Photo-switchable Collectors for the Flotation of Lithium Aluminate for the Recycling of the Critical Raw Material Lithium.

Abstract

Flotation of the mineral lithium aluminate by application of the natural product punicine and some derivatives as collectors is examined. Punicines, 1-(2´,5´-dihydroxyphenyl)-pyridinium compounds, are switchable molecules whose properties can be changed reversibly. They exist as cations, neutral mesomeric betaines, anions, and dianions depending on the pH. In light, they form radicals. Five punicine derivatives were prepared which possess β-methyl, β-chlorine, γ-tert.-butyl, and γ-acetyl groups attached to the pyridinium ring, and a pyrogallol derivative. LiAlO2 reacts with water to give species such as LiAl2(OH)7 on its surface. Flotations were performed applying the punicines in daylight, in darkness and under UV-irradiation (390 - 400 nm). The pH of the suspension, the collector´s concentration, the conditioning time as well as the flotation time were varied. The recovery rates strongly depend on these parameters. For example, the recovery rate of lithium aluminate was increased by 116% on changing the lighting condition from daylight to darkness, when the pyrogallol derivative of punicine was applied. UV, FTIR, TGA and zeta potential measurements as well as DFT calculations were performed in order to gain insight into the chemistry of punicines on the surface of LiAlO2 and LiAl2(OH)7 in water which influence the flotation´s results.