The effect of processed kimberlite effluent from the EkatiTM Diamond Mine on freshwater zooplankton
Date
2002
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Degree Level
Masters
Abstract
Broken Hills Proprietary Company Ltd. (BHP; now BHP Billiton Inc.,) Ekatia™ Diamond Mine, located approximately 300 km northeast of Yellowknife in Canada's
Northwest Territories, began mining operations in the fall of 1998. This diamond mine
has a life expectancy of at least 25 years, as more than five diamond bearing kimberlite pipes have been identified on BHP 's claim block. Diamonds are extracted from kimberlite using chemical free processes that reduce the ore to fine particles (≤0.5 mm).
Processed kimberlite effluent (PKE), which consists of these fine particles, water used
during the extraction process, coagulants, flocculants, and treated sewage effluent, is
disposed of in the designated containment facility, Long Lake. The Long Lake
Containment Facility (LLCF) has been subdivided into five cells, of which the first four
cells were designed to receive PKE and the last cell would act as a final monitoring
stage before water was discharged to the downstream aquatic environment. The
magnitude of effects PKE had on the ecosystem of the LLCF was evaluated through
field assessments of chemistry and zooplankton community structure from August 1998
to August 2000. The toxic components of PKE were determined through a series of baseline toxicity tests and toxicity identification evaluations (TIE) using Ceriodaphnia
dubia.
The loss of aquatic habitat, higher turbidity and significantly altered water chemistry resulting from PKE addition reduced zooplankton abundance in the receiving
cell of the LLCF to less than 10% of values prior to PKE depositions. From August
1998, prior to the addition of PKE, to August 2000 total water hardness, alkalinity, total
dissolved solids, pH, and total nitrogen significantly increased in all cells of the LLCF. In the cell farthest from PKE deposition, the concentrations of the following metals increased: barium from 6.6 to 24.3 μg/L; molybdenum from below detection (1.0) to 6.3 μg/L: strontium from 8.1 to 35.0 μg/L, and nickel from below detection (1.0) to 1.2 μg/L. Significantly greater increases in the concentration of these metals were noted in the cell directly downstream of PKE deposition.
Processed kimberlite effluent was chronically (7-d reproductive inhibition) toxic
to C. dubia at concentrations as low as 12.5% effluent. The following Phase I TIE
manipulations did not reduce the toxicity of PKE: ethylenediaminetetra-acetic acid
(EDTA) and sodium thiosulfate addition tests, aeration, and solid phase extraction (C-18 column). Toxicity of PKE was significantly reduced with major pH (to 3 or 11)
adjustments followed by filtration (0.45 μm). It is believed that the cationic polymer
(Magna Floc®) was the toxic component since the estimated final concentration of the
polymer in PKE was 1,000 times higher than the estimated 7-day EC50 to C. dubia of
0.014 mg/L. It is postulated that major pH adjustments altered the behaviour and
electrostatic charges of the kimberlite minerals in solution in such a manner that excess
cationic polymer became bound to the minerals and was no longer able to elicit a toxic
response.
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Citation
Degree
Master of Science (M.Sc.)
Department
Toxicology
Program
Toxicology