Preparation of Lithium Ion Adsorbent Using Low-Grade Pyrolusite: Preparation Method and Adsorption Performance

Abstract

A lithium ion adsorbent was prepared using low-grade pyrolusite by the following steps: (1) Manganese rich material (MRM) with higher Mn content was prepared by pyrolusite–NaOH molten salt roasting and washing processes to remove impurities in pyrolusite, such as silicon, iron, aluminum, etc. (2) the lithium ion adsorbent was obtained by extraction of lithium with hydrochloric acid from the precursor, which was synthesized via the solid-phase reaction between MRM and LiOH. Compositions of low-grade pyrolusite, MRM, precursor and lithium ion adsorbent were characterized by powder x-ray diffraction and x-ray photoelectron spectroscopy. Adsorption properties and selectivity of the adsorbent are also discussed. The results showed that in the NaOH roasting process, manganese was transformed to Na_0.7MnO_2.05 and silicon, iron, and aluminum became hydrosoluble Na₂SiO₃, Na₂Al_5.2O_9.4 and Na₃FeO₃, respectively. The manganese content in MRM increased from 24.6% to 50% in the conditions of a 600°C 2 h roasting temperature, and the NaOH–pyrolusite mass ratio was 1.5, after the washing process. The Li_1.27Mn_1.73O₄ precursor was synthesized at 750°C with good crystallization yielding a Li/Mn molar ratio of 3 via the LiOH and MRM roasting process. The value of Li⁺ extraction from the Li_1.27Mn_1.73O₄ precursor reached a maximum in the condition of 0.3 mol/L HCl solution at 40°C for 6 h. Before and after adsorption of Li⁺, the spinel structure of the adsorbent was not changed. The Li⁺ adsorption capacity of the obtained adsorbent reached 36.5 mg/g in a LiOH solution, which contained 2 g/L Li⁺ and remained at 34–35 mg/g after several cycles. The lithium ion adsorbent had better Li⁺ selectivity in the synthetic salt-lake brine solution, and the separation coefficients of Li⁺ to Na⁺ and K⁺ reached 44.15 and 33.56, respectively.