| The integration technology of polymelectrolyte-enthanced ultrafiltration wasinvestigated to separate low concentration of chromate by using PQ-6and PQ-22ascomplexing agent. The whole experiment was carried out in the cup type ultrafiltration devicewith polyether sulfone membrane. The ultrafiltration behavior of polyquaternium, PQ6-Cr(VI)and PQ22-Cr(VI) was studied in detail, and further investigated process of the concentration,dicomplexation of the complex and the diafiltration of polyquaternium.1. The effect of operating, such as the concentration of polyquaternium, temperature, pH,pore size of membrane, membrane fouling and concentration on membrane flux (J) andrejection coefficient (R) were investigated. By increasing the concentrations ofpolyquaternium, J was found to decrease slightly and R keep the same. With the pressureadding, J increased with linear relationship and R does not vary. When the temperatureincreased, J increase significantly and R declined slightly. With increasing pH value, Jdecreased mildly and R did not change. While molecular weight cut off membrane go up, theflux of pure water and polyquaternium increased and R reduced gradually. R was not variedwith the aggravation of membrane fouling, but J declined. the concentration experiment ofpolyquaternium, R was not varied with VCF. J decreace firstly with the Volume ConcentrationFactor(VCF) increasing. When VCF reached2, J did not change.2. The mechanism of complexation reaction of polyquaternium with Cr(VI) anion wasstudied by using infrared spectroscopy and ultraviolet spectrum. It is found that quaternaryammonium cationic group can perfectly bind metal anion of Cr(VI). Effects of polyelectrolytemetal ratio (PMR), pH value, operating pressure and temperature on R and J were studied inthe complexation system of PQ6-Cr(VI) and PQ22-Cr(VI) separately. It shows that J did notvary by increasing the PMR, but R increased firstly and then unchanged. With the pH valueincreasing, J declined slightly. When pH higher than10or lower than5, R reducedsignificantly. The flux was increased with the increasing of pressure or temperature, whichshows linear relationship., but R did not vary with pressure and temperature. In the process ofPQ6-Cr(VI) complexation system, the best operation condition is PMR=8and pH=9, while inthe PQ22-Cr(VI) system, The best are PMR=80and pH=9.3. We also researched the effect of extra addition anions(Cl-, NO3-, SO42-) on R and Junder best operation conditions. The result shows that R declined firstly and then keep theconstant when addition of KCl, KNO3or K2SO4in the concentration of PQ6-Cr(VI) andPQ22-Cr(VI) system. The influence degree of SO42-on R is greater than that of NO3-and Cl-.J declined slightly with nitrate ion in the concentration of PQ6-Cr(VI) system, but did notaffect by Cl-and SO42-.4. Ultrafiltration concentration processes of PQ6-Cr(VI) and PQ22-Cr(VI) system were investigated respectively. When the VCF increase from1to20, J decrease gradually and Crincrease quikly with linear relationship. R and Cpdid not vary with the VCF. Cr(VI) wasconcentrated effective. The decomplexation process of PQ6-Cr(VI) and PQ22-Cr(VI) werecarried. The concentrated retentate was used further for the decomplexation. Asdecomplexation time goes on, Crincrease slightly and J keep the constant. Cpfirstly and thenunchanged with the decomplexation time.In the diafiltration process of PQ6-Cr(VI) and PQ22-Cr(VI), when the diafiltration volumereaches250mL, as5times as feed liquid, the washing removal ratio of chromium could be ashigh as90%. Chromium can be extracted effectively. Polyquaternium can be recycled... |
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