World Gold Conference, Montreal Canada,2011
Mike Adams and Stuart Glen
ABSTRACT
Cyanide management practices on modern gold plants are becoming more onerous, due to environmental pressures, particularly for signatories to the International Cyanide Management Code.
Operations are therefore seeking to reduce levels of weak – acid dissociable (WAD) cyanide reporting to spigot discharge as well as to any eventual discharges from the tailings storage facility (TSF). Current gold industry standard processes primarily include the oxidation of cyanide by means of sodium meta-bisulfite (SMBS, or SO2) with air, Caro‟s acid (H2SO5) or hydrogen peroxide (H2O2). These processes require the transport and usage of expensive oxidizing reagents, along with the safety and environmental issues associated with these corro sive and toxic chemicals. Maelgwyn Mineral Services (MMS) has developed the MMS CN-D TM process, which utilizes the Aachen Reactor TM , a high-energy mass-transfer superoxygenation system, in conjunction with an activated carbon – based catalyst and no additional reagents, to increase the rate of cyanide oxidation to cyanate, the thermodynamically more stable form.
Testwork conducted at the Maelgwyn Australia testwork facility in Perth Australia is described, at
both pilot scale and continuous bench-scale, on a sample of tailings effluent obtained from an Australian gold plant. WAD cyanide is demonstrated to be lowered using the MMS CN-D TM process from an influent of 130mg/L to the required levels for discharge to TSF (<50 mg/L). The continuous test results showed stable operation over three residence time turnovers. The pilot- scale results demonstrated the efficiency of the process at the reasonably large scales required for engineering cost estimation.