To improve the membrane, if CoAlPO4-5 was appropriately added, it could inc
rease the rejection rate of metal ions compared with the PSf membrane. Besi
des, penetration rate would also increase, and the pressure applied could b
e lowered when the improved membrane was used. The optimum amount of CoAlPO
4-5 added for Co : Al : P = 0.1 : 0.92 : 1.0 is about 5 wt %, while for the
Co : Al : P = 0.08 : 0.93 : 1.0, this optimum value would shift toward a h
igher wt % because the latter has less active sites per unit weight of CoAl
PO4-5. The hydrated radius of metal ion had great influence on the rejectio
n rate. The larger the radius, for example, that of the +3 valence cations,
the higher the rejection rate would exhibit, and the rate for Cd2+ was muc
h lower because its radius was the smallest one. Moreover, although incompa
tibility existed in the improved membrane and the variation of applied pres
sure was limited, durability of this membrane under the operating condition
s was good. (C) 2001 John Wiley & Sons, Inc.