De-sliming followed by froth flotation for the recovery of phosphorus and enrichment of rare earth elements from Florida waste clay

Abstract

Reprocessing and valorization of secondary resources is a possible solution to alleviate the supply-demand disparity for critical materials. The current study investigated the recovery of P and enrichment of REEs from Florida waste clay (WC). Clays, dolomite, and quartz are the main associated gangue minerals, while apatite is the predominant P-bearing mineral, and monazite and xenotime are the rare earth minerals in this WC. A 1.5-in. diam. hydro-cyclone unit was initially employed for the removal of clays. Froth flotation was then examined for the separation of values from the cyclone underflow. Various depressants and surface modifying agents were assessed for both direct and reverse flotation separations. Results showed that the direct flotation does not offer a solution for the selective recovery of P from WC. Despite their documented affinity for apatite and rare earths, hydroxamic acid collectors do not produce a selective separation. A single-stage reverse cationic process provides a more economically viable route due to its capability to avoid the loss of REEs. Test results of the single-stage reverse cationic process indicated that the P2O5 grade was increased to 21 wt.% from an initial grade of ∼8 wt.% with a corresponding recovery of approximately 80%. The REE content was elevated from an initial value of 307.1 ppm to 800 ppm, with an 80% recovery resulting from the same process. The removal of clays, silicates, and carbonates up to a point to meet the medium-grade phosphate ore specifications also facilitates the subsequent recovery of REEs using chemical separation.