Phase reconstruction behavior and mechanism analysis of the electrolytic manganese residue decoupled residue pyrolysis process

Decoupled electrolytic manganese residue (DEMR) is the electrolytic manganese residue (EMR) after the removal of harmful components by double salt oxidation decoupling separation. An important direction for the bulk resource utilization of electrolytic manganese residue involves reconstructing its mineral phase composition, regulating the microstructure of the surface interface, improving the reactivity of the physical phase, and applying it to building materials through calcination. In this study, the thermal reaction behavior and pyrolysis mechanism of DEMR were revealed through thermodynamic and kinetic analysis combined with molecular dynamics (MD) simulations. The results show that the DEMR process can be divided into four stages. Stage 1 involves the first-order chemical reaction of the aqueous mineral phase removing free water, with an average activation energy (ΔG) of 6.85 kJ/mol. Stage 2 consists of stochastic nucleation and growth reactions, involving the decomposition of unstable sulfate, the removal of crystalline water from the aqueous mineral phase, and the decomposition of the carbon-containing organic matter, with an average ΔG of 126.43 kJ/mo1. Stage 3 is characterized by the phase boundary control reaction of heat-absorbing reconstruction of the stable mineral phase, with an ΔG of 255.46 kJ/mol. Stage 4 involves the heat-driven phase‒solid‒phase boundary chemical reaction of unstable minerals, with a ΔG of 205.54 kJ/mol. MD calculations show that there is a certain interaction energy between the oxides and CaSO₄ in DEMR, and Al₂O₃-Fe₂O₃ and Al₂O₃-MgO easily form relatively stable compounds. Between other mineral phases, which may adsorb to each other or form unstable complexes. CaSO₄-Al₂O₃, CaSO₄-Fe₂O₃, Al₂O₃-Fe₂O₃, and Al₂O₃-MgO readily form relatively stable compounds through hydrogen bonding or chemical bonding. What's more, Al₂O₃-SiO₂ and Fe₂O₃-SiO₂ form less stable compounds via van der Waals and Coulomb forces.