Uptake of Zn2+ ions by a fully iron-exchanged clinoptilolite. Case study of heavily contaminated drinking water samples

Clinoptilolite, a natural zeolite, was used for the synthesis of a high surface area clinoptilolite (Clin)–iron (Fe) oxide system, in order to be used for the removal of Zn2+ ions from drinking water samples. The new system was obtained by adding natural Clin in an iron nitrate solution under strongly basic conditions. The Clin-Fe system has specific surface area equal to 151 m2/g and is fully iron exchanged (Fe/Al=1.23). Batch adsorption experiments were carried out to determine the effectiveness of the Clin and the Clin–Fe system in removal of Zn from drinking water. Adsorption experiments were conducted by mixing 1.00 g of each of the substrates with certain volume of water samples contaminated with ten different Zn concentrations (from 7.65×10−5 to 3.82×10−2 M or from 5.00 to 2500 ppm Zn). For our experimental conditions, the maximum adsorbed Zn amount by Clin was 71.3 mg/g, whereas by the Clin–Fe system 94.8 mg/g. The main factors that contribute to different adsorbed Zn amounts by the two solids are due to new surface species and negative charge of the Clin–Fe system. 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. It was found that for most of the samples the Clin–Fe system releases lower concentrations of Ca, Mg and Na and higher concentrations of K than Clin, while the dissolution of Si/Al was limited. Changes in the composition of water samples, as well as in their pH and conductivities values were reported and explained.