Selective Lithium extraction from salt solutions by chemical reaction with FePO4

Abstract

The spectacular increase in lithium battery applications has raised the question of whether global lithium resources will be enough in the future. Experts in the field have estimated that the existing lithium resources will probably be sufficient to support demands until the year 2100, assuming that lithium batteries are recycled. Without lithium batteries being recycled, the resources are expected to be depleted in 50 years’ time. Therefore, there is a great interest in developing better methods of lithium recycling from batteries, and also, better methods of lithium extraction from natural resources.

Currently, lithium is extracted from natural brines via the lime soda evaporation process, i.e. a solar evaporation plus chemical plant process, which takes between 12 and 24 months. The drawbacks of this process are that it is complex, slow and inefficient. Also, the currently available methods of lithium recycling from batteries are too complex and expensive. Thus, the main objective of this work is to develop a novel, inexpensive and less timeconsuming approach to recover lithium chemically, from the lithium salts (lithium sources) that contain other metal cations.

The new process is also based on environmental concerns. A battery material, lithium iron phosphate (LiFePO4) has the olivine structure and heterosite structure once it discharges to iron phosphate (FePO4). This structure shows excellent properties of the charge/discharge reversibility. A few studies on the heterosite FePO4 have reported that it is more selective for lithium ions (Li+) over other cations. The main advantages of this structure are the small potential differences of the redox couple, i.e. Fe(II)/Fe(III), and the stability of LiFePO4 over a wide range of acid-based conditions in an aqueous solution.

This work investigates a novel process that may be superior to the lime soda evaporation process for extracting lithium. Heterosite FePO4 was employed to selectively remove Li+ from lithium sources with the support of a reducing agent, i.e. sodium thiosulphate (Na2S2O3). The resulting LiFePO4 can be directly sent not only to lithium battery industries, but also to other industrial uses. In principle, the other cations could be retrieved back into their sources. The novel process was examined and demonstrated lithium insertion into a heterosite FePO4, working as a framework, in aqueous salt solutions. The evaluation of this process is presented by the Li+ uptake value. The amount of Li+ uptake can be up to 46 mgLi +/gsolid where other cations (i.e. sodium, potassium, and magnesium) can take less than 3 mg/gsolid, using this process. Furthermore. This work could also be developed for future lithium recycling processes.

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Identifiers

ORCID for John Owen: orcid.org/0000-0002-4938-3693

ORCID for Nuria Garcia-Araez: orcid.org/0000-0001-9095-2379

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