An evaluation of the efficiency of commodas optical sorting of gold waste rock dumps

The treating of gold waste rocks in the gold mining industry has grown significantly in the last few years. The operation of a South African gold mining company treating a waste rock dumps with gold content varying between 0.2 to 0.9 g/t with the Commodas optical sorter to minimize the amount of gangue in the waste rock for further treatment was studied. The results obtained showed that the sorting machine has not been operating at the required set targets of 70% gold recovery and <0.1 Au g/t gold waste. The optical sorter was studied to establish the current operating parameters, determine the operating efficiency of the equipment and propose a solution to the deficiencies observed. The studies showed that the highest and second highest gold recovery percents of 71.2 and 61.6% were obtained when the average feed rates were 24.8 and 26 t/hr, while very low recoveries of 2.4 and 3.1% occurred at the feed rates of 46 and 29.5 t/hr; respectively. It was further observed that the waste grade, enrichment ratio and mass pull percent have no clear relationship with the gold recovery percent, while increasing grade of feed improved the concentrate grade. It is therefore proposed that the feed rate should be maintained in the range of 24.8 to 26 t/hr and the process parameters be further studied and adjusted so that gold recovery percents will be fairly proportional to the feed grade and mass pull into the concentrate and inversely proportional to the waste stream grade.