Contaminant Removal Performance of GRAFTA™
GRAFTA™ in its original form, with no alteration and engineering is a combination of graphene and graphene oxide nanosheets that have shown to be highly capable of adsorbing heavy metals and organic compounds from aqueous solutions.
Bench scale tests mostly conducted in the form of adsorption column tests along with batch adsorption tests (also known as isotherm tests) have been conducted for a variety of contaminants including heavy metals, organic compounds, and inorganics such as nitrate, phosphate, and sulfate, mostly for real-life contaminated waters from mining related tailing waters, oil and gas produced water, landfill leachate, and few other industrial wastewaters along with some water samples spiked with certain target contaminants.
The key advantage of using GRAFTA™ is that it simultaneously adsorbs both heavy metals and tough to remove organic compounds such as chlorinated solvents, petroleum hydrocarbon, polycyclic aromatic hydrocarbons (PAHs), Volatile Organic Compounds (VOCs) such BTEX (benzene, toluene, xylene, ethylbenzene) and more importantly PFAS which is currently under further investigation.
Recent performance test for the removal of a variety of metals including but not limited to copper and selenium from mining tailing waters, indicated that GRAFTA™ can remove these metals to nondetectable concentrations.
Typical retention times required to adsorb contaminants by over 90% removal efficiency is about 15 minutes to 45 minutes.
Heavy Metals Removal Using GRAFTA™
Extensive testing of both G1 and G2 using real-life and spiked waters, indicated that majority of heavy metals including but not limited to mercury, selenium, lead, arsenic, manganese, chromium, cobalt, cadmium and uranium are removed by G1 and G2 where applicable.
In some mine waters, selenium, being the main contaminant of concern, is present in form of selenate which along with relatively high concentration of nitrate makes the treatment challenging. To tackle the challenges, G2 which is amended with a reducing agent was used to effectively reduce selenate to selenite and elementals selenium which was then adsorbed by the graphenic structure of GRAFTA™.
A summary of the removal efficiencies using G1 and G2 for a variety of waters contaminated with heavy metals is presented as follows:
Organic Contaminants Removal Using GRAFTA™
G1 is most suited for a direct adsorption of organic contaminants including but not limited to petroleum hydrocarbons (F1 to F4), BTEX (benzene, xylene, ethylbenzene and toluene), chlorinated compounds (tetrachloroethylene, trichloroethylene, vinyl chloride and chloroform), phenolics (pentachlorophenol etc.), Polycyclic aromatic hydrocarbons (PAHs) at very high rates.
Inorganic Constituent Removal Using GRAFTA™
GRAFTA™ being a carbon-based adsorbent, was not necessarily designed for removal of inorganics such as nitrate, phosphate, sulfate and carbonate. However, experiments conducted on various waters with relatively high concentration of total dissolved solids (TDS) indicated that phosphate and ammonia are directly adsorbed by GRAFTA™ (G1).
However, considering the rising demand of the industry, in particular the mining sector, to remove relatively high concentrations of nitrate in tailing waters, GRAFTA™ was modified with a reducing agent to chemically reduce nitrate to ammonium, followed by adsorption of ammonium within the same reactor (vessel) on the graphenic structure (G2).