The role of multi-sulfidic mineral binary and ternary galvanic interactions in gold cyanidation in a multi-layer packed-bed electrochemical reactor

A multi-layer packed-bed electrochemical reactor (PBER) approach was used for studying the leaching behavior of associated and free (silica-trapped) gold from a series of synthetic multi-mineral systems consisting of pyrite, silica, Au, and successively, X = chalcopyrite, sphalerite and chalcocite. The PBER was filled with sieved powders of sulfidic minerals (pyrite, X), gold and silica arranged as electrically-isolated three-layer ||pyrite||X||silica|| and two-layer ||pyrite + X||silica|| systems. Introduction of gold successively in each layer of the three- and two-layer PBER systems highlighted the role of Au-pyrite, Au-X and pyrite-X binary, and Au-pyrite-X ternary galvanic interactions in the leaching of associated and free gold. The highest Au recovery was achieved within the pyrite layer while the lowest was within the silica layer. For the ||pyrite||chalcocite||silica|| system, depletion of free cyanide and surface passivation inhibited strongly gold leaching. Cyanidation experiments performed in the mixed ||sulfide||silica|| systems showed that the effect of Au-sulfide galvanic interactions largely depend on the mineralogical association between phases. The presence of galvanic effects between the associated minerals in the PBER was confirmed by a conjunction of electrochemical and chemical speciation studies. Increasing the pyrite-Au areal ratio increased gold leaching as a result of increased cathodic areas for oxygen reduction. However, gold leaching from mixed multi-mineral systems where multi-factorial galvanic contacts were enabled was controlled mostly by the relative area ratios between the associated sulfide minerals.