Sorption behavior of metal(III) phosphates toward Zn2+ was investigated using different concentrations, pHs, and temperatures. Ion exchange between protons from the surface and metal cations from solutions was found to be responsible for metal sorption by metal(III) phosphates. Dissociation constants of metal(III) phosphates and binding constants of the Zn2+ with metal(III) phosphates were determined using Henderson-Hasselbach and modified Langmuir equations, respectively. The sorption process in all the three metal phosphates was found tc, be endothermic in nature while the dissociation process was observed to be endothermic in AlPO4 and FePO4 and exothermic in CrPO4.