Direct reduction of heavy non-ferrous metals from sulfide compounds

Abstract

The paper summarizes the results of work done by the group of authors over many years on the direct reduction of heavy non-ferrous metals directly from sulfide compounds contained in concentrates (lead) and metallurgical products (copper, nickel) – white matte, copper and nickel concentrates of converter matte separation. In modern technology the recovery process itself includes the conversion of metal sulfides into oxygen compounds (oxidizing and sintering roasting) with the reduction of metals by carbon-containing reagents (coal, CO), as well as the reduction of copper and, partly, lead from oxide melts by sulfides. Sulfide conversion and reduction operations are associated with the release of sulfur- and carbon-containing compounds (SO₂, SO₃, CO, CO₂) and, consequently, with the need to capture and utilize gaseous and solid products. A fundamentally new process of direct reduction of metals from sulfides using their own sulfide sulfur as a reducing agent is proposed. The recovery process is implemented through the possible formation of short-circuited electrode pairs in the 2Me^z+–zS^2– system due to the implementation of donor-acceptor interactions, primarily π-binding. Successful process implementation is possible with the removal of electrochemical reaction products (product), in particular S⁰. Caustic soda is proposed as such a reagent. Using the example of a number of the above production materials, the possibility of metal reduction at temperatures of 550–700 °C is shown with the achievement of their deep extraction (over 99 %). Elemental sulfur, a product of sulfide sulfur oxidation, reacts with the caustic soda melt and accumulates in the form of non-volatile sodium compounds.