Removal of Zinc(II) Ions from Wastewater Using Natural Zeolites

Abstract

The kinetics of the adsorption of zinc(II) ions by natural zeolites was studied using pseudo-first and pseudo-second-order kinetic models. The objects of study were zeolites mined in East Transbaikalia. The X-ray phase analysis and IR spectroscopy data confirmed that natural zeolite-containing rock samples have the following composition: calcium heulandite Ca[Al2Si7O18]⋅6H2O and impurity rocks, namely, sanidine KAlSi3O8 and cristobalite SiO2. The dependence of the adsorption value on zeolite grain size was studied. It was shown that the adsorption value increases 3.8 times and reaches 0.075 mol/g as the grain size decreases from 5 to 0.1 mm. The kinetic study of zinc(II) ions adsorption was performed at pH 5.0–5.4 in the temperature range of 298–318 K. In a zeolite–zinc sulfate aqueous solution system, the adsorption equilibrium time was 120 min. It was shown that the zinc(II) ions adsorption rate decreases under the temperature increase. It was established that the kinetics of zinc(II) ions adsorption is best described by a pseudo-second-order model, the correlation coefficient values varying in the range of 0.998–0.999. The highest adsorption rate constant value of 0.446 g/(mmol⋅mm) corresponds to the temperature of 298 K. It was shown that zeolites demonstrate the highest adsorption value towards heavy metal ions at the temperature of wastewater. The proof-of-principle studies were performed to establish the feasibility of the recovery of copper(II), nickel(II), and zinc(II) ions from wastewater produced by galvanic manufacture using the studied minerals. The treatment process was performed under the conditions determined as optimal for model solutions. The efficiency of heavy metal ions removal was 85–89%.