Facile synthesis and characterization of ZnS polymorphs/Halloysite composite for efficiently selective adsorption of Al(III) from acidic rare earth ions solution

Removal of aluminum ion from rare earth ions solution by selective adsorption was one of the promising methods for green enrichment of the acidic rare earth solution containing aluminum ions. Herein, a series of ZnS polymorphs/halloysite composites and Wurtzite/Halloysite (WZ@Hal) with different wurtzite content were prepared by facile one-step hydrothermal method using halloysite as the substance. The phase composition, microstructure and specific surface area of the WZ@Hal composite were characterized and the selective adsorption behavior of the WZ@Hal composite for aluminum and rare earth ions under different conditions was studied. The results showed that WZ@Hal composite loaded with hexagonal wurtzite showed good adsorption selectivity for Al(III) with a spontaneous exothermic process, while SP@Hal composite loaded with cubic sphalerite displayed no obvious adsorption capacity for both Al(III) and Er(III) with an endothermic process. The WZ@Hal composite was synthesized through strong electron interaction between sulfur atoms of wurtzite with oxygen atoms on the surface of halloysite. The WZ@Hal exhibited a fast adsorption rate a fast adsorption rate (k2 was 0.0713 g.mg(-1).min(-1)) and an excellent selectivity coefficient (Ks was 237). The adsorption process of WZ@Hal for Al (III) in mixed solution was described by the pseudo-second-order kinetic model and controlled by the chemisorption. WZ@Hal showed excellent regeneration and maintained high selective adsorption performance in adsorption-desorption process. The adsorption mechanism was that aluminum ions were adsorbed by electron interaction with sulfur atoms of wurtzite and oxygen atoms of halloysite at the interface of the wurtzite and halloysite. WZ@Hal composite showed excellent selective adsorption performance in the adsorption and separation process of acidic mixed solution of aluminum ion and rare earth ions.