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 ml/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.

中文翻译：

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一种从红土渣中简便廉价制备磷酸铁的方法

摘要 红土浸出残留物很少受到关注，造成严重的环境问题和资源浪费。在本文中，提出了一种在磷酸盐介质中通过相变从红土残渣中制备磷酸铁的简便且廉价的方法。本研究中使用的红土浸出渣含有 59.2% 的赤铁矿形式的 Fe。基于 Fe2O3-H3PO4 体系的热力学分析和 X 射线衍射 (XRD) 和扫描电子显微镜 (SEM) 的表征，确定了相变机制和操作条件。相变分为溶解和沉淀两个阶段。相变应首先控制pH-0.4，有利于Fe2O3的溶解，然后将pH提高到1.8-3.9，完成FePO4的沉淀。在实验中，赤铁矿可以在以下最佳条件下完全转化为磷酸铁：90°C，3.0 mol/L H3PO4，3 h，液固比10:1 ml/g。XRD图谱和SEM图像表明产物的晶体结构和纯相与标准磷酸铁相匹配，微片聚集形成花状形态。此外，由磷酸铁合成的 LFP 在 0.1 C 下的初始放电为 146.1 mAh g-1，并且在不同的 C 倍率下显示出良好的循环性能。电化学阻抗谱显示前体合成的 Rct LFP 为 80.83 Ω。这种新颖简便的红土渣处理方法不仅解决了渣土堆积和铁资源浪费的环境问题，而且提高了红土的经济效益。