REMOVAL OF ARSENIC IN ENARGITE FROM COPPER ORES BY FLOTATION AND LEACHING IN NAHS MEDIA

摘要

Removal of arsenic (As) contained as enargite (Cu_3AsS_4) in copper ores and concentrates by flotation and leaching was performed in this work. Flotation was first conducted to separate Cu_3AsS_4 from other non-arsenic bearing copper–iron sulfides and other gangue to reduce As content to <0.5 wt per cent. The Cu_3AsS_4 fraction recovered as separate Cu concentrate is further treated by selectively leaching As in NaHS–NaOH solution for conversion to Cu2S and combine with clean concentrate in the flotation process for feed to smelters. Direct leaching of Cu_3AsS_4 ore and mixture of Cu_3AsS_4 and other copper concentrates with low As content was also investigated. In flotation, slurry pH and potential, reagent concentration, residence time, were investigated as main parameters to evaluate separation efficiency of Cu_3AsS_4 from pyrite (FeS_2) and chalcopyrite (CuFeS_2). Results showed that >98 per cent of Cu_3AsS_4 can be separated from FeS_2 and CuFeS_2 minerals at pH 4 within 5 min and As content in tailings or other sulfides reduced to <0.5 wt per cent. Leaching of enargite ore, concentrate or mixtures containing Cu_3AsS_4 with As content ranging from 0.8 - 10 wt per cent at varying conditions of temperature, pulp density, NaHS/NaOH conconcention, particle size, slurry stirring rate and reaction time have been investigated to evaluate As leaching. The results clearly show that >99 per cent of As in the samples can be selectively dissolved into solution with Cu_3AsS_4 transformed to Cu2S and As content in the leached residue reduced to <0.5 wt per cent. Leaching tests at pulp densities ranging from 100 - 1000 g/L showed that near complete removal of As can be achieved within 3 - 6 h depending on pulp density and arsenic content. At 1000 g/L >98 per cent of As was removed within 6h at 80°C. Flotation and leaching conditions to achieve separation and high As removal from Cu_3AsS_4 is discussed in this paper.