Anode slime leaching: the impact of process parameters on the dissolution of Cu, Ni, Se and Ag

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Katja Weichert, Thorsten Preiß, Harald Kadereit, Peter Stantke, Günther Leuprecht

Aurubis is one of the largest copper producers in the world, with an output of ca. 1.2 million tons of
copper cathodes per year. Starting from copper concentrates (Primary Copper Production), or copper
containing recycling materials (Secondary Copper Production), anodes with about 98 % of copper are
produced. The last impurities are removed by electrolysis (electrorefining), leading to high purity
cathodes with at least 99.99 % of copper. During electrorefining, elements less noble than copper are
dissolved, while elements more noble than copper will precipitate to the bottom of the refining cell.
Together with precipitates from the electrolyte, they form the anode slime. Here, precious metals as
well as valuable metals such as selenium or tellurium are accumulated. Depending on the concentrates,
the resulting anode slimes have different compositions and leaching behaviours.
Anode slime leaching at Aurubis aims particularly at the extraction of copper and nickel. Precious
metals and selenium are intended to stay in the residue for further treatment by oxidative smelting
in the cupellation furnace. Leaching is performed with sulphuric acid under oxidative conditions.
Two options are available to leach anode slime - atmospheric leaching and pressure leaching. While
pressure leaching usually leads to a very low copper content in the residue, it is also more challenging
in terms of maintenance and safety. On the other hand, additives are reported, that can be used
to enhance the extraction rates during atmospheric leaching. In general, sulphuric acid concentration,
oxygen partial pressure as well as leaching temperature and time are parameters, which can be
easily varied to obtain high recovery rates of Cu and Ni.
Here we present our results in terms of leaching rates of several elements depending on different
process parameters (e.g. temperature, sulphuric acid concentration and oxygen partial pressure) during
pressure leaching of anode slime.

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