The characterisation and behaviour of carbonaceous material in a refractory gold bearing ore

Abstract

Sulfide ore and a flotation concentrate from Fosterville contained 0.76% carbonate carbon, 0.18% native carbon and 0.20% organic carbon of which 4.5 ppm were n-alkane hydrocarbons. The concentrate yielded 0.99% native carbon, 0.28% carbonate carbon and 0.11 % organic carbon of which 19.7 ppm was n-alkane hydrocarbons. IR spectroscopy of the fulvic acid fraction of the flotation concentrate showed it to be similar to humic acid. The addition of representative levels of n-alkane hydrocarbons, carbonate carbon and humic acid to the oxidised ore indicated that these components had negligible effect on gold recovery. The addition of 0.2% native carbon decreased gold recoveries from 84.4% to 68.8% while 0.2% activated carbon reduced recovery to 3.1%. Native carbon when acidified, mimicking the environment of bacterial oxidation, resulted in recovery dropping from 84.4% to 61.0%. Gold recovery for a standard sulfide float was 92.5%. Sodium naphthalene sulfonate (SNS) was the only depressant to lower native carbon levels in the concentrates without reducing gold recovery. 275 g/t SNS depressed 45% of the native carbon and gold recovery was unchanged. Nitric acid oxidation and subsequent cyanidation of the SNS concentrates lead to overall gold recovery improving from 88.3% for a standard sulfide float to 92.0%.