Case Study: Selenium and Copper Remediation

Challenge

GRAFTA Nanotech Inc was engaged by a copper mining company, located in south-central British Columbia, to provide a sustainable solution for reducing concentrations of selenium and copper, currently exceeding the regulatory limits from seep waters.

Preliminary tests determined that the selenium was in the form of selenate (SeO6), a higher oxidation state that hinders the adsorption process. This along with high concentrations of other metals including copper resulted in accumulations in the seep water over time with no technically and economically feasible treatment option.

At present, apart from a trial biological treatment process which is yet to prove efficient, the contaminated water is stored and partly reused in the production system which in turn can gradually increase the concentration of selenium and copper making it even more difficult to remove using conventional methods.

Currently, the US EPA’s best available technology (BAT) for selenium removal has been biological treatment with adsorption of the oxidized selenium compounds on an organic substrate and subsequent digestion of the selenium oxides by microorganisms that convert the compounds to elemental selenium retained by the microbes.

This method provides passive selenium removal benefits but in many cases cannot effectively treat the volume of both process and run-off water required for discharge compliance.

Key Project Requirements

Meeting strict selenium and copper removal guidelines to discharge into receiving surface water bodies;
Small footprint of treatment system and minimal reliance on electromechanical requirements;
Short retention times and reasonable longevity;
Cost effectiveness of the treatment system;
Long-term sustainability.

Solution

GRAFTA™ 2.0 is an engineered graphene-based nanotechnology developed to target specific metals such as selenium.

Removal of copper was achieved through adsorption on graphene oxide nanosheets, while removal of selenium follows a two-step process of reducing selenate to selenite and elemental selenium which is immediately adsorbed by the graphene oxide layers in GRAFTA™ 2.0 in the same vessel.

The graphene and graphene oxide provide the most efficient platform for an end result water quality that lowers the concentration of target contaminants not only below discharge standards, but in most cases to nondetectable concentrations.

Results

Performance of GRAFTA™ 2.0 was tested through permeating the contaminated water with a selenium concentration of 144 ppb in the form of selenate and a copper concentration of over 66 ppb.

GRAFTA™ 2.0 lowered the concentration of both selenium and copper to below nondetectable concentrations with a retention time of 30 minutes.

Through over 38 passes, concentrations remained consistently nondetectable, and no breakthrough was achieved. Significant longevity is anticipated which promises long-term feasibility of using GRAFTA™ 2.0 to remove selenium and copper from the target water.

Outcomes

A GRAFTA™ pilot is being planned at the site for Spring 2023 in order to refine the design parameters for a full-scale implementation.