EPA-670/2-73-080
September 1973
Environmental Protection Technology Series
einoval of Heavy Metals From
Mine Drainage By Precipitation
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office ot Research and
Monitoring, Environmental Protection Aqency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
1. Environmental Monitoring
5 • Socioeconomic Znvjronmental Studies
This report has been assigned to the ENVIRONMEN AL
PROTECTION TECHNOLOGY series. This series
describes research pert orn ed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and nonpoint sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards..
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EPA-670/2-73-080
September 1973
REMDVAL OF HEAVY METALS
FROM MINE DRAINAGE BY PRECIPITATION
By
Laurence W. Ross
Grant No. 14040 FZC
Program Element IBBOlj-O
Project Officer
James Rouse
National Field Investigations Center
Office of Enforcement & General Council
Denver, Colorado 80225
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, B.C. 20^0
For sale by the Superintendent ot Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1
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EPA Review Notice
This report has been reviewed by the Environmental
Protection Agency and approved for publication.
Approval does not signify that the contents
necessarilY reflect the views and policies of the
Environmental Protection Agency, nor does mention
of trade names or commercial products constitute
endorsement or recommendation for use.
ii
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ABSTRACT
Heavy metals in mine drainage waters of the Roc1 y Mountains can be
removed by a two-stage process consisting of (1) neutralization followed
by (2) sulfide treatment. The first stage removes ferric and. aluminum
hydroxides, and the second (sulfide) stage precipitates the heavy metals
that are most objectionable as pollutants, and that are of possible interest
for economic recovery. The two-stage process has been demonstrated in the
laboratory and in a field experiment.
In the field, powdered lime was employed for neutralization, and barium
sulfide was employed as sulfide source in a two-stage treatment tank. The
ferric and. aluminum hydroxides failed to settle cthen even the slightest winds
disturbed the surface of the settling pond, but the sulfides settled within
a few feet downstream. The measured pH of treated stream.$ has proven entirely
satisfactory for control of chemical additions.
A computer program based on published values of equilibrium constants
and solubility-product constants is capable of adequate prediction of the
required chemical quantities for treatment, and of the resulting metal con-
centrations in solution.
The economics of chemical addition indicates that recovery of sulfides
(CuS, ZnS) for sale to smelters can partially offset the cost of treatment,
but never completely.
This report was submitted in fulfillment of Grant Number 14040 FZC between
the Environmental Protection Agency (EPA) and the grantee, University of Denver,
Denver, Colorado 80210.
111
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CO1 1TET TS
Section Page
I ConclusiOns 1
II RecommendatiOns 3
III Introduction 5
I V Technical Parameters of Metal-Bearing Mine
Drainage 9
V Preliminary Experimental Tests 13
VI Field Application of Chemical Treatment 25
VII Computer Simulation of Experimental Results 35
VIII Practical Aspects of Precipitation of Heavy
Metals From Mine Drainage Waters 14.7
IX References 53
X Acknowledgments 55
XI Appendix 1 57
V
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FIGURES
Page
1 MINE J, IN THE RED MOUNTAIN DISTRICT OF SOUHWESTERN
COLORALO. IT WAS BUILT PRINCIPALLY AS A DRAINAGE
TU N1NEL FOR OTHER MINES NEARBY. 7
2 MINE K, NEAR RED MOTJNTAIN PASS. DRAINAGE ENTERS THE
POND AT THE LEFT OF THE TRAILINGS PILES. 7
3 FRACTIONATION OF DISSOLVED Zn AND Fe FROM
SOLUTION BY BaS. THE SOLUTION CONTAINEr) 100 mg/i
OF EACH METAL. DASHED LINES ARE STOICHIOMETRIC
LINES. 114
++ ++ ++
I . FRACTIONATION OF Cu , Zn AND Fe FROM SOLUTION BY
Na 2 S.9H 2 0. THE SOLUTION CONTAINED 100 mg/i OF
EACH METAL. DASHED LINES ARE STOICHIOMETRIC LINES. 15
5 RESPONSE OF DISSOLVED Mn (100 mg/i) TO ADDITION OF
0.02 M SULFIDE SOLUTIONS. 16
6 RESPONSE OF DRAINAGE WATERS FROM MINES J AND K TO
SULFIDE ADDITION. THE EXTENT OF BUFFERING MAY
BE USED TO ESTIMATE THE TOTAL METAL CONTENT IN
SOLUTION. 18
7 TREATMENT CURVES FOR DRAINAGE WATER OF MINE BH (IDA ho).
TREATMENT WITH SULFIDE BEGINS AFTER NEUTRALIZATION
TOpH5. 19
v i.
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Page
8 TREATMENT CURVES FOR CREEK WATER, SOURCE BB (MONTANA).
TREATMENT WITH SULFIDE BEGINS AFTER NEUTRALIZATION
TOpH5. 20
9 TREATMENT CURVES FOR DITCH WATER, SOURCE BT (MONTANA).
TREATMENT WITH SULFIDE BEGINS AFTER NEUTRALIZATION
TO pH 5. THIS WATER HAD THE HIGHEST METALS CONCEN-
TRAT ION OF ANY WATERS FOUND IN THE ROC1C I43U1 1TAINS. 21
10 RES NSE CURVES OF SEVERAL DRAINAGE WATERS, SAMPLED
FROM OPEN SOURCES IN COLORAr , IDAHO AND MONTANA.
SOME ARE OBVIOUSLY ALKALINE, EVEN THOUGH OCCURING
IN CHIEFLY NYRITIC DISTRICTS. 23
11 NEUTRALIZATION CURVES OF WATER FROM MINERAL CREEK
(cOL0RA:1X)), WHERE THE FIELD STUNY WAS PERFORMED. 26
12 ILLUSTRATION OF THE FIELD INSTALLATION FOR TREATING
MINERAL CREEK NY THE TWO-STAGE PROCESS. WATER
ENTERS THE FIRST STAGE OF THE RECTANGULAR VESSEL
(RIGHT FOREGROUND). 28
13 SCHEMATIC DIAGRAM OF THE FIELD INSTALLATION FOR TWO-
STAGE TREATMENT. 29
11.1. THE FIELD INSTALLATION A Z ERECTED, BUT BEFORE THE
LIME AND SULFIDE FEEDING APPARATUS WAS ADDED. 31
15 CLOSE-UP OP THE TREATMENT FACILITIES OF THE FIELD
INSTALLATION. IN THE FOREGROUND IS THE TWO-STAGE
TREATMENT VESSEL. 31
vii
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Page
16 COMPARISON OF ASURED AND COMPUTED NEUTRALIZATION
CURVES FOR WATER OF MINERAL CREEK, TAKEN
FROM THE POND OF MINE K. 38
17 COMPUTED TWO-STAGE TREATMENT CtJRVES, WITH SULFIDE
TREATMENT (STAGE 2) CO!v2v ENCING AT pH )4 .0. 1 O
18 COMPUTED TWO-STAGE TREATMENT CURVES, WITH SULFIDE
ADDITION (STAGE 2) COMMENCING AT pH 5.0.
19 COMPUTED TWO-STAGE TREATMENT CURVES, WITH SULFIDE
ADDITION (STAGE 2) CONIvENCING AT pH 6.0. Ll2
20 COMPARISON OF THPX)RE’TICAL AND MEASURED NEUTRALIZATION
CURVES, tJNDER THE ASSUMPT ION OF NO VOLUME
INCREASE. L . 3
21 COMPARISON OF THEORETICAL AND MEASURED SULFIDE
TREATMENT CURVES, URDER THE ASSUMPTION OP NO
VOLUME INCREASE. pH. DENOTES TEE INITIAL pH.
22 SETTLING TESTS FOR A MIXED METAL SULFIDE FLOC AS A
FUNCTION CF SURFACTANT ADDITION. WATER FROM
MINE BH (IDAHO). SURFACTANT: CALGON M- 590
pH 5.5. 52
Vii ] -
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TABLES
No Pace
1 Results of Analyses - Metals (Heavy and/or Toxic) 6
ix
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SECTION I
CONCLUS IONS
Mine drainage waters of the Rocky Mountains often contain con-
siderable quantities of heavy metals, which connot be removed by
neutralization alone. A two—stage process of (1) neutralization,
followed by (2) addition of sulfide chemicals is shown to be effective
in removing practically all polluting metals at pH 6.5. This result
has been demonstrated in the laboratory and verified in the field.
A field treatment installation is feasible with very simple
facilities. The operations of chemical addition and sedimentation
of the resulting precipitates can be achieved in facilities essentially
of earthwork, with a minimum of construction and no process vessels
required. Auxiliary transfer and storage facilities consist of lime
solids-handling equipment; sulfide solution storage, pumping, and
metering equipment; and control instrumentation. These are relatively
inexpensive, but the necessity of storing solid lime and of handling
and mixing sulfide (BaS) is a critical economic factor.
Barium sulfide (BaS) is recommended for sulfide treatment because
Ba does not persist in the treated water, being completely precipitated
as BaSO 1 f. Lime (CaO) is selected for neutralization on economic
grounds.
A large settling pond is not necessary for recovery of the sulfide
precipitates (cuS, ZnS) of economic interest, because these minerals
precipitate very rapidly. However, the hydroxides (e.g., Fe(OH) 3 ,
Al(OI-r) 3 ) from the neutralization stage do not readily precipitate, and
this requires consideration of a second settling pond or of filtration
through earth.
There is evidence that addition of cationic flocculant in ppm
1
-------
concentrations aids in the sedimentation of su.lfides to a significant
extent.
Computer simulation of the response of mine drainage water to
chemical addition is feasible by use of published solubility-product
constants and equilibrium constants.
2
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SECTION II
RECOMt’4ENDAT TONS
The two-stage treatment process described in this report seems
fully capable of treatment of any metal-bearing mine drainage stream.
A continuous field test, on a drainage stream from an active or in-
active mine, is desirable in order to confirm the ease of controlling
metal removal, with pH as the criterion.
The fractionation of hydroxides (Fe(OH) 3 , ATL(OH) 3 ) from sulfides
(CuS, znS, MnS, etc.) needs to be explored further, in order to test
the feasibility of achieving relatively pure sulfide precipitates
under field conditions. It appears that a perfectly quiescent settling
pond may achieve hydroxide precipitation, so that sulfides can be
precipitated in a second pond without hydroxide contamination.
Finally, it is recommended that less expensive sources of sulfide
than those commercially available (e.g., BaS, Na 2 S, NaHS) be investi-
gated. This points directly to biologica.l production of E 2 S in situ
from the plentiful sc 2 available in drainage waters. The possibility
of biological generation of S 2 has been demonstrated by several
investigators (including the present investigators), and merits further
study.
3
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SECTION III
INTRO DtJCT ION
THE PROBLEM OF METAL-BEARING MThE DRAINAGE WATERS OF TIlE ROCKY
‘flUNTA INS
The Rocky Mountains have been the scene of intense mining
activity for more than a century. In several districts, the mineral
formations are highly pyritic, and the drainage from inactive as
well as active mines is intensely acidic and loaded with metals
toxic to aquatic life.
The Red Mountain district of the San Juan Mountains in
southwestern Colorado, where the field treatment portion of the
present study was performed, is characterized by a series of
tertiary volcanic rocks, intruded by a later volcanic pipe. Sulfide
minerals are especially prevalent in the pipe. The result is a
geologic situation that is especially conducive to metal-bearing
acid mine drainage, without the buffering influence of alkaline
minerals that are common elsewhere in the mining regions of the
Rocky Mountains. Such a predominance of sulfide minerals is not
the usual situation in the Rocky Mountains, but there are several
primary sulfide mineral districts in Colorado, Idaho, Montana and
Utah.
The characteristic feature of the metal-bearing drainage, as
illustrated in Table I, is high toxicity combined with relatively
small volume. Figures 1 and 2 show the two typical inactive mines
that supplied water for this study (Mines J and K). Interestingly,
no gold is found in the drainage of the region, and very little
5
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TABLE I
RESULTS OF ANALYSES - I TALS (NEAVY AND/OR TOXIC)
Water from Mine K
Iron
Date Arsenic Cadmit n Copper Total Lead Manganese Nickel Aluminum Zinc SO 14
Sample Field As Cd Cu Fe Pl Mfl Ni Al Zn
Coll’td . _____ pg/i pg/i pg/i pg/i pg/i pg/i pg/i pg/i pg/i mg/i
8/28/68 — 11,300 613 71,600 422,000 1410 9,110 300 32,200 181,000 1,980
9/12/68 2.8 14,300 744 87,000 525,000 450 12,700 350 39,300 215,000 2,480
10/01/68 2.6 i6, oo 814 99,200 609,000 390 14,700 420 46,200 239,000 2,840
10/24/68 3.0 18,200 814 101,000 651,000 390 15,100 48o 48,200 242,000 3,040
a 11/08/68 - 20,600 910 115,000 71)4,000 360 16,800 480 5)4,300 26)4,000 3,380
12/03/68 - 22,000 1,000 128,000 800,000 1440 19,000 510 62,500 294,000 3,820
4/28/69 2.7 12,300 1460 61,900 )406,000 46o 9,510 2140 31,600 135,000 1,830
6/014/69 2.8 10,700 660 74,900 423,000 500 7,000 250 29,000 174,000 1,930
6/17/69 3.1 7,750 520 60,100 336,000 40 ,o4o 230 24,600 246,000 1,570
7/02/69 2.6 6,010 440 51,600 291,000 1400 14,520 190 20,800 122,000 1,400
Data: Federal Water Pollution Control Administration
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FIGURE 1. Mine J, in
Colorado.
Tunnel for
the Red Mountain District of Southwestetn
It was Built Principally as a Drainage
Other Mines Nearby.
FIGURE 2. Mine K, near Red Mountain Pass. Drainage Enters the
Pond at the Left of the Trailings Piles.
7
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silver or lead, although all three metals are extensively mined
there. This fact is influential when metal recovery is discussed as
a means of offsetting the cost of pollution abatement.
8
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SECTION IV
TECHNICAL PARAMETERS OF }1ETAL-BEARIN( MThE DRAINAGE
Drainage waters from mines in the sulfide-mineral districts
of the Rocky Mountains are often highly acidic. The present
investigators, for example, have found pH i.it in the drainage pond
of mine K (Fig. 2), and the typical value for raw drainage water
is about 2.5 to 3.0 everywhere in such regions. The oxidation-
reduction potential of these mine drainage waters is generally
about +11.50 my.
Dissolved metals in these drainages include Fe, Zn, Al, Cu,
Mn, roughly in that order of concentration, and may also include
quantities of As and Hg at levels that are considered toxic. Iron
is practically always measured as total Fe (see Table i) because
of the difficulty of discriminating FC 3 and FC 2 , especially under
field conditions.
All these metals are capable of removal either by precipitation
as insoluble species (oxide, hydroxide, etc.) or by adsorption on
various minerals in one or another of their dissolved states. There
are several modern studies of hydroxide precipitation available
(1,2,3,11.) and one in which sulfide precipitation is considered (5).
Adsorption has been studied very recently, and work is continuing.
Perhaps the principal natural mechanism of elimination of toxic
metals (or “heavy’ t metals) from mine drainage waters is dilution
by ambient run-off from springs, rainfall, and snciwmelt, which will
raise the pH sufficiently to cause precipitation of the metal as
hydroxide. Despite these natural mechanisms, hundreds of miles of
streams in the Rocky Mountains are severely polluted and incapable
of supporting aquatic life.
9
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The present investigation concerns the deliberate precipitation
of metals by chemical addition, involving the following general
process:
+d + -m x MDd (i)
where M denotes metallic cation of valence (÷d)
D denotes anion of valence (-m)
x is the conversion, in moles, to insoluble species MDd.
For example, the most common precipitation process associated with
mine drainage waters is
Fe 3 + 3 OH Fe (011)3
+3
in which d = 3, m = 1, M is ferric ion Fe , and D is hydroxyl ion
OH
For precipitation reactions of this type, the ‘ t solu1 ility
product tt is defined as
[ M]m [ DJd = K
S
in which the activity of the solid MDd phase is assumed unity, i.e.,
l•d = • With this terminolo r, a mass blance for the situation
where precipitating chemicals are added yields (with brackets
denoting molar concentrations as usual):
+d m -m d
rM. - m.x. D -L,dx.
______ k ki (2)
I V Spi
where V is solution volume, i denotes solid phase, j denotes cation,
and k denotes anion.
10
-------
In aqueous medium, the dissociation of water must be considered:
+ 0H Yi HOH.
(3)
When the anion is sulfide ion, two additional equilibria must
be considered:
+ s_ 2
(14.)
+ - 13
It +HS H 2 S.
(5)
These three equilibria may also be expressed in terms of their
respective equilibrium constants, by means of a mass balance, as
follows:
1 K (6)
(7)
e
(8)
eHS
Here d x represents the demand of metal precipitation reactions
[
I
H - 1 - - 13 j [
73] f
V
H -y 1 -y 2
0H -
- E d x.
V
-
V
- dx.
V
HS +Y 2 3r 3
V
I H -y 1 -y 2 -y 31 [ HS+Y 2 -1 3
___ v JE v
H 2 S ÷
l v
11
-------
upon the anionic species OH and and d .y. represents the
demand upon these anions r reactions (3), (Li ) and (5). It should
be noted that the molar concentration [ OH] may be expressed as
which is the procedure actually used in computation, as
described in Section VII below.
The values of and Ke for the species involved in the present
investigation are subject to wide discrepancies, in the published
literature. It is not unusual to observe a variation of two or
three orders of magnitude, depending on the source. This point
will be discussed in relation to the findings of the investigation,
in Section VII below, where “best values” of and K for the
systems of interest will be recommended.
Only the simplest precipitation mechanisms are considered in
the present investigation. A vast number of ionic reactions are
possible with the species of interest in aqueous medium, and these
are catalogued in references 7 and 8. The justification for con-
sidering only the simplest is that these are the most favorable
equilibrium constants under the given conditions, and the other
possible reactions occur to negligible extent.
12
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SECTION V
PRELfl’IINAR EXPERIMENTAL TESTS
1. Simulated Drainage Waters
From examination of solubility product constants, it seemed
apparent that hydroxides and sulfides were the only reasonable
chemical species by which heavy metals could be precipitated from
mine drainage waters. Experimental tests of precipitation were
undertaken in the laboratory.
Initial experiments were conducted with pure solutions, prepared
in the laboratory. Figures 3 and 14. show that solutions containing
Fe, Zn and Cu respond to sulfide addition in a fashion very close
to theoretical expectations. This suggests that metals could be
fractionated from solution, which is economically attractive, as
discussed below.
These three metals, when alone in solution, respond to sulfide
addition in essentially theoretical fashion. However, manganese
departs significantly from stoichiometric agreement with total
sulfide added (Fig. 5). This behavior indicates that Mn precipitation
must be considered in combination with the reactions between sulfide
ion and water, eqns. (14.) and (5) in the preceding section.
Hydroxide precipitation is not investigated in experiments of
this type, because it is regarded strictly as a means of Fe and Al
elimination and pH adjustment.
The response of dissolved Fe, Cu Zn and Mn to addition of BaS
and Na 2 S.9H 2 0 solutions is practically identical. This indicates
that the sulfides are completely dissociated in solution. Barium
sulfide, BaS, is regarded as the leading contender for field use
because Ba precipitates as BaSO 14 , while Na remains in solution,
13
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10.0 100
8.0 80
E
6.0 60
z
0
a . —
) 1
4.0 40<
I-
L u
2.0 20
0 0
140
STOICHIOMETRIC EQUIVALENT S (from BaS)
+ + ++ ++
Fig. 3. Fractionation of Dissolved Cu , Zn and Fe From Solution by BaS. The
Solution Contained 100 mg/i of Each Metal. Dashed Lines are Stoichiometric
0 20 40 60 80 100 120
Lines.
-------
100
80
E
60
(1)
z
2
40
I-
LU
20
0
140
Fig. 4.
Fractionation of Cu and Fe From Solution
by Na 2 S 9H 2 0. The Solution Contained 100 mg/i of
Each Metal. Dashed Lines are Stoichiometric Lines.
8.0
6.0
U i
4.0
2.0
0 20 40 60 80 100 120
STOICHIOMETRIC EQUIVALENT S (from No 2 S9H 2 0)
-------
r
a
10 .0
8.0
6.0
4.0
2.0
0
0
Fig. 5. Response of Dissolved Mn (100 mg/I) to Addition of 0.32 M Sulfide
Solutions.
100
80
E
60 I
U i
( I )
U
z
400
z
C
20
STOICHIOMETRIC EQUIVALENT 5
-------
in violation of the announced policy of the EPA regarding addition of
polluting species to waterways. In addition, BaS is less expensive
than Na 2 S•9H 2 0, although more expensive than NaHS in commercial
quantities.
2. Actual Drainage Waters
When actual drainage waters are examined, the situation is much
more difficult to analyze. The most usefti tool (and certainly the
simplest) seems to be characteristic titration curves, also called
“fingerprint curves” that show the pH response of water samples to
addition of sulfide or hydroxide.
Figure 6 shows characteristic curves for mines J and K, from
titrations made on drainage waters collected in June, 1970. These
curves permit estimates of the metal content as follows:
Mine J 3 )3.14. meqJi
Mine K 11.2 meqJl
Measurements of metals on the same samples yielded the following
concentrations:
Mine 3 Mine K
Fe (total), mg/i 860 310
Zn, mg/i 280 l1 .i.1
Cu, mg/i 10.5 2.0
At this time, the investigation did not have access to efficient
means of analyzing metal concentrations. The concentrations above
were measured by the Department of Health, State of Colorado.
The characteristic curves shown in Figs. 7, 8 and 9 represent
drainage waters in Idaho and Montana, from samples taken in June,
1971. The drainage labeled BTP (Fig. 9) is by far the most potent
discovered in the entire investigation. It was taken from an open
17
-------
12.0
10.0
8.0
6.0
4.0
2.0
0
Fig. 6. Response of Drainage Waters
of Buffering MRY be Used to
From Mines J and K to Sulfide Addition. The Extent
Estimate the Total Metal Content in Solution.
H
20 30 40 50 60
SULFIDE ADDED, ml O.2M Na 2 S9H 2 O
-------
40
Fig. 7. Treatment Curves for Drainage Water of Mm BH (Idaho). Treat-
ment with Sulfide Begins After Neutralization to pH 5.
I0
9
T
I-. .
50
a
-J
::
I0
20
80
90
100
40 50 60
SULFIDE ADDED, ML 0.1 M Na 2 S
70 80
-------
40
50
90
l00
Fig. 8. Treatment Curves for Creek Water, Source BB (Montana).
Treatment with Sulfide Begins After Neutralization to pH 5.
0
0 .
-J
60
0
w
70
4
I-
L U
80
0 40
80 120 150 200 240 280
SULFIDE ADDED) MLOJM Na 2 5
-------
I0
Fig. 9. Treatment Curves for Ditch Water, Source BT (Montana).
with Sulfide Begins After Neutralization to pH 5. This
the Highest Metals Concentration of any Waters Found in
Rocky Mountains.
Treatment
water Had
the
-J
>
0
U i
-J
4
I-
I i i
200 300 400 500
SULFIDE ADDED, ML O.IMNo 2 S
-------
culvert in a Montana city, and it was probably drainage from a mining
or milling operation nearby.
A final set of characteristic curves is showr in Fig. 10
representing several relatively benign drainages from Colorado, Idaho,
and Montana. Several are definitely alkaline, even though taken
from mining regions where sulfide deposits are typical.
22
-------
0 10 20 30 40 50 60 70 80 90
SULFIDE ADDED, ML O.IM No 2 S
Fig. 10. Response Curves of Several Drainage Waters, Sampled from Open Sources in
Colorado, Idano and Montana. Some are Obviously Alkaline, even though
Occuring in Chiefly Pyritic Districts.
13
12
I I
I0
9
8
t )
7
T
6
5
4
2
0
-------
SECTION VI
F LD APPLICATION OF CHEMICAL TREATMENT
1. Concept of Field Chemical Treatment
The conclusion to be drawn from Sections I V and V is that
sulfide addition to mine drainage waters will eliminate the dissolved
metals. However, elimination of ferric iron and aluminum would
represent a waste of sulfide, because straightforward neutralization’
by dilution or addition of relatively inexpensive lime is sufficient
to remove these two metals.
Therefore the present investigators conceived the principle
of two-stage chemical treatment. In the first stage, neutralization
is achieved with lime (solid or slurry) to a certain pH level, and.
then sulfide is added to remove the remaining objectionable metals.
There would be no objection in principle to adding the two
chemicals (lime + sulfide) together, but this would. require a
foreknowledge of metal concentrations. Control by pH adjustment
is simpler and (as shown below) very successful for field adaptation.
The ultimate pH of the treated water was chosen as pH 6.5,
because this is the typical ambient pH of waters in the Red Mountain
district of southwestern Colorado, where the field study was performed.
The pH of treated water in the first stage was chosen as 5.0, since
this represents a point where the potential metals of commerce -- Cu
and Zn -- are still largely in solution, while Fe and Al are largely
precipitated (Fig. 11). The characteristic decline in curves of
metal concentration is due to dilution; precipitation is indicated
by distinct breaks in the curves. In practice, pH 6.o might be
preferable for transition from Stage 1 to Stage 2, because this
represents a greater economy in chemicals cost, but control would be
25
-------
E
0
I-
z
IL l
0
z
0
0
-J
LU
2
48
44
40
36
32
28
24
20
16
ML OF O.OIN NaOH
Fig. U. Neutralization Curves of Water From Mineral Creek (Colorado), Where the Field
Study ‘was Performed.
a.
-------
more difficult, particularly in Stage 2. As mentioned above, BaS is
the choice for sulfide addition.
The two-stage principle has several features in common with
the LHS process developed earlier (5). However, the two-stage
process makes use of the steep hydraulic gradients of the Rocky
Mountains for mixing, instead of mechanical mixing, and does not
require handling of H 2 S, or an elaborate mixing system. It is
noteworthy that the LH$ process does not always remove manganese,
the last metal to precipitate in the sulfide series, whereas Mn is
definitely removed in the two-stage process described here.
2. Field Experiment: Design
The field installation was constructed on Mineral Creek, at
Red Mountain, Colorado. The drawing in Fig. 12 shows the principal
features. The pond is 1 i0x20 ft and 3 ft deep, with an adjustable
outlet spiliway (left). The two treatment stages are achieved in
a rectangular wooden vessel (right foreground), which overflows into
the distribution trough which feeds the pond. The sulfide chemical
supply system is shown to the right of the treatment vessel. The
schematic drawing of Fig. 13 shows the key treatment features.
The pond was intended for settling of metal precipitates. It
was designed to provide a mean settling time of at least I hours,
adjustable by means of removable slats in the spiliway. The 1 4-hour
settling time was selected so that an 8-hour day would provide twice
this much time (i.e., twice the mean), based on the flow rate of
Mineral Creek, which was 30 gpm at the time of the experiment.
Mineral Creek was chosen for the field experiment because of
its accessibility and its high content of the metals of interest.
This creek rises above Red Mountain Pass, and receives drainage
from several inactive mines as well as ambient runoff, including
rain and snowmeit.
The two treatment stages were designed to contain the stream
flow just long enough for mixing with chemicals. Lime is fed either
27
-------
Fig. 12 Illustration of the field installation for treating Mineral Creek by the
two-stage process. Water enters the first stage of the rectangular
vessel (right foreground). Lime is also fed to the first stage, and
sulfide solution is pumped into the second stage.
00
-------
CD Contact Tank — Neutralization Stage
f ® Contact Tank — Sulfide Treatment Stage
Mineral Sulfide Solution Pump
Creek ® Sulfide Mixing Tank
® Distribution Trough
Fig. 13. Schematic Diagram of the Field Installation for Two-stage
Treatment.
Mineral
Creek
‘7
SpilIway
Se i ii fly
Pond
Li me
29
-------
to the influent or directly into the first stage. Sulfide solution
is fed by pump through a rotameter (Fig. 12) into the second stage.
Thus the mechanical equipment includes a lime feeder, a sulfide
solution pump, and a mixer for the sulfide solution tank. A method
of sulfide chemical supply to the tank must also be provided.
3. Field Experiment: Operation
Mineral Creek was diverted as indicated in Fig. 13, and the
pond was filled. The pond is shown in Fig. iLi., with the equipment
in position. (Mr. H. P. Larsen is shown operating the treatment
system). A close-up view of the operational facilities at the
experimental site is shown in Fig. 15.
Lime feeding proved to be very difficult in the field. Solids
feeders could not be employed when even the slightest wind was
blowing. This indicates a requirement for delivery of lime slurry
by a suitable slurry pump, but then a lime slurry mixing installation
is required. In the field experiment, lime was fed manually and
sulfide solution was prepared manually, but a centrifugal pump
delivered the sulfide solution to Stage 2. Electric power was supplied
by a portable generator.
The pH was very simple to control manually. The investigators
found that barium sulfide, in the form of “black ash,” presented
difficulties because it contained only 61 percent BaS by weight*.
The balance of black ash is inert, mostly insoluble, and conducive
to formation of a friable mass in the mixing tank.
Operating pH conditions were as follows:
pH 5.0 in Stage 1.
p1- I 6.5 in Stage 2.
Raw Mineral Creek water showed pH 2.6. A cationic surfactant polymer
was added at intervals to the Stage 2 effluent, at the rate of
* Measured in the laboratories of the tfniversity of Denver.
30
-------
Fig. 14. The Field Installation as Erected, but
before the Lime and Sulfide Feeding
Apparatus was Added.
Fig. 15. Close-up of the Treatment Facilities of
the Field Installation, In the Fore-
ground is the Two-stage Treatment Vessel.
-I—
1: ___
• : • ;;
p. t ,i
I
3].
-------
approximately 0.3 lb surfactant per 1,000 gal creek water.
+. Field Experiment: Results and Observations
The field experiment showed immediately that control of the
process by p1 - I control was feasible and simple. The small volume of
the treatment stages (35 cu ft in Stage 1, 15 cu ft in Stage 2)
contributes to the observed ease of p11 control, but the rapid mixing
is the most important element in control. This finding is encouraging
to the prospects of automatic control of the process.
However, another observation was even more influential to the
conduct of the experiment. Although the pond had been carefully
designed for hydraulic studies, this proved completely unnecessary,
because the sulfide precipitates settled immediately, even collecting
in the trough as a characteristic yellow-black slime. By contrast,
the yellow ferric hydroxide solids did not precipitate at all, but
instead were completely dispersed in the pond water. This phenomenon
was as striking and unmistakable as it was unexpected.
The differential settling effect depends strongly on the wind.
Overnight, in absence of wind, ferric hydroxide settled out and the
pond was clear in the morning.
The sulfide solids accumulated on the bottom. of the pond near
the distribution trough. The investigators were unable to obtain
good photographs of this phenomenon. Nevertheless the accumulation
of sulfide solids after only a few hours of operation was very
noticeable, and is regarded as very promising for eventual recovery
of copper and. zinc sulfides, in particular.
Daring the field experiment, pH was varied in the two stages
of treatment in order to provide checks on the effect of different
combinations. The results are summarized in the following table:
32
-------
Measured pH
Final Concentrations (ppn)
Sta€e 1 Stage 2 Fe (total ) Zn Mn Cu Al Ni
1. 5.0 5.9 0 12.7 6.li. 0 0 O.l3
2. 5.5 6.Li . 0 0.3 0.5 0 0 0.13
3. 5.0 5.5 0 30.0 6.8 0.5 0 0.29
5.0 5.6 0 30.0 7.1 0.3 0 0.19
5. 5.0 6.5 0 0.2 0.11 0 0 0.13
Chromium was also measured, but none was found. Experiment #5 is
the standard design condition, which was held at steady state for an
extended period.
For the conditions of experiment #5, the following concentrations
of the especially toxic metals Hg, Cd and As were found:
Hg 0 ppn
Cd 0.008 ppn
As 0 p n
5. Laboratory Support for Field Experiment
The project was greatly aided by the availability of the Atomic
Absorption Spectrometer of the Department of Metallurgy and Materials
Science. RoutIne analysis of major metal constituents (Fe, Zn, Cu,
Mn, Al) was thus made possible.
The Department of Health, State of Colorado, contributed
analytical assistance to the project at several t ies. Their
assistance was especially valuable for analysis of heavy metals in
very low concentration, where the atomic absorption instrument of the
University was not feasible.
In the field experiment, the pH meter of the laboratory of the
Department of Chemical Engineering, University of Denver, was used.
A portable meter for measurement of pH and oxidation-reduction
33
-------
potential was loaned by the Field Investigations Branch of the
Environmental Protection Agency, Denver, Colorado.
34
-------
SECTION VII
COMPUTER SIMESLATION OF EXPERITYIEW AL RESULTS
The laboratory results illustrated in Figs. 3, L 1 . and 5 suggest
that precipitation of dissolved metals can be achieved stoichiometrically
in response to sulfide treatment. The field results (Section vi) also
show that response to chemical treatment is rapid and sensitive.
For this reason, it is expected that actual mine waters may
closely obey the equilibrium relations of Section IV. Equation 12
has accQrdingly been written for the following cations: Fe 3 +, .A1 3 +
Cu 2 +, Zn 2 +, and Anions included for consideration are 01 -I and
Thus there are ten possible equations based on (2), and one
each based on eqns. (6), (7) and (8), a total of thirteen equations.
Likewise there are thirteen solubility-product and equilibrium
constants to be selected.
Butler (8) has pointed out that the very small magnitudes of
the quantities in such equations are outside the range of realistic
measurement. Thus it is sufficient to find a consistent set of
values. Particularly in the case of the sulfide equilibria, eqns.
( 1 i.) and (5), reported equilibrium constants may vary over two orders
of magnitude. Therefore the computer simulation necessarily includes
a search for the best choice of a set of K and K values.
sp e
The simulation is needed to predict the behavior of dissolved
metals under various combinations of (a) neutralization and (b)
sulfide treatment. There will be six algebraic equations to be
solved simultaneously in neutralization, and eight in sulfide
treatment. Both sets are nonlinear.
For solution, the second-order Newton-Raphson method of iteration
(9) was initially chosen to solve the set. The 6x 6 and 8x 8 matrices
35
-------
to be solved were approached by means of a standard computer routine
available for the Burroughs B 5500 digital computer. The method
consisted (in brief) of postulating a volume of solution, beginning
with 1 liter of raw mine water of known composition. A volume change
was specified, and the system was solved iteratively for the new pH
value and new metal concentrations. However, the method failed at
about pH 5.6, when the matrix set attained maximum size and the system
became extremely sensitive to correct guesses of new concentration
values for iteration.
The method ultimately used for the solution of this set of
equations was the regula falsi (false position) method, in which
the mathematics were less complex than in the Newton-Raphson method.
Now the pH is the variable of choice, and the system of equations
for iterative solution is illustrated by the following set:
= v 1 .io_P O - v ic
x Fe 3 - sp,Fe(CH) 3
2 10 3(pH -lk)
VK
+ sp,Al(OH)
— 3(pH iLl.)
V.K
+2 sp,Cu(OH) 2
= Cu - io2 1
VK
+2 sp,Zn(OH) 2
x =Zn - - 7- —
10 2 pH-1k)
VK
+2 sp,Mn(OH) 2
Mn -
36
-------
where V 1 = previous volume corresponding to p11-0.1
V = new volume, adjustable.
(Metal concentrations are from previous pH
conditions.)
A mass balance on the hydroxide ion concentration is written:
v.ioH_1 = v 1 .lo_1)_X 1 _3x 2 _ 3 _2x _2x 5 _2x 6 ÷(v_v 1 )lo_ 2
This equation then becomes a function of the volume.
F(V) = V 1 .l0lu1)_V.l0H1 _x 1 _3x 2 _3x 3 _2x _2x 5 _2x 6 +(V_V 1 )102
The above sets of equations are iterated until a value is
reached which approximates the exact solution of F(V) 0.
This set of equations is also nonlinear, but is not as sensitive
as the set required by the Newton-Raphsori formulation. For solution,
pH is incremented by 0.1 in each step. Volume is then incremented,
and the respective metal conversions (x.,) found by iterative solution.
In the computation, neutralization by addition of a weak
alkaline solution (assumed 0.01 N in 011) is applied until a certain
pH value is achieved. After this, addition of sulfide solution (also
0.01 N) of the same strength is applied until about pH 11.5, thus
achieving two-stage treatment as described in the preceding section.
The computer program, written in ALGOL for implementation on
the Burroughs B 5500 digital computer of the University of Denver,
is reproduced in Appendix I.
Typical results for neutralization alone are shown in Fig. i6.
Water from Mineral Creek, at the location where the field test was
conducted, was neutralized, and metal concentrations were monitored
(dashed curves). Computed results are given by the solid curves,
and the agreement is evidently fairly good. However, it appears
that at least one unreported metal species is present, as evidenced
37
-------
12
Fig. 16. Comparison of measured and computed meutralizatiori
curves for water of Mii ra1 Creek, taken from
the pond of Mine K.
6.0
0
‘C
I..
w 5.0
4.0
z
0
I—
3.0
1—
L i i
a.o
0
0
-J
I.0
w
II
10
9
8
7
Q.
0
6
5
4
VOLUME OF 0.01 N 0H ML
3
2
0
-------
by the lag in pH rise (beginning at about 4OO ml 0H addition) and
the delay in Zn precipitation, to the extent of about 1 meq. This
could possibly be attributed to arsenic , which has been found in
concentrations up to 20 mg/i in the nearby pond of Mine K, or to
molybdenum , which is common in the Rocky Mountains but which has
never been included in measurement series for the Red Mountain region,
either by state or federal investigators.
Figures 17, 18, and 19 show computed curves for two-stage treatment
based on sulfide addition beginning at pH 14 , 5, and 6, respectively.
An important feature of these results is the effect of simple
dilution. This imparts the typical negative slope to curves of metal
concentration vs. additive chemical volume, before the sharp break
point characteristic of a given metal species. If dilution is neglected,
which is permissible if solid chemicals are added , the computer
simulation is much simplified; typical results are shown in Figs. 20
and 21, compared with experimental results.
Simulated results are considered satisfactory in the case of
neutralization alone (Figs. 16, 20), but the case of sulfide addition
is more difficult (Fig. 21). The problem resides in the values of
K available (see above), and possibly also in departures from
equilibrium. Many differing values for solubility-product constants
are available, but the present investigation chose the following
values because they were most consistent with observed results:
Metal Hydroxide Sulfide
-36 -88
Ferric iron 1.lxlO 2.OxlO
Aluminum l.2x10 32 --
Cupric copper 6.Ox lO 7.7x10
Zinc 7.lxlO l.6xlO
Manganese 1. xlO 2.5xlO
These values were selected from values reported by published
39
-------
* 6.0
0
:5 .0
0
-J
0
4. 0
z
0
I-
<5.0
0 Z
U i
0
z 2 .o
0
0
-J
I.0
U i
0
Figure 17.
TOTAL VOLUME OF 0.01 N ANION) ML
Computed two-stage treatment curves, with sulfide
treatment (Stage 2) commencing at pH 4.0.
2
‘I
t0
a
8
7
8
5
4
3
2
0
600
I
a -
0 50 100 t50 200 250 I 300 350 400 450 500 550
OW lrl.rJ1 . 8’
-------
Fig. 18. Computed two-stage treatment curves, with
Sulfide Addition (Stage 2) Commencing at
pH 5.0.
0
‘C
a 5.0
I ..
-J
w
-j
o 4.0
I
z
0
I-
z
U i
C.,
0
C.,
-J
4
Ui
I2
I0
9
8
7
e
a-
5
4
3
2
TOTAL VOLUME OF 0.0! N ANION, ML
600
-------
12
Figure 19.
Computed two-stage treatment curves, with
sulfide addition (Stage 2) commencing at
pH 6.0.
F ’)
I I
l0
9
8
7
I
6
5
4
0H
3
2
TOTAL VOLUME OF O.OIN ANION, ML
0
600
-------
Fig. 20. Comparison of Theoretical and Measured
Neutralization Curves, Under the Assumption
of no Volume Increase.
II
I0
9
8
7
6
5
I
0.
4
3
2
00
I0
20
30 j
>
40 0
w
50
-J
60 w
70
80
90
0
mL of 1.0 N NaOH
100
-------
I’
mL. of 0.1 M Na 2 S
Fig. 21. Comparison of Theoretical and Measured Sulfide Treatment Curves, Under the Assumption
of no Volume Increase. pH. Denotes the Initial pH.
I0
9
8
7
6
=
0 .
3
S
4
0
2
a
-J
>
0
w
-J
I.-
U I
0 I 2 3 4 5 6 7 8 9 tO II 12 13 14 IS 16 17
-------
compilations (7,8,10,11). The values for the sulfide equilibrium
constants according to eqns. (14) and (5) were selected as follows (8):
K 1.3x10 13
e
K = l.0x10 7
eHS
Among previous investigators, only Lanford (12) has reported
a process for removal of several metal species in a two-stage
treatment process, with supporting equilibrium predictions. Lanford’s
results cannot be compared with those reported here, for several
reason, but principally because Lanford uses a set of K values that
is quite different from the values adopted here.
-------
SECTION VIII
PRACTICAL ASPECTS OF PRECIPITATION OF HEAVY METALS
FROM MINE DRAINAGE WATERS
Facilities Required
The results of the field investigation (Section VI) show that
the facilities necessary for chemical treatment are fundamentally
simple. The basic requirements include only
(1) complete mixing of chemicals with the drainage water,
(2) sufficient time for settling of precipitates.
For the first requirement, a mixing vessel is necessary, or
perhaps two vessels (neutralization + sulfide treatment). For a
permanent installation, this mixing capability should consist of a
permanent installation, this mixing capability should consist of a
basin (concrete, asphalted, wood reinforced, etc.) allowing a few
minutes of residence time. No mixing impellers are needed if the
hydraulic inflow rate is adequate to give the influent (polluted)
stream a vigorous swirling motion that will suspend the added lime.
Also required are the following equipment items:
Lime storage hopper
Lime feeder mechanism
Sulfide solution storage vessel
Sulfide solution pump and piping
Sulfide solution metering gauge
pH controller (optional -- see below).
For the second requirement, an earthen basin is satisfactory.
Ferric hydroxide (and probably aluminum hydroxide also) will not
settle In this basin unless it is absolutely quiescent, a difficult
47
-------
condition to achieve, but possibly attainable by laying a plastic
sheet(e.g., polyethylene) over the water surface. However, sulfide
compounds will settle in such a basin, and thus an open basin offers
a possible method of fractionating sulfides from hydroxides. Residence
time in such a pond should be about two hours.
Control
The present investigation has verified that pH is a suitable
variable for control of the precipitation process. The pH responds
instantaneously to chemical treatment; is a reliable index of
relative metal removal; and is easily measurable.
A pH controller, regulating the flow of sulfide solution to
the mixing vessel, is perfectly feasible. This would certainly be
recommended for large flows and other sensitive pollution situations
where the pollution hazard justifies the expense.
Logically, pH would be measured at the outlet of the sulfide
treatment stage. (The large time constant of the settling pond
indicates that the pond effluent stream is not the proper measurement
point for feedback control). This measurement regulates sulfide
addition; in principle, the pH of the lime treatment stage (first
stage) should also be regulated. However, the lime addition rate is
a less important factor in removal of toxic metals, and its adjust-
ment can be achieved manually at given intervals, especially in view
of the fact that the concentrations and the flow of most drainage
streams do not change significantly within a week or two.
For small operations, manual control may be adequate. The
operator would then simply vary the chemical addition rates to
chieve the desired pH, on (e.g.) a daily basis.
Economics of Chemical Treatment
It is unlikely that recovered sulfide precipitates can ever pay
the complete cost of treating mine drainage waters. However, these
sulfides can certainly provide a significant credit against treatment
8
-------
cost.
Zinc is the principal metal of economic interest, because it is
the major toxic metal constituent of mine drainage waters of the Rocky
Mountains (Table I). Copper is attractive economically, but it is often
present in quantities that yield unsalably low Cu content in the mixed
sulfide precipitate. No other metals occur in quantities that suggest
recovering them.
In a typical mixed-sulfide precipitate from a treated mine drainage,
Cu will constitute 10-15% of the weight, and Zn 25-35%. In addition, a
certain amount of dirt and other contaminants will reduce these concen-
trations by perhaps one—third. Thus the precipitates will yield (op-
timistically) a return* of
Cu -- 4.5 x 10 4 (a)(b) $/day
Zn -- 2.1 x l0 4 (a)(b) $/day
where
a = concentration in mg/l
b = stream flow rate in gpm.
For example, if the stream contains 50 mg/l Cu and is flowing at
100 gpm, then the return is
(4.5 x l0 )(50)(lO0) = $22.50/day
It should b emphasized that most smelters wi 1 i not purchase both
metals in a mixed precipitate. That is, they will ususally purchase Cu
or Zn but not both.
Costs of processing these concentrates include costs of instal-
lation and equipment, collection, and transportation. The present in-
vestigation has identified the installation arri equipment facilities
required, and the chemicals requirement. The required BaS for
precipitation of mixed sulfides Is about 1000 lb per day (at a
price of about $160/ton), and the lime requirement is about 1507.
*Estimate based on metals price quotation of 1 January 1972; metal values
based on typical smelter schedules of the American Smelting and Refining
Company (1971).
49
-------
of this, at a cost of about $20/ton, all based on a flow rate of 100
g n and concentrations as cited above.
In conclusion, as a means of estimating the potential value of
mixed sulfide precipitates, we define the gross minerals credit (GMc)
as follows:
gross value of cost of
minerals = mixed - treatment
credit ) sulfides ) L. . chemicals
or GMCSV-CC.
Based on metals quotations at the end of calendar year 1971, SV and
CC can be estimated by the following relations. For SV (in dollars
per day):
sv = (o.0l202) F( C •P + C •P ).
Cu Cu Zn Zn
Symbols have the following meanings:
CZn = Concentration of zinc and copper, respectively,
mg/i.
F = Flow rate of stream, hundreds of gpn.
p 1 ’ = Price of zinc and copper, respectively, on the
metals market, as published in Metal Week ,
dollars/lb.
The chemicals cost (cc) may be estimated from the following relation
(cc in dollars per day):
cc = [ C 3+/55.8 ÷ CA13+/27.0 I •F•( 7x1Q 2 )•P +
C .F.(2.14x10 2 ).P
met BaS
50
-------
where C 3+ , CA1 3 + = Concentration of ferric iron and aluminum,
respectively, mg/i.
C = Concentration of all other metallic species
met 3+ 3+
except Fe and Al , mg/i.
CaC’ BaS = Unit cost of CaO and BaS, respectively, $/lb.
It should be noted that GMC is exclusive of all operating and
transportation costs, as well as capital cost of facilities. The
smelter will discount the value of the concentrate for contamination,
and will impose certain surcharges. Smelter schedules are available
from the smelting companies upon request.
Use of Flocculant Chemicals
The field results (Section vi) indicate that there is probably
some advantage to be gained by adding a flocculating agent in two-
stage chemical treatment. The pronounced sedimentation behavior
observed in the field, where a flocculant was added, was much better
than laboratory results (13) led the investigators to expect.
Very little information is available on this subject. A usef’ul
paper on flocculation of metallic hydroxides from mine waters has
recently been published (1)4.), and the present investigation has
included a series of measurements of the rate of sedimentation of
mixed sulfides upon addition of various quantities of a cationic
surfactant as flocculant (Fig. 22). There is clearly some advantage
to be gained by use of surfactant flocculants, but each mine drainage
situation must be evaluated separately.
51
-------
100
80
I-
I-
‘Ii
70
0
z 80
0
I-
- 50
a
0
C)
I-
z
l i i
C,
TIME, MIN
Fig. 22. Settling Tests for a Mixed Metal Sulfide Floe As a Function of Surfactant
Addition. Water from Mine BH (Idaho). Surfactant: Calgon M-590. pH 5.5.
0 I 2 3 4 6 6
-------
SECTION IX
tT 1T Tf
1. Hill, R. D., Mine Drainage Treatment. State of the Art and
Research Needs . Cincinnati, Ohio: U. S. Department of the
Interior, Federal Water Pollution Control Administration. Mine
Drainage Control Activities. pp. 99 (December, 1968).
2. Wilmoth, B. C. and R. B. Scott, “Neutralization of High Ferric
Ion Acid Mine Drainage.” Paper Presented at the Third Symposium
on Coal Mine Drainage Research, Pittsburgh, Pennsylvania, May 19,
1970.
3. Hill, W. D., J. Water Pollution Control Fed . 14.1, pp. 1702-1715
(1969).
11.. Ohio State University Research Foundation, Acid Mine Drainage
Formation and Abatement . Washington, D. C.: U. S. Environmental
Protection Agency, Water quality Office. Rept. No. DAST-42, 11.4.010
FPR O1 4 ./71, pp. 82 (April, 1971).
5. Zawadzki, E. A. and R. A. Glenn, Sulfide Treatment of Acid Mine
Drainage . Monroeville, Pennsylvania: Bituminous Coal Research,
Inc., BCE Rept. No. L-290 (July 1, 1968).
6. Tyco Laboratories, Inc., Silicate Treatment for Acid Mine Drainage
Prevention . Washington, D. C.: U. S. Environmental Protection
Agency, Water Quality Office. Rept. No. 11.4.010 DLI or/71 pp. 914.
(February, 1971).
53
-------
7. St mm, W. and J. J. Morgan, Aquatic Chemistry . New York:
Wiley-Interscience (1970).
8. Butler, J. N., Tonic Equilibrium. A Mathematical Approach .
New York: Addison-Wiley Publishing Co. (1964).
9. Nielsen, K. L., Methods in Numerical Analysis . New York:
Macmillan Co. (1956).
10. Weast, R. C., ed., Handbook of Chemistry and Physics . 52nd
edition, Cleveland, Ohio: Chemical Rubber Co. (1971).
11. Sorum, C. H., Fundamentals of General Chemistry . Englewood
Cliffs, N. J.: Prentice-Hall (1963).
12. Lanford, C., Oil Gas J . 67, pp. 82_8L (March 31, 1969).
13. Pugsley, E. B., C. Y. Cheng,
“Removal of Heavy Metals from
Precipitation.” Water-1970 .
Symposium Series No. 107 pp.
D. M. Updegraff, and L. W. Ross,
Mine Drainage in Colorado by
Chemical Engineering Progress
75-89 (1971).
14. Mesaric, S. and S. Vuckovic, Kemija u Industriji , No. 9,
pp. 1 t43... 1 t48 (1970). English Translation in International
Chemical Engineering 11, pp. 302-308 (1971).
51i.
-------
AC OWLEDGEMENTS
This investigation was greatly assisted by the encouragement and
assistance of the dedicated public servants of the State of Colorado:
the Division of Water Pollution Control of the Department of Health,
and the Game, Fish, and Parks Department.
55
-------
APPENDEC I
COMPUTER PROGRAM FOR CALCULATION OF EQUILIBRIUM IN TREATED MINE
DRAINAGE WATERS
BEGIN
FILE IN CARD (2, 10);
FILE OUT LINE 1 (2, 15);
REAL PH, V, Vi, TEMP1, TEMP2, DELV H2S, STOT, SOLD, F 1, HS,
SBLK, CHANGE, VTEMP, FES, ALS, CUS, ZNS;
INTEGER I, Z, Si, S2, J, PL;
ARRAY M,X,KSP,C,MP,MCE [ O:8],
Ics [ i:8],Y [ i:8],PHS, VS,Y1S,Y2S ,Y3S10:150];
LABEL DONE ,TOP ,RESULT ,SULFUR ,ANSWER , HEAD ,HALF ,MIDDLE , FINIS,
ANFANG;
FORMAT Fl (5R10.6);
FORMAT OT (x6, “FE3 ” ,X11, “AL” ,X12, “CU” ,X12, “ZN” ,X12, “MN” ,X12,
FORMAT F2 (7(X1,E12.5x1));
FORMAT F3 (“END OF PROGRAM”);
FORMAT F5 (“ INITIAL OH K P VALUES FE+3 = “,E1O.2, ” AL =
E1O.2,” CU = “,E1O.2,” ZN = “,E1O.2,” MN = “,E1O.2);
FORMAT 6 (nuo.6);
FORMAT F7 ( 11 CHANGE PROM OH- TO B - - ADDITION”);
FORMAT F8 (l.i.R1O.6);
57
-------
FORMAT
Fil (3Rlo.6);
FORMAT F12 ( INITIAL SULFIDE KSP VALUES FE+3 = 11 ,E1O. 2,
CU = ‘ T ,E1O.2, tT ZN = !I,Elo.2, U MN = “,E1O.2);
FORMAT FJJ4. (5(xl,E12.5x1));
FORMAT F21 (x6, “Yl” ,X12, ‘ Y2” ,X12, ? Y3u ,X12, “PH t ’ ,X12, ?h U);
THE DATA IS READ IN AS THE KSP HYDROXIDE VALUES OF FE3 ,AL,
CU,ZN,MN,ON THE FIRST CARD, THEIR CONCENTRATIONS TN MOLES ON
THE SECOND CARD, THE PH, ORIGINAL VOLUME, AND TIlE DELTA
VOLUME ON TEE THIRD CARD, THE SULFIDE KSP VALUES ARE THEN
READ, H20, HS, H2S ON THE FOURTH CU, ZN, FE+3, AND MN ON
TIlE FIFTH, THE CHANGE FROM OH TO 5—- PRECIPITATION ON TIlE
(CARD,F1,I P [ 2],KSP [ 3] ,KSPP4J ,IcsP [ 5J, P [ 6];
(CARD,F1,M [ 2] ,ML3] ,MU4.J ,M [ 5 ] ,M [ 6]);
(cARD,F11,PH,V1,DELV);
(cARD,F11,KS [ 1J,KS [ 2],KS [ 3]);
(C D,F8, I [ )4J,KS [ 6J,KS [ 7],KS [ 8]);
(CARD,F6,CHANGE);
(LtNE,F5 ,KSPII2] ,KSP [ 3] ,KSP [ ’I.] ,KSP [ 5] ,KsP 16]);
(LTNE,F12 ,KS [ 7] ,KSP4],KS [ 6],KS [ 8]);
(LINE,POT);
(Lmm ,F2,M [ 2] ,Mr3] ,M [ 4J ,M 5] ,M [ 6] ,PH,V);
KSP [ 3];
Vi + DELV;
WRITE
KS [ 5]
V —
Si — 0; S2 f— 0; PL — 0;
Z — 2; J — 1;
FES M [ 2]; ALS — M [ 3]; CUS — ML 1 i-]; ZNS —
FOR I — 0 STEP 1 UT IL 1 DO
COI,flvIENT
ANFANG:
S DCTH CARD;
READ
READ
READ
READ
READ
READ
WRITE
WRITE
WRITE
58
-------
BEGIN
M jIJ.i—O; x [ I]4—O; icsp [ i].-o; c [ i]’ .—o; MP11]-o;
MCE [ I1 — 0;
END;
c [ 2] —3; C [ 3]..—3; c [ 1j —2; c [ 5]’.—2; C [ 6].—2;
IF PH CHANGE THEN GO TO SULFUR;
TOP: FOR I — 2 STEP 1 UNTIL 6 DO
BEGIN
MCE [ I] — (VxKSP [ I1) / (lo*(C [ I]x(PH-1).l.)));
x [ i] — M [ I] - MCE [ I];
IFX [ I] O THENXLI].-O;
IF PH > 6.7 THEN X [ 3] .- 0;
END;
IF PH > 11.0 THEN IF PH 8.8 THEN
BEGIN
MCE [ 2] - (vx2.5x10*(-17)) / lo*(PH - 1 14.);
X [ 2]4— M [ 2] — MCE [ 2];
IF x [ 2] <0 THEN x [ 2] — 0;
x [ 2J .—x [ 2] / 3;
EN])
ELSE IF M [ 2] 6.7 THEN IF M [ 3] ALS THEN
BEGIN
X [ 3] - V x 3xlOxlO*(PH-1ll .) - M [ 3J;
x [ 3]4-X [ 3] / 3;
END:
IF PH > 9.5 THEN IF M [ 1 4 .]
-------
BEGIN
x [ L ]÷-v x 7.lxlO*(- 6 )xlO*(PH-1 1 +) -
xt ] —X [ 14] / 2;
END
IF PH > 9.9 THEN IF M [ 5J 11.0 THEN X [ 2] - 3xX [ 2];
60
-------
IF PH > 6.7 THEN X [ 3J .— -3xX [ 33;
IF PH > 8.8 THEN X [ 2] — -x [ 2];
IF PH >9.5 THEN x [ L .].—-2xx [ 1 i.];
IF PH >9.9 THEN X [ 5] — -2xX [ 5];
FOR I - 2 STEP 1 UNTIL 6 DO
MEl] 4—M I] — x [ r];
FOR 1.— 2 STEP 1 UNTIL 6 DO
MPh] 4- M [ I]/V;
CO tENT THE RESULTS ARE PRINTED OUT WITH THE METAL CONCENTRATIONS IN
ls’K)LES PER LITER;
WRITE (LINE, P2 ,MPh2],MP [ 3],I [ l .],MP [ 5],MP [ 6],PH,V);
FOR I — 2 STEP 1 UNTIL 6 DO
BEGIN
IF Mh.I] <0 THEN
MEl] — 0;
END;
PHS [ J]i-PH; VS [ J]4-V; yis [ ]e—x [ i]; Y2S [ JJ -O;
Y3S [ J]i- 0; J -J + 1;
S1. -O; 32*-C; PL O;
Vii - V;
V.- V + DELV;
PH ‘- PH + 0.1;
IF PH CHANGE THEN GO TO SULFUR;
GO TO TOP;
SULFUR: 51+- 0; S2 .— 0; SOLD i— 0; H23 - 0; HS 0;
DELV*— DELV / 2;
WRITE (line,F7);
M17J M [ 2]; M [ 8] - M [ 6J; M [ 6J M [ 5J; MIS] — M13];
FOR I *- 1 STEP 1 UNTIL 8 DO
[ i] - 0;
HEAD: y [ 1] i —Vix lOx-(PH-]A.1) - vx10*(PH-1I .);
Y [ 2] (1O*(-PH)x(SOLD + (V-V1)xLO*(-2) + ( cs [ 2]xHs)/
(lo*(-PH)+Ics [ 3])) - Ks [ 2]x(Hs+( [ 3JxH2s)/(1o*(-PH) +
61
-------
S [ 3 ])))/(1O*(_PH)+KS [ 2]_(KS [ 2]X1O*(Pk{))/(bO*( M) +
KS [ 3]));
y [ 3] .- ((1o*(_pHflx(Hs+y2fl_Ks [ 3]xH2s)/(lo*(_PH)+Ks [ 3]);
Ve- _VxlO*(_PH) + vi x io*(_PH+o.1)-Y [ 1]-Y [ 2]-Y [ 3J;
STOT - SOLD—Y [ 2J + lo*(_2)x(v-V1);
C0 NT A TEST IS MADE FOR CONVERGENCE;
IF FL = 7 THEN GO TO HALF;
IF Si = 1 THEN IF S2 2 THEN PL - PL + 1;
IF FV O THEN
BEGIN
IF Si 1 THEN TEMP2 - 0.5 x TEMP1 ELSE TEMP2 +- DELV;
S2ř— 2;
V V +TEMF2;
END
ELSE
BEGIN
IF S2 = 2 THEN TEMP1.— 0.5 x TEIvIP2 ELSE TEMP14— 0.5 x
DELV;
S1’— 1;
V —V - TEMP1;
END;
GO TO HEAD;
HALF: SOLD — SOLD - Y [ 2] + lo*(_2)x(v_V1);
STOT .- SOLD; Si - 0; 52 — 0;
IF STOT 0 TEEN GO TO ANSWER;
V1 —V; V —V+DELV; PL’—O;
CO!vIMEM1? A SULFIDE CONCENTRATION WHICH SATISFIES THE PH CONDITION IS
CALCULATED FIRST. THEN THE CORRESIONDING PRECIPITATIONS FOR
THAT SULFIDE CONCENTRATION ARE CALCULATED;
MIDDLE: MCED4] ‘— ((v*2)xKs [ )d)/STOT;
SBLK- STOT x 10*10;
COMMENT KS [ 7] IS FROM LINKE AND EQUALS i. +5 x 10-87;
MCE [ 7J — ((v*5)XKS [ 7])x(SOLK*(_3));
62
-------
MCE [ 7] .- MCE [ 7J x 103f(_114);
IF MCE [ 7] <0 THEN MCE [ 7] e-O ELSE MCE [ 7J— SQRT(MCE [ 7]);
MCE [ 6J 1— ((V*2)xicsE6])/ST0T;
MCE [ 8]4—((V*2) x Ks [ 81)/sToT;
MCE [ 53 - (vxxs [ sJ) / (1O*(c [ 3Jx(w_]A)));
FOR I”- + STEP 1 UNTIL 8 DO
BEGIN
Y [ iJ — M [ I] - MCE [ IJ;
IF LiJ 0 THEN [ i] ‘.—O;
END;
y [ 7J — 0.5 x yL 7J;
fli— _Y [ UJ_Y [ 63_3xY [ 7J_Y [ 83+(v_v l)x lO*(_2);
COMMENT A TEST IS MADE FOR CONVERGENCE;
IF FL = 5 THEN GO TO ANSWER;
IF S i = 1 THEN IF S2 = 2 THEN PL’-PL + 1;
COMMENT TEE NEW VOLUME ,V, IS ADJUSTED SO THAT BY IS MINIMUM;
IF BY S 0 TEEN
BEGIN
IF Si = 1 THEN TEMP2-O.5 x TEMP 1 ELSE TEMP24—DELV;
82’.- 2;
V— V + TE;
END
ELSE
BEGIN
IF 32 2 THEN TEMP1.*- 0.5 x TEMP2 ELSE TENPi — 0.5 x
DELV;
53i- 1;
Vi-V - TEMP 1;
END;
GO TO MIDDLE;
ANSWER: FUR I . .- U STEP 1 UNTIL 8 DO
BEGIN
MLII *—M [ I] — Y [ IJ;
IF M [ IJ 0 THEN MLII —O;
63
-------
MP [ I] - M [ I]/V;
END;
WRITE (LThE,F2,MPL7],MPL5], P [ 14],MP [ 6J,MP [ 8] ,PH,v);
PHS [ JJ - PH; VS [ JJ - V; yisL J e-y [ i]; Y2S [ J] 4—Y [ 2];
Y3S [ J] .—Y [ 3]; J —J + 1;
S14—O; S24—O;
V1 — V;
V —V + DELV;
PL 0;
HS —IIS +Y [ 2J -y [ 3];
IF I -IS <0 ThEN HS - 0;
H2S —H2S +Y [ 3];
IF H2S O THEN H2S’—O;
PH — PH + 0.1;
IF pjj 11.6 THEN GO TO DDNE;
GO TO HEAD;
DONE: WRITE (LINE [ PAGE]);
WRITE (LINE,F21)
WRITE (LINE,F1-l.,FOR I..— 1 STEP 1 UNTIL J tx [ yis [ i],
y2S [ I],Y3S [ I],PHS [ III,VS [ I]]);
CHANGE 5.0;
FINIS: WRITE (LINE,F3);
END.
6 .
-------
SELECTED WATER - Report No. 2. 3. Acc ssion No.
RESOURCES ABSTRACTS VV
INPUT TRANSACTION FORM
4. Tjtje S. Report Date
Removal of Heavy Meta].s from ! ftne rcige by Precipitation 6.
8 Performing Organizasion
R p i Nc .
7. Author(s
Laurence W. Ropn 10. Project No.
Department of Chemical Engineering and Metallurgy
University of Denver, Denver, Colorado 80210 11. Contract, Grant No.
14040 FZC
. vpe of Rep and
f r -s . .
12 . o i Oi1snszafton
15. Supplementary Notes
Environmental Protection Agency report number EPA-670/2-73-080, September 1973.
16. Abstract Heavy metals in mine dr intjge waters of the Roc1ç r I’buntains can be removed by -
a two-stage process consisting of (1) neutralization followed by (2) sulfide treatment.
The first stage r ves ferric and. alumintun hydro d.des, and. the second aulfide) stage
precipitates the heavy metals that are most objectionable as pollutants, and. that are of
possible interest for economic recovery. The two-stage process has been demonstrated
in the laboratory and in a field exper 4 nv nt.
In the field, powdered 1 1in was n!ployed for neutralization, and barium sulfide
was en p].cyed as sulfide source in a two-stage treatment tank. The ferric and aluminum
hydroxides failed to settle when even the slightest winds disturbed the surface of the
settling pond, but the sulfides settled within a few feet downstream. The measured pH
of treated streams has proven entirely satisfactory for control of chemical additions.
A con uter pro ’wn based on pllblished values of equilibrium constants and solubility
product constants is capable of adequate prediction of the required chemical quantities
for treatment, and of the resulting metal concentrations in solution.
The economics of chemical addition indicates that recovery of sulfides (CuB, ZnS) for
sale to smAl tars can partially offset the cost of treatment, but never cnmrjletely.
ha. Descriptors
Acid MI.ne Drainage*, metals (heavy)*, chemical treatment, barium sulfide,
neutralization
lib. Identifiers
Roc1 r I buntain Region*, Colorado, San Juan I buntains
.17c. COWRR Field & Group -
18. Availability 19. Securily Class, 21. No. of Send To:
(Report) Pa as
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
20. SecurIty C . 22. U.S. DEPARTMENT OF ThE INTERIOR
WASHINGTON. D . 20240
Abstractox Laurence W. Roes j IOStIIUIV)Ti University of Denver
WRSIC 102 {REV. JUNE 1971) - G P 0 488-935
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