Screening-Level Operational Comparison of Commercial Sulfuric Acid Dosage and Measured ORP–pH Regimes during Atmospheric Leaching of a Ferruginous Nickel Laterite

Atmospheric sulfuric acid leaching of ferruginous nickel laterites requires balancing valuable-metal transfer, acid use, total Fe loading, reductant consumption, and residue mineralogy. This screening-level study compares eight tests (PQH01–PQH08) conducted at 94–98 °C with 96 wt.% commercial H₂SO₄ solution at 293.5–552.2 kg solution/t dry ore. Redox values are reported as measured oxidation–reduction potential (ORP) on the original instrumental scale. Because ORP, pH, acid dosage, solids concentration, agitation, and metallic-bar exposure varied simultaneously, responses are interpreted as operational associations and reported as final-PLS yields per unit dry ore mass, not extraction or recovery. At nearly identical mean acid dosages of 543.6 and 543.3 kg solution/t dry ore, the higher-ORP G3 pair was associated with approximately 89% lower specific bar loss, 38% lower total Fe loading, 43% lower Fe/Ni, and 39% lower Fe/Co than the lower-ORP G1 pair, without an important Ni or Co yield penalty. Final residues showed lower relative modal contributions from Mg-bearing silicates, while residual Ni was concentrated in Fe oxyhydroxides and Ni-bearing Si–Fe plasma. Mn oxides were below the automated-mineralogy reporting limit in all residues. The transferable contribution is a screening framework showing that prolonged metallic-bar reduction may impose substantial reductant and total-Fe penalties without proportional valuable-metal benefit.