Optimizing flotation separation of fluorapatite from Florida waste clay using a multiscale approach

This study combines flotation experiments and ab initio simulations to improve the anionic flotation of fluorapatite from Florida waste clay (FWC) by investigating the depressing effects of sodium silicate and citric acid, in presence of sodium oleate (NaOl), on dolomite, quartz, and fluorapatite. First, we show that the order of natural floatability with NaOl of the three pure minerals is fluorapatite > dolomite > quartz, in agreement with the first-principles calculations. Second, sodium silicate has a strong calculated affinity with fluorapatite surface, which explains the dramatical drop observed experimentally in the floatability of this mineral. From ab initio simulations, citric acid exhibits a poor affinity for fluorapatite surface but a strong affinity for dolomite and quartz surfaces, even stronger than NaOl, related to strong differences in the adsorption mechanisms. This trend in terms of affinities is consistent with the trend in terms of floatabilities, observed on pure minerals. Consistently, during FWC flotation, citric acid allows an efficient and satisfactory depression of gangue minerals (quartz and dolomite) and enhances P recovery and grade by 14% and 2%, respectively. Using citric acid in FWC flotation makes possible the efficient beneficiation of this material with a cleaner product compared to the classical processes.