Case Study: Copper, Nickel and Selenium Remediation
A decommissioned open pit copper mine filled with water. The water in the pit requires treatment and discharge annually to treat the contaminants of concern (mainly copper), that enter the pit through runoff from the surrounding waste rock. The pit acts like a sump within the watershed, pulling the surrounding groundwater and surface water to collect in the pit.
Copper is the main parameter of concern for the operator, with the area having a naturally high level of copper contaminating the surface and groundwater.
The background copper concentrations in the surface water surrounding the site are naturally high due to the high copper content in the bedrock. Therefore, the allowable discharge limits provided by the ministry are quite low relative to other sites because the receiving waters do not have the capacity to handle more “loading” of copper. Other parameters of concern include Nickel and Iron, although in much lower concentrations.
Current challenges of the existing treatment systems such as liming to chemically precipitate copper and other metals as well as prospective biological treatment systems, have raised the operator’s need for a more cost-effective, technically viable system that can sustainably remove copper and other metals from the subject water for the long-term.
Key Project Requirements
Meeting strict copper, nickel and selenium 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;
GRAFTA™2.0 is an engineered graphene-based nanotechnology developed to target specific metals such as copper and selenium.
Removal of copper and nickel 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.
The performance of GRAFTA™2.0 was tested by permeating the contaminated water with the following concentrations:
Copper at 33 ppb
Nickel at 23 ppb
Selenium at 3 ppb
GRAFTA™ 2.0 lowered the concentration of copper and selenium to below nondetectable concentrations and nickel to discharge compliant levels, with a retention time of 30 minutes.
GRAFTA™ 2.0 consistently maintained the concentration of selenium and copper below the strict guidelines that would allow the site to discharge the treated water into receiving surface bodies and as well as to reuse the treated water in the mining process complying with quality and quantity aspects of water conservation.
A GRAFTA™ pilot is being designed for testing at the site for Spring 2023 in order to refine the design parameters for a full-scale implementation.