Acid treatment of copper sulfide middlings and rougher concentrates in the flotation circuit of carbonate ores

The beneficial effect of leaching of carbonate gangue from flotation middlings and rougher concentrates with sulfuric acid prior their final flotation has been presented. This process was effectively applied within the existing flotation circuit in order to facilitate floatability of difficult-to-treat carbonate black shale copper ores. The leaching of flotation feed with sulfuric acid selectively decomposes the carbonate gangue and leads to selective liberation of sulfide minerals, enhancing flotation results. It was shown, that after leaching out of 50–70% of carbonates from flotation feed, both flotation recovery and concentrate grade increased considerably in relation to results observed for unleached feed. The products of acidic leaching comprise gypsum, soluble magnesium sulfate and gaseous carbon dioxide. Carbon dioxide evolving during the reaction favorably creates the non-oxidizing atmosphere in the pulp during leaching and effectively prevents the digestion of metals from sulfide minerals. The beneficial effect of acid leaching on flotation was evidently confirmed during the pilot tests performed on several feed materials. The application of sulfuric acid leaching for flotation feed resulted in pronounced enhancement of flotation results (both metal recovery and concentrate grade) and could provide a rational use of H2SO4, particularly if it becomes a troublesome and difficult-to-sale product of copper metallurgy. Recently, the sulphuric acid prices are rather high.