Cd Sorption from Aqueous Solutions by Natural Clinoptilolite and Its Modified Forms Clinoptilolite -Na and Clinoptilolite -NH 4

A natural zeolite, clinoptilolite, from a deposit in Sonora, Mexico was used for the removal of Cd ions from aqueous solution with a Cd concentration in the range 1-10,000 ppm. To improve the sorption properties, the natural clinoptilolite was conditioned by means of cation exchange in Na and NH 4 solutions. Natural and the two treated forms of clinoptilolite were used in Cd sorption experiments, and the results were compared to assess the effects of the conditioning processes. The reduction of Cd in the aqueous solution, measured by atomic absorption spectroscopy, and the corresponding increase of Cd loaded in the clinoptilolite powders, as measured by EDS, as a function of cation-exchange time, revealed the Cd sorption properties of the three types of clinoptilolite powders. The results show that natural clinoptilolite has the capacity to remove Cd from the aqueous solutions, and that such capacity improves when it is modified to the clinoptilolite-Na and clinoptilolite-NH 4 forms. Both the percentage of Cd removed from the aqueous solution and the amount of Cd loaded in clinoptilolite are higher for the modified Na and NH 4 forms in the complete range of Cd aqueous solution concentrations analyzed. Among the modified clinoptilolite forms, the NH 4 showed the better Cd sorption properties with higher percentages of Cd removed from the water solutions and higher Cd loaded into the powders after sorption experiments. Based on this work, it is concluded that natural clinoptilolite is a promising mineral for the removal of heavy metals, such as Cd, from contaminated water.