Optimization of Hydrometallurgical Recovery of MnO2 from Dry Cell Waste Using Response Surface Methodology

Abstract

This study aims to recover manganese dioxide from depleted dry cell batteries using a hydrometallurgical process optimized by response surface methodology (RSM). The research is motivated by the high industrial demand for imported MnO₂ and environmental issues associated with hazardous spent battery waste. The recovery process involved microwave-assisted leaching using 1.2 M H₂SO₄ with the addition of H₂O₂ reductant (0–2% w/v), followed by oxidative precipitation using 0.25 M KMnO₄. Variables tested included reductant concentration and leaching time. Based on RSM optimization using the central composite design model, optimum conditions were achieved at an H₂O₂ concentration of 2% w/v and a leaching time of 39.15 min. Under these conditions, a recovery rate of 96.76% was obtained with a desirability value of 0.805 and a model R² of 0.9151. The final product exhibited Mn purity of 96.10–97.33%, a significant increase from the raw material (64.61%) and surpassing the commercial MnO₂ standard (>92%). This research highlights the synergistic integration of microwave-assisted heating and chemical reduction. While previous studies have applied these techniques independently, their combined effect drastically accelerates the extraction kinetics, reducing the leaching time to under 40 min, which is significantly faster than conventional methods while still achieving commercial-grade purity from complex secondary waste. This study demonstrates that microwave-assisted hydrometallurgy is a highly time-efficient and sustainable approach for recycling battery waste into high-value industrial raw materials, supporting sustainable development goals principles.