An Investigation into the Leaching of Enargite Under Atmospheric Conditions
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The leaching behaviour of enargite was studied under atmospheric pressure. The kinetics of enargite dissolution appear to be extremely slow under the conditions studied using both small scale shake flasks and bench scale stirred tank reactors. An enargite concentrate and a purer mineral specimen were utilized and the effect of numerous variables including temperature, particle size, acidity, oxygen flow rate, iron addition, redox potential and pyrite addition were investigated. The initial rate of copper dissolution from enargite was relatively fast up to about 40% copper extraction but this was followed by a much slower dissolution rate. The first stage is thought to be reaction rate controlled while the latter stage appears to be diffusion controlled. The activation energy was determined to be 32 kJ/mol for the concentrate and 33 kJ/mol for the pure specimen in the temperature range of 55-85°C. In the presence of high concentrations of copper sulphate, enhanced copper recovery was observed for the pure enargite specimen. This could be the result of a change in the reaction product layer on the enargite surface and perhaps the formation of intermediate Cu2S. Previous work has shown that adding excess pyrite enhances copper extraction from enargite but these results could not be reproduced. Particle size reduction appears to be the most effective method to increase extraction rates, however only 70% copper recovery and 35% arsenic recovery was achieved after 24 hours of leaching at d80=2μm. At these reaction rates, it appears that enargite dissolution at atmospheric pressure will not be an economical process compared to other technologies such as high temperature/pressure oxidation or roasting.