Removal of Ni (II) and Cr (III) by complexation-ultrafiltration using rotating disk membrane and the selective separation by shear induced dissociation

Removal of Ni (II) and Cr (III) from aqueous solutions by complexation-ultrafiltration and the selective separation by shear induced dissociation were investigated using rotating disk membrane (RDM). Experiments were carried out as a function of pH and mass ratio of PAAS to metal (P/M) for the removal of Ni (II) and Cr (III) by polyacrylate sodium (PAAS) as complexing agent and the results revealed that the optimum conditions were pH 7.0 and P/M 25. Effect of rotating speed (n) on the rejection of complexes of PAAS with nickel (PAA-Ni) and chromium (PAA-Cr) at different pHs were studied and the results proved that both PAA-Ni and PAA-Cr complex would dissociate when n exceeded a certain value. The critical shear rates, at which PAA-Ni or PAA-Cr complex began to dissociate, were calculated at different pH values, and the critical shear rate of PAA-Cr complex was greater than that of PAA-Ni complex at the same pH, which indicated that the stability of PAA-Cr complex was stronger than that of PAA-Ni complex. Furthermore, the influences of operation parameters on selective separation coefficient (beta(Ni/Cr)) were investigated and the results showed that the rotating speed and pH significantly affected beta(Ni/Cr). Finally, shear induced dissociation was used to effectively separate Ni(II) and Cr(III) and regenerate PAAS at 1800 and 2500 rpm, respectively.