Studies On Separation Of Palladium (Ⅱ) By Complexation-ultrafiltration Process

Complexation-ultrafiltration process has been investigated for separation of palladium (II)from its low concentration solutions with the help of poly (acrylic acid) sodium salt (PAAS)and polyethyleneimine(PEI) respectively. Ultrafiltration behaviors of PAAS and PEI solutionswere investigated respectively. The effects of various parameters on permeate flux (JPAAS、JPEI) and rejection coefficient (RPAAS、RPEI) were investigated. Results show that, both JPAASand JPEIdecline slightly with increasing time, and increase linearly with increasingtransmembrane pressure, and increase with increasing temperature, and do not change withincreasing pH at pH>5. Both RPAASand RPEIwere stable basically with increasing time, anddecrease with increasing transmembrane pressure or temperature, but increase with pH.The resistance model for membrane fouling was established in the processes ofpolyelectrolyte solutions Ultrafiltration. The effects of various parameters on membraneresistance (rf) were investigated. It is found that, rfincreases with transmembrane pressure,but decreases with temperature. If pH is reduced below5,rfdecreases rapidly with pH. Then,the concentration experiment was carried out. When volume concentration factor reaches16,J declines significantly. PAAS concentration in the retentate (Cr) increases linearly, whereasPAAS concentration in the permeate(Cp)does not change during a long period until theconcentration process is coming to the end. Further, the concentrated PAAS solution waswashed by using the deionized water. With increasing the volume of washing water, Crdecreased insignificantly, while Cpdecreased gradually to zero.The spectrochemical of polyelectrolyte and polyelectrolyte-Pd(II) were established byusing infrared spectroscopy and ultraviolet spectrum respectively, and show that,polyelectrolyte and palladium(II) have a chemical complexing action, which lay thefoundations for intercepting complex by ultrafiltration membrane. The processes ofComplexation-ultrafiltration、 decomplexation equilibrium and infiltration ofpalladium(II)-polyelectrolyte solutions were researched, The effects of various parameters onJ、RPAASand RPEIwere investigated, results show that, In the process of palladium(II)-PAASComplexation-ultrafiltration, The best Complexation conditions are PMMR=1.8and pH=6,but in the process of palladium(II)-PEI Complexation-ultrafiltration, The best Complexationconditions are PMMR=0.13and pH=6.The concentration of polyelectrolyte-Pd(II) solutions were established, results show that,J decline slightly and RPdwas close to1in the best condition of complexation.Thedecomplexation experiment of palladium(II)-polyelectrolyte was established at pH=3andtook about13minutes to get the decomplexation equilibrium. The decomplexation percentageof palladium(II)-PAAS complex reached56.3%. Further, a diafiltration experiment wascarried out by using the decomplexation solution, which corresponded to palladium removalratio of97.1%, and PAAS can be used again. But The decomplexation of palladium(II)-PEI which took19min was difficult, and the decomplexation percentage reached only36.7%,corresponded to palladium removal ratio of80%.The complexing mechanism ofpolyelectrolyte with palladium(II) were investigated by using infrared spectroscopy andultraviolet spectrum respectively，and show that, polyacrylic acid sodium is use the twogroups of-C=O and-OH to complex rare metals ions, while polyethyleneimine is use-NH2tocomplex rare metals ions.