Characterization and selective dissolution of copper values in a lean multiphasic ore

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Prof. Iyiola Olatunji Otunniyi, Prof. Peter Mendonidis

Meeting the increasing global non-ferrous metals demand has been sustained by increased attention
to recycling and lean occurrences. In pursuit of the latter, in this work, detailed characterization to
identify valuable mineralization and first round investigation toward recommending an extraction
route were carried out on a rock formation in a part of the Anka schist belt (SW Nigeria). Using
XRD, optical microscopy, SEM-EDS, image analysis, and wet assaying, copper was found to occur
in the ore as chalcocite (Cu2S), covellite (CuS), cuprite (Cu2O) and malachite (CuCO3.Cu(OH)2),
co-occurring with hematite and barite, within a feldspartic quartzite host rock. The grains are finely
disseminated down to one micron with random instances of relatively coarse composite grains. This
mineralogy presents a selective leaching task, to leach the copper sulphides and oxides from other
oxides, which will seek to maximize copper recovery with least iron recovery. For a sweep across
probable leaching chemistries, acid and alkali oxidative leaching were investigated using three different
lixivants. Alkali oxidative leaching using ammonia solution with hydrogen peroxide rejected
the iron most and gave the cleanest solution, but ammonium persulphate extracted the copper most,
at copper leach solution assay of 942 mg/l. The lixivants behavior was linked to a specific mineralogical
feature of the occurrence, subject to further studies. Other probable alternatives for investigations
in exploiting this occurence, based on the observed mineralogical features, were mentioned.
From this first round investigations, the occurence pass for a lean multiphasic copper ore which is
amenable to selective alkali oxidative leaching of the copper values in exploitation prospects.

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