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

Flotation of the mineral lithium aluminate by application of the natural product punicine from Punica granatum 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 ß-methyl, ß-chlorine, γ-tert.-butyl, and γ-acetyl groups attached to the pyridinium ring, and a pyrogallol derivative. On the other hand, LiAlO2 reacts with water to give species such as LiAl2(OH)7 on its surface. Flotations were performed applying the punicines in daylight (3000 lux), in darkness (<40 lux) and under UV-irradiation (4500 lux, 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.

Lithium aluminate flotation by pH- and light-switchable collectors based on the natural product punicine.

Derivatives of the natural product punicine [1-(2',5'-dihydroxyphenyl)pyridinium chloride] were developed as switchable collectors for the flotation of lithium-containing engineered artifical minerals (EnAMs). These EnAMs are e.g. formed by pyrometallurgical processing of end-of-life lithium-ion batteries. Depending on the pH value and the lighting conditions, punicines exist in water as cations, two different electrostatically neutral mesomeric betaines, anionic tripoles, radical cations or radical anions. The radical species form by photochemically induced disproportionation reactions. We prepared punicine derivatives introducing alkyl chains in the pyridinium moiety (4-methyl, 4-ethyl, 4-octyl and 4-undecanyl) to install hydrophobic groups and examined the recovery rates of the flotation of lithium aluminate (LiAlO2). We varied the lighting conditions (darkness, daylight, LED irradiation at λ = 390-400 nm) and the pH value, the collector's and frother's concentration, and the flotation time. With our collectors, recovery rates of lithium aluminate up to 90% were accomplished when the flotation was conducted in Hallimond tubes exposed to daylight at pH 11 in water.

Improvement of the froth flotation of LiAlO2 and melilite solid solution via pre-functionalization.

In this work froth flotation studies with LiAlO2 (lithium-containing phase) and Melilite solid solution (gangue phase) are presented. The system was optimized with standard collectors and with compounds so far not applied as collectors. Furthermore, the principle of self-assembled monolayers was introduced to a froth flotation process for the first time resulting in excellent yields and selectivities.