PROCESS OPTIMIZATION FOR O&M COST SAVINGS A CASE STUDY FOR GOLD MINING EFFLUENT TREATMENT

Stantec Consulting Ltd. (Stantec) was retained in March 2006 by Williams Operating Corporation (WOC) to perform an optimization study of mining wastewater treatment at the WOC facility in Marathon, Ontario. The primary objectives of this optimization study were i) to identify potential opportunities to optimize the treatment system in order to reduce chemical costs; ii) to identify mechanisms of multiple heavy metals removal, with particular attention to antimony (Sb) and molybdenum (Mo), in gold mining process wastewater treatment; iii) to develop robust design guidelines for Sb and Mo removal; and iv) to reduce operational costs while achieve effluent discharging limits. In order to achieve these objectives, Stantec conducted a series of bench- and full-scale tests. The results showed that both satisfactory Sb and Mo removal rates could be achieved through a co-precipitation process using ferric sulphate as a coagulant. The appropriate dosing rate of ferric sulphate should be determined by the mass ratio of ferric and antimony. Lime was recommended to WOC for pH adjustment in order to removal some heavey metals, such as copper (Cu), zinc (Zn), nickel (Ni), and lead (Pb). This study found that WOC could reduce chemical cost by approximately 50%, while the ETP could still discharge effluents that met the current regulations.