ROASTING AND LEACHING OF WITWATERSRAND PYRITE CONCENTRATES.

Many of the pyrite concentrates produced at South African gold and uranium mines contain economically significant amounts of nickel, copper, and cobalt, apart from gold and uranium. In some cases these concentrates are leached for uranium, followed by roasting and cyanidation of the calcine for the extraction of the gold. An important finding of the investigation was that the conditions producing favorable base-metal sulphation (and hence solubility in water) also produced good sulphation of the uranium values that had not been extracted in a conventional leach of the original pyrite. Thus, if the pyrite is subjected to a sulphating roast followed by quenching in water (or dilute acid), it should be possible for the uranium to be extracted in improved yield. From well-sulphated calcine the dissolution of base metals and uranium appeared to be fairly independent of leaching pH, time, and temperature. On an inadequately sulphated calcine, low pH values during leaching gave increased extraction of copper and uranium but did not have a significant effect on the dissolution of nickel and cobalt. The extraction of uranium increased with increasing leaching time and temperature, while only longer times at a low pH value markedly improved the extraction of copper.