Recycling graphite from spent lithium-ion batteries plays a significant role in relieving the shortage of graphite resources and environmental protection. In this study, a novel method was proposed to regenerate spent graphite (SG) via a combined sulfuric acid curing, leaching, and calcination process. First, we conducted a sulfuric acid curing–acid leaching experiment and systematically investigated the effects of various operation conditions on the removal of impurities. Regenerated graphite was obtained after a sequential calcination at 1500 °C, and its morphology and structure were characterized by using X-ray diffraction, Raman spectroscopy, and spherical aberration electron microscopy analysis. The results show that the impurity removal efficiency by sulfuric acid curing–acid leaching is much higher than that by direct acid leaching, and the purity of the regenerated graphite can reach 99.6%. Additionally, the regenerated graphite displays favorable characteristics in morphology and structure, which are close to that of a commercial unused material. The regenerated graphite exhibits good electrochemical performance in charge capacity and cycle. The initial charge capacity and retention rate are 349 mA h/g and 98.8%, respectively. This recycle method has the advantages of low energy consumption and low waste acid discharge and can be performed by easily available equipment, so it may have great prospect for the industrial-scale recycling of SG.

The wet chemical processes of LiFePO4, hydrothermal synthesis and hydrometallurgical recovery, are of great importance during the life cycle of LiFePO4. To analyze these two processes, E-pH diagrams for the Li-Fe-P-H2O system are plotted from 298 to 473 K in this study. The E-pH diagrams can well explain the practical operating conditions of hydrothermal synthesis and hydrometallurgical recovery and provide thermodynamic basis for them. Besides, suitable conditions for the hydrothermal synthesis of LiFePO4 are obtained from the E-pH diagrams, including high temperature, low redox potential, optimum pH 7.8–8.4, and excess stoichiometric lithium. As found in the E-pH diagrams, LiFePO4 will change to ferric phosphate by promoting the redox potential, while lithium will be extracted to the aqueous solution. Based on the above results, a method is proposed for the selective leaching of lithium from spent LiFePO4, which is successfully verified by leaching experiments. At room temperature (298 K), neutral pH (7.0), and low liquid–solid ratio (5:1), 95.4% of lithium can be extracted using 2.7 M H2O2 as the oxidant, while iron remains in the residue. This method shows a promising commercial value as it can realize the selective extraction of valuable lithium from spent LiFePO4 and avoid using large amounts of acid and alkaline.

The continuously increasing demand for lithium has made it one of the strategic metals, rendering its exploitation of critical importance. Natural α-spodumene is still the primary resource of lithium extraction. The traditional process for the treatment of α-spodumene generates immense quantities of waste residue and needs a high-temperature heat treatment, leading to high energy consumption. In addition to lithium, α-spodumene is rich in aluminum and silicon, and thus it is a potential raw material for zeolite synthesis. Herein, a novel process was developed for the clean and efficient extraction of lithium from α-spodumene coupled with the synthesis of hydroxysodalite zeolite. By hydrothermal alkaline treatment, α-spodumene was converted into hydroxysodalite; the lithium in α-spodumene was released into the solution and subsequently recovered by precipitation with Na2CO3. A lithium extraction efficiency of 95.8% was obtained under optimum conditions: temperature of 250 °C, NaOH concentration of 600 g/L, liquid/solid ratio of 5:1, stirring speed of 500 rpm, and reaction time of 2 h. In addition, the influences of various factors on the composition and textural properties of the product were analyzed using XRD, SEM, TG, N2 adsorption/desorption, and FTIR.

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