Sequential Bioleaching of Pyritic Tailings and Ferric Leaching of Nonferrous Slags as a Method for Metal Recovery from Mining and Metallurgical Wastes

Abstract

In this work, we proposed a method for biohydrometallurgical processing of mining (old pyritic flotation tailings) and metallurgical (slag) wastes to recover gold and other nonferrous metals. Since this processing allows the removal of toxic metals or at least decreases their content in the solids, this approach may reduce the negative environmental impacts of such waste. The proposed process was based on pyritic tailings’ bioleaching to recover metals and produce leach liquor containing a strong oxidizing agent (ferric sulfate) to dissolve nonferrous metal from slag. This approach also allows us to increase concentrations of nonferrous metals in the pregnant leach solution after pyritic waste bioleaching to allow efficient extraction. The old pyritic tailings were previously leached with 0.25% sulfuric acid for 10 min to remove soluble metal sulfates. As a result, 36% of copper and 35% of zinc were extracted. After 12 days of bioleaching with a microbial consortium containing Leptospirillum spp., Sulfobacillus spp., Ferroplasma spp., and Acidithiobacillus spp. at 35 °C, the total recovery of metals from pyritic tailings reached 68% for copper and 77% for zinc; and subsequent cyanidation allowed 92% recovery of gold. Ferric leaching of two types of slag at 70 °C with the leachate obtained during bioleaching of the tailings and containing 15 g/L of Fe3+ allowed 88.9 and 43.4% recovery of copper and zinc, respectively, from copper slag within 150 min. Meanwhile, 91.5% of copper, 84.1% of nickel, and 70.2% of cobalt were extracted from copper–nickel slag within 120 min under the same conditions.