Selective extraction performance of Ni, Cu, Co, and Mn adopted by a coupled leaching of low-grade Ni-sulfide ore and polymetallic Mn-oxide ore in sulphuric acid solutions

The coupled leaching of ocean polymetallic nodule and low-grade nickel sulphide ore in sulphuric acid solution was investigated, especially in performance on selective extraction of Ni, Cu, Co, and Mn. This work can be divided into three parts. First, the advantageous selective metal extraction conditions, parallel to the optimal coupled leaching conditions, were measured by coupled leaching tests which adopted the Ni, Mn, Cu, Co, and Fe dissolution efficiency. Under the optimal conditions, the extraction ratios of Ni, Mn, Cu, Co, and Fe are 96.8%, 97.3%, 92.2%, 97.9%, and 28.9%, respectively. Second, electrochemical tests revealed that multi-metal simultaneous extraction from two ores depends on the reduction-oxidation dissolution of a corrosion cell of the nodule cathode and the sulphide ore anode. The results showed that acidity and Fe 3+ ion affected dissolution of both ores significantly; high valence manganese oxide reduction takes precedence which is in control of the Ni, Mn, Cu, and Co dissolution of the nodule; Ni, Cu, and Co extraction from the nickel ore is a course of sulphide minerals oxidative conversion which significantly affected by Fe 2+ -containing sulphide oxidation. Third, the separation performance of iron substance in the solution was determined by the transformation of minerals phases of the leached residues, showing that Fe-bearing minerals dissolved to Fe 3+ ion then precipitated as iron vitriol or oxide during the selectively coupled leaching. The selectively coupled leaching of low-grade multi-metallic sulphide ore and oxide ore mainly rests with the transformation of Fe-containing species in the system. • A new approach adopted redox activities of the minerals for selective metal extraction from refractory ores. • The fundamental of selective extraction of Ni, Mn, Cu, and Co from Fe in low-grade ores coupled leaching was measured. • The prominence condition of metal selective extraction in the low-grade Mn-nodule-Ni-ore coupled leaching was determined.