Abstract
The co-precipitation thermodynamics of the Li+–Fe2+/Fe3+–Al3+–F−–SO42−–PO43−–H2O system at 298 K is studied, aiming to understand the precipitation characteristics. Based on the principle of simultaneous equilibrium and the mass action law, the missing Ksp values of AlF3 and FeF3 were estimated. The results of thermodynamic calculation demonstrate that Al3+ and F− in the sulfuric acid leachate could be preferentially precipitated in the form of AlPO4 and FeF3 by the precise adjustment of the final pH value. Only a small amount of P and Fe was lost by the precipitation of Fe3(PO4)2·8H2O, FePO4, and Fe(OH)3 during the purification process. Controlling the oxidation of ferrous ions effectively is of critical significance for the loss reduction of P and Fe. Precipitation experiments at different pH value indicated that the concentration of Al3+ and F− in the leachate decreased as the final pH value rose from 3.05 to 3.90. When the final pH value was around 3.75, aluminum and fluoride ion impurities could be deeply purified, and the loss rate of phosphate ions and iron ions could be reduced as much as possible. Relevant research results can provide theoretical guidance for the purification of leachate in the wet recycling process of lithium-ion batteries.
Highlights
Greenhouse gas emissions are severely aggravating global climate change, and all countries should formulate national policies to achieve zero carbon emissions [1,2].China, for instance, has pledged to peak nationwide CO2 emissions by 2030 and achieve carbon neutrality by 2060 [3,4]
Given that the service life of power batteries is approximately 5–8 years, it is predicted that the cumulative decommissioning of powder batteries in China will reach 90.5 GWh from 2020 to 2022, of which spent LiFePO4 batteries will account for 53.8% (48.7 GWh) [7]
Spent LiFePO4 cathode powder was provided by a battery recycling company (Nantong, China), and it was separated from aluminum foils by thermal treatment and screening
Summary
Greenhouse gas emissions are severely aggravating global climate change, and all countries should formulate national policies to achieve zero carbon emissions [1,2]. The hydrometallurgical process is the mainstream technology for lithium iron phosphate batteries treatment in Chinese recycling enterprises because of its low energy consumption, high product purity, and wide adaptability of raw materials. This process mainly involves pretreatment, leaching (selective leaching of Li or simultaneous leaching of Fe and Li), purification, and preparation of battery materials. H2 SO4 is widely used as a leaching agent by lithium battery recycling companies due to its low price, easy fabrication, and strong acidity Various impurity ions, such as Al, Cu, and F, will inevitably enter the leachate and affect the physicochemical properties of regenerated electrode materials. To validate the feasibility of thermodynamic calculation, trisodium phosphate dodecahydrate was used as neutralizer and ascorbic acid as a reducing agent to control the final pH value of Metals 2021, 11, 1641 sulfuric acid leachate within predetermined range in an inert atmosphere and monitor the changes of Al, F, P and Fe contents in the leachate
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