their rates of ascent measured
using the graduated column and a stopwatch.
After a predetermined interval, foaming was interrupted
and the foam present in the tower was permitted to drain and
collapse for 30 minutes. When the amount of foam produced was
small, the foam present in the tower was pushed or blown into
the receptacle. In either case, the total weight of the flask
and contents W, after foaming was recorded. After W, was
ascertained, foaming was resumed. After a predetermined time
interval, the second foam was collected and its weight was
determined by weighing the flask with the remaining liquid.
Subsequently, the collection of the third foam was started,
14
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and so on until foaming was ceased.
Theoretically, W, - W was the weight of the wet foa*
fully corrected for evaporation. If the wet foam was weigflii^
the mass W~ obtained was smaller than W, - W because of
evaporation. The difference between Wf and Yf, - W has not
been systematically investigated.
In some experiments an additional foam collection was
performed. When the foaming ability of the bulk liquid waft
reduced such that at a given rate gas flow no foam rose over
the top of the tower, then the residual liquid was transferred
from the 3-neck flask into a large beaker. The gas dispersing
tube was immersed in the beaker and an inverted glass funnel
was placed above the liquid so that its lower rim was about
1 cm above the surface of the liquid (Figure 3). The stem of
the funnel was attached by rubber tubing into a partially
evacuated flask. The foam formed in the beaker was sucked up
into the funnel and collected in the flask. Samples of all
foam and liquid fractions were collected for analyses.
FIGURE 3
Beaker Foaming Apparatus
15
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3. Analytical Methods
Initial solution, foam and residual solution samples were
analyzed for water, surfactant, iron, calcium, manganese,
magnesium and sulfuric acid as required by the chemical composi-
tion and purpose of the various foaming experiments. The
methods used are referenced below.
(1) Water. Since water was always present in much
greater amounts than the dissolved components,
its quantity was determined simply by weighing.
When the mass of an initial solution was re-
duced by foaming from W - W. grams (see p.11),
it was permissible to ascribe the weight loss
W - W( to water removed with the foam.
(2) Surfactant. Surfactants analyzed were sodium or
ammonium salts of ring substituted and non-
substituted aliphatic sulfonates and can be repre-
sented by the formula R-O-SO2-ONa. These sur-
factants form colored complexes with ionic dyes
and can be determined colorimetrically (2).
(3) Iron. Three methods were used to determine Fe
depending on the concentration of surfactant
present. When small relative amounts of sur-
factant were present, iron was determined colori-
metrically as Fe(II) with 1,10-phenanthroline
after reduction with hydroxylamine hydrochloride
solution (3). When large relative amounts of sur-
factant were present, iron was determined colori-
metrically as Fe(III) with potassium thiocyanate
after oxidation of surfactant with nitric and per-
chloric acids and oxidation of iron with ammonium
persulfate (4).
Alternately, total iron was determined directly
using an atomic absorption spectrophotometer (AA)
s
without destruction of surfactant (5). Towards
16
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the end of this contract all iron determinations
were run on the AA.
(4) Calcium. Three methods were used to determine Ca
depending on the relative amounts of surfactant
and iron present. When the ratio of calcium to
iron was large and the relative amounts of sur-
factant small, Ca was determined directly by EDTA
*
titration using "Calcein" indicator without
prior oxidation of the surfactant (6 ). When the
ratio of calcium to iron was small or moderate,
calcium was determined colorimetrically with
potassium permanganate after oxidation of the
surfactant and separation of iron and calcium
by oxalate precipitation of calcium (4 ). Toward
the end of the contract, calcium was determined
directly with the AA without eliminating either
surfactant or iron ( 5).
(5) Manganese. Manganese was determined colorimetri-
cally as potassium permanganate after destruction
of surfactant with sulfuric and nitric acids and
after oxidation of manganese with potassium
periodate ( 4).
(6) Magnesium. Magnesium was determined directly on
the AA without prior treatment ( 5).
(7) Sulfuric Acid. Sulfuric acid was determined by
titration with standard sodium hydroxide using
methyl orange as the indicator (4).
(8) pH. pH values were determined with a standard
temperature corrected meter, glass electrode and
calomel reference electrode.
* Mention of commercial products is for clarification only and
does not imply endorsement by the Federal Water Quality
Administration.
17
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SECTION V
RESULTS AND DISCUSSION
1. Surfactant Screening Tests
As noted in the Introduction, the ability of a surfactant
to produce a persistent foam is requisite for efficient foam
separation. Thus the first screening of surfactants was for
foam production and persistence under chemical conditions
similar to acid mine drainage. The surfactants tested were
restricted to inexpensive compounds available in commercial
quantities. The compositions of many of the surfactant com-
pounds were proprietary, and thus they contained unknown con-
stituents in unknown amounts.
The surfactants tested are listed in Table I with brief
comments on the test results. Those surfactants which pro-
duced persistent foams were tested for accumulation of metal
ions in the foams. Some of these tests were conducted under
contracts with the Office of Saline Water (7 )( 8). In general,
the non-ionic surfactants (Deriphat 160, Deriphat 170C,
Arlacel 60, Brij 58, Tween 60, Emulphogene BC-720 and Igepon AC-78)
accumulate iron and manganese under acid conditions to a much
smaller extent than the anionic surfactants (sodium dodecyl
sulfate, Alipal CO-433, Alipal CD-128 and Alipal EO-526) ( 8).
It was found that iron and manganese are more readily concentrated
in the foam of Alipal EO-526 than in those of sodium dodecyl
sulfate or Deriphat 170C (8 ). It appears that this superior
accumulation is partly, or mainly, a result of the more rapid
drainage of Alipal foams ( 8). Alipal CD-128 is a new sur-
factant of similar character to Alipal EO-526 except that it
is claimed by the manufacturer to be biodegradable (Table I).
Alipal EO-526, Alipal CD-128 and sodium dodecyl sulfate
were chosen on the basis of the above described tests for the
foam separation tests to follow. As a result of the foam separa-
tion tests, it is concluded that other factors, such as foam
18
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TABLE I
Surfactant Screening Tests
Surfactant Compound*
Deriphat 160
Source*
Nature
Test Results
Deriphat 170C
Arlacel 60
Brij 58
Tween 60
Emulphogene BC-720
Igepon AC-78
Sodium dodecyl
sulfate
Alipal CD-433
General Mills Inc.
General Mills Inc.
Atlas Chemical Industries
Atlas Chemical Industries
Atlas Chemical Industries
disodium N-lauryl-
-iminodipropionate
(mainly) N-laury -
myristil-ft - amino-
propionic acid
sorbitan monostearate
polyoxyethylene
hexadecyl ether
a polysorbate
General Analine & Film Corp. tridecylorypoly
(ethylenoxy)ethanol
General Aniline & Film Corp. coconut acid ester
of sodium isethionate
duPont de Nemours Corp.
sodium lauryl sulfate
General Aniline & Film Corp. lower homolog of
Alipal EO-526
Required high air
rate to produce foam.
Difficult to dissolve
in H2O.
Similar to Deriphat 160
Required very high air
rate to produce foam.
Satisfactory foam pro-
duction and persistence.
Satisfactory foam pro-
duction and persistence.
Low foam persistence.
Low foam persistence.
Good foam production
and persistence; slow
foam drainage.
Satisfactory foam pro-
duction and persistence.
-------
TABLE I (continued)
Surfactant Compound*
Alipal CD-128
Alipal EO-526
Source*
Nature
Test Results
General Analine & Film
Corp.
General Aniline & Film
Corp.
ammonium salt similar
to Alipal EO-526 but
of aliphatic nature
sodium salt of a sul-
fated alkylphenoxy
poly(ethyleneoxy)
ethanol
Good foam production
and persistence.
Good foam production
and persistence.
to
o
* Mention of commercial products is for clarification only and does not imply endorse-
ment by the Federal Water Quality Administration.
-------
drainage time, air sparging rate and surfactant to metal concen-
tration ratio, are more important for effective metal separa-
tion than any of the three surfactants.
None of the surfactants tested showed specificity for
any of the metals tested. Since the choice of surfactants
was limited to inexpensive, commercially available compounds,
the choice was limited. It is evident from our work that
to find a specific surfactant will require testing of a less
restricted class of compounds and, possibly, synthesis of
special compounds. It would be expected that such a specific
compound would be expensive and not immediately available for
foam treatment of acid mine drainage.
2. Foam Separation Tests
The usual acid mine drainage contains two highly objectionable
components, namely iron and sulfuric acid. In addition, sig-
nificant amounts of calcium,manganese and magnesium are often
present. In principle it is possible to foam separate iron
from sulfuric acid and neutralize the acid as a secondary
process. In contrast, the acid could be neutralized prior to
foam removal of iron. Both these possibilities were investi-
gated. In theory, if a surfactant exists which combines with
one metal in preference to another, then the two metals could
be selectively separated by foaming. The results of the sur-
factant tests exposed no such selective surfactants within the
class of inexpensive, commercially available detergents in-
vestigated.
In the first set of experiments the amounts of ferrous
sulfate and sulfuric acid in the initial solutions were equi-
valent. These experiments were conducted with simplified acid
drainage to define feasibility for foam separation of iron in
acid media. The second set of experiments tested the removal
of iron and calcium from partially - neutralized solutions of
simplified acid mine drainage. The third set of experiments
21
-------
investigated the removal of iron and calcium after limestone
neutralization of simplified solutions of acid mine drainage.
|9 sedition the effect of temperature on foam separation was
investigated. The fourth set of experiments investigate the
y*»oval of manganese and iron from simplified acid mine
drainage. The fifth set of experiments investigate the foam
of iron calcium and magnesium from synthetic and
acid mine water.
(1) Foam Separation of Iron from Acid Solutions
In these tests the amounts of ferrous sulfate and
acid in the initial solutions were equivalent. The
used were commercial grade sodium dodecyl sulfate
, Alipal CD-128 and Alipal EO-526. The operating para-
«, analytical results and dependent variables for the
|J| Mperiments in this set are presented in Tables II, III and
IV.
Tto Effect of the Surfactant:Iron Concentration Ratio
It is evident from the data in Tables II and III
ferrous iron can be successfully separated from sulfuric
acid solutions by foaming. Figure 4 shows the dependence of
iron removal on the concentration ratio of surfactant to iron.
Af th« trend line indicates, iron removal increases with the
?f tiff, It would be expected that increasing the ratio above
§ Cfftain value should have negligible effect on iron removal.
t a in Figure 4 tends to suggest this, as the trend line
be drawn with a slope approaching zero as the ratio in-
At present it is not known what compound of iron is
in the walls of foam lamellae when sodium dodecyl sul-
ffttf or an Alipal is the foaming agent. It is possible that
tfcip compound is simply the ferrous salt of the surfactant
anion. The three surfactants used in the foam separation tests
»ay be represented by the formula RS04Na. A salt of this type
if lively to react with ferrous sulfate according to the equation
22
-------
CO
00
Experiment No.
Air Rate, cm3-sec
Foaming Time, min
Drainage Time, sec
Initial Solution
Weight, g
Surfactant
Initial Surfactant
Concentration, ppm
Initial Fe Concentration,
ppm
Surfactant
Initial
Fe
Initial pH
Residual Solution
Weight, g
Water Loss with Foam, °f
Residual Surfactant
Concentration, ppm
Residual Fe Concentra-
tion, ppm
Residual pH
Foam Weight, g
Fe Removed, %
Surfactant Removed, %
Accumulation Ratio:
Foam:
Fe
Surfactant
H2S04
Residual Solution:
Fe
Surfactant
H2S04
1
3
124
2200
2007
NDS
984
9.4
105
5.1
1997
0.50
813
1.6
4.8
10
83
18
260
19
0.2
0.8
2
6
70
1100
2007
NDS
1019
9.4
108
5.1
1953
2.7
838
2.1
5.0
54
78
20
49
2.5
0.2
0.8
TABLE
3
6
195
1100
2070
NDS
873
101
9.6
3.25
2018
2.5
610
76
3.22
52
27
32
8
11
2.4
0.7
0.7
0.9
II
4
3
185
2200
2200
NDS
840
286
2.9
2.61
2198
0.091
700
264
2.82
2.1
8
17
30
102
6
0.9
0.8
0.9
5
6
125
1100
2200
NDS
815
277
2.9
2.62
2174
1.2
720
254
2.82
26
9
13
6
12
0.7
0.96
0.9
0.9
6
3
135
2200
2070
NDS
900
976
0.92
2.50
2069
0.048
770
940
2.52
1.3
4
15
34
140
1.3
0.9
0.86
1.0
7
6
120
1100
2070
NDS
882
1030
0.86
2.50
2021
2.4
682
950
2.51
49
10
25
2.2
9.2
0. 12
0.92
0.77
0.95
8
6
95
1100
2007
CD- 12 8
1050
12.5
84.0
3.64
1957
2.5
1040
7.2
3.59
50
44
3
17
1.9
0.6
0.99
9
6
95
1100
2070
CD- 12 8
1030
103
10.0
2.75
1980
4.3
880
99
2.80
90
8
18
1.7
0 . 9&
0.85
-------
TABLE III
Experiment No.
Air Rate, cm3-sec
Foaming Time, min
Drainage Time, sec
Initial Solution
Weight, g
Surfactant
Initial Surfactant
Concentration, ppm
Initial Fe Concen-
tration, ppm
Surfactant
Initial
Fe
Initial pH
Residual Solution
w Weight, g
Water Loss with Foam,
Residual Surfactant
Concentration, ppm
Residual Fe Concen-
tration, ppm
Residual pH
Foam Weight, g
Fe Removed, %
Surfactant Removed, %
Accumulation Ratio:
Foam:
Fe
Surfactant
H2S04
Residual Solution:
Fe
Surfactant
H2S04
10
6
120
1100
2070
EO-526
1670
11.5
145
3.70
1985
4.1
1200
3.9
3.72
22
66
29
48
2
-
0.34
0.7
-
11
6
145
1100
2070
EO-526
1260
90
14
2.85
2048
1.1
400
76
2.90
22
17
69
6
30
-
0.9
0.3
-
12
6
120
1100
2200
EO-526
1160
300
3.9
-
2179
0.95
570
290
-
21
4
51
3.4
19
-
0.97
0.5
-
13
6
240
1100
2200
CD- 12 8
850
245
3.5
2.4
2110
4.1
630
176
2.4
90
31
29
1
8
0.04
0.7
0.7
1.2
14
6
240
1100
2200
CD- 12 8
1700
279
6.1
2.3
1936
1.2
1350
-
2.1
264
-
30
0.5
1.6
-
_
0.8
-
15
6
180
1100
2070
EO-526
980
950
1.0
2.0
2046
1.2
500
840
1.9
24
13
50
1.7
33
1.2
0.4
0.5
1.0
16
6
180
1100
2200
EO-528
4830
300
16
2.25
2132
3.1
4080
278
2.20
68
10
18
1.9
3.9
1.3
0.93
0.84
1.0
17
6
180
1100
2200
EO-526
23 Su
288
8.3
2.30
2140
2.7
1750
243
2.20
60
18
29
2.2
9.4
1.3
0.8
0.7
1.0
-------
.
OI
z
O
90
80
70
60
50
40
30
20
10
*"
A
Data
\
S*
from
\
X*
exp
\
S
0
eriments
I
1 1
^
1-17
1
X
*
10 20 30 40 50 60 70 80 90 100 110 120 130 140
INITIAL SOLUTION SURFACTANT: IRON CONCENTRATION RATIO
FIGURE 4 EFFECT OF SURFACTANT: IRON RATIO ON FOAM SEPARATION OF IRON
-------
2RSO4Na + FeSO4 (RSO4)2Fe + Na2SO4.
If such an equilibrium really is established, it may be expected
that increasing the ratio of RSO4Na to FeSO4 would shift it
toward the right and thus increase the concentration of
(RSO4)2Fe. Hence, an increase in the above ratio should raise
the iron concentration in the foam walls and, consequently,
improve foam separation of iron. This expectation is proved
in Figure 4.
The Effect of pH
Figure 5 indicates that iron removal is increased as
pH is increased. Since pH and iron concentration in the initial
solutions vary inversely as a result of manner of solution
preparation, the trend shown in Figure 5 is not completely clear.
The effect of pH on iron removal cannot be ascertained from these
results. However, results obtained for the Office of Saline
Water (8) showed that Alipal EO-526 was capable of iron separa-
tion in acid and neutral solutions. In a solution containing
590 ppm surfactant and 4.5 ppm iron, the accumulation ratios
for iron were 20 at pH 1.9, 13 at pH 2.9 and 44 at pH 7.3.
Effect of Surfactants
As the concentration of surfactant in a solution is in-
creased, the rate of surfactant removal at a constant gas rate
is seen to increase (Figure 6). It would be expected that
the rate of surfactant removal would not increase indefinitely
with an increase in surfactant concentration. At some concen-
tration the available surfactant in solution will be sufficient
to completely saturate the bubble surfaces as they pass through
the bulk liquid. Above this concentration, only an increase
in the bubble surface area passed through the liquid would
26
-------
to
a
z
O
Of.
90
80
70
60
50
40
30
20
10
SUR
A
FACTANT
NDS
CD-128
EO-526
t
1 1
^
/
-*.*
/**!
h-i i
A
/
A
/
l 1
/
/
/
/
/
/
Data 1
ixperimen
1
/
'
rom
ts 1-17.
> 12345
INITIAL SOLUTION pH
FIGURE 5 EFFECT OF pH ON IRON REMOVAL
-------
o
X
^
c
"I
at
VI
20
18
16
14
12
10
8
6
4
2
1
<
96
6.
t
!URF
<
v
V i
\
ACTANTS
Nn<
CD-128
EO-526
EO-526
w6 **
<*&?
Exp<
^6-
B F>
i p i i ^ 1
I I I I -4
) 1 2 3 4 5 6 7 8 9 10 11 12
INITIAL SURFACTANT CONCENTRATION , ppm x 1O"3
3 -1
(Numbers indicate air rate, Cm; Sec ~ )
FIGURE 6
EFFECT OF SURFACTANT CONCENTRATION ON SURFACTANT
REMOVAL RATE
28
-------
increase the rate of surfactant removal. Also, if the critical
micelle concentration for the surfactant was surpassed, excess
surfactant would not increase its removal rate. The fact that
a minimum surfactant concentration is required to simply sustain
a persistent foam is indicated in Figure 6. A surfactant con-
centration much below about 800 ppm is inadequate for foam
separation. The results of the first 18 experiments (Figures
4 and 5) indicate no difference among the three foaming agents
as far as iron removal is concerned.
The Effect of Drainage Time
The main effect of increased foam drainage is a reduc-
tion in the volume or weight of the foam collected. Figure 7
shows that for a given surfactant:iron concentration ratio
the volume reduction factor (defined as the volume of initial
solution divided by that of the collapsed foam) increases with
drainage time. The percentage removal of iron is neither
systematically or significantly affected by drainage time.
Multiple Foaming Experiment - Experiment 18
In this test 9 foam fractions were collected. After
the ninth foam the residual solution was foamed in a beaker,
and the foam was collected by suction as shown in Figure 3.
The operating parameters and analytical results are shown in
Table IV.
From the experimental data, the rate of iron removal
can be calculated as a function of the surfactant:iron concen-
tration ratio (Figure 8). Figures 8 and 4 are similar, as
they indicate that the percentage removal and removal rate for
iron are 'strongly dependent on the surfactant:iron concentration
ratio. As discussed previously (p.22 )9 the removal rate will
not increase indefinitely with the surfactant:iron ratio. How-
ever, for the iron and surfactant concentrations used, the above
conclusion is valid.
29
-------
15
O 10
ID
_i
O
Indicate percen t
iron removal
Initial surfactant
to iron ratio.
u 1100 2200
DRAINAGE TIME, SEC
FIGURE 7
EFFECT OF DRAINAGE TIME AND INITIAL SURFACTANT:
IRON RATIO ON VOLUME REDUCTION FACTOR
(Volume reduction factor is the ratio of the initial
solution volume to the collapsed foam volume.)
30
-------
TABLE IV
Experiment 18
-I
Air Rate, 6 cm3.sec ; Drainage Time, 1100 sec; Surfactant, Alipal EO-526
Cumulative
CO
Initial Solution
First Foam
Second Foam
Third Foam
Fourth Foam
Fifth Foam
Sixth Foam
Seventh Foam
Eighth Foam
Ninth Foam
Residual Solution
Beaker Foam
Final Residual
Solution
Foaming
Time,
min
i -
185
205
185
205
200
195
245
150
125
in
70*
Concentration
Weight,
g
2220
77
164
129
109
113
97
97
.44.5
16.5
-
174
Surfactant,
ppm
10760
45500
13700
19400
24700
25400
20000
21300
22700
19700
1700
600
Fe, Acid,
ppm
277 570
880 890
270 700
480 540
450 840
440 810
470 790
480 890
490 730
820 1030
130 360
300 500
Fe
Removal
%
11.7
7.7
10.8
8.5
8.6
7.9
8.1
3.8
2.3
-
9.1
Surfactant Fe
Removal, Removal,
% %
16.3
10.4
11.7
12.6
13.4
9.0
9.6
4.7
1.5
-
0.49
11.7
19.4
30.2
38.7
47.3
55.2
63.3
67.1
69.4
69.4
78.5
Surfactant
Removal,
16.3
26.7
38.4
51.0
64.4
73.4
83.0
87.7
89.2
89.2
89.7
260
100 360
78.5
89.7
Water loss with foam was 38% through the ninth foam and 46% including the beaker foam.
* Air rate, 62 cm3-sec"
-------
CO
(0
0
x 5
c
*
" 4
f*
^ 3
LU
oe
Z
2 2
u_
0
UJ 1
ui 1
<
ot
I
Data from experiment 18 with foam numbers
indicated.
- [~ I Indicates Fe concentrations ii
L J subjected to foaming.
9
i solution
102 cm" column x-section area.
6
[l88~
IS
1
r 'f7'7^
1 1
L ?s
5xfoon
*Xf^« LVJ
^*17ll
<149] 7 "
^ L ^ J
9
k
I^Oilp
L J[23
.^
9J
I i i i i
0 20 25 30 35 40
SURFACTANT: IRON CONCENTRATION RATIO FOR INITIAL AND SUCCESSIVE
RESIDUAL SOLUTIONS
FIGURE 8
Rate of iron removal as a function of the surfactant: Iron ratio
-------
(2) Foam Separation of Iron and Calcium from Partially
Neutralized Solutions
Because of the low solubility of ferric hydroxide,
it is likely to precipitate whenever the pH exceeds 4.0.
Consequently, a neutral solution of ferrous or ferric ions
is unstable. When acid mine drainage contains ferrous sul-
fate and sulfuric acid and when the acid is converted into
a neutral sulfate (such as calcium sulfate of sodium sulfate),
a precipitate or a colloidal solution of ferric hydroxide is
obtained. However, it is possible to neutralize the main
part of sulfuric acid and to stop before the pH reaches or
exceeds 4.0. If lime is the base used for neutralization, a
slightly acid mixture of ferrous sulfate and calcium sulfate
results.
Contrary to sulfuric acid, calcium sulfate is poorly
soluble in water. The solubility of gypsum little depends on
temperature and is equal to about 2.1 g of anhydrous CaSO4 in
1 kg of water. As 136 g of CaSO4 are obtained from 98 g of
sulfuric acid, the above solubility corresponds to the concen-
tration of 1.5 g of H2SO4 in 1 kg. Thus, when there are more
than 1500 ppm of sulfuric acid in the liquid treated with lime,
the liquid after treatment will be a nearly saturated solution
of gypsum. If the initial liquid is less concentrated, no
sediment will occur but the solution submitted to foaming will
contain CaSO4 instead of H2SO4.
It was necessary to know how this substitution would
affect foam fractionation. If the foam separation of iron is
enhanced in the presence of CaSO4 then it might be advisable
to neutralize the mine discharge before submitting the filtrate
to foam fractionation. In contrast, if the accumulation ratios
are lowered by substituting CaSO4 for H2SO4, then the foam
fractionation treatment would have to precede the neutralization
step.
3'3
-------
Twenty-five experiments (Nos. 19-33) were conducted
to determine the effect of partial neutralization on the foam
separation of iron and calcium. As the sulfuric acid concen-
tration in the mine drainage may be both higher and lower than
1500 ppm, both saturated and unsaturated gypsum solutions were
tested as a vehicle for ferrous sulfate. The experimental, de-
tails are presented in Appendix A.
The effect of partial lime neutralization and increased
calcium on the foaming process is evident through comparison of
experiments 10 and 29. In both, the calculated concentration
of Alipal CD-128 was 1000 ppm and the calculated concentration
of ferrous ion was 10 ppm; the first solution also contained a
small amount of sulfuric acid while the second was a saturated
solution of gypsum. Experiment 10, a drainage time of 1100 sec
was maintained without any difficulty, but in the gypsum solu-
tion no drainage longer than 250 seconds could be achieved. A
similar difference is observed in experiment 2 and 21, in which
sodium dodecyl sulfate was the foaming agent. Table V lists
the respective accumulation ratios.
TABLE V
Comparison of Foam Separation in Sulfuric Acid and Gypsum Solutions
In 0.00035 N H2SO4 In Saturated Gypsum Solution
Drainage: 1100 sej? Drainage: 250->340 sec
Accumulation Ratio for Iron
NDS 49 4
Alipal 48 1
The ratio of calcium to iron in the experiments 21 and
29 was 62:1. If this ratio is much less, the depressing effect
of calcium naturally is less pronounced. This can be seen by
comparing experiments 5 and 24. Each initial solution contained
34
-------
about 1000 ppm of sodium dodecyl sulfate and 275 ppm of ferrous
iron; in experiment 5 the matrix was 0.1 N H2SO4 and in experi-
ment 24 150 ppm of calcium was present. This calcium concentra-
tion was so low that drainage time could be increased to 1200
seconds, so that it was nearly equal to the drainage time in
experiment 5 (1100 seconds). The accumulation ratio for iron
was 6 in dilute sulfuric acid and 2 in gypsum solution. When
Alipal CD-128 was used instead of sodium dodecyl sulfate in
otherwise identical experiments (see experiments 13 and 30),
the accumulation ratio was near 1 in both acid and gypsum solu-
tions. It must be concluded that no benefit is realized by
partial neutralization with lime before foaming.
(3) Foam Separation of Iron and Calcium after Limestone
Neutralization
Presumably, acid mine water will eventually have
to be neutralized. Since calcium carbonate is an abundant
material and is suitable for neutralization, it has potential
wide use. In the reaction
H2SO4 + CaC03 = CaSO4 + H2O + CO2
gaseous carbon dioxide is liberated. The question arises whether
CO2 can be substituted, at least in part, for the sparging air.
One mole of sulfuric acid produces 1 mole of carbon
dioxide which, at the standard temperature and pressure, occu-
pies about 22 liters. Ten millimoles of sulfuric acid would
thus produce about 220 cm3 of C02. This volume can be compared
with the volume of air used for foaming a similar solution. In
experiment 16, 68 g of foam were collected after injecting air
for 180 minutes at the rate of 6 cm3-sec" for a total volume
of 64800 cm3. By calculation, substituting 220 cm3 of CO2 for
an equal volume of air would not yield a considerable savings.
Nevertheless, tests were made. It was found that, at the low
concentrations of sulfuric acid used, the rate of evolution of
CO2 was too low to be useful.
35
-------
In previous experiments, iron was removed by foaming
without any significant alteration in the acid content. If
free sulfuric acid is not permitted in treated drainage,
neutralization of the acid would be necessary as a secondary
step subsequent to foaming. In principle, both steps can be
performed simultaneously. Base can be added to the acid
drainage as sparging is begun. Alternately, the acid drainage
could be neutralized prior to foaming.
Thirteen experiments (Nos. 34-46) were conducted to
determine the effect of limestone neutralization on foam separa-
tion of iron and calcium. The practicality of simultaneous
neutralization and foam separation and of neutralization prior
to foam separation were investigated. The effect of tempera-
tures to near freezing were investigated. The experimental
details are presented in Appendix B.
In the experiments on foam separation of colloidal
ferric hydroxide the accumulation ratios never exceeded 5. The
separation of colloidal ferric hydroxide was unsuccessful be-
cause the foaming conditions used were designed to operate with
soluble ions. Colloidal iron can be removed effectively in
systems designed to do so (9)(10)(11)(12).
The results of foaming colloidal solutions were not
always reproducible. Foaming was usually conducted soon after
neutralization of sulfuric acid with calcium carbonate when
oxidation of ferrous iron and formation of particulate ferric
hydroxide were in process. Thus the chemical and physical nature
of the solution (e.g., the ferrous to ferric iron ratio and
the average particle size) varied from hour to hour and from test
to test.
Neutralization prior to foaming causes additional
load on the foam separation process because of the additional
metal ions introduced. The oxidation of ferrous iron and the
formation of ferric hydroxide increases the amount of base required
36
-------
for neutralization. For every mole of ferrous iron oxidized
and reacted to form ferric hydroxide, two moles of hydrogen ion
are produced. Thus, if ferrous iron is foam separated from
acid drainage before oxidation, the subsequent neutralization
will be less costly. Also, divalent ions are more effectively
removed from solution by foaming than are trivalent or higher
valent ions (13). Considering these facts, removal of iron
from acid drainage as ferrous ion would be more efficient than
oxidation and neutralization prior to foaming.
Experiments 45 and 46 were performed at temperatures
between 1° and 8°C. The accumulation ratios for colloidal
ferric hydroxide were 2.3 and 3 which is higher than in analo-
gous experiments 42-44 conducted at 23° + 2°. Foam fractiona-
tion works at low and ambient laboratory temperatures equally
well.
(4) Foam Separation of Manganese and Iron from Acid Solution
Experiments 47-50 were designed to determine the
efficiency of foam separation for removing manganese from acid
solution (8). Experimental details are presented in Appendix C.
Several conclusions can be drawn from experiments 47-
50. Manganese is accumulated in and removed from solution by
the foam. Iron and manganese appear to be removed in proportion,
iron at about 90% and manganese at about 50% under the experimental
conditions. Thus, it would be expected that efforts to increase
iron removal would result in an increase in manganese removal.
No significant difference in the removal of iron, cal-
cium and manganese appears to result from the use of either Ali-
pal EO-526 or Alipal CD-128. However, the use of Alipal EO-526,
at a given concentration, results in less water removed with the
foam.
pH in the range 3.3 - 5.6 has no apparent effect on
iron and manganese removal and water loss. However, calcium is
more completely removed at the lower pH values.
37
-------
(5) Foam Separation of Iron, Calcium and Magnesium from
Synthetic and Real Acid Mine Drainage
Eight foam separation experiments (Nos. 51 - 58) were
conducted with synthetic and real acid mine drainage. The com-
position of synthetic acid mine water used in experiments 51-
52 was: ^
0.997 g FeSO4-7H2O )
0.344 g CaS04.2H20 ) Dissolved in one
0.186 g A12(S04)3-18H20 ) 1±tep of Q>01 N ^^
0.246 g MgS04-7H2O
0.024 g MnSO4.H2O
Similar compositions are common in actual acid mine drainage.
Calculated for the three most concentrated metal ions, the liquid
contained 200 ppm of ferrous iron, 80 ppm of calcium, and 24 ppm
of magnesium. Its pH was 2.0.
The six experiments 53 - 58 were performed on actual
mine water samples at the South Greensburg Discharge (FWQA
No. 16-003) in western Pennsylvania on February 5, 1970. The
details for experiments 51 - 58 are presented in Appendix D.
The few experiments performed on artificial and real
acid mine drainage indicate that accumulation of iron, calcium
and magnesium in foam is feasible in complex solutions. The
production of persistent foams was greatly reduced in the complex
solutions. The addition of gelatin (experiments 55 and 56) im-
proved foam production and persistence. It is evident that fur-
ther work is required with surfactants for increasing foam pro-
duction in complex mixtures.
The sample of natural acid mine drainage was subjected
to foaming within 24 hours of sampling. Before the foaming ex-
periments were started, significant oxidation and precipitation
of ferric hydroxide iron had occurred as evidenced by red pre-
cipitate in the sampling containers. Thus, the inconsistencies
in duplicate experiments 57 and 58 are explained by colloidal
38
-------
iron and the well known scavenging properties of ferric hydroxide
for other soluble metal ions.
The surfactants employed were selected for low cost,
not selectively for particular ions. Consequently, when cal-
cium, magnesium, aluminum and other metal ions are present, the
surfactant is distributed among them. Hence, the ratio of sur-
factant to iron required to achieve a useful accumulation in the
foam must be greater than when ferrous ions are the only multi-
valent cations in solution. Further research is required to
clarify the inter-relationship between complex solutions, sur-
factant and foam production.
39
-------
SECTION VI
ECONOMIC EVALUATION AND SUMMARY
The capital and operating costs for batch treatment of
acid mine drainage can be estimated with the data from experi-
ments 1-18. Table VI gives a material balance for removing
the major metallic constituent, ferrous iron, at an effective
rate of 0.1 mgd. The material balance was constructed from
data obtained in the numerous batch experiments conducted to
date. It represents a conservative estimate of the degree of
foam separation obtainable under simple batch operation with-
out surfactant recovery, regeneration and reuse, and without
complete foam drainage.
If the concentration of surfactant is kept large enough
to maintain a surfactant to iron ratio sufficient to provide
complete reaction of iron and surfactant and equilibrium adsorp-
tion of surfactant to bubble surfaces within bubble residence
times in the solution, then the rate of iron separation will be
based on the volume rate of air passed through the solution.
Greater than 99 per cent of the iron can be removed by keeping
the surfactant to iron concentration ratio at 40 (as indicated
by the data in Figures 6 and 8). In order to remove this quan-
tity of iron, the residual surfactant concentration remains
relatively high and a final suction foaming (see Figure 3) is
required to reduce this concentration. As shown in Table VII,
the chemical costs are significantly reduced by the final suction
foaming assuming that the recovered surfactant can be reused.
Thus, methods to recover, regenerate and reuse surfactant are
required to reduce costs. The chemical cost estimate is based
on a surfactant cost of 30 cents per pound and a NaOH cost of
5 cents per pound. These costs can probably be reduced by pur-
chase of large quantities.
The material balance (Table VI) and the chemical cost
estimate (Table VII) are calculated on 0.1 mgd, but can be scaled
40
-------
TABLE VI
Material Balance for Batch Foam Separation of Iron
0.1 MGD 0.1 MGD (2) 0.1 MOD (2)
,,, Pilot-Plant Scale ,2-. Pilot Plant Scale Pilot Plant Scale
Working Parameters^ Initial Solution ^ ' Residual Solution Suction Foaming
Water Volume, 1
Fe, g
Fe , ppm
Fe Removal Rates (3),
- g-min"
- g-cm~3 air
Fe Removal, %
Surfactant, g
Surfactant, ppm
^Surfactant Removal Rates
initial - g-min~'
initial - g-cm~3 air
average - g-cm~3 air
Surfactant Removal, %
Air Rate, cm3 -sec"'
Air Volume
Water Volume
Drainage Time, sec
2.2
.576
277
3.0 x 10"4
8.34 x 10~n
70
21.45
10,760
(4)
1.80 x 10~2
5.00 x 10"5
3.14 x 10~5
89
6
2.78 x 102
1100
1.50 x 105
4.50 x 104
300
8.34 x 10*
8.34 x 10"n
1.80 x 10*
12,000
3.87 x 10
5.00 x 10"5
3.14 x 10"5
1.67 x 10fc
3.60 x 102 (5)
1100 (6)
9.3 x 104 8.1 x 104
500
5.4
99
1.00 x 105-7.44 x 104 2.11 x 104
1080 - 800 (7) 260
94 - 96 (8) 98
1.67 x 107
-------
Table VI (continued)
0.1 MOD 0.1 MGD(2) 0.1 MGD (2)
Pilot-Plant Scale Pilot Plant Scale Pilot Plant Scale
Working Parameters(1) Initial Solution(2) Residual Solution Suction Foaming
Foaming Time, rain
Surfactant
Fe
Water Loss,
Weight Ratio
1695
40
38
540
40
38
70
46
to
(1)
(2)
(3)
(4)
(5)
(6)
(7)
Based on Experiment 1-18.
Based on Scale increase of Experiments
1 - 18.
Fe removal rate held constant by holding
Surfactant
Pe
ratio at 40; see Figure 8.
Surfactant rate will decrease as surfactant concentration is decreased by foaming, see Figure 6.
Air volume to water volume ratio increased to increase air-liquid surface area throughput and
thus increase Fe removal.
Pilot-scale foaming apparatus designed to maintain drainage time.
1080 ppm -based on average surfactant removal rate; 800 ppm based on minimum surfactant
concentration to sustain persistent foam (Figure 6).
(8) Surfactant removal increased due to increase in airrwater volume ratio.
-------
TABLE VII
Chemical Cost Estimate
Chemical costs are based on the material balance (Table VI)
and the following conditions:
1. Surfactant 0.30 ft-lb"
2. NaOH 0.05 #-lb~'
3. OH:Fe mole ratio equals 3 for surfactant
regeneration
Additional Suction
For Pilot-Plant Foaming for Reduction of
Material Balance Surfactant Loss
Water Volume, 1 1.50 x 105
Fe Removal, g 4.45 x 104
NaOH used for sur- 9.51 x 104
factant regeneration, g
Surfactant Loss, g 1.00 x 105 2.11 x 104
NaOH Cost, $ 10.50 10.50
Surfactant Cost, $ 66.00 13.90
Total Chemical Cost, $ 76.50 24.40
Total Chemical Cost 1.93 .61
per 1000 gal, ft
-------
up linearly for 1.0 mgd. Consideration of process scale criteria
required to maintain a workable system is expressed in the con-
ceptual process plant design shown in Figure 9. Those process
scale criteria include foam drainage time, residence time of a
bubble in the liquid, foaming time, and the effective volume
treatment rate. The process conceptually operates in a cylindri-
cal foaming tank with a larger diameter cylindrical foam draining
tank and drains while passing radially at a slight grade through
the drainage section. The foam is collected at the circumference
of the draining tank.
The near complete removal of iron and the reduction of
surfactant by suction foaming is accompanied by considerable
entrainment of water with the foam (low volume reduction factor
= 2.2; see Figure 7). Since the volume reduction factor is pro-
portional to drainage time, a means of increasing foam drainage
is required.
An equipment cost estimate is given in Table VIII for effec-
tive process rates of 0.1 and 1.0 mgd based on the process schema-
tic in Figure 10. Estimated power costs for both scales of batch
treatment are given in Table IX. Power costs are based on a rate
of 2.8 cents per kilowatt-hour and would be high for many areas.
Using the delivered equipment costs, the total capital costs
for both 0.1 and 1.0 mgd batch foam separation plants are esti-
mated (Tables X and XI).
In summary, the operating costs for 0.1 and 1.0 mgd foam
separation are estimated in the range of 0.71 - 2.16 .ft-1000 gal
under the conditions stipulated in the estimates and in exclusion
of personnel salaries. The capital cost estimates for complete
plants range $4.13 - 6.46 x 105 and $1.53 - 1.7 x 10* for
0.1 mgd and 1.0 mgd capacities, respectively. It is estimated
that the cost per unit volume of treatment can be reduced by
continuous flow in contrast with batch operation. The basic
equipment costs and thus the capital costs are possibly over esti-
mated for continuous flow operation since the capacity of the
44
-------
45m
TTTtm
FIGURE 9
CONCEPTUAL DESIGN OF A FEASIBLE FOAM SEPARATION PLANT
FOR BATCH TREATME/WT OF ACID MINE WATER. (DIMENSIONS
. SHOWN ARE FOR AN EFFECTIVE TREATMENT OF 0.1 MOD.)
LEGEND
A Foaming tank D Foam drainage path
B Foam drainage tank E Foam exit
C Foam flow path F Air
45
-------
TABLE VIII
Estimate of Delivered Equipment Costs
(ENR Index 1308)
0.1 MGD 1.0 MGD
Feed Pump, Centrifical, '
50 ft head, ,
100-2000 gal-rain" , 30-50 hp motor ft 1,600 - 2,175
50 ft head,
6.25 x 103 gal-min , 3 - 2000
gal-min 'pumps, 50 hp motors each -ft 6,000 - 7,000
Air Compressors,
3.33 x 103 ft3-min~ , reciprocating, 34 hp 37,500 -81,000
3.33 x 104 ft3-rain"' , centrifical 250,000-280,000
turbine, 300 hp
Surfactant Pump,
Rotary 100-500 gal-min"' 1,060 - 2,380
Centrifical 1000-2000 gal-min~' 1,600 - 2,175
Foaming Tank, Cast iron,
37,500 gal 11,000 -12,500
375,000 gal 35,000 -37,500
Foam Draining Tank, Cast iron,
460,000 gal 50,000 -62,500
4,600,000 gal 125,000-140,000
Surfactant Regeneration Tank,
20,000 gal 8,100 -10,000
200,000 gal 12,500 -15,000
Surfactant Storage Tank,
2,000 gal 2,250 0 2,500
20,000 gal 8,100 -10,000
5111,510-173,055 $438,200-491,675
46
-------
Feed Pump
Surfactant Recycle
Foaming and Drainage
Tanks
Air Comp. I
Treated Water
Surfactant
Pump
Tank A
Sludge Removal
FIGURE 10
SCHEMATIC DIAGRAM FOR BATCH FOAM FRACTIONATION
REMOVAL OF IRON
TANK A Surfactant regenerator and thickening.
TANK B Fresh surfactant storage.
Gravity flow.
47
-------
TABLE IX
Estimation of Power Costs for Process Equipment at O.Q28#-KWH
-I
0.1 MOD
Feed Pump, 50 hp
Air Compressor
Surfactant pump
$.hr~'
1.05
0.71
0.21
Time per Batch
hr
.312
9
9
.328
6.390
1.890
8.608
.009
.170
.050
.229
1.0 MGD
Feed Pumps, 3-50 hp
Air Compressor
Surfactant Pump
Time per Batch
hr
Cost per Batch Cost per
1000 gal,
3.15
6.26
1.05
1.00
9.00
9.00
3.15
56.50
9.45
.009
.150
.025
69.10
.184
48
-------
TABLE X
Capital Costs Estimate - 0.1 MOD
(Accuracy Averages + 15 to -30 Percent (15))
1. Delivered equipment costs from references
and on current index basis ."till,510 - 173,055
2. Installed equipment costs
Item 1 x 1.43 159,459 - 247,468
3. Process piping 23,918 - 37,120
Type plant Per cent of item 2
Solid-fluid 15
4. Instrumentation 11,162 - 17,322
Amount of automatic control Per cent of item 2
Some 7
5. Buildings and site development 31,891 - 49,493
Type of plant Per cent of item 2
Outdoor 2
6. Auxiliaries 0
Extent Per cent of item 2
Existing 2
7. Outside lines 4,783 - 7,424
Average length Per cent of item 2
Short 3
8. Total physical plant costs 231,213 - 358,827
Sum of items 2+3+4+5+6+7= subtotal
9. Engineering and construction 80,924 - 125,589
Complexity Per cent of item 8
Simple 35
10. Contingencies 57,803 - 89,706
Type process Per cent of item 8
Subject to change 25
11. Size factor 42,646 - 71,765
Size Plant Per cent of item 8
Experimental unit (<*5,000) 20
12. Total plant or fixed capital costs:
Sums-of items 8 + 9 + 10 + 11 = total $412,586 - 645,887
49
-------
TABLE XI
Capital Costs Estimate - 1.0 MOD
(Accuracy Averages +15 to -30 Percent (15))
1. Delivered equipment costs from references
and en current index basis $ 438,200 - 491,675
2. Installed equipment costs 626,626- 703,095
Item 1 x 1.43
3. Process piping 93,993- 105,464
Type plant Per cent of item 2
Solid-fluid 15
4. instrumentation 43,863- 49,216
Amount of automatic control Per cent of item 2
Some 7
5. Buildings and site development 125,325 - 140,619
Type of plant Per cent of item 2
Outdoor 20
6. Auxiliaries 0
Extent Per cent of item 2
Existing 0
7. Outside lines 18,798 - 21,092
Average length Per cent of item 2
Short 3
8. Total physical plant costs
Sum of items 2+3+4+5+6+7= subtotal 908,605 - 1,019,486
9. Engineering and construction 299,839 - 336,430
Complexity Per cent of item 8
Simple 33
10. Contingencies 227,151 - 254,871
Type process Per cent of item 8
Subject to change 25
11. Size factor 90,860- 101,948
Size Plant Per cent of item 8
Small commercial plant
(#0.5-2 x 10 ) 10
12. Total plant or fixed capital costs
Sums of items 8 + 9 + 10 + 11 = total $1,526,455 - 1,712,735
50
-------
feed pumps could be significantly reduced. The tanks and air
compressors would remain of the same capacities. The key to
reducing operating costs is reuse of surfactant.
The specific conclusions reached and recommendation
extended as a result of this research are listed in Sections
I and II, respectively.
In general, the feasibility of foam fractionation for treat-
ment of acid mine drainage has been established. However, two
areas are in need of further research. Methods to promote more
rapid and complete foam drainage and methods to increase sur-
factant recovery, regeneration and reuse are required.
Surfactant type and the design of foam drainage chambers
are two important controls of foam drainage in need of further
investigation. With development of efficient methods for
surfactant reuse, the costs of foam separation could be signi-
ficantly reduced. In addition, with more efficient economic
use of surfactant, the use of a wider range of surfactants without
as rigid cost restraints could be investigated.
Our work to date and that of others (16)(17)(18)(19) suggest
that continuous foam fractionation has great potential for im-
proving the removal of metal ions from mine drainage. Virtually
any full-scale foam separation would be most efficiently conducted
on a continuous flow basis. The results of batch experiments
should be extended to continuous flow operation.
51
-------
SECTION VII
ACKNOWLEDGMENTS
The experimental work was performed under the direction
of Dr. J. J. Bikerman. Analytical work and foaming tests
were conducted by Messrs. D. Cameron, W. Wheeler and Miss
J. Urban. The report preparation was performed by personnel
in the Inorganic Chemistry Department of Horizons, Incorporated.
They include Drs. J. J. Bikerman, P. J. Hanson and S. H. Rose.
The support of the project by the Federal Water Quality
Administration and the help provided by Mr. R. D. Hill, the
project officer, is gratefully acknowledged.
52
-------
SECTION VIII
REFERENCES
1. Bikerman, J. J., 1953, Foams, Reinhold, New York, p.
2. Jones, J. H., 1945, General Colorimetric Method for Determination
of Small Quantities of Sulfonated or Sulfated Surface Active
Compounds, J. Assoc. Off. Agr. Chem., 28:398-409.
3. ASTM 1969, 1969 Book of ASTM Standards, Part 23, Water; Atmos-
pheric Analysis, ASTM, Philadelphia, Pa., 1036 p.
4. Kolthoff, I. M. and E. B. Sandell, 1952, Textbook of Quantitative
Inorganic Analysis, Macmillan, New York, 759 p.
5. Perkin-Elmer Corporation, 1968, Analytical Methods for Atomic
Absorption Spectrophotometry, Perkin-Elmer, Norwalk, Conn.
6. Diehl, H. and J. L. Ellinboe, 1956, Indicator for Titration of
Calcium in Presence of Magnesium using Disodium Dihydrogen Ethylene-
diamine Tetraacetate, Anal. Chem., 28:882.
7. Horizons Incorporated, 1968. Foam Fractionation of Inorganic Solu-
tions, Final Report, Contract No. 14-01-0001-1265 with the Office
of Saline Water, Washington, D. C., 52 p.
8. Horizons Incorporated, 1969, Foam Fractionation of Inorganic Solu-
tions, Final Report, Contract No. 14-01-0001-2118 with the Office
of Saline Water, Washington, D. C., 50 p.
9. Grieves, R. B., 1968, Studies on the Foam Separation Process,
British Chem. Eng. , 13:77-82.
10. Rubin, A. J. , 19.68, Removal of Trace Metals by Foam, Separation
Processes, J.Am. Water Works Assoc., 60:832-846.
11. Grieves, R. B. and D. Bhattacharyya, 1968, Foam Separation of
Colloidal Particulates:Rate Studies, J. Appl. Chem., 18:149-154.
12. Grieves, R. B., D. Bhattacharyya and W. L. Conger, 1969, Foam
Separation Processes:Ion Flotation of Simple and Complexed Anions
and Microflotation of Colloidal Particulates, In:Unusual Methods
of Separation, Chem. Eng. Progress, 65:29-35.
13. Hardwick, W. H., Unpublished work, Cited in: P. F. Wace, P. J. Alder
and D. L. Banfield, 1968, Foam Separation Process Design, In: Unusual
Methods of Separation, Chem. Eng. Progress Symposium Series (A.I.Ch.E.)
65:19-28.
14. Peters, M. S. and K. D. Timmerhaus, 1968, Plant Design and Economics
for Chemical Engineers, 2nd ed., McGraw-Hill, New York, 850 p.
15. Vilbrandt, F. C. and C. E. Dryden, 1959, Chemical Engineering Plant
Design, McGraw-Hill, New York, 534 p.
53
-------
16. Newson, I. H., 1966, Foam Separation:The Principles of Governing
Surfactant Transfer in a Continuous Foam Column, J. Appl. Chem.
16:43-49.
17. Schonfeld, E., and A. H. Kibbey, 1967, Improving Strontium
Removal from Solution by Controlled Reflux Foam Separation, Nucl.
Appl., 3:353-359.
18. Lemlich, R., 1968, Adsorptive Bubble Separation Methods, Ind.
Eng. Chem., 60:16-29.
19. Wace, P. F., P. J. Alder, and D. L. Banfield, 1968, Foam Separation
Process Design, In: Unusual Methods of Separation, Chem. Eng.
Progress Symposium Series (A. I. Ch. E.) 65:19-28.
54
-------
SECTION IX
APPENDICES
Appendix A. Experimental Detail:Foam Separation of Iron and
Calcium from Partially Neutralized Solutions, Experiments 19-33.
In many of the following experiments, the duration of foam
drainage is marked for every foam; e.g., (10 g; 1100 sec)
means that 10 g of wet foam were collected (after correction
for evaporation) at a foaming rate such that the drainage lasted
1100 seconds.
Experiment 19
This experiment was similar to no. 18 in that foaming was
extended until the surfactant concentration in the residual solu-
tion was greatly reduced. However, the initial solution con-
tained calcium chloride and manganese sulfate instead of sul-
furic acid. Its composition was 2.2 g Alipal EO-526, 2 milli-
moles calcium chloride, 2.27 mg ferrous chloride, and 11 mg
MnSO4-H2O in 2245 cm3 of aqueous solution. Thus, the weight
concentrations were 980 ppm Alipal EO-526 solution (or about
590 ppm solid surfactant), 36 ppm calcium, 4.5 ppm iron, and
1.5 ppm manganese.
The solution was foamed with compressed air in a foam
tower of 7.0 cm2 cross-section and 49 cm height. Consequently,
the rate V of foaming (cm3-sec" ) corresponded to a drainage
time equal to t = 343/V sec. The volume rate V was changed
from time to time as indicated in the results.
The first residual solution, whose composition is shown
in the 10th line of the table, was foamed in a beaker, as
illustrated-in Figure 3. The llth line indicates the composi-
tion of the foam thus obtained, and the 12th, the composition
of the second residual solution.
55
-------
Experiment 19 (continued)
en
Oi
Analytical Results:
Initial Solution
First Foam
Second Foam
Third Foam
Fourth Foam
Fifth Foam
Sixth Foam
Seventh Foam
Eighth Foam
Residual Solution
Beaker Foam
Second Residual
Solution
Test Results;
First 8 Foams
Beaker Foam
Foaming Foam Drainage
Time, Collected Time, Surfactant Calciu
min g sec ppm ppm
-
120
780
120
240
180
60
60
Several
-
15
-
-
75
18
66
268
51
27
57
59
-
175
-
Surfactant
Removal
83%
95%
1100 (980) 34
490 2760
1040 19800
515 3430
294 2030
295 4650(?)
206 2670
50 - 100 1090
25 730
250
255
75
Ca Fe
Removal Removal
57% 90%
62% 82%
(36
110
400
83
66
87
50
50
46
20
21
20
m Iron
ppm
) 5.0 (4.5)
7.2
16.7
10.5
11.1
10.6
?
10.5
2.0
0.7
3.2
1.4
Water Loss
with Foam
28%
35%
-------
Experiment 20
This experiment was analogous to experiment 19, except
that Alipal CD-128 was used instead of Alipal EO-526. Alipal
CD-128, if otherwise suitable, would be preferable to Alipal
EO-526 as CD-128 is biodegradable. The pH of the initial solu-
tion was 3.4. See Analytical and Test Results on page 58.
Experiment 21
Two grams of sodium dodecyl sulfate +3.5 cm3 of 0.1 M
FeSO4 were added to 2 liters of saturated gypsum solution.
The initial pH was 5.8. As no foam could be produced at lower
rates, the rate of air injection was maintained between 2.8 and
_ |
3.6 cm3-sec in a 42 cm tall foam tower with a cross section
of 23 cm2. Thus the drainage time varied between 340 and 270
seconds.
Analytical Results:
Surfactant Iron Calcium
Initial Solution 980 ppm 9.24 ppm (theor.9.8) 618 ppm
Residual Solution 516 8.50 228
Foam (33 g) 17600 33.4 500
Test Results:
Surfactant Ca Fe Water
Removal Removal Removal Loss with Foam
1 Foam 48% 64% 9.5% 1.6%
Accumulation
Ratio 18 0.8 3.6
57
-------
Experiment 20 (continued)
Analytical Results:
01
oo
Initial Solution
First Foam
Second Foam
Third Foam
Fourth Foam
Fifth Foam
Sixth Foam
Residual Solution
Test Results;
6 Foams
Foaming Foam Drainage
Time Collected Time, Surfactant Calcium
min g sec ppm ppm
- 950 (980) 34.4 (36)
750
270
240
60
7
2
^
Surfactant
Removal
49%
16
82
296
171
194
127
1030 9800
490 4500
298 1830
211 1560
49 1110
27 945
800
Ca Fe
Removal Removal
67% 90%
470
114
46
47
32
29
(?) 19
Water Loss
with Foam
39%
Iron
ppm
4.9 (4.5)
114
24
2.3
1.4
1.4
1.5
0.8
-------
Experiment 22
Two grams of sodium dodecyl sulfate +3.5 cm3 of 0.1 M
FeSO4 in 10 cm3 of saturated gypsum solution were added to
1900 cm3 of water. The initial pH was 4.4.
Analytical Results:
Surfactant
Initial Solution 980 ppm
Residual Solution 450
First Foam (10 g;
1100 sec)
Second Foam (118 g
300 sec)
Third Foam (113 g;
225 sec)
13000
6200
3200
18
Calcium
3.2 ppm
0.8
114
89
2.3
Test Results
Surfactant
Removal
3 Foams
62%
Accumulation
Ratio 13
, 6, 3
Ca
Removal
79%
36, 28, 0.7
Fe
Removal
99%
17, 7, 2
Water
Loss with Foam
18%
Exper iment 23
Two grams of sodium dodecyl sulfate + 35 cm3 of 0.1 M FeSO4
in 100 cm3 of saturated gypsum solution were added to 1900 cm3
of water. The initial pH was 2.95.
Analytical Results:
Surfactant
Initial Solution 980 ppm
Residual Solution 390
First Foam'(13 g; 925 sec) 8200
Second Foam (180 g; 160-107 sec)6200
Third Foam (117 g; 100 sec 4300
or less)
Calcium
32 ppm
24
142
180
53
59
-------
Experiment 23 (continued)
Test Results:
Surfactant Ca Water
Removal Removal Loss with Foam
3 Foams 66% 36% 15%
Accumulation
Ratio 8.3, 6.2, 4.3 4.4, 5.7, 1.7
Experiment 24
Two grams of sodium dodecyl sulfate + 100 cm3 of 0.1 M
FeSO4 in 500 cm3 of saturated gypsum solution were added to
1400 cm3 of water. The initial pH was 2.45.
Analytical Results:
Surfactant Calcium
Initial Solution 980 ppm 270 ppm
Residual Solution 180 230
First Foam (41 g; 1200 sec) 5300 590
Second Foam (260 g; 140-60 sec)4100 310
Test Results:
Surfactant Ca Water
Removal Remova1 Loss with Foam
2 Foams 84% 28% 15%
Accumulation
Ratio 4.5, 4.2 2.2, 1.2
60
-------
Experiment 25
Two grams of sodium dodecyl sulfate + 35 cm3 of M FeSO4
were combined in 2 liters of saturated gypsum solution. The
initial pH was 2.40.
Analytical Results:
Surfactant
Initial Solution 1100 ppm
Residual Solution 460
First Foam (12 g;
140 sec)
Second Foam (27 g:
115-82 sec)
28000
6600
2 Foams
Test Results:
Surfactant
Removal
59%
Accumulation
Ratio 26, 6
Ca
Removal
2, 0.4
16500
9400
Fe
Removal
0%
18, 10
Calcium
618 ppm (theor.)
1100
270
Water Loss
with Foam
1.9%
Experiment 26
Eight grams of sodium dodecyl sulfate + 35 cm3 of 0.1 M
FeSO4 in 100 cm3 of saturated gypsum solution were combined
with 1900 cm3 of water. The initial pH was 3.2.
Analytical Results:
Surfactant
Initial Solution 3820 ppm
Residual Solution 1760
First Foam (98 g;
1200 sec)
Second Foam'(139 g;
1200 sec)
Third Foam (183 g;
1200 sec)
6600
11500
17000
Iron
80 ppm (the or,
50
1120
3300
2900
98)
Calcium
32 ppm
63
153
134
61
-------
Experiment 26 (continued)^
3 Foams
Test Results:
Surfactant
Removal
63%
Accumulation
Ratio 1.7, 3.0, 4.4
Ca
Removal
Fe
Removal
50%
14, 41, 36
Water Loss
with Foam
21%
Experiment 27
Eight grams of sodium dodecyl sulfate + 100 cm3 of 0.1 M
FeSO4 in 500 cm3 of saturated gypsum solution were added to
1500 cm3 of water. The initial pH was 2.85.
Analytical Results:
Surfactant
Initial Solution 4000 ppm
Residual Solution 3130
First Foam (35 g;
960 sec)
Second Foam (280 g:
960-40 sec)
12000
10400
Iron Calcium
300 ppm(theor. 275) 128 ppm
? 128
400 290
320 50 (?)
2 Foams
Test Results:
Surfactant
Removal
33%
Accumulation
Ratio 3, 2.6
Ca
Removal
15%
2.3, 0.4
Fe
Removal
1.3, 1.1
Water Loss
with Foam
15%
62
-------
Experiment 28
Eight grams of Alipal CD-128 + 35 cm3 of 0.1 M FeSO4
in 100 cm3 of saturated gypsum solution were combined with
1900 cm3 of water. The initial pH was 2.9.
Analytical Results:
Surfactant
Initial Solution
Residual Solution
4000 ppm (theor.)
3300
First Foam (39 g;
1100 sec)
Second Foam (30 g
1100 sec)
Third Foam (58 g;
variable)
13000
28200
52200
3 Foams
Test Results:
Surfactant
Removal
23%
Accumulation
Ratio 5.2, 7.0, 13
Ca
Removal
56%
2.6, 5.2, 23
Iron
Calcium
98 ppm (theor.) 30.4 ppm (theor.
14.4 29'5)
39
210
430
1220
Fe
Removal
63%
2.2, 4.4, 12
81
157
706
Water Loss
with Foam
6.2%
Experiment 29
Two grams of Alipal CD-128 +3.5 cm3 of 0.1 M FeSO4 were
combined with 2 liters of saturated gypsum solution. The
initial pH was 4.15.
Analytical Results:
Surfactant
Initial Solution
Residual Solution
1000 ppm(theor.1000)
420
First Foam (58 g;
250-220 sec)
Second Foam (227 g
220-250 sec)
Third Foam (88 g;
120V70-*50 sec)
3500
2500
4100
Iron
7.2 ppm
6
9.5
10
Calcium
800 ppm(theor.618)
944
1100
710
1050
63
-------
Experiment 29 (continued)
3 Foams
Test Results:
Surfactant
Removal
66%
Accumulation
Ratio 3.5, 2.5, 4.1
Ca
Removal
0
1.4, 0.9, 1.2
Fe
Removal
32%
1.3, 1.2, 1.4
Water Loss
with Foam
19%
Experiment 30
Alipal CD-128 2.05 g + 100 cm3 of 0.1 M FeSO4 in 500 cm3 of
saturated gypsum solution were combined with 1400 cm3 of water.
Analytical Results:
Surfactant
Initial Solution 1100 ppm(theor.1025)
Residual Solution 650
First Foam (62 g;
350->210 sec)
Second Foam (227 g;
126 sec)
4000
3500
Iron
240 ppm
210
240
130
Calcium
150 ppm (theor.)
164
190
42
2 Foams
Test Results:
Surfactant
Removal
49%
Accumulation
Ratio 3.7, 3.2
Ca
Removal
6.3%
1.3, 0.3
Fe
Removal
25%
1.0, 0.6
Water Loss
with Foam
14%
64
-------
Experiment 31
Alipal CD-128 8.03 g + 100 cm3 of 0.1 M FeSO4 in 500 cm3
of saturated gypsum solution were added to 1400 cm3 of water.
Analytical Results:
Surfactant Iron Calcium
Initial Solution 3900 ppm(theor. 4015) 230 ppm 200 ppm
(theor. 275) (theor. 150)
Residual Solution 2640 285 152
; 1890° 23° 52°
g'' 950° 42° 28°
B:
Test Results:
Surfactant Ca Fe Water Loss
Removal Removal Removal with Foam
3 Foams 38% 30% 0 8.3%
Accumulation
Ratio 4.8, 2.4, 3.8 3.5, 1.9, 2.0 1.0, 1.8, 0.4
Experiment 32
Two grams of Alipal CD-128 + 35 cm3 of M FeSO4 were added
to 2 liters of saturated gypsum solution. The initial pH was 2.4.
Analytical Results:
Surfactant Iron
Initial Solution 1060 ppm (theor.1000) 840 ppm (theor. 980)
Residual Solution 750 890
First Foam (17 g: 740 sec) 8900
Second Foam (79 g; 4800 830
740-»530 sec)
65
-------
Experiment 32 (continued)
Test Results:
Surfactant Fe Water Loss
Removal Removal with Foam
2 Foams 33% 0 4.7%
Accumulation
Ratio 8.3, 4.5 1.0
Analytical data for calcium is absent because titra-
tion with EDTA and calcium was unsuccessful when the iron con-
centration was comparable to that of calcium. Attempts to se-
quester iron by adding an excess of potassium cyanide or to pre-
cipitate ferric hydroxide with hydrogen peroxide and ammonia
followed by titration of the supernatant liquid were unsuccess-
ful. When the bxalate method was adopted, not sufficient sample
remained for analysis.
Experiment 33
Two grams of sodium dodecyl sulfate + 35 cm3 of 0.1 M FeSO4
in 100 cm3 of saturated gypsum solution were combined with 1900 cm3
of water.
Analytical Results:
Surfactant Iron Calcium
Initial Solution 940 ppm(theor.980) 84 ppm 32 ppm(theor.30)
(theor. 93)
Residual Solution 140 63 16
2° B: 165°° 34° 44°
<235 g; 440°
Test Results:
Surfactant Ca Fe Water Loss
Removal Removal Removal with Foam
2 Foams 87% 56% 34% 12%
Accumulation
Ratio 17, 4.7 14, 2.2 4
66
-------
Appendix B. Experimental Detail;Foam Separation of Iron and
Calcium after Limestone Neutralization, Experiments 34 - 46.
Experiment 34
In this experiment 50 cm3 of 0.1 M H2SO4 and 50 cm3 of
0.1 M FeSO4 were diluted with 900 cm3 of distilled water in a
3-neck flask. One g of commercial sodium dodecyl sulfate (con-
taining about 0.45 g of the active surfactant) was introduced.
The pH of the initial solution was 3.0. Ten pellets of chemi-
cally pure calcium carbonate (0.07 g each) were sequentially
added to the flask. Foam production from CO2 evolution was
negligible, but the pH was raised to 5.0. With the introduction
of air through a dispersion tube, the lowest air rate at which
(in the foam tower used) a foam could be collected was 4 cm3-sec
(corresponding to a drainage time of approximately 250 sec).
With drainage times varying between 250 and 160 sec, 167 g of
wet foam were collected in 3 hours. The concentration of iron
in this foam was 170 mg-kg as compared to 279 mg-kg"' in the
_f
initial solution and 112 mg-kg in the residual solution.
Apparently ferric hydroxide formed in the flask was not concen-
trated in the foam. The aliquot withdrawn from the residual
solution contained less ferric hydroxide precipitate than the
part not analyzed. The concentration of calcium in the foam
was 420 mg-kg . The amount of calcium needed for neutralizing
50 cm3 of 0.1 M H2SO4 is 200 mg. Thus, some calcium was accumu-
lated in the foam. It is not known, however, whether calcium
carbonate powder was entrained with the foam and analyzed to-
gether with soluble calcium. The concentration of calcium in
the residual solution was 480 mg-kg~ ; presumably, some solid
calcium carbonate was determined again.
Test Results:
67% removal of iron and 17% water loss with foam.
67
-------
Experiment 35
To obtain a more copious evolution of foam, more concen-
trated solutions were used. 175 cm3 of 0.1 M H2SO4, 175 cm3 of
0.1 M FeSO4 and 1 g of technical sodium dodecyl sulfate were
diluted with 650 cm3 of water. The initial concentration of
iron was 980 mg'kg" . Ten calcium carbonate tablets (0.35 g
each) were added to the solution. Foam formation by CO2 evolution
was negligible. The flask was left 16 hours during which pre-
cipitation of ferric hydroxide occurred. An aliquot of the
supernatant solution contained 370 mg-kg of iron, meaning
that the precipitation was incomplete and that colloidal ferric
hydroxide was presumably still present. The supernatant solu-
tion also contained 110 mg-kg" surfactant. Apparently the
major part of the surfactant was adsorbed by the precipitate.
The liquid and precipitate were foamed, but negligible
foam could be collected even at an air rate of 20 cm3-sec"
(corresponding to a drainage time of 50 sec). An aliquot of the
supernatant solution contained 31 mg-kg~ of iron and 69 mg-kg
of surfactant. Ferric hydroxide precipitation was more complete
after aging.
The first supernatant solution contained 1400 mg-kg" of
calcium. As the concentration sufficient to neutralize 175 cm3
of 0.1 M H2SO4 in one liter is 700 mg-kg" , some calcium car-
bonate powder must have been suspended in the solution. The
second supernatant solution contained 650 mg-mg" . This again
shows that the separation between precipitate and solution was
more complete after aging.
Test Results:
No foam produced.
68
-------
Experiment 36
Because of the difficulties caused by the presence of
suspended matter, the design of the tests was altered. In-
stead of adding calcium carbonate directly to the acid solu-
tion, the solution was filtered through a bed of calcium
carbonate.
Thirty five grams of calcium carbonate powder were spread
on a sintered glass filter and a solution of 100 cm3 0.1 M
H2S04, 100 cm3 0.1 M FeSO4 and 1900 cm3 of water was filtered
slowly through. The pH of the filtrate was 5.8 to 5.9. As
the filtrate contained suspended ferric hydroxide, it was
filtered through a filter paper. The iron content of the
I
second filtrate was 20 mg-kg as compared to an initial con-
centration before filtration of 266 mg-kg~ . The second fil-
trate was foamed with 2 g of technical sodium dodecyl sulfate.
Foam was produced only at a high gas rate corresponding to a
drainage time of 310 sec. Altogether, 157 g of foam was col-
lected. The concentration of surfactant in it was 200 mg-kg" .
Apparently the main part of the surfactant was adsorbed by the
precipitate. The iron concentration in the foam was 52 mg-kg
so that the accumulation ratio was 2.6. The surfactant concen-
tration in the residual solution was 47 mg-kg~ , about 0.23
that in the foam, while the iron content was 15 mg-kg~ , about
0.29 that in the foam.
The residual solution was foamed in a beaker and 389 g of
foam collected by suction through an inverted funnel. The
concentration of surfactant in the foam was 92 mg-kg~ (accumu-
lation ratio of about 2) to 18 mg-kg~ and the iron concentra-
tion lowered from 266 to 2 mg-kg" .
Filtration through calcium carbonate naturally intro-
duced calcium into the solution. Calcium in the first filtrate
was 1800 mg'kg" which is much greater than would be produced
(190 mg-kg"') by neutralizing the sulfuric acid. In the second
filtrate calcium was 180 mg-kg"1. Apparently, the second fil-
tration removed the suspended calcium carbonate particles. In
69
-------
the first foam, 500 mg«kg~ calcium was present (accumulation
ratio was 2.8). The calcium concentration in the first and
the second residual solutions was 400 and 470 mg-kg ,
respectively.
Test Results(foam separation):
Surfactant Fe Water Loss
Removal Removal with Foam
1 Foam 95% 31% 7.5%
Beaker Foam 99% 93% 20%
Accumulation
Ratio 0.2, 2 2.6, 2.4
Experiment 37
A solution containing 100 cm3 0.1 M H2SO4, 100 cm3 0.1 M
FeSO4 and 1900 cm3 water at a pH of 2.7 was filtered through
150 g of calcium carbonate powder placed in a layer approxi-
mately 4 cm thick. Since the filtrate contained ferric hy-
droxide, it was filtered again through an 8 cm thick calcium
carbonate bed (300 g CaCO3).
Two grams of sodium dodecyl sulfate were added to the
_ i
second filtrate. The second filtrate contained 550 mg'kg
active surfactant, 58 mg«kg~ iron and 640 mg-kg calcium.
The pH was 6.1. Thus, the major part of iron (208 out of 266
_ 1
mg-kg ) was removed by the reaction with calcium carbonate
while some carbonate powder passed into the filtrate.
The second filtrate was foamed at a drainage time of 170
seconds. The concentrations in the 78 g of foam collected
were 1625 mg-kg calcium. Thus, the accumulation ratio for
the surfactant was 3.0 and colloidal ferric hydroxide and cal-
cium were not collected in the foam.
70
-------
_ I
The first residual solution contained 219 mg-kg sur-
factant, 2 mg-kg" iron, and 500 mg-kg"1 calcium. The solu-
tion was foamed and 406 g of wet foam were collected. The
concentrations in the foam were 569 mg-kg surfactant (accumu-
lation ratio 2.6), 3 mg-kg"' iron, and 580 mg-kg"' calcium.
The concentrations in the second residual solution were 58 mg.kg
surfactant, 2 mg.kg"1 iron, and 500 mg-kg~' calcium. Thus, there
was also practically no accumulation of either iron or calcium
in the second foam.
2 Foams
Test Results:
Surfactant
Removal
92%
Ca
Removal
40%
Fe
Removal
95%
Water Loss
with Foam
23%
Accumulation
Ratio 3.0, 2.6
Experiment 38
A liquid consisting of 100 cm3 0.1 M H2SO47 100 cm3 0.1 M
FeSO4 and 1900 cm3 of water was filtered as in experiment 36.
The filtrate was clear and had a pH of 6.0. After the addition
of 2 g sodium dodecyl sulfate, it contained 570 mg'kg active
surfactant, 65 mg-kg"1 iron, and 680 mg'kg" calcium. Again,
the major part of iron (201 out of 266 mg.kg" ) was removed
by reaction with CaCO3 while greater amounts of calcium were
introduced.
The filtrate was foamed at a drainage time of 130 seconds.
Altogether 61 g of foam were collected. The concentrations in
the residual solution were 345 mg-kg"1 surfactant, 66 mg-kg"'
iron, and 625 mg-kg~' calcium.
Test Results:
No marked removal of either iron or calcium was
achieved.
71
-------
Experiment 39
A solution containing 100 cm3 0.1 M FeSO4, 100 cm3 0.1 M
H2S04 and 1900 cm3 water was filtered through 200 g of calcium
carbonate spread on a porous glass plate in a layer about 5 cm
thick. The pH of the filtrate was 6.1. The filtrate was
foamed with 2 g of commercial sodium dodecyl sulfate containing
about 45% of the active ingredient. The drainage time was 70
seconds because little foam was produced at a lower air rate.
Analytical Results:
Surfactant Iron Calcium
Initial Solution 266 ppm (theor).
Filtrate 890 ppm 7 500 ppm
Foam (82 g) 7300 36 890
Residual Solution 300 5 450
Beaker Foam (188 g) 820 13 570
Second Residual n ^ .
Solution 17° d'4 32°
Test Results:
Surfactant Ca Fe Water Loss
Removal Removal Removal with Foam
1 Foam 68% 13% 31% 3.9%
Beaker Foam 83% 44% 58% 8.9%
Accumulation
Ratio 8, 2.7 1.8, 1.3 5, 2.6
72
-------
Experiment 40
A solution containing 100 cm3 0.1 M FeS04, 100 cm3 0.1 M
H2SO4 and 1900 cm3 water was filtered through 200 g of calcium
carbonate spread on a porous glass plate in a layer about 5 cm
thick. The pH of the filtrate was 6.1. Three grams of Alipal
CD-128 were added, and the solution was foamed at drainage time
of 1050 seconds.
Analytical Results:
Surfactant
Initial Solution
Filtrate
Foam (102 g)
Residual Solution
(no stirring)
Residual Solution
(after stirring)
1840 ppm
9800
1790
1870
Iron
266 ppm (theor.)
110
8
130
Calcium
52 0 ppm
500
800
Test Results
Surfactant
Removal
1 Foam
3.1%
Ca
Removal
0
Accumulation
Ratio
Fe
Removal
0
0.08
Water Loss
with Foam
4.8%
73
-------
Experiment 41
Because colloidal ferric hydroxide could not be attached
to the films of sodium dodecyl sulfate or Alipal CD-128 and
because gelatin has been used to promote such attachments, an
attempt was made to foam a filtrate of the type in experiments
36-40 after addition of 0.5 - 1 g gelatin. The initial pH was
6.6. As no stable foam was obtained, the pH was lowered to 4.5
and then to 2.5. Since foam persistence was not markedly im-
proved by these changes, 0.177 g Alipal CD-128 was added to the
solution which contained 1 g gelatin in 2 liters at pH 2.5. The
drainage time was 700 seconds.
Analytical Results:
Surfactant
Initial Solution
Filtrate 88 ppm (theor,)
Foam (295 g) 390
Foam (71 g) 490
Residual Solution 28
Iron
266 ppm(theor.)
90
170
130
27
Calcium
450 ppm
730
730
500
2 Foams
Test Results
Surfactant
Removal
74%
Accumulation
Ratio 4.4, 5.6
Ca
Removal
8.2%
1.6. 1.6
Fe
Removal
75%
1.9, 1.4
Water Loss
with Foam
17%
74
-------
Experiment 42
The initial solution was identical with those used be-
fore, containing 100 cm3 0.1 M FeSO4, 100 cm3 0.1 M H2SO4,
and 1900 cm3 water. It was filtered through 150 g of cal-
cium carbonate and 0.1 g Alipal CD-128 and 0.1 g gelatin was
added to the filtrate. After these additions the pH was 4.4.
The liquid was foamed first at a drainage time equal to 850
sec and then at 170 sec.
Analytical Results:
Surfactant
Iron
Calcium
Initial Solution 236 ppm (theor.266)
Filtrate 59 ppm(calcd. 50) 110 250
Foam (49 g) 510 130 780
Foam (176 g) 140 90 580
Residual Solution 27 120 480
Test Results:
Surfactant
Removal
2 Foams
Accumulation
Ratio
59%
9, 2.4
Ca
Removal
0
3, 2.3
Fe
Removal
2.6%
1.1, 0.8
Water Loss
with Foam
11%
75
-------
Experiment 43
This is a repetition of experiment 42. The pH of the fil-
trate after the addition of gelatin and Alipal CD-128 was 4.5.
The duration of drainage is shown in the results.
Analytical Results:
Surfactant
Initial Solution
Filtrate 59 ppm(calcd.50)
Foam (39 g; 850 sec) 640
Foam (70 g; 750 sec) 340
Residual Solution 33
Iron Calcium
289 ppm(theor.266)
150 560 ppm
300 800
60 720
120 570
2 Foams
Test Results:
Surfactant
Removal
37%
Accumulation
Ratio 13, 7
Ca
Removal
3.5%
1.4, 1.3
Fe
Removal
24%
2,0.4
Water Loss
with Foam
5.2%
Experiment 44
This is a repetition of experiment 43 except that the pH
of the filtrate was adjusted to 6.4 by adding 25 cm3 of 0.1 M
Na2CO3 solution.
Analytical Results:
Surfactant Iron Calcium
Initial Solution 370 ppm(theor.266)
Filtrate 54 ppm(theor.50) 160 390 ppm
Foam (170 g; 850 sec) 220 100 540
Foam (85 g; 850 sec) 270 100 610
Residual Solution
(stirred)
23
130
550
76
-------
Experiment 44 (continued)
Test Results
Surfactant
Removal
2 Foams
63%
Accumulation
Ratio 4
Ca
Removal
0
1.4, 1.6
Fe
Removal
28%
0.6, 0.6
Water Loss
with Foam
12%
Experiment 45
Experiments 45 and 46 were similar to experiments 36 - 44,
except that foaming was performed at low temperatures. The tem-
perature of all previous experiments was 21°C - 25 °C. Since the
temperature of the acid mine drainage may be near 0°C, it was
necessary to ascertain the feasibility of foam fractionation at
reduced temperatures.
A solution of 100 cm3 0.1 M FeS04 , 100 cm3 0.1 M H2SO4 and
1900 cm3 water was filtered through 150 g of calcium carbonate
spread on a fine grade sintered glass funnel. One gram gelatin
and 0.1 g Alipal CD-128 were added to the filtrate. The pH was
6.6. The filtrate was kept between 2° and 8°C and subjected
to foaming.
Analytical Results:
Surfactant
Initial Solution
Filtrate 57 ppm(theor . 50)
Foam (78 g; 700 sec) 600
Residual Solution 4=
- - £f \J
(stirred)
Iron
Calcium
277 ppm(theor.266)
120 540 ppm
280 810
162
Test Results:
Surfactant
Removal
1 Foam 24%
Accumulation
Ca
Removal
2.
Ratio
10
1.5
Fe
Removal
0
2.3
Water Loss
with Foam
3.7%
0
77
-------
Experiment 46
The preparation of the solution for foaming was identical
to experiment 45. The pH of the solution was 6.6. The tem-
perature of the solution was kept at 1° to 8°C and subjected
to foaming.
Analytical Results:
Surfactant
Initial Solution
Filtrate 58 ppm (theor. 50)
Foam (56 g; 800 sec) 1290
Residual Solution 16
(stirred)
Iron Calcium
260 ppm(theor. 266)
76 660 ppm
200 660
1.5 330
1 Foam
Test Results:
Surfactant
Removal
73%
Accumulation
Ratio 22
Ca
Removal
51%
1.0
Fe
Removal
98%
Water Loss
with Foam
2.7%
78
-------
Appendix C. Foam Separation of Manganese and Iron from Acid
Solution, Experiments 47 - 50
Experiment 47
A solution containing 1.1 g Alipal EO-526, 80.2 mg Ca,
10 mg Fe and 3.6 mg Mn in 2.25 1 water was successively foamed
at six increasing air rates. The initial solution pH was 5.5.
The first residual solution was foamed in a beaker and 275 g
wet foam was collected.
Analytical Results:
Initial Solution
First Foam
(61 g; 505 sec)
Second Foam
(30 g; 390 sec)
Third Foam
(23 g; 300 sec)
Fourth Foam
(34 g; 110 sec)
Fifth Foam
(168 g; 27 sec)
Sixth Foam
(48 g; 16 sec)
First Residual
Solution
Beaker Foam (275 g)
Second Residual
Solution
Surfactant
500 ppm
7800
5400
2960
900
310
310
30
80
Calcium
36 ppm
157
128
102
59
38
29
29
30
Iron
4 . 1 ppm
9.5
9.1
10.8
29.3
14.5
0.68
0.68
0.68
Manganese
1 . 3 ppm
2.25
1.4
4.0
2.4
1.3
0.9
1.6
12
28
0.38
0.65
Test Results:
Surfactant
Removal
First 6 Foams 95%
Beaker Foam 98%
Ca
Removal
32%
44%
Fe
Removal
86%
93%
Mn
Removal
21%
63%
Water Loss
with Foam
16%
28%
79
-------
Experiment 48
A solution containing 2.2 g Alipal EO-526, 80.2 mg Ca, 10 mg
Fe and 3.6 mg Mn in 2.25 1 water was successively foamed at
eight increasing air rates. The initial solution pH was 3.3.
The first residual solution was foamed in a beaker and 175 g
wet foam was collected.
Analytical Results:
Surfactant
Initial Solution
First Foam
(75 g; 490 sec)
Second Foam
(18 g; 1040 sec)
Third Foam
(66 g; 510 sec)
Fourth Foam
(268 g; 290 sec)
Fifth Foam
(51 g; 200 sec)
Sixth'Foam
(27 g; 107 sec)
Seventh Foam
(60 g; 50 sec)
Eighth Foam
(59 g; 12 sec) 730
First Residual Solution 25
Beaker Foam (175 g) 255
Second Residual Solution
Test Results:
1120 ppm
2760
19800
3430
2030
4650
2760
1090
Calcium
34 ppm
110
400
83
66
87
50
50
46
20
21
20
Iron
5.0 ppm
7.2
16.7
10.5
11.0
10.6
Manganese
10.5
2.0
0.7
3.2
5.2
2.7
0
4.2
3.1
3.3
First 8 Foams
Beaker Foam
Surfactant
Removal
rams 98%
,m 298%
Ca
Removal
57%
62%
Fe
Removal
90%
>90%
Mn
Removal
>46%
>46%
Water Los
with Foam
28%
35%
80
-------
Experiment 49
A solution containing 1.1 g Alipal CD-128, 80.2 mg Ca, 10 rag
Fe and 3.6 mg Mn in 2.25 1 water was successively foamed at six
increasing flow rates. The initial solution pH was 5.6. The
first residual solution was foamed in a beaker and 525 g wet
foam was collected.
Analytical Results:
Initial Solution
First Foam
(50 g; 520 sec)
Second Foam
(64 g; 280 sec)
Third Foam
(25 g; 200 sec)
Fourth Foam
(104 g; 98 sec)
Fifth Foam
(79 g; 51 sec)
Sixth Foam
(52 g; 27 sec)
First Residual
Solution
Beaker Foam (525 g)
Second Residual
Solution
Surfactant
560 ppm
5700
1900
1720
660
800
710
190
240
235
Calcium Iron Manganese
34 ppm 3.4 ppm 1.4 ppm
48
82 1.5
80 10 3.0
47 0.8 1.6
46 1.8
49 0.4 0.9
26 0.4 0.9
28 0.9
24 0.31 0.9
Test Results:
Surfactant
Removal
First 6 Foams 72%
Beaker Foam' 75%
Ca
Removal
36%
58%
Fe Mn Water Loss
Removal Removal with Foam
90% 45% 20%
95% 61% 40%
81
-------
Experiment 50
A solution containing 2.2 g Alipal CD-128, 80.2 mg Ca,
10 mg Fe, and 3.6 mg Mn in 2.25 1 water was successively foamed
at six increasing air rates. The initial solution pH was 3.4.
Analytical Results:
Surfactant
Calcium
Iron
Manganese
Initial Solution
First Foam
(16 g; 1040 sec)
Second Foam
(82 g; 490 sec)
Third Foam
(296 g; 290 sec)
Fourth Foam
(171 g; 210 sec)
Fifth Foam
(194 g; 50 sec)
Sixth Foam
(127 g; 27 sec)
Test Results
Surfactant
Removal
955 ppm
9800
4500
1830
1560
1120
945
:
Ca
Removal
34 ppm
460
114
46
47
32
29
Fe
Removal
4 . 9 ppm
114
24
2.3
1.4
1.4
1.5
Mn
Removal
2
12
4
1
1
1
1
.0
.2
.1
.6
.8
.5
.7
W;
w:
First 6 Foams 78%
66%
90%
58%
Water Loss
with Foam
39%
82
-------
Appendix D. Foam Separation of Iron, CaIcium and Magnesium from
Synthetic and Real Acid Mine Drainage, Experiments 51 -
Experiment 51
58.
Two grams sodium dodecyl sulfate was added to 2 liters
synthetic acid mine water, and the
for a total of 6 hours.
Analytical Results :
Surfactant
Initial Solution 1240 ppm
Foam (66 g; 53CM-270 sec) 18600
Foam(71 g; 190-^140 sec)6760
Residual Solution 165
Test Results:
Surfactant
% Removal 88
Accumulation Ratio 15, 5.5
Water Loss was 6.9%
Experiment 52
Repetition of Experiment 51.
Analytical Results:
Surfactant
Initial Solution 1370 ppm
Foam(158 g;
530-»270 sec) 5600
Foam (246 g;
190^140 sec) 2600
Residual Solution 97
Test Results:
Surfactant
% Removal 94
Accumulation Ratio 4.1, 1.9 0
resulting
Iron
122 ppm
215
160
120
Iron
8
2, 1.3
Iron
115 ppm
95
110
110
Iron
24
.8, 1.0
liquid was
Calcium
83 ppm
250
110 -
68
Calcium
24
3, 1.3
Calcium
88 ppm
140
88
70
Calcium
36
1.5, 1.0
foamed
Magnesium
19 ppm
30
25
21
Magnesium
0
1.6, 1.3
Magnesium
40 ppm
50
40
33
Magnesium
34
1.2, 1.0
Water Loss was 20%
83
-------
Experiment 53
Two grams Alipal CD-128 were added to 2 liters natural
acid mine water and the solution was foamed for 5.5 hours. The
initial solution pH was 4.5.
Analytical Results:
Initial Solution
Foam (34 g;
270+800 sec)
Foam (19 g;
800 sec)
Residual Solution
Surfactant
1270 ppm
5500
10200
810
Iron
90 ppm
105
110
70
Calcium
220 ppm
240
310
200
Magnesium
85
100
160
89
ppm
Test Results:
Surfactant Iron Calcium
% Removal 38 22 9.1
Accumulation Ratio 4.3, 8.0 1.2, 1.2 1.1, 1.4
Water Loss was 2.6%
Magnesium
0
1.2, 1.9
Magnesium
Experiment 54
Two grams sodium dodecyl sulfate were added to 2 liters
natural acid mine water and the solution was foamed for 5.5 hours.
The initial solution pH was 4.5.
Analytical Results:
Surfactant Iron Calcium
Initial Solution
Foam (75 g;
360 sec)
Foam (20 g;
360-»180 sec)
Residual Solution
Test Results:
% Removal
Accumulation Ratio
Water Loss was 4.7%
1190 ppm
16700
10500
56
s :
Surfactant
96
14, 8.8
71 ppm
167
290
79
Iron
0
2.3, 4.1
207 ppm
780
360
160
Calcium
26
3.8, 1.7
85 ppm
99
123
73
Magnesium
18
1.2, 1.4
-------
Experiment 55
One gram sodium dodecyl sulfate -was added to 2 liters natural
acid mine water. The initial solution pH was 4.5. Since the
foam did not rise above the top of the tower, the foam present
in the tower was washed into a receptacle and analyzed as the
"first foam". To the residue, 1.0 g gelatin dissolved in
100 cm3 natural acid mine water was added. The solution was
foamed at drainage time of 510 seconds. The total foaming time
was 6 hours.
Analytical Results:
Acid Mine Water
Initial Solution
First Foam (34 g)
Second Foam (454 g)
Residual Solution
Surfactant
540 ppm
19300
385
2
Iron
71 ppm
79
315
137
62
Calcium
168 ppm
171
700
230
158
Magnesium
79 ppm
117
163
176
107
Test Results:
Surfactant Iron Calcium
% Removal > 99 29 28
Accumulation Ratio 36,0.7 4,2 4.1,1.3
Water Loss was 24%
Magnesium
29
1.4, 1.5
85
-------
Experiment 56
One gram Alipal CD-128 was added to 2 liters natural acid
mine water. Two foams were collected in 6 hours of foaming.
When the foam ceased to reach the top of the tower, 1.0 gram
gelatin dissolved in 100 cm3 natural acid mine water was mixed
with the residual solution and a third foam collected.
Analytical Results:
Surfactant
Initial Solution
Foam (55 g;
350-»520 sec)
Foam (62 g;
350^150 sec)
Foam (130 g;
3000 sec)
Residual Solution
590 ppm
5800
5400
1080
360
Iron Calcium
55 ppm
Magnesium
171 ppm 82 ppm
240
270
80
65
260
260
150
159
108
111
59
89
Test Results:
Surfactant
% Removal 46
Acpumulation Ratio 10, 9, 2
Water Loss was 12%.
Iron
0
4, 5, 1.5
Calcium
18
1.5, 1.5, 1.5
Magnesium
4.5
0.9, 1.3, 1.3
86
-------
Experiment 57
Two grams Alipal EO-526 were dissolved in 2 liters natural
acid mine water. The liquid was foamed for a total of 14 hours
in which three foam fractions were collected. Then the residual
solution was transferred into a beaker and foamed. The foam
was removed by suction (Figure 3).
Analytical
Acid Mine Water
Initial Solution
Foam (45 g;
400 sec)
Foam (61 g;
400 sec)
Foam (70 g;
400 sec)
First Residual
Solution
Beaker Foam
Second Residual
Solution
Results:
Surfactant
1130 ppm
7500
11800
8000
220
500
110
Iron Calcium Magnesium
68 ppm 156 ppm 87 ppm
89 182 100
190
170
300
61
72
57
210
230
210
152
165
149
110
154
82
87
66
83
Test Results:
Surfactant
% Removal:
First 3 Foams ^ SO
Beaker Foam ^ 90
Accumulation Ratio 7, 10, 7;
Iron
"36
2, 2, 3.4;
Magnesium
Calcium
18
1.2, 1.2, 1.2; 1.1, 1.5, 0.8
Water Loss was 8.8% for the first three foams.
87
-------
Experiment 58
Repetition of Experiment 57.
Analytical Results:
Initial Solution
Foam (17 g;
900 sec)
Foam (20 g;
900 sec)
First Residual
Solution
Beaker Foam
Second Residual
Solution
Surfactant
1000 ppm
34000
24800
340
800
260
Iron Calcium Magnesium
75 ppm 157 ppm 110 ppm
250
315
76
83
81
410
335
160
310
153
200
175
88
202
105
Test Results:
Surfactant
% Removal
First Two Foams
Beaker Foam
Accumulation Ratio
/^74
34, 25
Iron
4, 4
Calcium
2.6, 2.1
Magnes ium
~s 20
<" 4
1.8, 1.6
Water loss was 1.9% for the first two foams.
88
-------
BIBLIOGRAPHIC:
Horizons Incorporated, Treat-
ment of Acid Mine Drainage by
Foam Separation, Final Report,
FWQA Program No. 14010 DEE,
Contract No. 14-12-496
August, 1970
ABSTRACT
Basic experiments were con-
ducted to establish the feasi-
bility of foam fractionation in
the treatment of acid coal mine
drainage for the removal of the
metal ions iron, calcium, man-
ganese and magnesium. The
ACCESSION NO.
KEY WORDS:
Foam Separation
Acid Coal Mine
Drainage
Metal Ion Removal
Iron
Calcium
Manganese
Magnesium
Surfactant
Treatment Costs
BIBLIOGRAPHIC:
Horizons Incorporated, Treat-
ment of Acid Mine Drainage by
Foam Separation, Final Report,
FWQA Program No. 14010 DEE,
Contract No. 14-12-496
August, 1970
ABSTRACT
Basic experiments were con-
ducted to establish the feasi-
bility of foam fractionation in
the treatment of acid coal mine
drainage for the removal of the
metal ions iron, calcium, man-
ganese and magnesium. The
ACCESSION NO.
KEY WORDS:
Foam Separation
Acid Coal Mine
Drainage
Metal Ion Removal
Iron
Calcium
Manganese
Magnesium
Surfactant
Treatment Costs
BIBLIOGRAPHIC:
Horizons, Incorporated, Treat-
ment of Acid Mine Drainage by
Foam Separation, Final Report,
FWQA Program No. 14010 DEE,
Contract No. 14-12-496,
August, 1970
ABSTRACT
Basic experiments were con-
ducted to establish the feasi-
bility of foam fractionation in
the treatment of acid coal mine
drainage for the removal of the
metal ions iron, calcium, man-
ganese and magnesium. The
ACCESSION NO.
KEY WORDS:
Foam Separation
Acid Coal Mine
Drainage
Metal Ion Removal
Iron
Calcium
Manganese
Magnesium
Surfactant
Treatment Costs
-------
independent variables controlling foam separa-
tion of metal ions were determined to be the
concentration ratio of surfactant to iron,
the air volume throughput, the foam drainage
time, the total dissolved salt content and
the type of surfactant used.
The major part of iron, calcium, manganese
and magnesium can be foam separated from acid
solution by proper control of the independent
variables. Reduction of residual surfactant
concentration in the treated water and reduc-
tion of water entrained with the foam are two
areas in need of further investigation.
Operating and capital costs are estimated
for 0.1 and 1.0 MGD batch treatment plants.
independent variables controlling foam separa-
tion of metal ions were determined to be The
concentration ratio of surfactant to iron,
the air volume throughput, the foam drainage
time, the total dissolved salt content and
the type of surfactant used.
The major part of iron, calcium, manganese
and magnesium can be foam separated from acid
solution by proper control of the independent
variables. Reduction of residual surfactant
concentration in the treated water and reduc-
tion of water entrained with the foam are two
areas in need of further investigation.
Operating and capital costs are estimated
for 0.1 and 1.0 MGD batch treatment plants.
independent variables controlling foam separa-
tion of metal ions were determined to be the
concentration ratio of surfactant to iron,
the air volume throughput, the foam drainage
time, the total dissolved salt content and
the type of surfactant used.
The major part of iron, calcium, manganese
and magnesium can be foam separated from acid
solution by proper control of the independent
variables. Reduction of residual surfactant
concentration in the treated water and reduc-
tion of water entrained with the foam are two
areas in need of further investigation.
Operating and capital costs are estimated
for 0.1 and 1.0 MGD batch treatment plants.
-------
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05D
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Federal Water Quality Administration, Department of the Interior,
Washington, D. C.
Treatment of Acid Mine Drainage by Foam Separation
10
22
Authors)
Bi kerman , J . J .
Hanson, P. J.
Rose, S. H.
1 X Project Drxignation
FWQA Program No 14010 DEE
21 /Vole
Citation
Federal Water Quality Administration, Washington, D. C.
Descriptors (Starred First)
*Foam Separation, *Acid Coal Mine Wastes, *Iron, *Calcium, *Magnesium, *Surfactant,
Treatment Cost, Water Purification
25
Identifiers (Starred First)
27 I Abstract
' Basic experiments were conducted to establish the feasibility of foam
fractionation in the treatment of acid coal mine drainage for the removal of the
metal ions iron, calcium, manganese and magnesium. The independent variables
controlling foam separation of metal ions were determined to be the concentration
ratio of surfactant to iron, the air volume throughput, the foam drainage time,
the total dissolved salt content and the type of surfactant used.
The major part of iron, calcium, manganese and magnesium can be foam
separated from acid solution by proper control of the independent variables.
Reduction of residual surfactant concentration in the treated water and reduction
of water entrained with the foam are two areas in need of further investigation.
Foam separation was tested on add drainage, partially lime neutralized
drainage and complete limestone neutralized drainage. Tests on model solutions
Indicate that treatment of raw acid drainage is most feasible at present.
Operating and capital costs are estimated for 0.1 and 1.0 MGD batch
treatment plants.
Abstractor
Institution
HnHrnns, Tnrnrpnrated
SEND TO: WATER RESOURC
WR:1O2 IREV. JULY 196ft)
WRSIC
RCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 20240
U. S. GOVERNMENT PRINTING OFFICE : 1971 O - 410-310
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