Study On Treatment Of Molybdenum(VI) And Tungsten(VI) In Aqueous Solutions With Polymer-enhanced Ultrafiltration

Polymer-enhanced ultrafiltration process was investigated for the treatment ofmolybdenum （VI） and tungsten （VI） from aqueous solutions. This process included theaddition of polyquaternium-6（PQ6） as a water soluble polymer to bind selectivelymolybdenum （VI） and tungsten （VI）, which was followed by an ultrafiltration operation withpolysulfone hollow fiber. Based on theoretical research of PQ6to bind molybdenum （VI） andtungsten （VI）, the total recirculation polymer-enhanced ultrafiltration process has beenstudied systematically. The integration of four experiments including concentration,decomplexation, diafiltration and reuse of regenerated polymer was carried out. At last,selective separation of molybdenum （VI） and tungsten （VI） has been also discussed.1. The complexation models of PQ6binding molybdenum （VI） and tungsten （VI） wereestablished for mechanism research. The Freundlich model was found to be the best fit for theexperimental data. Determination of the binding capacity of PQ6with molybdenum （VI） andtungsten （VI） was studied at different operating parameters. Effects of various operatingparameters such as transmembrane pressure, polymer/metal mass ratio（PMMR）, pH,operating time and the added chloride ion and sulfate ion concentration on molybdenum （VI）rejection coefficient (R_Mo) and tungsten （VI） rejection coefficient （R_W） were investigated. Theresults showed that transmembrane pressure had no effect on R_Moand R_Win the pH range3-9.The best PMMR for molybdenum （VI） and tungsten （VI） were7and3, while the bindingcapacity of PQ6were7mg PQ6/mg molybdenum （VI） and3mg PQ6/mg tungsten（VI）,respectively. With the operating time adding, R_Moand R_Wincreased rapidly, the equilibrationtime for the complexation-ultrafiltration process was20min. When chloride ion and sulfateion concentration increased, R_Moand R_Wdecreased rapidly at different pH.2. Effects of different operating parameters such as transmembrane pressure,polymer/metal mass ratio（PMMR）, pH, operating time and the added chloride ion and sulfateion concentration on molybdenum （VI） permeate flux (J_Mo) and tungsten （VI） permeate flux（J_W） were studied. It was found that, J_Moand J_Wincreased quickly with transmembranepressure increasing from15kPa to75kPa. J_Moand J_Wobtained in the pH range3-9and werealmost equal. J_Moand J_Wdecreased slightly with increasing PMMR and prolongation of theoperating time. When chloride ion and sulfate ion concentration increased, J_Moand J_Wdid notvary at different pH.3. The integration of four experiments including concentration, decomplexation, diafiltration and reuse of regenerated polymer was carried out at pH7. Results showed thatR_Mo, R_W, molybdenum （VI） concentrations in the penetrant （C_p,M_o） and tungsten （VI）concentrations in the penetrant （Cp,W） did not change with volume concentration factor （VCF）.RMoand RWis about1,C_p,M_oand Cp,Wwere always about0.04mg/L. Molybdenum （VI）concentrations in the retentate （C_r,M_o） and tungsten （VI） concentrations in the retentate （C_r,W）increased linearly with VCF in the process of concentration. When VCF reached16, C_r,M_oandC_r,Wincreased from both0.04mg/L to317.5mg/L and316.5mg/L, respectively. JMoand JWdeclined slowly, the loss ratio was about15%. The concentrated retentate was used further forthe decomplexation. It took about6min to reach the decomplexation equilibrium at chlorideion concentration of50mg/L. The decomplexation percentage of molybdenum （VI）-PQ6complex and tungsten （VI）-PQ6complex reached55.7%and56.1%, respectively. In thediafiltration process, molybdenum （VI） and tungsten （VI） can be extracted effectively byusing50mg/L chloride ion solution, and when the diafiltration volume reaches7L,molybdenum （VI） and tungsten （VI） can be extracted effectively. JMoand JWnearly did notvary. The regenerated PQ6was used to bind molybdenum （VI） and tungsten （VI） at variouspH values, the binding capacity of the regenerated PQ6is close to that of fresh PQ6, and therecovery percentage of binding capacity for molybdenum （VI） and tungsten （VI） were as highas92.1%and93.8%, respectively.4. Effects of operational parameters on selective separation coefficients（S） formolybdenum （VI） and tungsten （VI） were investigated. The concentration process of themixture metal ion system was also curried out. It was found that S did not change with pH,and increased with PMMR adding clearly. In the concentration process, the two kinds ofmetal ions can be separated to some extent. While VCF increasing, permeate flux of themixture metal ion system declined slowly, RWwas close to1but RMowas very low.