Capture and release mechanism of La ions by new polyamine-based organoclays: a model system for Rare-Earths recovery in urban mining process

Uptake and release capability of a new organoclay material were assessed with the final goal to evaluate its applicability in recovering REs from solutions. Capture and release capability have been tested towards a La ions model solution, and interaction mechanism and reactions, active in both capture and release processes, were related to the nature of the organoclay and the operating process parameters. The studied system, polyamine-based organoclay, is able to capture and release La ions with high efficiency. Capture involves three distinct mechanisms: ion exchange reaction with interlayer cations, surface adsorption, and finally, coordination by the polyamine. 2.5 mmol/g of amino-groups in a linear ethylene-amine based organoclay are enough to remove all the lanthanum ions in solution when contacted with containing 0.48 mmol/gclay,, i.e. 2600 ppm/clay. 12 coordinating sites are needed for each lanthanum ion. Finally, the organic part of the sorbent solid is highly stable, being unmodified upon many cycles of use. The release step is greatly pH dependent, and the optimised pH is equal to 1. Under these conditions, release efficiencies are always higher than 80%. Appling multiple steps and intermediate re-basification, very high and reproducible global efficiencies (up to 90%) are reached.