Use of clinoptilolite and an Fe-overexchanged clinoptilolite in Zn2+ and Mn2+ removal from drinking water

Clinoptilolite, a natural zeolite, was used for the synthesis of a high surface area clinoptilolite-iron oxide system (Clin–Fe system) to be used for the removal of Mn2+ and Zn2+ ions from drinking water samples. The new system was obtained by adding natural clinoptilolite to an iron nitrate solution in the presence of KOH solution. The Clin–Fe system had a specific surface area equal to 151 m2/g and was fully iron exchanged (Fe/Al = 1.23). Batch adsorption experiments were carried out to determine the effectiveness of the Clin and of the Clin–Fe system in the removal of zinc and manganese from drinking water. For our experimental conditions, the maximum adsorbed Mn amount for Clin was 7.69 mg/g, whereas that for the Clin–Fe system was 27.1 mg/g. The respective values for the adsorption of Zn were 71.3 mg/g and 94.8 mg/g. In addition, the release of counterbalanced ions (i.e. Ca2+, Mg2+, Na+ and K+) was examined, as well as the dissolution of framework Si and Al. Desorption experiments were also carried out to determine which of the substrates is more effective in holding the adsorbed metals on its surface sites.

By considering the maximum adsorbed Mn/Zn amounts on the Clin–Fe system we conclude that such a mixed system could be used for the purification of contaminated water samples — groundwater as well as wastewaters. Another possible use is as a water softening material, since it can reduce the hardness of the water samples by adsorbing Ca and Mg ions from them. The desorption experiments revealed that the Clin–Fe system can hold most of the adsorbed Mn and Zn ions and release in the aquatic phase significantly small Mn/Zn amounts as compared to the initially adsorbed. On the contrary, Clin can hold Zn2+ ions but the desorption of Mn2+ ions is high and reaches almost 30–50% for the most of the samples. Moreover, the fact that the new system is inexpensive, easily regenerated and harmless for human beings as well as, for the environment, could characterize the Clin–Fe system as a very promising metals adsorbent.