Separation Of Indium, Iron, Zinc And Its Mass Transfer By Microfluidic Enhanced Extraction

Indium is a kind of precious rare metal, widely used in electronic industry such as liquid crystal display of ITO target materials, energy industry and manufacturing low melting alloy. Indium is commonly associated with minerals such as zinc, lead, copper and tin. Solvent extraction is a commonly used method for the purification of indium from zinc oxide dust leaching solution obtained from the zinc hydrometallurgical process. However, such conventional solvent extraction of indium inherent with disadvantages such as higher consumption of solvents, low extraction efficiency, significant co-extraction, easily emulsifying phenomenon and fire hazard. As an emerging new technique, microfluidic technology has many merits such as larger interfacial area and concentration gradient, short diffusion length, facilitating a higher mass transfer rates. In this paper, the effect of pH of the aqueous phase, D2EHPA concentration, contact time and other parameters on extraction efficiency of In3+, Fe3+ Zn2+ was investigated.First, the extraction mechanism and composition of extracted complex were determined. The conclusions are obtained as follows:(1) the composition of extracted complex:InA3·3HA; (2) chemical equation of extraction reaction:In3+(a)+3(H2A2)(O) (?) [InA3·3HA](o)+3H+(a).Then, two-phase fluid type was studied in the double " Y" type microchannel. The effect of pH of the aqueous phase, D2EHPA concentration, contact time, channel size, contact interface to volume ratio on extraction efficiency of In3+, Fe3+ Zn2+ was investigated and the effect of stripping agent concentration, channel size, contact time on stripping efficiency of In3+ was also studied, In the double "Y" type chip, the laminar flow was formed by aqueous phase and organic phase. At contact time of 2.52s, extractant volume fraction of 30% and initial solution pH of 0.423, the extraction efficiency of In3+, Fe3+ and Zn2+ was 99.55%,3.63% and 1.68%, respectively in the double "Y" type chip with 600μm width. At the extraction equilibrium of In3+, mass transfer coefficient of In3+ was up to 6.432×10-4(m·s-1). At contact time of 25.2s and stripping agent concentration of 160g/L, stripping efficiency of In3+ was 99.67% and mass transfer coefficient of In3+ was up to 0.556×10-4 (m·s-1) while concentration of Fe3+ and Zn2+ was lower than 0.03 g/L with good separation of In3+ from Fe3+ and Zn2+ through the process of extraction and stripping.The effect of main parameters such as flow velocity and pH on the extraction efficiency of In3+, Fe3+ and Zn2+ was investigated and the effect of stripping agent concentration and flow velocity on stripping efficiency of In3+ was also studied in an interdigital micromixer. At a phase flow velocity of 7.0 mL/min and contact time of 0.034 s, the extraction efficiency of In3+ was more than 99% but that of Fe3+ and Zn2+ was low without emulsification. At the extraction equilibrium of In3+, mass transfer coefficient of In3+, Fe3+ and Zn2+ was 144.307 s-1,1.018 s-1 and 0.750 s-1, respectively. At a phase flow velocity of 9.0 mL/min and contact time of 0.027 s, stripping efficiency of In3+ was 98.92% and mass transfer coefficient of In3+ was up to 169.808 s-1.Finally, the amplification of micro fluid extraction was studied in the independent-developed pilot-plant equipment. The effect of flow velocity and phase ratio on extraction efficiency of In3+, Fe3+ and Zn2+ was investigated. At a phase flow velocity of 500 mL/min, extractant volume fraction of 30% and initial solution pH of 0.423, the extraction efficiency of In3+, Fe3+ and Zn2+ was 99.81%,1.24% and 0.32%, respectively, with good separation of In3+ from Fe3+ and Zn2+.