Beneficiation of a gold bearing enargite ore by flotation and As leaching with Na-hypochlorite

The deep mineralized bodies of the Italian Serrenti-Furtei gold-bearing deposit, located in southern Sardinia, contain substantial amounts of enargite-luzonite and pyrite with subordinate tennantite, covellite, chalcopyrite and arsenopirite. The gold, which occurs as grains of between a few tens of micrometres and submicron size, is not amenable to direct cyanidation. These ores are beneficiated by bulk flotation using sulphydryl collectors and the resulting concentrates are then pyrometallurgically processed to produce gold and copper. However, the concentrates contain significant amounts of arsenic, severely reducing their market value; the abatement of this highly toxic metal in the flue gas to comply with stringent emission limits, increases processing costs significantly. In order to reduce the arsenic content in the concentrates and hence the penalties incurred, we carried out an investigation on enargite leaching using sodium hypochlorite to selectively dissolve the arsenic. By suitably adjusting the main influencing variables, leaching was found to be effective, achieving 96% arsenic removal without significant Au and Cu losses, increasing the commercial value per tonne of concentrate.