|
Many of the known gold deposits in the world contain cyanide-soluble copper minerals such as chalcocite, covellite, bornite, cuprite, malachite and azurite. Many such gold ores are not being mined, or have been abandoned after the start of operations, due to the metallurgical challenges and high cost of treating the cyanide-soluble copper minerals in the ore. The presence of leachable copper in a gold ore body results in low gold recovery and/or high cyanide consumption and destruction costs, as well as complications in the gold recovery circuit, whether gold recovery is by adsorption on activated carbon, electrolysis or cementation on zinc dust.
In recent years, the SART process (Sulphidization–Acidification– Recycle–Thickening) has been developed in which the cyanide associated with the copper cyanide complex is released, allowing it to be recycled back to the leach process as free cyanide, thereby reducing the overall cyanide consumption. Copper is also recovered as a valuable, high-grade Cu2S by-product which can grade around 70% Cu. The implementation of this technology is so far limited to a few projects, but interest is rapidly growing in either developing new gold mines or in the re-starting of operations that were prematurely terminated due to poor gold recoveries and unattractive economics.
The SART Process, as originally developed, uses chemical sulphide reagents, such as sodium hydrosulphide (NaHS), to precipitate copper and zinc (if present) and convert cyanide to HCN gas, under weakly acidic conditions. Chemical sulphide can be replaced by lower cost biogenically-produced hydrogen sulphide, which has the added advantage of lowering the acid demand by one third for copper cyanide treatment and by half for zinc cyanide.
The construction of BioteQ’s first commercial scale SART plant which will use biogenically produced sulphide reagent is currently in progress at the Lluvia de Oro mine in Sonora, Mexico, in joint venture with Columbia Metals Corporation. Use of the same technology for Columbia’s La Jojoba property is planned for 2008. Click here for more information about BioteQ’s developing projects.
|
