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COPPER AND ZINC LEACHING FROM FLOTATION WASTES

А. Г. Булаев

Abstract

Sulfide ore processing is characterized by significant losses of non-ferrous and precious metals into various wastes including flotation tailings, which is presently considered as promising source of different metals along with low grade ores. Old flotation tailings, which have been accumulated in significant quantities during the exploration of some mineral deposits, usually contain a wide range of minerals, including sulfides (pyrite, chalcopyrite, sphalerite), sulfates, hydroxides, hydroxysulfates, etc. Thus, sulfide flotation tailings are complex polymineralic aggregates formed during long-term storage containing various base metals. Different hydrometallurgical methods including bioleaching and acid leaching were proposed to extract metals from different samples of flotation tailings. In the same time, pregnant solutions obtained during leaching of old flotation tailings often contained high concentrations of iron ions, which can be by an order of a magnitude higher than concentrations of base metals, that impedes further extraction of non-ferrous metals from pregnant solutions Thus, processing of old flotation tailings should provide selective extraction of valuable metals and obtaining solutions appropriate for further extraction of non-ferrous metals. The goal of the present work was to study the possibility of selective extraction of non-ferrous metals from old flotation tailings using acid leaching. Leaching was performed with sulfuric acid solutions (from 0.5 to 10%) and distilled water. Leaching was carried out using glass columns, which were loaded with 100 g of old tailings, and leaching was performed with 100 mL of acid solutions. The sample of old flotation samples contained 0.22% and 0.17% of copper and zinc, respectively, as well as 17% of iron. Percolation leaching made it possible to extract of 55 to 69 % of Zn and of 51 to 76% of Cu. Zn concnetrations in pregnant solution were of 1.3 to 1.6 g/L, while Cu concentrations were of 1.6 to 2.4 g/L. Ferric iron ions concentrations in the pregnant solutions were of 0.5 to 9.8 g/L, while total concentrations of ferric and ferrous iron were of 1.5 to 25.1 g/L. Iron ion concentration corellated with sulfuric acid concentration. Thus, it was shown, that extraction of both non-ferrous metals and iron depended on sulfuric acid cocnetration in leach solution. In the same time, copper and zinc extraction were close to maximum, when sulfuric acid concentration was 2.5%. Increase in sulfuric concentration above 2.5% led to the increase in iron concetration in the pregnant solutuion. Thus, it was possible to reach selective leaching of non-ferrous metals and to obtain solutions with relatively low concentrations of iron ions. High iron concentration in pregnant solutions impedes further Cu and Zn extraction. Therefore, indicated regularities may be used for the development methods of hydrometallurgical processing of old flotation tailings for the obtaining the solutions appropriate for non-ferrous metal extraction.

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