The MEND Project 3.11.1: “Treatment of A cidic Seepages Employing Wetland
Ecology and Microbiology has reached the completion of its fourth year. The project
has been financially supported by Inco, Denison, Environment Canada, CANMET and
by the Centre de Recherche Minérales (CRM). The objectives of the project are to
determine the conditions which will lead to the treatment and amelioration of acid mine
drainage (AMD) through the use of ecological microbial processes. Those occur
naturally in wetlands, lake and ocean sediments. The Makela Test Cell System was
intended to provide flow control for a typical seepage from a base metal tailings dam.
Under flow control, natural Fe3+ hydroxide precipitation and acidification rates were
determined. Conditions which are required to promote microbial sulphate reduction and
alkalinity-generation were to be identified. The microbially-mediated treatment of acid
mine drainage is referred to as ARUM (Acid Reduction Usina Microbioloav}.

The construction of retention cells at the perimeter of the phreatic line of the tailings
dam was complex. This terrain is hydrologically unstable and dikes are prone to
slumping. Permeable dikes were used to provide sheet flow, and impermeable dikes,
providing flow control, were required to separate the retention cells. Frequent repairs
on the cell system were needed from the beginning of construction in 1989 until
summer 1991. By the end of the summer of 1991 flow control was achieved, and a
prototype of a floating cattail cover, which allows the ARUM system to develop, was
finally installed. Project activities are given below for each year.

Year 1 (1989/1990): In the first year, the Test Cell System was constructed and
hydraulic adjustments were made to control flow. Test work in 200 L drums
(ARUMators), containing organic amendment and equipped with sampling ports,
showed that microbial alkalinity-generation in tailings seepages is possible. ARUMator
3, a 12 m3 fibreglass tank with an 800 L inner sleeve containing the organic
amendment, was installed at the end of the Test Cell System. This would facilitate
testing of the ARUM processes under completely controlled conditions.

Increases in pH in the ARUMators were reported from 2.5 to 5.7. Decreases in nickel
concentrations from 91 mg/L in a sample from a surface port to 1.7 mg/L in a bottom
sample of the same ARUMator were noted. These observations lead to the recognition
that the process is sediment-bound and that a floating cattail cover was needed.
Cattails rooted in the organic amendment would rapidly deplete the nutrients required
for the ARUM ecosystem. A floating vegetation mat, however, would not only provide
organic matter to the sediment below, but also enhance reducing conditions in the
water column between the sediment and the floating cattail mat.

The research of the first year was reported in June 1990 in a report entitled: MEND
Project 3.1 1.1 “Treatment of Acidic Seepages Employing Wetland Ecology and
Microbiology, Final Report”, by M. Kalin, June 1990. DSS Contract Number
23440-8-9264. A peer review was carried out on the report, and the project was found
technically sound .

Year 2 (1990/1991): After the first winter, the Test Cell System required readjustment
of the hydraulic conditions. It was established that the lowest controllable flows were 3
– 5 L/min. The maximum flow, which the system could sustain without structural failure,
was determined to be 300 L/min. Baseline chemistry of the system was defined in the
second year.

Ground water contributions, amounting to less than 1 L/min, were found to have no
detectable effects on the water chemistry. The conditions under which precipitation of
ferrous (Fe2+) and ferric (Fe3+) hydroxide takes place in the precipitation cell (Cell 1 )
were defined. A baffle system was installed in Cell 1 which facilitated settling of the
hydroxides. This cell discharged a clear, acidic solution with low iron concentrations to
Cell 2.

Organic amendment was placed in Cells 3 and 4, between snowfencing curtains. Flax
bales mixed with hay bales were used to provide the substrate on which the microbial
ecosystem would grow and where alkalinity would be generated. Through the activity
of the sulphate reducers, hydrogen sulphide is generated, which results in the
precipitation of metal sulphides. An extensive microbiological investigation was carried
out in the laboratory to define the growth requirements of the alkalinity generating
microbes.

A report on the work completed in the second year was submitted in March 1991.
MEND Project 3.1 1.1 “Treatment of Acidic Seepage Employing Wetland Ecology and
Microbiology, Final Report”, by M.Kalin, March 1991. DSS Contract Number
23440-0-9065.

Year 3 (1991/1992): In the first two years of the project, the ecological conditions
required for microbial alkalinity-generation were defined. Floating cattail mats were
installed on Cells 3 and 4 in 1991. The third year was, therefore, the first opportunity to
demonstrate the ARUM process under defined flow conditions. The optimum
configuration required for the establishment of the ARUM process had only been
achieved by late July, due to problems encountered with bank stability in late May
1991. Slumping of the tailings dam blocked the bypass ditch, preventing regulation of
the flow to the Test Cell System.

The ARUM process works from the sediment upwards, and thus, its effects would first
be seen in the lower part of the water column in Cells 3 and 4. The flow was adjusted
to 1 L/min by mid July. By mid September 1991, differences in metal concentrations of
water on the surface and in the lower parts of the water column were large. In Cell 4,
the nickel concentrations at the surface ranged from 43 mg/L to 74 mg/L. The range in
the lower part of the water column (50 – 60 cm) was 12 mg/L to 33 mg/L. In Cell 3, the
first ARUM cell receiving the low pH AMD, the nickel concentrations ranged between
23 and 51 mg/L at the surface, while the lower part of the water column had
concentrations between 15 and 24 mg/L. This represents approximately a 50 %
reduction of the nickel concentrations. Copper was present in both cells at the surface
in concentrations ranging from < 1 to 4 mg/L and reduced by the ARUM process in the
lower part of the cells to 1 or < 1 model.

At a flow rate of 1 L/min, the water in Cells 3 and 4 has a retention time of just over 4
months. The surface water, however, short-circuits and therefore, the pH of the
discharged water had only slightly increased from 2.5 to 3.2. However, 27 kg of
alkalinity has been generated in water leaving Test Cell 4 after passing over the
actively ARUMating lower water column, where the pH is as high as 6.0. If water were
to be discharged from the bottom of Cell 4, reduced metal concentrations with a high
pH water would leave the system by the end of the third year.

The results of the third year indicated that, in the Test Cell System, alkalinity
generation had taken place. The work of the third year was reported in March 1992.
MEND Project 3.11.1 “Treatment of Acidic Seepages Employing Wetland Ecology and
Microbiology, Final Report”, by M. Kalin, March 1992. DSS Contract Number
23440-0-9065.

Year 4 (1992/1993): Due to dam stability problems during spring thaw and freezing of
the dikes along with the control valve, the system was closed during the winter of 1992
to 1993 As the cattail rafts were planted late in 1991 growing season, growth was
restricted to a few plants. By the beginning of the 1992 growing season, adjustments
were made in the root zone. The floating cover was functional by July 1992 and the
system was ready to be monitored.

In 1989 and 1990, there was no flow control and flows were very variable. With short
retention times (4.2 days in Cells 1 and 2 and 3.26 days in Cells 3 and 4 at 40 L/min)
Fe3+ hydroxide precipitation occurred throughout the system. When flow control was
established at 1 L/min, retention time could be increased to an estimated 168 days in
Cells 1 and 2. In 1992, Fe3+ hydroxide precipitation facilitated the removal of at least
94 % of the iron load in Cell 1 and produced an acidity loading of 100 to 600 g/day in
the water entering the ARUM cells (Cells 3 and 4).

The final configuration, established by the end of 1991, allowed for the establishment
of ARUM in Cells 3 and 4. In 1992, with a retention time of 131 days, the ARUM
system (Cells 3 and 4) removed 80 – 87 % of the nickel loading, 77 – 98 % of the
copper loading, 10 – 20 % of the sulphur loading, and 47 – 73 % of the acidity loading
from the seepage water.

This report presents the summary of those components of the microbial ecosystem
which play major roles in the ARUM process. The relationships between wetland
ecosystems and ARUM processes are given in Section 2. In Section 3, the Test Cell
System is described, outlining the events which finally lead to flow control and floating
cattail rafts in 1992. The water chemistry, the hydrology with and without microbial
activity, as well as the iron hydroxide precipitation, are described in Section 4. In
Section 5, the data obtained in the research program are used to define the operating
parameters, such as nutrient supply and chemical conditions. The expected
performance and the applications of the process are discussed in Sections 6 and 7. In
Section 8, the limitations of the microbial approach are outlined. Some economic
considerations are presented in Section 9. It is concluded in Section 10 that the project
has provided the technical basis to define the conditions required to utilize microbial
amelioration of AMD in decommissioning seepage collection ponds, open pits and
polishing ponds.