Dissolution kinetics of iron oxides in clay in oxalic acid solutions

Clay samples containing 8.15% iron oxides and 27.49% alumina were leached in oxalic acid. Leaching experiments were performed in aqueous solutions of oxalic acid of 0.2-2 mol/L at 40-80℃ for up to 90 min. The mixed kinetic mechanism, i.e., t/τ=[(1-2X/3)-(1-X)^2/3]+b[1-(1-X)^1/3], seemed to be the most appropriate one to fit the kinetic data of leaching iron oxides contained in clay in the aqueous oxalic acid solutions. The Arrhenius activation energy for leaching in the 1.8 mol/L oxalic acid was found to be 41.035 kJ/mol.