Thermodynamic and quantum chemistry calculations of species in the molten AlCl3–MCl (M = Li, Na, K) system

The Hall–Héroult process dominates aluminum production but suffers from high energy demands and pollution. This study investigates the aluminum chloride process as an alternative method by analyzing species behavior in AlCl₃–MCl (M = Li, Na, K) molten salts at 373–473 K and 933–1033 K through quantum calculations and mathematical modeling. When initial AlCl₃ < 50 mol%, Cl⁻ and AlCl₄⁻ dominate at 933–1033 K, with minor temperature effects. When initial AlCl₃ > 50 mol%, AlCl₄⁻, Al₂Cl₇⁻ and Al₂Cl₆ dominate at 373–473 K. Increasing AlCl₃ concentration decreases AlCl₄⁻ fraction; Al₂Cl₇⁻ fraction peaks at 66.7 mol% AlCl₃ then declines; Al₂Cl₆ fraction steadily increases. Higher temperatures promote Al₂Cl₇⁻ conversion to AlCl₄⁻ and Al₂Cl₆. Redox calculations show preferential Cl⁻ discharge at the anode when AlCl₃ < 50 mol%. At AlCl₃ > 50 mol%, Al³⁺ in Al₂Cl₆ discharges at the cathode and Cl⁻ in Al₂Cl₇⁻ discharges at the anode.