Substantiation of a Combined Technology for the Hydrometallurgical Beneficiation of a Pyrrhotine-Containing Charge Based on Pressure Oxidation Leaching Using Ferric Sulfate as a Pyrrhotine Oxidizer

Two series of comparative experiments are carried out to select the most effective version of pressure oxidation technology (POT) for processing a pyrrhotine-containing charge (PCC) consisting of a mixture of ELNPP TCP and NPC NCP (enriched low-nickel pyrrhotine product and nickel-pyrrhotine concentrate). In the first version (basic), a standard oxidizing agent (oxygen) is used for pressure oxidation leaching (POL); in the second version, iron(III) sulfate is used. The use of iron(III) sulfate in comparison with oxygen makes it possible to significantly increase all the main indicators of the hydrometallurgical beneficiation of PCC. The substitution of iron(III) sulfate for oxygen in the POL operation after optimizing the operation parameters of the “head” POT operations is shown to achieve a high quality of the autoclave sulfide concentrate (ASC; 13–14% Ni) and the completeness of extraction of valuable components into it, namely, 96–97% nickel and 93–95% PGMs. An important competitive advantage of POL processes using iron(III) sulfate is that the formation of a bulky precipitate of iron hydroxides is almost completely excluded during the oxidation of pyrrhotine. In the version of “oxygen” leaching of PCC, it is the formation of this precipitate that causes a high level of the PGM losses with waste technological tailings technology and limits the possibility of improving the quality of ASC. A schematic diagram of POT is proposed for the POL-based hydrometallurgical beneficiation of PCC (ELNPP TCF, NPC NCP, SPM TCF, etc.) using iron(III) sulfate. This scheme can be implemented on the basis of the existing fleet of equipment for the hydrometallurgical production of the Nadezhda metallurgical plant at the minimum capital costs