The modification of MnO2·0.5H2O by Al/Mg doping to enhance lithium adsorption and reduce manganese dissolution with application to brines

Lithium extraction by ion sieve adsorption possesses the merits of a simple, low cost process of less pollution. In this article, lithium ion sieve MnO2·0.5H2O modified by doping with Al/Mg was obtained by hydrochloric acid pickling of precursor, which was formed by hydrothermal reaction of Mn2O3 with LiOH·H2O followed by a sintering process with Al2O3/MgO. The structure analysis indicated that the spinel structure of [MnO6] framework was observed in MnO2·0.5H2O. The lithium adsorption process reached equilibrium within 24 h and obeyed the pseudo second-order and Langmuir isotherm models. Attribute to the expanded surface area and increased Mn4+ proportion, the ion sieve doped with Al or Mg exhibited better performance in terms of lithium adsorption capacity and extent of manganese dissolution than undoped sample, and the best doping ratio were both 4%. Through doping 4% Al and 4% Mg, the adsorption capacity of doped samples in LiOH solution (CLi+ = 600 mg/L) was increased to 46.8 mg/g and 45.8 mg/g, respectively, from 40.1 mg/g, and the extent of manganese dissolution in the pickling dropped to 3.67% and 3.58% from 4.42%, respectively. Generally, adsorption capacity and selectivity of 4% Al-doped ion sieve is better than 4% Mg-doped ion sieve, therefore 4% Al-doped ion sieve is an ideal adsorbent. This study can provide a reference value to further research on efficient lithium adsorption.