xvEPA
United
Environmental Protection
Agency
of
Technology Description: Lime treatment of acid mine drain-
age (AMD) and acid rock drainage (ARD) is a relatively simple
chemical process where low pH AMD/ARD is neutralized using
lime to reduce acidity and precipitate dissolved metals as metal
hydroxides. The U.S. Environmental Protection Agency (EPA),
in cooperation with the state of California and Atlantic Richfield
Company, evaluated lime treatment of AMD and ARD at the
Leviathan Mine Superfund Site located in a remote, high altitude
area of Alpine County, California. Two treatment systems were
evaluated in 2002 and 2003; an active lime treatment system op-
erated in two modes, a Biphasic mode for treatment of AMD with
high metals concentrations at flows up to 700 liters per minute
(L/min), and a Monophasic mode for treatment of a combined
AMD/ARD with high metals concentrations at flows up to 250
L/min; and a semi-passive Alkaline Lagoon for treatment of ARD
with relatively low metals concentrations at flows up to 110 L/
min. EPA evaluated each lime treatment systems' ability to neu-
tralize acidity and to reduce concentrations of five primary tar-
get metals (aluminum, arsenic, copper, iron, and nickel) and five
secondary water quality indicator metals (cadmium, chromium,
lead, selenium, and zinc) in the AMD and ARD to below EPA-
mandated discharge standards. Historically, the concentrations
of the five primary target metals in AMD and ARD released into
Leviathan Creek have exceeded EPA-mandated discharge levels by
up to 3,000 fold, resulting in fish and insect kills in the creek and
downstream receiving waters.
Lime treatment chemistry involves reaction of excess lime with
AMD or ARD (usually at a pH of 2 to 3), to raise solution pH
to 7.9 to 8.2. At elevated pH, metal hydroxides and gypsum
(calcium sulfate) precipitate from the AMD/ARD as shown in the
following reaction:
Ca(OH)20 + Me7+/Me3+ fa , + H,SO4 -»
Mc(OH)/Mc(OH),(s) + SaS04"(s) /Hp
Where Me2+/Me3+ = dissolved metal ion in either
a +2 or +3 valence state
(1)
At Leviathan Mine, the active lime treatment system consists of re-
action tanks, flash/flocc mixing tanks, plate clarifiers, a filter press,
and a settling pond. Operated in Monophasic mode, the active
treatment system was evaluated for its ability to treat a combined,
moderate ARD/AMD flow without regard to the type of metal or
concentration. In this case, the resulting solid waste stream exhib-
ited hazardous waste characteristics due to high arsenic and nickel
concentrations, requiring disposal in a treatment, storage, and
disposal (TSD) facility. Operated in Biphasic mode, the active
lime treatment system was evaluated for its ability to treat a high
AMD flow where concentrations of arsenic were relatively high.
The overall chemical reaction is the same as for the Monophasic
mode; however, metals precipitation is conducted in two phases.
In Phase I, the active treatment system is held at a pH of 2.8 to
3.0 creating a small quantity of precipitate containing high arsenic
concentrations, which when dewatered, exhibits hazardous waste
characteristics and requires off site disposal in a TSD facility. In
Phase IT, the pH is raised to 7.9 to 8.2 and the remaining metals
are precipitated, creating a much larger quantity of solid waste;
however, arsenic concentrations are low enough that the Phase
II solid waste is not classified as a hazardous waste and can be
disposed of on site. Separating the arsenic into a smaller solid
waste stream significantly reduces materials handling and disposal
costs.
The Alkaline Lagoon treatment system is a continuous flow, lime
contact system, which was evaluated for its ability to treat low
flow ARD with relatively low metals content. The system consists
of air sparge/lime contact tanks where initial flocc formation oc-
curs, bag filters to capture approximately 60 percent of the flocc,
and a multi-cell settling lagoon for extended lime contact with the
remaining dissolved metals and precipitation of metal hydroxide.
The solids captured in the bag filter and settled in the lagoon arc
not classified as a hazardous waste and can be disposed of on site.
"Waste Applicability: Conventional methods of treating AMD
and ARD involve the capture, storage, and batch or continuous
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treatment of water using lime addition, which neutralizes acidity
and precipitates metals. Lime treatment technology is applicable
to precipitation of any metal the solubility of which is pH sensi-
tive. The active lime and alkaline lagoon treatment systems are
simply improvements to conventional lime treatment technology.
Either treatment system can be modified to treat wastes of varying
metals type or content in a single or multi-step process. Active
lime treatment appears to be applicable in situations where flow
rates are high and the treatment season is short, while the semi-
passive alkaline treatment lagoon favors a lower flow rate and ex-
tended treatment season.
Evaluation Approach: Evaluation of the lime treatment technolo-
gies occurred between June 2002 and October 2003, separated by
winter shutdown. During operation of the lime treatment sys-
tems, multiple sampling events were conducted for each of the
treatment systems. During each sampling event, EPA collected
metals data from each systems influent and effluent streams,
documented metals removal and reduction in acidity within each
systems unit operations, and recorded operational information
pertinent to the evaluation of each treatment system. 'The treat-
ment systems were evaluated independently, based on removal ef-
ficiencies for primary and secondary target metals, comparison
of effluent concentrations to EPA-mandated discharge standards,
and on the characteristics of and disposal requirements for the
resulting metals-laden solid wastes. Removal efficiencies of indi-
vidual unit operations were also evaluated.
The primary objectives of the technology evaluations were:
• Determine the removal efficiencies for primary target met-
als over the evaluation period
• Determine whether the concentrations of the primary tar-
get metals in the treated effluent are below the discharge
standards mandated in the EPA Action Memorandum
In addition, the following secondary objectives were intended to
provide additional information that will be useful in evaluating
the technologies:
• Document operating parameters and assess critical operat-
ing conditions necessary to optimize system performance
• Monitor the general chemical characteristics of the AMD
or APJ3 water as it passes through the treatment system
* Evaluate operational performance and efficiency of solids
separation systems
* Document solids transfer, dewatering, and disposal opera-
tions
• Determine capital and operation and maintenance costs
Evaluation Results: Both treatment systems were shown to be
extremely effective at neutralizing acidity and reducing the con-
centrations of the 10 target metals in the AMD and ARD flows
at Leviathan Mine to below EPA-mandated discharge standards.
In general, removal efficiencies for the 10 target metals exceeded
90 percent. In addition, the active Biphasic treatment system was
shown to be very effective at separating arsenic from AMD prior
to precipitation of other metals, subsequently reducing the total
volume of hazardous solid waste produced by the treatment sys-
tem. Three tables summarizing the outcome of the technology
evaluations are provided.
Table 1. Active LimeTreatment System Removal Efficiencies: Biphasic Operation in 2002 and 2003
Target
Metal
Number of
Sampling
Events
Average
Influent
Concentration
(M9/L)
Standard
Deviation
Average
Effluent
Concentration
(M9/L)
Standard
Deviation
Exceeds
Discharge
Standards
(Y/N)
Average
Removal
Efficiency
(%)
Range of
Removal
Efficiencies
(%)
Primary Target Metals
Aluminum
Arsenic
Copper
Iron
Nickel
12/1
12/1
12/1
12/1
12/1
381,000
2,239
2,383
461,615
7,024
48,792
866
276
100,251
834
1,118
8.6
8.0
44,9
34.2
782
1.9
2,5
66,2
15.4
N
N
N
N
N'
99,7
99.6
99,7
100
99.5
99.2 to 99,9
99.2 to 99,8
99.4 to 99,8
99, 9 to 100
99.2 to 99,9
SecondaryWater Quality Indicator Metals
Cadmium
Chromium
Lead
Selenium
Zinc
12/1
12/1
12/1
12/1
12/1
54.4
877
7.6
4,3
1,469
6.1
173
3.6
3.9
176
0.70
5.7
2.0
3.8
19.3
0.28
12.2
1.1
1.5
8,9
N
N
N
N
N
98,7
99,3
78,3
NC
98,7
97.5 to 99.4
93.8 to 99,9
69.2 to 86,7
NC
97,4 to 99.4
NC = Not calculated as influent and effluent concentrations were not statistically different
ug/L = Microgram per liter
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Table 2. Active LimeTreatment System Removal Efficiencies: Ponophasie Operation in 2003
Target
Metal
Number of
Sampling
Events
Average
Influent
Concentration
(Mg/U
Standard
Deviation
Average
Effluent
Concentration
(Mg/U
Standard
Deviation
Exceeds
Discharge
Standards
(Y/N)
Average
Removal
Efficiency
(%)
Range of
Removal
Efficiencies
(%)
Primary Target Metals
Aluminum
Arsenic
Copper
Iron
Nickel
7
7
7
7
7
107,800
3,236
2,152
456,429
2,560
6,734
252
46.4
49,430
128
633
6.3
3.1
176
46.8
284
3.5
1.5
130
34.7
N
N
N
N
N
99.5
99.8
99.4
100.0
97.9
99.0 to 99.8
99.7 to 99. 9
99.0 to 99,7
99, 9 to 100.0
95.7 to 99,3
Secondary Water Quality Indicator Metals
Cadmium
Chromium
Lead
Selenium
Zinc
7
7
7
7
7
26.1
341
6.2
16.6
538
14.1
129
3.6
13.6
28.9
0.2
3,0
1.6
2.1
5.6
0,027
3,8
1.3
0.43
3.6
N
N
N
N
N
99.1
99,0
74.6
93.1
98.9
98.4 to 99,7
95. 6 to 99,8
48. 3 to 89.8
91.0 to 94.4
97.7 to 99,6
ug/L = Microgram per liter
Table 3. Alkaline Lagoon Treatment System Removal Efficiencies in 2002
Target
Metal
Number of
Sampling
Events
Average
Influent
Concentration
(Mg/U
Standard
Deviation
Average
Effluent
Concentration
(Mg/U
Standard
Deviation
Exceeds
Discharge
Standards
(Y/N)
Average
Removal
Efficiency
(%)
Range of
Removal
Efficiencies
(%)
Primary Target Metals
Aluminum
Arsenic
Copper
Iron
Nickel
8
8
8
8
8
31,988
519
13.5
391,250
1,631
827
21.9
2,5
34,458
47,0
251
5,8
5,5
148
22.6
160
3.2
2,0
173
10,3
N
N
N
N
N
99.2
98.9
58.3
100
98.6
98,0 to 99.5
97.6 to 99.5
27.7 to 74.5
99. 9 to 100
97.2 to 99,1
Secondary Water Quality Indicator Metals
Cadmium
Chromium
Lead
Selenium
Zinc
8
8
8
8
8
0.2988
19,3
5,1
3,3
356
0.0035
2,0
1,2
1.6
6,6
0.4
2,3
1.7
3.2
14.2
0,1
0,9
0.8
1.3
8,6
N
N
N
N
N
NC
88.5
66.4
NC
96.0
NC
83,1 to 92. 3
37.7 to 78.9
NC
90,6 to 98.2
NC = Not calculated as influent and effluent concentrations were not statistically different
ug/L = Microgram per liter
Key findings from the evaluation of the two treatment systems,
including complete analytical results, operating conditions, and
a cost analysis, will be published in a Technology Capsule and an
Innovative Technology Evaluation Report.
For further information contact:
Edward Bates, U.S. EPA Project Manager
EPA National Risk Management Research Laboratory
Office of Research and Development
26 West Martin Luther King Dr.
Cincinnati, OH 45268
(513) 569-7774
bates. edward(3>epa.gov
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v°/EPA
United
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH
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