A comparative study on textural characterization:cation-exchange and sorption properties of crystalline alpha-zirconium (IV),tin (IV),and titanium (IV) phosphates

摘要

Tetravalent metal phosphates (M=Zr,Ti,and Sn) were prepareda nd characterized by XRD,surface properties,and TG-DTA.The cation exchange and sorption behavior of these metal phosphates toward transition metal ions such as Cu~(2+),Co~(2+),and Ni~(2+) have been studied comparatively as a function of temperature and concentration.The adsorpiton process was foudn to increases with increase in temperature and concentration.The selectivity order for alpha-titanium and alpha-tin phosphates is Cu~(2+)>Co~(2+)>Ni~(2+),whereas for alpha-zirconium phosphate it is Cu~(2+)>Ni~(2+)>Co~(2+).The ion exchange capacity of alpha-titanium phosphate is greater than those of other phosphates,which is explained on the basis of the surface behavior,disorderness of the system,degree of hydrolysis of incoming guest adsorbate metal ions,and structural steric hindrance of the exchangers during adsorption and sorption.The distribution coefficient,Gibbs free energy,enthalpy and entropy values indicate that the ion-exchange processes are spontaneous.