820K71001
11(010 05/71
NEUTR0L0SIS TREATMENT OF ACID MINE DRAINAGE
By
Ronald D. Hill, Roger C. Wilmoth, and Robert B. Scott
WATER QUALITY OFFICE
ENVIRONMENTAL PROTECTION AGENCY
Robert A. Taft Water Research Center
Cincinnati, Ohio ^5226
Paper to be presented at the 26th Annual
Purdue Industrial Waste Conference, Lafayette,
Indiana, May 4-6, 1971.

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NEUTROLOSIS TREATMENT OF ACID MINE DRAINAGE*
by
Ronald D. Hill, Roger C. Wilmoth, and Robert B. Scott
Water Quality Office
Environmental Protection Agency
SUMMARY AMD CONCLUSIONS
The Water Quality Office, EPA, Mine Drainage Field Site at Norton,
West Virginia, has successfully demonstrated that the combination of two
known mine drainage treatment processes can produce over 98 percent water
recovery and less than two percent of easily disposed inert sludge.
In the past the Environmental Protection Agency, (EPA) Water Qual-
ity Office (WQO), and the Office of Saline Water (OSW) have cooperated in
studies of the application of reverse osmosis to mine drainage in which
the reverse osmosis unit and technical assistance have been supplied by
OSW and feed water treatment and technical operation by WQO. This co-
operative project had successfully demonstrated that reverse osmosis could
recover up to 80 percent of the water from acid mine drainage, but left
unanswered the problem of disposal of the concentrated waste product, brine.
At the conclusion of the first joint project, WQO initiated another
project to solve the brine problem. OSW continued to cooperate by provid-
ing the reverse osmosis unit. During this project, WQO technologists dem-
onstrated in a 380 hour test run that 90 percent water recovery through
reverse osmosis, was possible. Calcium sulfate fouling of the membranes
was overcome through pressure variation techniques.
* Ronald D. Hill, Chief, Mine Drainage Pollution Control Activities, Robert
A. Taft Water Research Center, Cincinnati, Ohio. Roger C. Wilmoth and
Robert B. Scott, Project Engineers, Norton Mine Drainage Field Site, Nor-
ton, West Virginia.
EPA, WQO Publication Number lUOlO	05/71

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2
At the same time the Norton Field Site, WQO, had been conducting
studies in neutralizing acid mine drainage and into the disposal of the
sludge which results from this process. A combination of the neutraliza-
tion and reverse osmosis process was conceived by the Norton staff and
experiments implemented. Brine from the reverse osmosis unit was cycled
through the neutralization plant and the clarified water blended into
the reverse osmosis feed. The resulting process, which has been dubbed
"neutrolosis" by the staff, extracts 9&" percent of the water from acid
mine drainage and produces a sludge suitable for disposal through per-
manent landfill. Salt rejection exceeded 99 percent. The breakthrough
for this process was treatment of the acid mine drainage with (a) 96+
percent water recovery and (b) elimination of the brine as a disposal
problem.
Specific conclusions drawn from this study were:
(1)	A reverse osmosis-neutralization process can obtain 98 per-
cent water recovery when operated on a high ferric to ferrous
ratio iron acid mine drainage water.
(2)	A high quality water and an inert sludge with no brine stream
is produced by this combination process.
(3)	A reverse osmosis unit can treat a high ferric iron acid mine
drainage at a 91 percent water recovery without resulting in
permanent fouling of the modules.
(U) Salt rejection exceeding 99 percent can be obtained.
(5) The major unknown yet to be resolved in the reverse osmosis-
neutralization treatment of acid mine drainage is the long-
term effect of the process on membrane life and performance.

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3
BACKGROUND
The feasibility of treating acid mine drainage with a high ferric
to ferrous iron ratio (greater than 4:1) by reverse osmosis to produce a
water suitable for domestic use had been demonstrated through cooperative
fll(2)*
research by the Office of Saline Water (OSW) and the WQO, EPA.
During these initial studies OSW supplied the equipment and a consultant
and WQO operated the equipment and made the test runs. Most of these
studies were conducted at water recovery rates** between 50 and 75 percent
(although one test was as high as 80 percent) because of the fear of foul-
ing the membranes with iron and/or calcium sulfate. At recoveries of
greater than 70 to 75 percent, calcium sulfate was above the saturation
concentration and a potential danger of fouling the membranes was present.
It was concluded from these studies that water recoveries up to 80
percent could be accomplished without uncontrollable iron or calcium sul-
fate fouling of the membranes and that between 97 and 99 percent salt
(2)
rejection*** could be obtained. Typical performance data are shown
in Table 1. These studies did not consider the major potential pollution
problem associated with the disposal of the brine.
The WQO was deeply concerned with the disposal and pollution prob-
lems associated with the waste brine that constituted from 20 to 25 percent
of the water treated in the reverse osmosis plant. One proposed solution
* Numbers in parenthesis refer to references listed at end of report.
** Water Recovery ($) = Product Water Produced X 100/Water Treated.
*** Salt Rejection ($) = Concentration in Feed Water Minus Concentration of
Ion in Product Water X 100/Concentration of Ion in Feed Water.

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k
TABLE I
f 2 )
Typical Performance Data at 7*+.^ Percent Water Recovery^ 1
Raw	Product	Percent
	Feed	Water	Re j ection
pH
Conductivity, Micromhos/cm
Acidity (CaCO-), mg/l
Ca, mg/l
Mg, mg/l
Al, mg/l
Fe, mg/l
SO^, mg/l
2.7
b.k

1,350
55
97.9
6ol+
l+
99.8
115
2
99.3
38
0.9
99.2
39
3.1
97.3
153
0
100
936
k.2
99.8
to this problem was increasing the recovery rate to a maximum, thus pro-
ducing the smallest volume of brine. With this goal in mind, WQO entered
(3)
into a contract with Gulf Environmental Systems, Incorporated to eval-
uate ultra high water recovery. OSW assisted by supplying the reverse
osmosis equipment. WQO conducted the studies with the consultation of
Gulf Environmental Systems.
This study showed that the reverse osmosis unit could be operated
(U)
at 91 percent + 1 percent for extended periods of time. ' Although foul-
ing of the membranes at the discharge end of the plant did occur, these
calcium sulfate scales could be removed by operating the unit at 50 percent
recovery for short periods of time, thus flushing them from the membranes.
The Norton Mine Drainage Field Site also has an active research
program in the neutralization of acid mine drainage. The staff conceived
that the reverse osmosis process could be combined with the neutralization
process to produce a maximum amount of high quality water and a minimum
volume of waste products. The process conceived was the operation of the
reverse osmosis unit at maximum recovery, neutralization of the brine, and

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5
recycle of the neutralized brine water back to the reverse osmosis unit.
This system would produce only product water plus a small amount of sludge
containing the iron, calcium, sulfate, aluminum, etc. The process was
named neutrolosis (a combination of neutralization and reverse osmosis).
PROCEDURES
The reverse osmosis equipment was a 10,000 gpd rated unit manufac-
tured by Gulf Environmental Systems, Incorporated.* The unit utilized five
4-inch by 10-feet long pressure vessels. Each pressure vessel contained
three type 3009-A modules, which are two leaf, fabric-backed modules 3 feet
long, 3.75 inches in diameter, and contain 50-square feet of high-selectiv-
ity modified cellulose acetate membrane. A pressure vessel contained 150
square feet of membrane for a unit total of 750 square feet of membrane
area.
A flow diagram of the reverse osmosis unit is presented in the
top portion of Figure 1. Pressurized sand filters and 10 micron cartridge
filters were used to remove suspended solids from the raw feed water before
the water entered the reverse osmosis unit. This precaution was necessary
as suspended solids can plug the small brine channels in the spiral-wound
reverse osmosis configuration.
The pressure vessels were arranged in a 2-2-1 array in order to
maintain as nearly as possible a uniform brine flow through each vessel.
The first two vessels were in parallel. Brine from these vessels was-
combined to be the feed water for vessels 3 and U, then combined and served
as feed to vessel 5.
*Mention of commercial products is for clarification only and does not imply
endorsement by the Environmental Protection Agency.

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6
In order to reach a recovery rate of 91 percent and not have in-
sufficient flow in the final vessel, it was necessary to recycle part
of the "brine. A brine flow of 3.0 gpm through each module was felt
necessary to minimize membrane fouling due to boundary layer problems.
For neutrolosis operation, brine from the reverse osmosis unit
passed into a 50-gallon stainless steel reaction tank where lime was
added (see lower portion of Figure l). The water was neutralized to a
pH of only ij-,3 to U.5 because past experience had shown that at this pH most
of the iron and aluminum were removed.If the pH were raised too high,
a danger existed that when the neutralized v/ater was recycled instantaneous
iron precipitation would occur resulting in fouling of the membrane vessels.
The neutralized brine passed from the reactor to an upflow settling
tank, where the suspended solids were removed. The supernatant water
was then filtered to remove any remaining suspended solids and then re-
cycled to the reverse osmosis unit.
IVo high recovery reverse osmosis runs (without neutralization) were
made. For 100 hours the unit was operated at 91 percent recovery. The
second run was for 2-3l hours at 91 percent recovery during the day and 85
percent at night. The latter operation was necessary because personnel
were not available for 2h t'our surveillance and the unit was left unattended
at night. During the run, operational and water quality data were collected
regularly. The test was terminated because the high pressure pump failed.
Three "neutrolosis" runs were made. The first run was a feasibility
study for 29.5 hours with the primary reverse osmosis unit operating at
91 percent water recovery. The second was for 99*6 hours, again at 91 per-
cent recovery. The third run was for 130.6 hours at 80 percent primary

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F URE I
FLOW DIAGRAM FOR NEUTROLOSIS TESTS
^REVERSE OSMOSIS~UNIT
10 MICRON
CARTRIDGE
HIGH PRESSURE
PUMP
SAND
FILTER
FILTERS
P*,TUBE
JT

^TUBE 3
L-fe TUBE 4^
'-'h	^
PRODUCT'
-r
RECYCLE BRINE
O
U^T7JU77T^77
TUBE 5 o)i
BRINE

O
pH METER
^UPFLOW^
Settling tank
g (1200 GAL) 5
PRODUCT
SLUDGE
LIME NEUTRALIZATION UNIT
CARTRIDGE filter
sand filter
lime feeder

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8
water recovery. The latter test \ms made to determine if ultra high re-
coveries were needed during the first pass in order to obtain maximum
overall water recovery.
The raw acid mine drainage treated in these studies has the follow-
ing typical characteristics:
Acidity (CaCO_)	-	600 g/l
Total Iron ^	-	100 mg/l (95$ ferric)
Calcium, Ca,	-	100 mg/l
Magnesium, Mg	-	Uo mg/l
Aluminum	-	Uo mg/l
Sulfate	-	900 mg/l
pH	-	2.7
Conductance	950 microrahos/cm
RESULTS
In Table II, the results of the high recovery test at 91 percent
are reported. The overall rejection and product water quality were not
as good at 91 percent recovery (Table II) as at 75 percent (Table I).
However, because of the brine recycle the membranes were receiving a feed
water with much higher concentration (see feed water versus blended feed
water in Table II). As the concentration of the feed increases, the con-
centration in the effluent also increases. When rejection was determined
on the basis of blended feed water, the rejections are the same magnitude
at 91 percent recovery as at 75 percent recovery. In a fullscale plant,
brine recycle would not be necessary and thus, better product water qual-
ity would be expected, probably similar to that reported in Table I.
The flux decline during the 100 hour run was from 11.6 to 9*8 gallons
per square foot per day. At the end of the run, the water recovery was
reduced to 50 percent, thereby, forcing more water through the brine chan-
nels. This process was found to restore the flux to 11.0, probably by
the removal of calcium sulfate. To further evaluate the flushing of mem-
brane fouling materials, samples were taken Immediately before and 30

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9
minutes after lowering the recovery rate from 91 to 85 percent. A mass
balance revealed that at 91 percent recovery, the quantity of all con-
stituents entering the unit were within analytical error of being the
same as those leaving. Thus, the buildup on material on the membrane
occurred at a slow rate. After leaving the recovery to 85 percent, the
mass balance showed that approximately 30 percent more calcium, sulfate,
iron, aluminum and magnesium were being discharged than entered the unit.
This result showed that flushing was occurring and that the material
building up in the unit was more than just calcium sulfate.
The results obtained during the 91 percent day-85 percent night
water recovery operating mode was similiar to those reported in Table II.
Less membrane fouling occurred at 85 percent than at 91 percent recovery
however, the flux rate could be recovered in both cases by flushing.
The conclusion drawn from these tests was that the reverse osmosis
unit could be operated at 90 percent recovery and not have uncontrollable
membrane fouling. The problem of disposing of the brine still remained.
A summary of the first "neutrolosis" test run is presented in Table
III. During this run the primary water recovery was established at 91
(5)
percent. Past research had shown that the acidity, iron and aluminum
were almost entirely removed when the acid mine drainage was neutralized
to a pH of 4.5. Thus, the brine was neutralized to pH 4.7. Raising the
\
pH to a higher level might result in instantaneous precipitation of the
iron and plugging of the membrane. As seen in Table III, the neutralization
process reduced the acidity, aluminum, calcium, iron and sulfate but did
not completely remove them. Therefore, the continued recycling of these

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10
TABLE II
Summary of 91 Percent Water Recovery Test
Average Water Recovery, Percent
Range of Water Recovery, Percent
Average Pressure, psi
91.2
90.6 to 93.1
606
Average Feed Water Temperature, ~F	44
Water Flux Rate, Corrected to 10 C, gal./sq. ft./day: start of run
end of run - $.8, range 95 - 13.4
Length of Run, Hours	-	100
11.6,


Q


b
Tube
^ b
Overall

Raw
Blended


Rejection Rejection

Water
Feed Water
Brine
Product
Percent
Percent
Conductance, Mmhos/cm
1,190
4,210
9,600
248
95
79
PH
2.7
2.2
2.0
3.4
	
--
Acidity (CaCO ), ing/l
633
2,584
5,91^
116
96
82
Ca (CaC0_), mg/l
266
1,206
2,756
7.5
99
97
Mg (CaCO^), mg/l
134
750
1,671
2.8
99
98
S0U, mg/i
810
4,024
9,542
16.8
99
98
Fe, mg/l
110
528
1,190
2.8
99
97
Al, mg/l
35
172
398
1.1
99
97
blended feed was the mixture of raw water and recycled brine actually pumped
to the reverse osmosis unit.
13Tube rejection is the percent decrease in concentrate based on the water the
membranes were actually receiving, e.g., blended feed - product X 100/blended
feed. Overall rejection is the efficiency of the whole process, e.g., feed
water - product water X 100/feed water.
neutralized brine would not cause a buildup on these ions. Manganese which
is not removed at a low pH will continue to build up until its saturation point
is reached. This buildup may be too great for good reverse osmosis perfor-
mance and a periodic blow down will, be necessary.
Total system water recovery was 99 percent. For every 100 gallons
treated, 99 gallons of product water were produced and one gallon of sludge.
Membrane fouling occurred at the very high primary water recovery (91 per-
cent) utilized during this run. Flushing the unit every 20 to 24 hours was
successful in restoring the flux rate.

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TABLE in
Summary of Neutrolosis Test I
Reverse Osmosis Unit Water Recovery	- 91 percent
Total Water Recovery "Neutrolosis" System	- 99 percent
Pressure, psi	- 602
Water Temperature, F	-	58
Raw Water Flow, gpm	-	5.02
Product Water Flow, gpm	-	4.97
Brine Water Flow, gpm	-	0.48
Neutralized Brine Recycled,	gpm -	0.43
Average Water Flux, gal/sq.	ft/day at 77 F -	15.4
Length Run, Hours	99*6
Neutralized	Salt*5
Raw Blended	Brine Product Rejection
Water Feed Brine Recycled Water Percent
Conductance, Mmhos/cm
1720
5160
10,000
3680
335
93
pH
2.7
2.2
20
4.7
34
-
Acidity, Mg/l
657
2680
6030
462
130
95
Magnesium, Mg/l
38
271
5^7
312
2
99
Calcium, Mg/l
100
473
1130
755
3
99
Aluminum, Mg/l
38
187
405
65
1
99
Iron, Mg/l
117
516
1210
2
2
99
Sulfate, Mg/l
982
4680
11,100
0
3
CJ
21
99
Alkalinity, Ilg/l
0
0
0
1
0

a
Blended feed was a mixture of raw water, recycled brine and recycled neu-
tralized brine. This water was pumped to the reverse osmosis unit.
Salt rejection % = blended feed concentration minus product water concen-
tration X 100 divided by blended feed concentration.
In order to relieve some of the fouling problem, the second "neutrolosis"
test run was made at 82 percent water recovery. A summary of this test run
is presented in Table IV. The "neutrolosis" process water recovery was 98.7
percent or essentially the same as with 91 percent unit water recovery. Foul-
ing of the membrane was less than at the high recovery and less flushing was
necessary. Salt rejection was approximately 99 percent for all multivalent

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12
TABLE IV
Summary of Neutrolosis Test II
Reverse Osmosis Unit Water Recovery	-	82 Percent
Total Water Recovery "Neutrolosis" System	-	98.7 Percent
Pressure, psi	-	600
Water Temperature, F	-	6l
Raw Water Flow, gpm	-	U.83
Product Water Flow, gpm	-	^.77
Brine Water Flow, gpm	-	1.31
Neutralized Brine Recycled, gpm	-	1.25
Average Water Flux, gal./sq.ft/day at 600 psi at 77 F -	12.3
Length Run, Hours	-	130

8.

Neutralized

Salt ^
Raw
Blended

Brine
Product
Rejection
Water
Feed
Brine
Recycled
Water
Percent
1660
3000
56UO
2500
213
93
2.
7 2.5
2.
3 M
3.7
-
585
1150
21+30
175
36
97
0
0
0
7
0
-
133
U60
939
8U5
2
99
^3
91
I89
30
1
99
101
2lh
*+59
7
1
99
13^0
3010
6380
3U90
18
99
32
118
25U
131
1
99
Conductance, Mmhos/cm
pH
Acidity, Mg/l
Alkalinity, Mg/l
Calcium, Mg/l
Aluminum, Mg/l
Iron, Mg/l
Sulfate, Mg/l
Magnesium, Mg/l
8L
Blended feed was a mixture of raw water, recycled brine, and recycled neu-
tralized brine. This water was pumped to the reverse osmosis unit.
^Salt rejection $ = blended feed concentration minus product water concen-
tration x 100 divided by blended feed concentrate.
ions. The product water quality was also better because a less concentrated
feed water was introduced. In a larger sized unit where brine recycle would
not be necessary, the product water at 91 and 82 percent recovery would be
the same.
The optimum primary water recovery has not yet been determined. The
reduced fouling at lower water recovery must be balanced with the higher
capital cost of a larger neutralization system. Total system water recovery,
salt rejection and chemical costs for neutralization would be approximately
the same.
The "neutrolosis" concept is a significant breakthrough in reverse
osmosis technology. Converting 99 percent of the acid water into a high

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13
quality product water and the remaining one percent into a dense wet sludge
is a dramatic result. Further studies on this process are "being carried
out by the Water Quality OCfice.
ACKNOWLEDGMENTS
The authors wish to acknowledge the effort and innovations of Alvin Irons,
Curtis Corley, Randolph Lipscomb, James Kennedy and Howard Howell, all of
the Environmental Protection Agency's Norton Mine Drainage Field Site. They
also acknowledge the assistance of James H. Sleigh, Gulf Environmental Sys-
tems and the Office of Saline Water for the use of the reverse osmosis unit.
REFERENCES
(1)	Rusvak, A. and Nusbaum, I., Reverse Osmosis Field Testing on Acid Mine
Waters at Norton, West Virginia, Report to Office of Saline Water under
Contract 1^-01-0001-12^3, by Gulf General Atomic, Inc., Aug. 6, 1968.
(2)	Riedinger, A. B., Reverse Osmosis Field Testing on Acid Mine Waters at
Norton, West Virginia, Report to Office of Saline Water under Contract
14-01-0001-1836 by Gulf General Atomic, Inc., January 17, 1969.
(3)	Treatment of Acid Mine Drainage - Reverse Osmosis, Contract 1^-12-525
(l!K)10 DYG) between Federal Water Quality Administration and Gulf Gen-
eral Atomic, Inc., April, 19^9 
(U) Acid Mine Waste Treatment Using Reverse Osmosis, by Gulf Environmental
Systems Company, Water Pollution Control Research Series Number 11*010 DYG,
Environmental Protection Agency, Water Quality Office, Washington, D.C.
(In Press)
(5) Neutralization of High Ferric Iron Acid Mine Drainage, by Roger C. Wilmoth
and Ronald D. Hill, Water Pollution Control Research Series Number ll+OlO
ETV 08/70, Environmental Protection Agency, Water Quality Office, Wash-
ington, D.C., August, 1970.

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