Study On Treatment Of Rhenium (Ⅶ) In Aqueous Solutions With Polyquaternium-enhanced Ultrafiltration

Polyquaternium-enhanced ultrafiltration process was investigated for thetreatment of rhenium（Ⅶ） from aqueous solutions. This process included the additionof polyquaternium-6（PQ6） and polyquaternium-7（PQ7） as a water soluble polymerto bind rhenium（Ⅶ）, which was followed by an ultrafiltration operation withpolysulfone hollow fiber. Based on theoretical research of PQ6and PQ7to bindrhenium（Ⅶ）, the total recirculation polyquaternium-enhanced ultrafiltration processhas been studied systematically. The integration of four experiments includingconcentration, decomplexation, diafiltration and reuse of regenerated polyquaterniumwas carried out.1. Effects of pH value, temperature and operating time on PQ6and PQ7membrane flux （J） and rejection coefficient （R） were studied. When pH valueincreased from3to9, both of PQ6and PQ7J and R did not vary with pH value. Withincreasing the temperature, both of them J were increased linearly and R did notchange. With increasing the operating time, both of them J were decreased slightly,and R did not always vary. Further, the concentration、the diafiltration and set upconcentration model were carried out at pH=7. When volume concentration factorreached20, PQ6and PQ7J were decreased, R were close to1. In diafiltration PQ6and PQ7J were increased slightly and the loss ratio are12.7%、47.2%, R wereincreased gradually with increasing the diafiltration volume and then reached1.Thediscontinuous closed-loop experiments have been set up to study the influence ofpolymer concentration and operation time on design parameters. Next, the presence ofconcentration-polarization and fouling has been firstly studied and subsequentlyquantified by means of a resistance in series model. Moreover, a design equation thatrelates permeate flux to feed concentration has been obtained. Finally, theconcentration evolution in recirculation loop has been successfully modelled.2. Effects of polyelectrolyte/metal mass ratio （PMMR）, pH value,temperature,operating time, Cl^-and SO42-on PQ6-Re（Ⅶ） and PQ7-Re（Ⅶ） R、J werestudied. It was found that, RPQ6-Re（Ⅶ）and RPQ7-Re（Ⅶ）increased significantly，wereclose to1, JPQ6-Re（Ⅶ）and JPQ7-Re（Ⅶ）decreased slightly with increasing PMMR. WhenpH value increased from3to9, RPQ6-Re（Ⅶ）、RPQ7-Re（Ⅶ）、JPQ6-Re（Ⅶ）and JPQ7-Re（Ⅶ）didnot vary with pH value. With increasing the temperature, RPQ6-Re（Ⅶ）and RPQ7-Re（Ⅶ） did not change, JPQ6-Re（Ⅶ）and JPQ7-Re（Ⅶ）increased linearly. With increasing theoperating time, RPQ6-Re（Ⅶ）and RPQ7-Re（Ⅶ）did not always vary, JPQ6-Re（Ⅶ）andJPQ7-Re（Ⅶ）decreased slightly. With increasing the concentration of Cl^-and SO42-,RPQ6-Re（Ⅶ）and RPQ7-Re（Ⅶ）decreased gradually, then did not change. JPQ6-Re（Ⅶ）andJPQ7-Re（Ⅶ）declined slightly with the Cl^-and SO42-concentration.3. The integration of four experiments including concentration, decomplexation,diafiltration and reuse of regenerated polyquaternium was carried out at pH7. Resultsshowed that PQ6-Re（Ⅶ） concentrations in the penetrant (C_{p,PQ6-Re（Ⅶ）}) andPQ7-Re（Ⅶ） concentrations in the penetrant (C_{p,PQ7-Re（Ⅶ）}) did not change withvolume concentration factor （VCF）, about0.04mg/L and0.1mg/L, respectively.PQ6-Re（Ⅶ） concentrations in the retentate (Cr_{p,PQ6-Re（Ⅶ）}) and PQ7-Re（Ⅶ）concentrations in the retentate (C_{r,PQ7-Re（Ⅶ）}) increased linearly with VCF in theprocess of concentration. When VCF reached40in PQ6-Re（Ⅶ）, Cr_{p,PQ6-Re（Ⅶ）}increased from5mg/L to198.3mg/L. When VCF reached20in PQ7-Re（Ⅶ）,C_{r,PQ7-Re（Ⅶ）}increased from10mg/L to188.1mg/L. RPQ6-Re（Ⅶ）and RPQ7-Re（Ⅶ）areabout1. JPQ6-Re（Ⅶ）and JPQ7-Re（Ⅶ）declined slowly, the loss ratio was about20.1%and24.2%, respectively.The concentrated retentate was used further for the decomplexation. It tookabout10min to reach the decomplexation equilibrium at sulfate ion concentration of100mg/L Na₂SO₄in PQ6-Re（Ⅶ）.The decomplexation percentage reached45.6%. Ittook about30min to reach the decomplexation equilibrium at sulfate ionconcentration of500mg/L Na₂SO₄in PQ7-Re（Ⅶ）. The decomplexation percentagereached53.3%. JPQ6-Re（Ⅶ）and JPQ7-Re（Ⅶ）nearly did not vary.In the diafiltration process, using100mg/L Na₂SO₄in PQ6-Re（Ⅶ）, when thediafiltration volume reaches1L, rhenium（Ⅶ） can be extracted effectively, thewashing removal ratio （WR） of rhenium could be as high as97.5%. Using500mg/LNa₂SO₄in PQ7-Re（Ⅶ）, when the diafiltration volume reaches4L, rhenium（Ⅶ） canbe extracted effectively, the washing removal ratio （WR） of rhenium could be as highas94.7%. JPQ6-Re（Ⅶ）and JPQ7-Re（Ⅶ）nearly did not vary. The regenerated PQ6、PQ7were used to bind rhenium（Ⅶ） at fixed pH values, the binding capacity of theregenerated PQ6、 PQ7are close to that of fresh PQ6、 PQ7, and the recoverypercentage of binding capacity for rhenium（Ⅶ） were as high as92.1%and83.3%,respectively.