Investigation and optimization of influencing parameters on the copper extraction from a low-grade oxide deposit by acid leaching

Recovery of copper (II) from a low-grade deposit obtained from the rejects of a crushing circuit was investigated by means of leaching using H₂SO₄ solution. Sulfuric acid concentration was between 30-180 g/L, solid content was set at 10-60%, particles were in the size range of-1 + 2 mm, and the leaching time was 5-60 min. Initially, a screening step was utilized involving a full factorial design (FFD) with four factors at two levels and two replications. Normal probability plot of residuals, analysis of variance (ANOVA), surface plots, and contour plots were used to study the effects of the main operational parameters and their interactions. The results of ANOVA, F-Test and t-student test showed that at 95% confidence level, the sulfuric acid, solid content, leaching time, and the 2-way interaction of them considerably affected Cu(II) extraction, and increasing their value positively influenced the Cu(II) extraction. A factorial regression model was developed to relate Cu(II) extraction and the operational variables. The fitted model presented a good agreement between the experimental data and the predicted values with a correlation coefficient (R²) of 0.9989. Optimization of Cu(II) extraction suggested that the optimum conditions for Cu(II) extraction (Re = 72%) were sulfuric acid: 90 g/L, solid content: 50%, particle size: under 2 mm, and leaching time: 30 min.