THE ASTER PROCESS: TECHNOLOGY DEVELOPMENT THROUGH TO PILOTING, DEMONSTRATION AND COMMERCIALIZATION

摘要

Environmental legislation associated with the land disposal of cyanidation tailings and water discharge is becoming increasingly stringent world-wide, thus enforcing the treatment or recycling of contaminated water streams. Furthermore, micro organisms used in the bioleaching of sulphide minerals in particular, have a low tolerance to thiocyanate and cyanide species making the recycle of contaminated process water to BIOX? plants impossible. It is predominantly the reaction between residual cyanide and reactive sulphur species which results in the formation of SCN" up to ~ 5000 mg/L, which renders the upstream recycling of this solution impractical.The delivery therefore of an improved and integrated water mass balance for subsequent upstream re-usage in BIOX? applications saw the development of the ASTER process, viz., the Activated Sludge Tailings Effluent Remediation process.Laboratory and pilot scale testing of the ASTER process in batch flasks and continuous fed reactors at scales of 0.08, 0.8, 2, 6 and 25m3 showed batch degradation rates of approximately 75 mg/L/hr SCN" was attainable at 25°C, while up to 87 mg/L/hr (un-optimised) SCN" (corresponding to +66% removal) was attainable in the first stage reactor. These derived degradation rates corresponded to batch start test SCN" concentrations of 1800 mg/L and continuous fed reactor feed concentrations of ~ 2100 mg/L respectively.The success and process robustness demonstrated during various pilot runs, on different mine tailings solutions prompted Barberton Mines in the Mpumalanga province of South Africa to go ahead with a full scale ASTER plant in 2009. The plant was designed to treat tailings dam solution at their Consort plant for concentrate preparation to be fed to their BIOX? plant. To facilitate the fundamental process aspects, a development program between Gold Fields and the University of Cape Town (UCT) was initiated which draws on advanced microbiological analyses and sequencing techniques. The first phase focuses on optimising the process conditions and effects of heavy metals and cyanide, and a second more fundamental phase involves modelling and characterisation of the microbial consortium.The Consort ASTER commercial plant has a capacity of 320 m~3/d tailings solution, a design retention time of 12 hours with feed SCN" and free CN" concentrations of 120 mg/L and 30 mg/L respectively. To date the plant has been performing well with degradations in excess of 99% being achieved.This paper discusses the development of the ASTER process through to its first commercialisation at the Barberton Mines, Consort plant. Finally, a further two case studies is described showing how the ASTER process is developing to support projects in the Philippines and Australia.