Cryogenic-crosslink synthesis of Ba(OH)2@gelatin microcapsules for the removal of sulfate in lithium refinery

Abstract

Sulfate (SO42−) is a major impurity in the production of battery-grade LiOH from acid leaching of ores using H2SO4. The conventional process to remove SO42− by precipitation with Ba2+, however, is difficult to control stoichiometrically in industry, and overdosed Ba2+ frequently causes secondary contaminations. Moreover, fine particles of BaSO4 precipitate require extra steps to remove, which significantly increases the cost of separation. To overcome these limitations, we developed a novel adsorbent, the Ba(OH)2@gelatin microcapsule, by embedding Ba(OH)2 inside the matrix of gelatin through a special cryogenic-crosslink method using liquid nitrogen to snap-freeze the gelatin-Ba(OH)2-water droplets followed by glutaraldehyde solutions to crosslink. The physical properties and SO42− adsorption performance were investigated to testify the microcapsules' potential in industrial removal of SO42− to below the 20 ppm threshold. The microcapsules can withstand a pressing force of 4 N and a maximum deformation of 73% on average, showing considerable physical strength and elasticity. It served as an effective domain for SO42− adsorption, in the best scenario reducing SO42− from 200 to 10 ppm, following a pseudo-second order kinetic model. The SO42− loaded Ba(OH)2@gelatin microcapsules can be easily removed from the treated solution and the potential contaminations of BaSO4 precipitate and overdosed Ba2+ can be avoided. The spent gelatin microcapsules can be regenerated by reloading with Ba2+ and recover the SO42− removal capacity for multiple cycles.