Separation of submicron SiO2 and SnO2 particles via liquid-liquid extraction using ZnCl2 and SDS

• Separation of submicron SiO 2 and SnO 2 can be achieved by the addition of ZnCl 2 and SDS using liquid-liquid extraction. • Concentration of ZnCl 2 and SDS plays a crucial role in the separation efficiency. • Separation of SiO 2 and SnO 2 is strongly influenced by the pH value, especially at higher concentrations of ZnCl 2 and SDS. Selective separation mechanisms for particles smaller than 1 µm need to be investigated, as known separation methods lose both efficiency and selectivity at this small size. As a model case, it was therefore investigated whether a separation of SiO 2 and SnO 2 could be achieved using an interface between two immiscible liquids, namely MilliQ water and n -hexane. The separation required the generation of a selective separation feature. This could be achieved by specific adsorption of the Zn-species followed by selective adsorption of sodium dodecyl sulphate (SDS), as this can cause a selective hydrophobization of one of the two materials in the mixture. This ensures that only the target particle system (SnO 2 ) can be transferred to the oil phase and SiO 2 should therefore remain in the aqueous phase. In this study, different ZnCl 2 , SDS concentrations and pH values were investigated to achieve a selective separation of both materials. This revealed differences within the concentration series regarding the amount of ZnCl 2 and SDS, but also differences between the investigated pH values. The best separation results for both pH values were achieved for the lowest salt concentration 0.025 mM ZnCl 2 .