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

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

  • Date palm waste biochars alter a soil respiration, microbial biomass carbon, and heavy metal mobility in contaminated mined soil 2017-04-19

    Abstract

    A 30-day incubation experiment was conducted using a heavy metal-contaminated mined soil amended with date palm feedstock (FS) and its derivative biochars (BCs) at three pyrolysis temperatures of 300 (BC-300), 500 (BC-500), and 700 °C (BC-700) with different application rates (0.0, 5, 15, and 30 g kg−1) to investigate their short-term effects on soil respiration (CO2–C efflux), microbial biomass carbon (MBC), soil organic carbon (SOC), mobile fraction of heavy metals (Cd, Cu, Pb, Zn, Mn, and Fe), pH, and electrical conductivity (EC). The results showed that FS and BC-300 with increasing addition rate significantly reduced soil pH, whereas SOC, CO2–C efflux, and soil MBC were increased compared to the control. On the contrary, BC-500 and BC-700 increased soil pH at early stage of incubation and have small or no effects on SOC, CO2–C efflux, and MBC. Based on the results, the date palm biochars exhibited much lower cumulative CO2–C efflux than feedstock, even with low-temperature biochar, indicating that BCs have C sequestration potential. Applying BC-700 at 15 and 30 g kg−1 significantly reduced cumulative CO2–C efflux by 21.8 and 45.4% compared to the control, respectively. The incorporation of FS into contaminated soil significantly increased the mobile content of Cd and Mn, but decreased the mobile content of Cu. However, BC-300 significantly reduced the mobile content of Cd, Cu, Pb, and Zn. It could be concluded that low-temperature biochar could be used as a soil amendment for reducing heavy metal mobility in mining contaminated soil in addition to minimize soil CO2–C efflux.

  • Historical record of anthropogenic polycyclic aromatic hydrocarbons in a lake sediment from the southern Tibetan Plateau 2017-04-17

    Abstract

    High-altitude lake sediments can be used as natural archives to reconstruct the history of pollutants. In this work, the temporal distribution of polycyclic aromatic hydrocarbons (PAHs) was determined in a sediment core collected from the southern Tibetan Plateau (TP), which was dated by using the 210Pb dating method and validated with the 137Cs fallout peak. The concentrations of the anthropogenic PAHs (Σ8PAH) in the sediment core ranged from 0.83 to 12 ng/g dw, and the fluxes of the Σ8PAH were in the range of 2.1–27 g/cm2/year. The temporal variations in the concentration and input flux of anthropogenic PAHs were low with little variability before the 1950s, and then gradually increased from the 1950s to the 1980s, and an accelerated increase was observed after the early 1980s. The content of total organic carbon played an insignificant role in affecting the time trends of PAHs in the sediment core. Diagnostic concentration fractions of PAH components indicate PAHs in the lake sediment of the southern TP which are mainly from biomass burning and/or from long-range atmospheric transport.

  • Determination of the potential implementation impact of 2016 ministry of environmental protection generic assessment criteria for potentially contaminated sites in China 2017-04-12

    Abstract

    The Ministry of Environmental Protection of China issued a 3rd draft edition of risk-based Generic Assessment Criteria (the MEP-GAC) in March 2016. Since these will be the first authoritative GAC in China, their implementation is likely to have a significant impact on China’s growing contaminated land management sector. This study aims to determine the potential implementation impact of the MEP-GAC through an in-depth analysis of the management context, land use scenarios, health criteria values adopted and exposure pathways considered. The MEP-GAC have been proposed for two broad categories of land use scenarios for contaminated land risk assessment, and these two categories of land use scenarios need to be further delved, and a MEP-GAC for Chinese cultivated land scenario ought to be developed, to ensure human health protection of Chinese farmers. The MEP-GAC have adopted 10−6 as the acceptable lifetime cancer risk, given the widespread extent and severe level of land contamination in China, consideration should be given to the decision on excess lifetime cancer risk of 10−5. During risk assessment process in practice, it is better to review the 20% TDI against local circumstances to determine their suitability before adopting it. The MEP-GAC are based on a SOM value of 1%, for regions with particularly high SOM, it might be necessary to develop regional GAC, due to SOM’s significant impact on the GAC developed. An authoritative risk assessment model developed based on HJ25.3-2014 would help facilitate the DQRA process in practice. The MEP-GAC could better reflect the likely exposures of China’s citizens due to vapour inhalation by using characteristics of Chinese exposure scenarios, including China-generic building stock, as inputs into the Johnson and Ettinger model as opposed to adoption of the US EPA parameters. The MEP-GAC once implemented will set the trajectory for the development of the investigation, assessment and remediation of land contamination for years.