The ion exchange and sorption properties of crystalline Tin bis(monohydrogen orthophosphate) monohydrate of composition Sn(HPO4)(2). H2O were studied in an aqueous solution of KCI over the temperature range 300-320 K, varying the pH and metal ion concentration in the solution. The data were explained on the basis of the law of chemical equilibrium. The metal ion sorption data were fitted to the Langmuir adsorption equation to evaluate the Langmuir parameters. The extent of adsorption was found to increase with an increase in temperature and metal ion concentration in the selectivity order Cu2+ > Co2+ > Ni2+. The Langmuir parameters were used to calculate the thermodynamic functions like standard entropy, enthalpy, and free energy changes during the process Of sorption,