Removing Thallium (I) Ion from Aqueous Solutions Using Modified ZnO Nanopowder

Abstract

In this study, the adsorption of thallium (I) ion as a dangerous pollutant from aqueous solution onto modified ZnO nanopowder as a fairly cheap adsorbent has been examined in batch mode. It was known that modification of the adsorbent was necessary to reach a significant adsorption percentage. The adsorbent used here was modified by sodium phosphate solution. The effect of experimental conditions such as initial pH of solution, contact time, adsorbent dosage, initial concentration of thallium and temperature is studied. The results showed the dependence of the adsorption percentage to these conditions specially its pH. The maximum adsorption percentage of Tl (I) ions at 25±1^oC was 92.8%. Freundlich isotherm model provided a better fit with the experimental data than Langmuir and Temkin isotherm models by high correlation. Separation factor, R_L, values showed that modified ZnO nanopowder was favorable for the adsorption of Tl (I) ion. The negative value of ΔH⁰ showed that Tl (I) sorption is an exothermic process and the negative value of ΔS⁰ represented that there is a little decrease of randomness at the solid-solution interface during sorption.