GRAFTA Nanotech
Selenium and Selenate removal from Industrial and Mining Wastewater.
The Selenium Removal Challenge
Selenium, a toxic contaminant with potential for bioaccumulation, is often found in mining related wastewaters and tailings. The mining industry faces a significant challenge regarding selenium removal to meet stringent environmental guidelines for effluent discharge.
The selenium removal challenge mainly lies in the fact that, in most cases, particularly in the mining sector, selenium is found in a higher oxidation state, making it almost impossible to utilize any adsorption-based removal process. The common approach for removing selenium requires the development of sophisticated water treatment technologies at large scale, including but not limited to biological treatment processes.
GRAFTA™, an innovative graphene-based nanotechnology designed for the efficient removal of various contaminants from industrial and mining wastewater, has shown outstanding performance in removing selenium from mining waters and other types of wastewaters.
GRAFTA™ is well suited for removing higher oxidation state selenium (i.e. selenate) by a combination of chemical reduction and adsorption. This data sheet provides a technical overview of GRAFTA™'s mechanisms, performance metrics, and application requirements for targeting selenium.
GRAFTA™ Product Line
GRAFTA™ comprises micro-scale inert particles embedded with numerous layers of graphene and graphene oxide nanosheets. The product is available in two formulations:
GRAFTA™ 1.0 (G1)
Designed for the adsorption of heavy metals and organic compounds. The core graphene based solution targeting metals, petroleum hydrocarbons, PAHs, BTEX, wide range of VOCs and Semi-VOCs including but not limited to chlorinated solvents (e.g. PCE, TCE, etc.), PCBs and a range of inorganics such as ammonia and phosphate.
GRAFTA™ 2.0 (G2)
GRAFTA™2.0 is engineered to add chemical reduction capability targeting reductive removal of metals particularly in higher oxidation states to target contaminants like selenium present as selenate followed by adsorption within the same matrix.
GRAFTA™ particles
The unique structure of GRAFTA™ provides a massive surface area for adsorption, ensuring exceptional contaminant removal efficiency.
Selenium Removal Process using GRAFTA™
In various tests conducted on mining waters contaminated with selenium in form of selenate, GRAFTA™2.0 (G2) was successfully used to reduce the relatively high influent concentrations to below regulatory limits if not to undetectable levels.
The two-step process is as follows:
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Reduction: Selenate (SeO₄²⁻) is chemically reduced to selenite (SeO₃²⁻) and elemental selenium (Se⁰) by the reducing agents in G2.
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Adsorption: The resulting selenite and elemental selenium are adsorbed onto the graphene oxide nanosheets.
This combined reduction-adsorption mechanism can be accommodated by using only G2 ensuring efficient selenium removal from contaminated water sources.
Selenate Removal Performance
Numerous bench scale tests have been conducted to evaluate the performance of GRAFTA™2.0 (G2), in combined reductive-adsorptive removal of selenium from real and simulated mine waters.
A number of tests performed on real mine waters containing selenate indicated an outstanding removal efficiency (over 99%; typically, down to non-detectable selenium concentration in the effluent).
A longer-term selenate removal test showed a persistent removal of selenate using G2, up to 7,500 pore volumes (equivalent of about 6 months of run-time), from a constant feed of 56 ug/L of selenate in the influent to lower than 10 ug/L in the effluent. The test was terminated at pore volume 7,500, yet, as shown in the graph below, it was expected to achieve a longevity of over several thousand pore volumes until breakthrough or G2 saturation point.
Influencing Factors
G2 performance in removal of selenate is not hindered by environmental factors such as temperature or some of the typical chemical composition of the water subject to treatment.
There is no need to adjust the pH of water prior and after removal by G2.
In most cases, it is expected to have other ions and metals be present in waters subject to selenium (selenate) removal. Our comprehensive testing has showed that other metals such as copper that typically coexist with selenium, are also removed simultaneously.
Application Requirements
Large-scale application of G2 for selenate removal is simple and can be achieved by using any type of above ground vessel (tanks of various sizes and shapes, and made of either polyethylene or steel), that can house G2 and accommodate a preferably upflow hydraulic regime provided by minimal pumping requirement where gravity feed is not viable.
Retention time (Empty Bed Contact Time (EBCT)) of 30 minutes typically results in over 99% removal of selenate, and depending on the subject water chemical composition, shorter retention times can be considered to achieve similar removal rates. It has also been observed that increasing retention time can potentially increase the removal efficiency and extend the longevity of the system.
End-of-Life Management
A standard GRAFTA™ system
GRAFTA™ exhibits minimal leaching of adsorbed contaminants, ensuring environmental safety.
Toxicity Characteristic Leaching Procedure (TCLP) tests have confirmed that leachate concentrations are below regulatory limits, facilitating safe disposal or repurposing of spent media.
Further Case Studies
GRAFTA™2.0 has been applied in a number of real world waters with excellent results.
GRAFTA Nanotech Inc was engaged by a copper mining company, to provide a sustainable solution for reducing concentrations of selenium and copper, currently exceeding the regulatory limits from seep waters. Read more...
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. Read more...
GRAFTA™: A Selenium Removal Solution
GRAFTA™2.0 offers an effective solution for selenium removal from industrial and mining wastewater, achieving non-detectable effluent concentrations with relatively short retention times.
To find out how GRAFTA™ can solve your selenium contamination issues contact us today,