Abstract:Removal of Co(II) from aqueous solutions by complexation-ultrafiltration was investigated using polyacrylic acid sodium (PAAS) as complexing agent with the help of rotating disk membrane, and the shear ability of PAA-Co complex was studied. The effects of the mass ratio of PAAS to Co(II) (P/M) and pH on the rejection of Co(II) were studied, and the optimum conditions were P/M=8 and pH=7. The rejection of Co(II) was over 97% when the rotating speed of the disk (n) was less than 710 r/min at the optimum P/M and pH. The distribution of the forms of cobalt on the membrane surface was established by the membrane partition model, and the critical shear rate, the smallest shear rate at which the PAA-Co complex begins to dissociate, was calculated to be 1.4×10⁴ s^-1, and the corresponding rotating speed was 710 r/min. The PAA-Co complex dissociated when the shear rate was greater than the critical one. The regeneration of PAAS and recovery of Co(II) were achieved by shear-induced dissociation and ultrafiltration.

Key words: shear stability; critical shear rate; PAA-Co complex; shear-induced dissociation; complexation-ultrafiltration