Environmentally Friendly Strategy for Treating In Situ Leaching Solutions of Ion-Adsorption Type Yttrium-Rich Heavy Rare-Earth Ore by a Bubble-Supported Organic Liquid Membrane

A novel environmentally friendly strategy based upon bubble-supported organic liquid membrane (BSOLM) extraction using saponified naphthenic acid as extractant is proposed in the present work for treating the in situ leaching solutions of ion-adsorption type yttrium-rich heavy rare-earth ores in South China. It was revealed that selectively preferential separation of non-yttrium rare earths from yttrium can be achieved, while the electrolyte aluminum salt can be retained in the raffinates for subsequent return as the leaching reagent for performing in situ leaching of ion-adsorption type heavy rare-earth ores. The BSOLM extraction exhibits an obvious advantage over conventional extraction in promoting the competitive mass transfer and separation of coexisting rare earths from yttrium and other non-rare-earth impurity ions. Using erbium as a representative of heavy rare earths, it was found that the differences in diffusive mass transfer rate of Er3+, Y3+, and Al3+ ions in the boundary layer of laminar flow near the surface of the extractant liquid membrane result in their enhanced separation. The BSOLM extraction prevents the convective disturbance along the normal vertical direction of the interface due to the irregular movement of dispersed oil droplets in the conventional extraction and therefore inhibit the co-extraction of Al3+ ions. The effects of Al3+ ion concentrations in aqueous feed solutions, initial aqueous pHs, concentrations of naphthenic acid, and its saponification degree on the separation efficiency were investigated. Experimental results confirmed that competitive hydration and adsorption of Al3+ ions at the interface play an important role in increasing the difference in concentration distribution of Er3+ and Y3+ ions near the interface during BSOLM extraction; therefore, the separation of rare earths from yttrium can be controllable.