New method uses waste to clean arsenic from lake contaminated by gold mine

The site construction. Credit: Jeff Bain and Joanne Angai

Arsenic leached into the lake from the tailings of the abandoned Long Lake gold mine, which operated intermittently until 1937 and produced approximately 200,000 metric tons of tailings, discharged directly into the non-containment environment.

Now, a team of researchers from the University of Waterloo has shown that a passive form of remediation that uses common waste can remove virtually all arsenic from lake water samples. Their results are published in the Hazardous Materials Journal.

Scientists have found that mixing wood chips, leaf mulch, and iron filings (leftover from car engine manufacturing) with limestone creates conditions that favor the growth of bacteria. Bacteria extract arsenic from water by converting it to a solid form which is essentially trapped in the waste filter.

Joanne Angai is the lead author of the study and conducted the research as part of her Masters in Earth Sciences at the University of Waterloo. Passive treatment is a cost-effective approach to remediation, she said. “Active treatment involves pumping water out of the ground, treating it, and then putting it back, whereas with passive methods you treat the water where it is,” she said. There are also fewer ongoing operational requirements and lower costs associated with process oversight.

Passive treatment is also more environmentally friendly, according to Carol Ptacek, co-supervisor of Angai’s thesis and member of the research team. “It uses less energy, which helps mitigate or reduce greenhouse gas emissions often associated with active treatment systems,” said Ptacek, a professor in the Department of Earth and Environmental Sciences. from the University of Waterloo.

The researchers used a variety of different techniques – including water chemistry, next-generation genomic sequencing and synchrotron studies – to determine what reactions occurred when they pumped contaminated lake water through columns. acrylics filled with reactive material. When they tested water samples that had passed through the mixture, they found that the arsenic concentration had dropped significantly.

Using the University of Saskatchewan’s Canadian Light Source SXRMB beamline, the team examined waste cores and confirmed that they had trapped almost all of the arsenic in the form of a mixture of arsenic sulphides and arsenic bound to iron minerals. Ptacek says having access to the CLS beamline and its scientists allowed them to generate useful results from the study. “The synchrotron provided a definitive characterization of the composition and structure of the reaction product in a very effective and efficient manner,” says Ptacek.

Although this approach to capturing groundwater contaminants before they reach surface waters has been applied in other cleanup projects, this is the first study to show that the method is effective when it is used with water that is low pH and high in arsenic. Ptacek and fellow research team member David Blowes developed and patented the use of organic carbon and zero-valent iron for remediation in the late 1980s and early 1990s, when that they were graduate students at the University of Waterloo. While initially using the two types of waste separately, they later discovered the benefits of combining the two.

“Joanne’s work demonstrates that it is possible to treat water in harsh conditions,” Blowes said. “I think we will push these types of systems further, into more extreme conditions than in the past. This really opens the door to treating water with much lower pH and higher contaminant concentrations than what we had considered before.”

A remediation plan for the site is being developed, and Blowes, also a professor in the Department of Earth and Environmental Sciences and co-supervisor at Angai, said the new approach could be applied to ongoing efforts.

An inexpensive solution to remove arsenic from drinking water

More information:
Joanne U. Angai et al, Removal of Arsenic and Metals from Mining Waste-Impacted Groundwater Using Zero-Valency Iron and Organic Carbon: Laboratory Column Experiments, Hazardous Materials Journal (2021). DOI: 10.1016/j.jhazmat.2021.127295

Provided by Canadian Light Source

Quote: New method uses waste to clean arsenic from lake contaminated by gold mine (January 17, 2022) Retrieved January 18, 2022 from arsenic-lake-contaminated-gold.html

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