Facile and inexpensive preparation method of iron phosphate from laterite residue

Abstract Laterite leach residue receives minimal attention, which causes severe environmental problems and resource wastage. In this paper, a facile and inexpensive method is proposed for preparing iron phosphate from laterite residues via phase transformation in phosphate medium. The laterite leach residue used in this study contains 59.2% Fe in the form of hematite. Based on the thermodynamic analysis of the system Fe2O3–H3PO4 and characterization of X-ray diffraction (XRD) and scanning electron microscope (SEM), phase transformation mechanism and operating conditions are determined. Phase transformation is divided into two stages, namely, dissolving and precipitating. Phase transformation should control pH-0.4 at first, which is beneficial to dissolving Fe2O3, and then increase pH to 1.8–3.9 to finish the precipitation of FePO4. In experiments, hematite can be completely transformed into iron phosphate at the following optimal conditions: 90 °C, 3.0 mol/L H3PO4, 3 h, and liquid-to-solid ratio of 10:1 mlL/g. XRD patterns and SEM images show that the crystal structure and pure phase of product match the standard iron phosphate well, and micro sheets aggregate to form a flowerlike morphology. Additionally, the initial discharge of the LFP synthesized by iron phosphate is 146.1 mAh g−1 at 0.1 C and shows good cycling performance at different C-rates. Electrochemical impedance spectroscopy shows that the Rct LFP synthesized by precursors is 80.83 Ω. The novel and facile method to treat laterite residue solves not only environmental problems of residue accumulation and wastage of iron resource but also improves the economic benefits of laterite.