Study On Partitioning Performance Of Vanadium,Molybdenum And Tungsten In Nonionic Surfactant Aqueous Two-phase Systems

Vanadium,molybdenum and tungsten are important rare metals and are widely used in all kinds of areas and are recovered and separated by organic solvent extraction method.In order to overcome the disadvantages of the method in safety and ecotope,the extracting performance and the extraction mechanism of vanadium(V),molybdenum(VI)and tungsten(VI)were studied with aqueous two-phase systems(ATPS)composed of Triton X-100(L35,PEG1000,PEG2000,PEG4000)+ sulfate + water without using any extractant,to provide theoretical foundation for industrial application.The studied results on extracting performance of vanadium,molybdenum and tungsten indicated that the effect of hydrophilia/hydrophobicity of surfactants on the distribution coefficient and extraction rate of vanadium,molybdenum and tungsten is an important factor,and the sulfate has facilitation and NaCl/NaNO3 has inhibition to the partition of vanadium,molybdenum and tungsten in surfactant-rich phase.The temperature dependence of the distribution coefficient has evident relationship with the nature of surfactants and solutes.The studied results on the stripping performance of vanadium,molybdenum and tungsten loaded in surfactant micellar phases showed that the stripping performance is principally influenced on(NH4)2CO3 concentration,temperature and phase ratio,and the single-stage extracting and stripping rate of vanadium,molybdenum and tungsten can get to above 95%and 90%,respectively.The researched results on the separation performance of vanadium,molybdenum,tungsten and metal cation concomitants,such as Fe(?),Co(?),Ni(?),Cu(?),Zn(?),Mn(?),Al(?)and Cr(?)showed that the effect of aqueous pH on the separation performance is evident,and the effect of the concentration of vanadium,molybdenum and tungsten,and metal cations on the separation performance is not obvious.The separation efficiency is close to that of traditional organic solvent extraction system.The extraction thermodynamic analysis results showed that the relationship between InD and 1/T accords with non linear Van't Hoff equation,indicating that the free energy change,enthalpy change and entropy change are the function of temperature.The analysis results on the driving mechanism indicated that the driving force of solutes transferring in two phases has close relationship with the surfactant structure and solute nature.The theoretical number of stages at selected extraction isotherms are obtained by McCabe-Thiele diagrams and it is found that vanadium,molybdenum and tungsten are completely extracted both in two theoretical stages.By researching the structure of polyacid anions and the effect of charge modifiers on the extracting performance of vanadium,initial and equilibrium pH in aqueous phase,FT-IR,Raman spectrum and dynamic light scattering,the extraction mechanism of vanadium,molybdenum and tungsten in the aqueous two-phase systems can be determined that polyacid anions are extracted into the hydrophilic outer shell of nonionic surfactant micelle depending on the electrostatic interaction between polyacid anions and the quasi cations of protonated C-O-C group and tertiary amine under the conditions of the hydration of phase-forming sulfate.