Application of Box-Behnken design to determine the optimal conditions of reductive leaching of MnO2 from manganese mine tailings

Management of mining manganese residues by a hydrometallurgical processing is a solution to remedy the harmful presence of manganese residues in nature. Understanding the mechanism that governs the leaching process is a major importance to optimize the various factors involved in the reaction; this article is devoted to this subject. The application of leaching process to extracting Mn from a manganese mine tailings was investigated using a software based design of experiments. The Box-Behnken experimental design was used to provide data for modeling and the variables of model were potassium oxalate concentration, solid-to-liquid ratio and sulphuric acid concentration. The recoveries of Mn are selected as response of design. The optimum condition under which the Mn recoveries are the highest is determined using statistical analysis and analysis of variance (ANOVA). A quadratic model with good adherence to the experimental data in the domain analyzed was developed, which was used to plot the response surface curves and to perform process optimization. The results showed that Mn recovery was 80% under the optimum conditions: a ratio S/L = 50 g/L-70 g/L approximately; also, sulfuric acid concentration is 1.1 to 1.3 M and oxalate concentration in range 0.35 to 0.45 M, time and temperature of the process were 30 min and 25°C, respectively. The methodology employed allowed to evaluate and identify the effects and interactions of the considered variables with statistical meaning in the process response, i.e., the highest recovery of Mn after 30 min of reaction.