Separation of Zn(II) from Zn-Ni-Co sulphate solution by di-(2-ethylhexyl) phosphoric acid (D2EHPA) using a slug flow microreactor

Separation of Zn2+ from sulphate solution containing Ni2+ and Co2+ using di-(2-ethylhexyl)phosphoric acid (D2EHPA) has been carried out in capillary microreactors. Well-defined slug flows are formed at total flow rates of 0.1-4 mL/min, and the slugs size and specific interfacial area are determined. The effects of saponification degree of D2EHPA, extractant concentration, and residence time on extraction and separation of these three metal ions are investigated. Meanwhile, conventional batch experiments at 94 s and equilibrium experiments at 8 h are also done in parallel at different extractant concentrations. Compared with conventional batch experiments, better extraction and separation performance, e.g. 2.7-38.9 times higher of beta(Zn/Ni) and 3.9-34.9 times higher of beta(Zn/Co), is obtained in the slug flow microreactor. In addition, the overall volumetric mass transfer coefficient k(L)a and overall mass transfer coefficient k(L) are measured. Compared with other microreactors and the batch mixer-settler, the used slug flow microreactor shows higher k(L)a values of Zn.