SEGH Articles

Student led remediation study of Manitoban Gold mine

21 March 2011
Jill Maxwell was the joint winner of the Hemphill prize for best oral presentation at Galway SEGH 2010. She describes her work on the remediation of arsenic contamination by a natural wetland at New Britiannia Mine, Manitoba.

A study at the University of Manitoba investigated the effectiveness of a natural wetland as a remediation system for arsenic contamination derived from mine waste at New Britannia Mine (NBM), Snow Lake, Manitoba, Canada. At this deposit, gold is associated with arsenopyrite which is finely ground and treated with cyanide during processing. Subsequent oxidation of the arsenopyrite in the mine waste is the primary cause of arsenic contamination at the mine site.

Gold was extracted from arsenic-rich ore bodies in Snow Lake, by Nor-Acme Mine from 1949 to 1958 and then by NBM from 1995 to 2002. Nor-Acme left two major sources of arsenic contamination on the mine property, a small tailings area and the arsenopyrite residue stockpile (ARS). Concentrated residue was stockpiled in the ARS in hopes of finding economical means to recover the remaining refractory gold contained in the residue. A later attempt to extract gold from the residue through use of a lined leach pad added to the contamination. Although NBM capped the ARS and revegetated the area of the leach pad in 2000, elevated arsenic concentrations (up to 13 mg/L) have been detected in surface water in a wetland runoff area (RA) on the mine property. These values are well above the World Health Organization guideline of 0.001 mg/L. Water from the RA flows through a wetland toward Snow Lake, the source of drinking water for the Town.

A biogeochemical survey was employed to assess the passage of arsenic from the RA down the flow path toward Snow Lake. The study aimed to identify the distribution of arsenic and iron between surface water, soil and aquatic plants along the flow path, and to determine the mechanism for arsenic sequestration by plants and soil in the wetland. Surface water, soil and common cattail and water sedge plants were collected for total geochemical analyses by ICP-MS. Plants were separated into samples of roots, live shoots and dead shoots. Additional plant samples were squeezed by hydraulic press to extract fluids contained in cell vacuoles. Plant vacuoles and solid envelopes were then separately analyzed for total arsenic using ICP-MS. Root sections were prepared for electron microprobe (EMP) imaging and element mapping of arsenic and iron. In the field, surface water was passed through strong cation and strong anion exchange cartridges to separately retain As(III), As(V), MMA and DMA. Following elution in the laboratory the separate aliquots were analyzed for total arsenic.

Results of the flow path survey revealed the greatest fraction of arsenic in the RA was sequestered in organic soil (~ 4000 mg/kg), followed by plant roots (~ 900 mg/kg in sedge, 800 mg/kg in cattail), dead shoots (~ 800 mg/kg in sedge, 3 mg/kg in cattail), live shoots (~ 40 mg/kg in sedge, 3 mg/kg in cattail) and surface water (~ 1 mg/kg). Total geochemical analyses indicated that arsenic in the system is commonly associated with iron in all sample media. In surface water, arsenate is prevalent over arsenite and ~50% of arsenic existed in a methylated form. Separate analysis of cell vacuoles and envelopes and EMP element mapping showed arsenic to be sequestered with iron within in the cell walls of sedge and cattail roots and shoots.

The study indicated that a natural wetland can be very efficient at sequestering arsenic, reducing the environmentally available concentration by a factor of ten within 200 m and reducing concentrations in surface water well below international guidelines. Understanding the factors controlling sequestration of trace elements and heavy metals in wetlands can prove valuable in efforts to remediate environments influenced by mining and characterizing risk for the remobilization of sequestered elements.

Jill Maxwell, Barbara Sherriff, Elena Khozhina, Department of Geological Sciences, University of Manitoba, Winnipeg, MB, Canada

Keep up to date

SEGH Events

Submit Content

Members can keep in touch with their colleagues through short news and events articles of interest to the SEGH community.

Science in the News

Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

  • Biochar-based constructed wetlands to treat reverse osmosis rejected concentrates in chronic kidney disease endemic areas in Sri Lanka 2017-12-01


    The objectives were to investigate the potential remedial measures for reverse osmosis (RO) rejected water through constructed wetlands (CWs) with low-cost materials in the media established in chronic kidney disease of unknown etiology (CKDu) prevalent area in Sri Lanka. A pilot-scale surface and subsurface water CWs were established at the Medawachchiya community-based RO water supply unit. Locally available soil, calicut tile and biochar were used in proportions of 81, 16.5 and 2.5% (w/w), respectively, as filter materials in the subsurface. Vetiver grass and Scirpus grossus were selected for subsurface wetland while water lettuce and water hyacinth were chosen for free water surface CWs. Results showed that the CKDu sensitive parameters; total dissolved solids, hardness, total alkalinity and fluoride were reduced considerably (20–85%) and most met desirable levels of stipulated ambient standards. Biochar seemed to play a major role in removing fluoride from the system which may be due to the existing and adsorbed K+, Ca+2, Mg+2, etc. on the biochar surface via chemisorption. The least reduction was observed for alkalinity. This study indicated potential purification of aforesaid ions in water which are considerably present in RO rejection. Therefore, the invented bio-geo constructed wetland can be considered as a sustainable, economical and effective option for reducing high concentrations of CKDu sensitive parameters in RO rejected water before discharging into the inland waters.

  • Medical geology of endemic goiter in Kalutara, Sri Lanka; distribution and possible causes 2017-12-01


    This study assesses the distribution of goiter in the Kalutara District, Sri Lanka in order to find causative factors for the occurrence of goiter even after the salt iodization. A questionnaire survey was conducted at the household level and at the same time iodine and selenium levels of the water sources were analyzed. Questionnaire survey results indicated the highest numbers of goiter patients in the northern part where the lowest were found in the southern sector which may be due to the presence of acid sulfate soils. Females were more susceptible and it even showed a transmittance between generations. Average iodine concentrations in subsurface water of goiter endemic regions are 28.25 ± 15.47 μg/L whereas non-goiter regions show identical values at 24.74 ± 18.29 μg/L. Surface water exhibited relatively high values at 30.87 ± 16.13 μg/L. Endemic goiter was reported in some isolated patches where iodine and selenium concentrations low, latter was <10 μg/L. The formation of acid sulfate soils in the marshy lands in Kalutara district may lead to transformation of biological available iodine oxidation into volatile iodine by humic substances, at the same time organic matter rich peaty soil may have strong held of iodine and selenium which again induced by low pH and high temperature were suggested as the instrumental factors in the endemic goiter in Kalutara district. Hence, geochemical features such as soil pH, organic matter and thick lateritic cap in the Kalutara goiter endemic area play a role in controlling the available selenium and iodine for food chain through plant uptake and in water.

  • Nickel accumulation in paddy rice on serpentine soils containing high geogenic nickel contents in Taiwan 2017-12-01


    We investigated the extractability of nickel (Ni) in serpentine soils collected from rice paddy fields in eastern Taiwan to evaluate the bioavailability of Ni in the soils as well as for demonstrating the health risks of Ni in rice. Total Ni concentrations in the soils ranged were 70.2–2730 mg/kg (mean, 472 mg/kg), greatly exceeding the natural background content and soil control standard in Taiwan. Available Ni concentration only accounts for <10% of total soil Ni content; 0.1 N HCl-extractable Ni was the more suitable index for Ni bioavailability in the soil to rice than was diethylenetriaminepentaacetic acid (DTPA)-extractable Ni. The accumulation ability of rice roots was much higher than that of its shoots; however, compared with those reported previously, our brown and polished rice samples contained much higher Ni concentrations, within the ranges of 1.50–4.53 and 2.45–5.54 mg/kg, respectively. On the basis of the provisional tolerable Ni intake for adults recommended by the World Health Organization (WHO), daily consumption of this rice can result in an excessive Ni intake.