In the present investigation,two zeolite-rich turfs from Guaymas and El Cajon (State of Sonora),which were conditioned with a sodium chloride solution and subsequently modified with a thiourea solution,were chosen to evaluate the removal of Cd from aqueous systems.The zeolitic materials were characterized by scanning electron microscopy and X-ray diffraction.The surface area was also determined.The experiments were performed in a batch system,and the influences of pH,contact time between phases,and the concentration of Cd in the solution on the adsorption by sodium or thiourea-modified zeolite-rich tuff were investigated.It was found that the efficiency of Cd ion removal from aqueous solutions is influenced by the pH of the aqueous systems.The Cd adsorption kinetic data were well fitted to a pseudo-second-order model in all cases.The Langmuir and Langmuir-Freundlich isotherms adequately described the Cd sorption behavior by the zeolite from El Cajon pretreated with NaCl and the zeolite from Guaymas modified with thiourea,respectively.