Microwave roasting of flash flotation concentrate containing pyrite, arsenopyrite and carbonaceous matter

Refractory gold ores are difficult to treat, and several techniques have been proposed with the aim of increasing gold extraction. A necessary prerequisite for processing such ores is to remove the refractoriness through oxidation of sulphides and carbonaceous matter, which are the key components for the refractoriness. Roasting is one of the methods utilised in dealing with refractoriness. In this study, flash flotation concentrate containing sulphides and carbonaceous matter was investigated to ascertain its susceptibility to roasting under microwave irradiation. The major minerals present in the concentrate were quartz, pyrite, arsenopyrite and muscovite. The concentrates responded strongly to microwave irradiation. Temperatures above 1200 °C could be attained after heating 50 g samples for 10 mins. Removal of sulphur, arsenic and carbonaceous matter during the microwave roasting process was above 92%. Volatilisation of organic carbonaceous matter from 4.4% to 0.2% resulted in 72% reduction in preg-robbing activity. The rapid removal of the volatile components led to cracking and foliation of the residual calcine particles, thus eliminating the need for regrinding of the pretreated concentrate prior to cyanidation. Direct cyanidation of the calcine extracted over 95% of the gold content while samples roasted in an electrical resistance furnace at 650 °C and 750 °C gave gold recoveries of 84% and 91% respectively.