A facile, inexpensive material for gold mining tailings treatment and removal of thiocyanate (SCN) using a PIM-based technology.
Thiocyanate (SCN‐) is a major constituent in waste water produced by many industrial processes. Some industrial waste water (effluent), such as those from the steel industry, petrochemical industry and water produced through the gasification of coal, often contains a significant concentration of SCN‐. SCN‐ is a common cyanide reaction product of industrial effluent where cyanide (CN‐) is used.
Case 1 . Decrease gold recovery
Gold mines use a blend of tailings and fresh water in the flotation of the crushed gold (Au) ore in order to reduce overall water consumption (see Fig. 1)
SCN‐ in the water blend reduces the efficiency of the flotation of gold ore by decreasing the hydrophobicity of the sulfidic particles containing gold which leads to the undesired effect of a decrease in overall gold recovery - in some cases up to 6% depending on the chemical composition of the gold ore.
Case 2 . SCN- groundwater contamination
SCN- is toxic to aquatic organisms. Groundwater around tailings dams contains high concentration of SCN-, in one instance an Australian gold mine was found to have SCN- up to ~ 200 mg/L.
To prevent contamination of proximal rivers, lakes etc, expensive pump systems are required to dislocate the bore/groundwater to the tailings dams . Upon mine closures, the dislocation process is required for 10-20 years and in the case of one particular Australian gold mine, the groundwater will require detoxification from SCN- at a rate of 20-30 ML per annum.
Polymer inclusion membranes (PIMs) are a relatively new type of self-supporting liquid membrane that are designed to extract ions or neutral molecules from solutions. PIMs typically incorporate a base polymer (usually PVC or cellulose triacetate), an inexpensive commercially available liquid extractant, which acts a carrier, and an optional plasticiser or modifier.
Very often the extractant acts as a plasticiser. Extractants for anions (eg. SCN-) are often tertiary amines (Alamine 336) or quaternary ammonium salts (Aliquat 336, a mixture of quaternary ammonium chlorides). PIMs are homogenous, optically transparent and mechanically strong.
Since PIMs do not incorporate solvents and offer better selectivity and enrichment factors than conventional solvent extraction, they are deemed to be environmentally friendly. PIMs allow for continuous separation since the target chemical species is extracted across and isolated. PIMs are highly selective and can be fine tuned by modifying the membrane composition.
The inherently flexible and robust characteristics of PIMs allow for the incorporation into industrial flat sheet & hollow fibre separation modules. In essence, PIMs are inexpensive and easy to manufacture and to incorporate into existing industrial set-ups and as such are able to quickly and efficiently remove SCN- from tailings solutions.
A PCT application PCT/AU2011/001034 entitled "Process for treating thiocyanate containing aqueous solution" was filed 22th August 2011.
UoM is seeking partners to development and commercially exploit the technology. Contact Michael Jorgensen for further information.
Professor Spas Kolev, Emeritus Professor Robert Cattrall, Ms. Yongsoo Cho.
Professor and Lloyd Smith Medal recipient Spas Kolev, in addition to his work on membrane separation, University of Melbourne School of Chemistry, has a focus on developing flow analytical techniques for on-line environmental and industrial monitoring and has a concern for Phytoremediation of contaminated soil and biosolids by metal hyperaccummulating plants.
Emeritus Professor Robert Cattrall holds an honorary position in the School of Chemistry and his interests involve the study and application of membranes for separation of metals particularly in hydrometallurgy.
Ms. Yongsoo Cho is a PhD student in the School of Chemistry at the University of Melbourne.
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