Li+ Extraction from Spinel-Type LiMn2O4 in Different Eluents and Li+ Insertion in the Aqueous Phase

In order to afford a possible way to avoid manganese dissolution during Li⁺ extraction/insertion of spinel-type LiMn₂O₄, the elution properties of HCl, (NH₄)₂S₂O_8, and Na₂S₂O₈ were studied and the adsorption performance of Li⁺-extracted samples was characterized in Li⁺-containing solution. The results showed that Li⁺ was extracted by two different pathways: with manganese loss and without manganese loss. In the Li⁺ extraction process with manganese loss, ionic sieve was obtained after extracting Li⁺ from its precursor LiMn₂O₄, with accompanying partial transformation of Mn³⁺ to Mn⁴⁺ and Mn²⁺ by disproportionation reaction. This change caused the destruction of the framework and weight loss of ionic sieve due to the dissolution of Mn²⁺ in the solution. In the Li⁺ extraction process without manganese loss, Li⁺ was extracted with the reaction that part of Mn³⁺ was oxidized to Mn⁴⁺ by S₂O₈^2-. The Li⁺-extracted sample contained a small number of H⁺ which should exchange Li⁺ during this type of elution. The two Li⁺ extraction pathways also indicated that Li⁺ could not be completely eluted from the ionic sieve precursor. The uptake of Li⁺ on the ionic sieve was incomplete.