Box–Behnken Design Application to Study Leaching of Pyrolusite from Manganese Mining Residue Using Olive Mill Wastewater as Reductant

Abstract

The leaching capacity of olive mill wastewater (OMW) for pyrolusite mine tailings (MnO2) was evaluated using the Box–Behnken experimental design of response surface methodology. The selected test parameters include the concentration of sulfuric acid, the OMW dosage chemical oxygen demand (COD), the solid/liquid ratio S/L, and particle size. It was determined that the MnO2 dissolution increased with an increase in the sulfuric acid concentration and the OMW dosage, and with a decrease in the solid/liquid ratio. The particle size does not have significant influence on the manganese recovery. A quadratic polynomial model has been developed to predict the amount of manganese extraction from pyrolusite for other operating conditions that were not directly tested. The leaching ability was evaluated based on manganese recovery (Mn%) and the removal capability of chemical oxygen demand (COD%). The predicted values for the responses agreed well with experimental values; R2 (correlation coefficient) values for Mn% and COD% were 0.9602 and 0.9687, respectively. Within the design space, the optimum conditions for the lixiviation of MnO2 in terms of manganese recovery and COD removal were established and include [H2SO4] of 3 mol L−1, OMW in range of 23 g L−1 to 25 g L−1 COD, and pulp density in range of 90 g L−1 to 100 g L−1. Under these conditions, the response values generated by the model are Mn% ∼49% and COD% >40%. These values show good agreement with those obtained in the validation test. This study has demonstrated that it is possible to use the olive mill wastewater as a reductant agent to recover manganese from a pyrolusite mining residue.