Instability behavior of bubble supported organic liquid membrane in extraction of low-concentration rare earths from in-situ leaching solutions of ion-adsorption ores

Gas bubble supported organic extractant liquid membrane exhibits a promising potential in enhanced extraction and separation of low-concentration rare earths from the in-situ leaching solutions of ion-adsorption ores. However, instability of organic liquid membrane on the surface of gas bubbles might result in dissolution loss of organic extractant in the flowing-out aqueous raffinates and bring serious organic pollution if the raffinates are recycled for re-leaching of rare-earth ores. The present work focuses on the mechanism of the instability of organic extractant P507 liquid membrane on the surface of bubbles during rare-earth extraction. Various effects, including volume flow rate of aqueous feed solution, initial aqueous pHs and concentrations of co-existing impurity ions, saponification degree of P507 and pre-loaded concentration of rare earths in organic phase, on the stability of organic liquid membrane are discussed. Experimental results reveal that the stability of organic liquid membrane depends on three kinds of forces exerting on the surface of bubbles, i.e., the shear force F-s, the interface tension F-t and the dispersion force F-d. The occurrence of F-t and F-d are benefit for the stability, but F-s is not. The competition of the two component forces of F-s respectively with F-t and F-d will result in instability of organic liquid membrane and an increase in the concentration of total organic phosphorus in the flowing-out raffinates. The present work provides a theoretical basis about how to control the stability of organic extractant liquid membrane on the surface of gas bubble. Based on the suggested new technique by bubble supported organic liquid membrane extraction, a green and environmentally friendly strategy is suggested for replacing the traditional ammonium bicarbonate precipitation to extract low-concentration rare earths from in-situ leaching solutions of ion-adsorption ores.