Acidic recirculation water and effluents generated by the mining industry and bearing heavy metals can have a significant environmental impact on this region. Due to high concentrations of non-ferrous metals (5.2–300 mg/dm3 Cu; 50–450 g/dm3 Zn), such waters can be used as a raw material for producing concentrates for further recovery of metals from them. This study looked at the recirculation water of the Soryinsk tailings pod, the underspoil waters of the Novo-Shemursk deposit and the Urupsky GOK mine waters. The aim of the study is to develop a process for selective extraction of copper into a product that can be further processed into a final product. The most common techniques used to remove ions of heavy non-ferrous metals from industrial wastewater include neutralization techniques. In this case, however, a considerable share of non-ferrous metals get wasted. At the same time, reagent techniques (e.g. sulphidation in the acidic pH region) enable to selectively extract such metals into concentrates that can then be used in the conventional non-ferrous metal production technology. A sulphur solution in sodium hydroxide was used as a sulphidizer for selective extraction of copper from polycomponent wastewater. The sulphur solution was produced at the temperature of 115–120 oC, the mass ratio NaOH:S of 1:1 and the sulphur concentration of 350 g/dm3. Use of sulphur dissolved in sodium hydroxide helped extract copper in the form of sulphides from complex solutions. It resulted in a high recovery of copper (94–99.9%) and a high-concentration copper concentrate (8.9–27.5%). It was found that iron (III) interacts with sulphide ions forming elemental sulphur, which can be reused for conditioning of copper concentrate in sodium hydroxide. Thus, the sulphur can be reused and the concentration of copper can be increased to 24%. The physical properties of particles in copper sulphide concentrates determine the high rate of solid phase precipitation from the slurry. Sulphide particles are characterized with a high negative charge (–80…–100 mV) and the size of the 90% of the particles reaching 68.9 μm. The authors developed a process flow diagram for extracting copper from low-grade complex solutions. The process involves regular addition of sulphidizer to the existing water flow, detention of a solid copper phase and, when necessary, conditioning of copper concentrate.

The large volume of recycling waters from the Soryinskoye tailing pond (up to 1300 m3/h) offers interesting possibilities for processing concentrates despite the low copper content (5.2-16.4 mg/l). Sulfides precipitation is the most efficient method of heavy metal ions removal from water. In this study, a sulfur solution in sodium hydroxide was used as a sulfidizing agent for precipitation. Commercial liquid alkali (NaOH – 46) and commercial sulfur were the initial agents. Due to the concentrated alkali, dissolution could be carried out at 115-120∘С, which is higher than the melting point of sulfur. Stable solutions were obtained at a weight ratio of NaOH: S = 1: 1 and a sulfur concentration of 350 g/l. During the laboratory and scale-up laboratory tests, the optimal consumption of sulfidizing agent was determined (110% of the stoichiometry for the formation of Cu2S, and copper extraction into the precipitate from the solution was more than 90.0% with high selectivity towards Zn and Fe). An extended analysis of the composition of the sediment (x-ray fluorescence spectrometer SPECTRO XEPOS) obtained during pilot trials showed that the main elements are, %: sulfur 58.4; oxygen 16.2; copper 8.9; iron 5.7; calcium 4.7 and arsenic 3.8. The total fraction of impurity elements does not exceed 2.3%. This study assumes use of the product conditioning to obtain concentrate with increased copper content and sulfur return to sulfidation stage. Keywords: acid mine drainage, copper recovery, chemical treatment, sulfide precipitation