Microwave-enhanced reduction of manganese from a low-grade pyrolusite ore using pyrite: process optimization and...

The inefficient leaching of manganese is the main factor hindering the commercialization of the reduction process during manganese recovery using pyrite as the reducing agent. Hence, a new method for improving recovery efficiency and reducing the cost is required. This study uses microwave heating as a strengthening method to extract Mn²⁺ from pyrolusite and the leaching conditions are optimized. It was found that the extraction rate of Mn²⁺ could reach 95.07% under microwave heating through the conditions of H₂SO₄ is 1.2 mol/L, m(pyrolusite)/m(pyrite) equals to 10:2, leaching temperature is 90 ℃, and a liquid-solid (L/S) ratio of 10:1. The achieved extraction rate was higher than that of 75.08% under the conventional heating achieved at the same conditions. Besides, experimental studies have found that microwave heating can change the process and direction of chemical reactions, shorten the reaction time, and reduce sulfuric acid. Finally, the kinetic study indicates that the leaching process under microwave heating is controlled by surface chemical reactions. The equation of leaching kinetics is 1 - (1 - x)^1/3 = 3425.32/r₀·[H₂SO₄]^1.316·[FeS₂/MnO₂]^0.907·exp(- 45.03/(RT)·t. The activation energy is 45.03 kJ/mol. Meanwhile, through a scanning electron microscope and particle size analyzer, microwave heating has a significant influence on reducing the ore diameter and increasing the specific surface area of the sample. This study aims to provide an experimental trial case for studying the mechanism of microwave-enhanced leaching process during manganese recovery using pyrite as the reducing agent. The reported kinetics research may guide the development of the industrial application for Mn recovery.