Sorption behavior of metal(III) phosphates toward Zn2+ was investigated usi
ng different concentrations, pHs, and temperatures. Ion exchange between pr
otons from the surface and metal cations from solutions was found to be res
ponsible for metal sorption by metal(III) phosphates. Dissociation constant
s of metal(III) phosphates and binding constants of the Zn2+ with metal(III
) phosphates were determined using Henderson-Hasselbach and modified Langmu
ir equations, respectively. The sorption process in all the three metal pho
sphates was found tc, be endothermic in nature while the dissociation proce
ss was observed to be endothermic in AlPO4 and FePO4 and exothermic in CrPO
4. (C) 1999 Academic Press.