A facile method for efficient synergistic oxidation of Fe2+ in phosphorus-sulfur mixed acid system with a mixture of oxygen and ozone

The recovery of iron phosphate involves the addition of oxidizer to oxidize Fe 2+ in the spent LiFePO 4 (LFP) material to Fe 3+ and the agent commonly used is hydrogen peroxide (H 2 O 2 ). Nevertheless, H 2 O 2 has disadvantages of high price, easy decomposition and low utilization efficiency. In this manuscript, a facile method is proposed for efficient synergistic oxidation of Fe 2+ in spent LFP leachate with a mixture of oxygen and ozone. Specifically, we found by thermodynamic computations that the dominant oxidation groups of ozone during oxidation varied with acidity. The oxidation would produce a large number of iron-phosphate complex groups (Fe 3 H 6 (PO 4 ) 3+ 4 , FeH 8 (PO 4 ) − 4 and Fe 2 HPO 4+ 4 ) in the phosphorus-sulfur mixed acid system, leading to a paradoxical pH drop. The optimized conditions for H 2 O 2 oxidation were explored. It was determined experimentally that oxidation by gas mixture and O 2 belonged to the firstorder and second-order reactions with activation energies of 28.68 kJ/mol and 34.61 kJ/mol, respectively, which were both controlled by a mixture of chemical reaction and diffusion. The optimized oxidation method was finally determined by evaluating the cost and oxidation rate of the oxidizers. The results in this study offer a promising method for new low-cost and efficient Fe 2+ oxidation for industrial production.