Multiscale Flotation Testing for the Recovery of REE-Bearing Fluorapatite from a Finnish Carbonatite Complex Deposit Using Conventional Collectors and Lignin Nanoparticles

Apatite and rare earth elements (REEs) are vital to the European Union’s economic growth and resource security, given their essential roles in fertilizers, green technologies, and high-tech applications. To meet rising demand and reduce reliance on imports, the exploitation of domestic deposits has become increasingly important. This study investigates the beneficiation potential of ore from a carbonatite complex (Finland), focusing on the recovery of fluorapatite concentrate through froth flotation. This research addresses two key objectives: evaluating the potential for REE enrichment alongside fluorapatite concentration using conventional anionic and amine-based reagents, and assessing separation efficiency when partially substituting the most effective conventional collectors with bio-based organosolv lignin nanoparticles. Adequate recovery rates for apatite and REEs were achieved using common anionic collectors, such as hydroxamate and sarcosine, yielding P grades of 23.4% and 21.5%, and recoveries of 96.4% and 89.2%, respectively. Importantly, concentrate quality remained stable with up to a 30% reduction in conventional collectors and the addition of organosolv lignin. Bench-scale trials further validated the approach, demonstrating that lanthanum and cerium recoveries exceeded 71%, alongside satisfactory apatite recovery. Lignin nanoparticles were observed to interact with both minerals; however, the interaction was more pronounced in the case of phlogopite, which exhibited a markedly greater increase in surface hydrophilicity following treatment, suggesting a stronger affinity or surface modification effect, which was beneficial to the performance of the separation process.