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 Cd

2+

(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 5.9×10

4

s

-1

1.01×10

5

s

-1

and 1.31×10

5

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.