Use of an iron-overexchanged clinoptilolite for the removal of Cu 2+ ions from heavily contaminated drinking water samples

Abstract

Clinoptilolite, a natural zeolite, was used for the synthesis of a high surface area clinoptilolite–iron oxide system, in order to be used for the removal of Cu 2+ ions from drinking water samples. The solid system was obtained by adding natural clinoptilolite in an iron nitrate solution under strongly basic conditions. The Clin–Fe system has specific surface area equal to 151 m 2 g −1 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 copper 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 10 different Cu concentrations (from 3.15 × 10 −5 to 315 × 10 −2 M or from 2.00 to 2000 ppm Cu). For our experimental conditions, the maximum adsorbed Cu amount on Clin was 13.6 mg g −1 whereas on the Clin–Fe system was 37.5 mg g −1. The main factors that contribute to different adsorption capacities of 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. Ca 2+, Mg 2+, Na + and K +) was examined, as well as the dissolution of framework Si and Al. It was found that for the 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.