Synthesis of granulated H4Mn5O12/chitosan with improved stability by a novel cross-linking strategy for lithium adsorption from aqueous solutions

Adsorption is one of the most promising methods for lithium recovery from aqueous solutions. Herein, eco-friendly chitosan (CTS) was used to prepare granulated H4Mn5O12 (HMO) ion-sieve for lithium adsorption from aqueous solutions. It was found that the hydroxyl and amino groups in CTS can react with the epoxy group and alkyl chloride in epichlorohydrin (ECH) under acidic and alkaline conditions, respectively. This unique property resulted in the adequate cross-linking of CTS and the uniform distribution of HMO in the CTS matrix by a novel two-step cross-linking strategy with ECH as the cross-linking agent. Especially when the superfine hydrogen-type rather than lithium-type ion-sieve was coated by this method at a mass ratio of CTS/HMO = 1:1, the material exhibited high thermal and chemical stability. The dissolution loss of Mn was no more than 1.15% in 0.25 mol·L−1 HCl even after 24 h continuous stirring, and it still maintained good thermal stability at 433 K. When the material was used for Li+ (25.78 mg·L−1) recovery from geothermal water which is characterized by high temperature, the adsorption capacity reached 11.4 mg·g−1 with a recovery rate of 88.42% at a solid-to-liquid ratio of 4 g·L−1. Because chitosan is widely applied for the preparation of various adsorption materials, the cross-linking strategy developed in this work provides a new idea for the preparation of chitosan-based composite materials with high stability and adsorption properties.