Abstract: Removal of cadmium (Ⅱ) ions from dilute aqueous solutions by complexation-ultrafiltration using rotating disk membrane was investigated. Polyacrylic acid sodium (PAAS) was used as complexation agent, as key factors of complexation, pH and the mass ratio of PAAS to Cd²⁺ (P/M) were studied, and the optimum complexation-ultrafiltration conditions were obtained. The effects of rotating speed (n) on the stability of PAA-Cd complex was studied with two kinds of rotating disk, disk I (without vane) and disk Ⅱ (with six rectangular vanes) at a certain range of rotating speed. Both of the rejection could reach 99.7% when n was lower than 2370 r·min^-1 and 1320 r·min^-1, for disk I and disk Ⅱ, respectively. However, when rotating speed exceeds a certain value, the critical rotating speed (n_c), the rejection of Cd (Ⅱ) decreases greatly. The distribution of form of cadmium on the membrane was established by the membrane partition model, and the critical shear rate (γ_c), the smallest shear rate at which the PAA-Cd complex begins to dissociate, was calculated based on the membrane partition model and mass balance. The critical shear rates (γ_c) of PAA-Cd complex were 5.9×10⁴ s^-1, 1.01×10⁵ s^-1, and 1.31×10⁵ s^-1 at pH=5.0, 5.5, and 6.0, respectively. In addition, the regeneration of PAAS was achieved by shear induced dissociation and ultrafiltration.

Key words: Complexation-ultrafiltration, Membrane, Regeneration, Shear stability, Critical shear rate, Shear induced dissociation

摘要： Removal of cadmium (Ⅱ) ions from dilute aqueous solutions by complexation-ultrafiltration using rotating disk membrane was investigated. Polyacrylic acid sodium (PAAS) was used as complexation agent, as key factors of complexation, pH and the mass ratio of PAAS to Cd²⁺ (P/M) were studied, and the optimum complexation-ultrafiltration conditions were obtained. The effects of rotating speed (n) on the stability of PAA-Cd complex was studied with two kinds of rotating disk, disk I (without vane) and disk Ⅱ (with six rectangular vanes) at a certain range of rotating speed. Both of the rejection could reach 99.7% when n was lower than 2370 r·min^-1 and 1320 r·min^-1, for disk I and disk Ⅱ, respectively. However, when rotating speed exceeds a certain value, the critical rotating speed (n_c), the rejection of Cd (Ⅱ) decreases greatly. The distribution of form of cadmium on the membrane was established by the membrane partition model, and the critical shear rate (γ_c), the smallest shear rate at which the PAA-Cd complex begins to dissociate, was calculated based on the membrane partition model and mass balance. The critical shear rates (γ_c) of PAA-Cd complex were 5.9×10⁴ s^-1, 1.01×10⁵ s^-1, and 1.31×10⁵ s^-1 at pH=5.0, 5.5, and 6.0, respectively. In addition, the regeneration of PAAS was achieved by shear induced dissociation and ultrafiltration.

关键词: Complexation-ultrafiltration, Membrane, Regeneration, Shear stability, Critical shear rate, Shear induced dissociation