Evaluations of pH and High Ionic Strength Solution Effect in Cadmium Removal by Zinc Oxide Nanoparticles

For human and environmental health protection, it is necessary to remove excess cadmium in industrial wastewaters before discharging them to environment. Some laboratory experimental batch study was done to evaluate the effects of the initial cadmium concentration, adsorbent dose, pH, ionic strength, and contact time on the cadmium removal efficiency by zinc oxide nanoparticles. All tests were performed in 100 ml solution at constant temperature of 25°C and mixing rate of 150 rpm. The residual cadmium concentration in the solution was determined using flame atomic absorption spectroscopy. Statistical analyses were performed on data using SPSS16 software by applying Mann-Whitney and Kruskal-Wallis tests and the result designing graphs were provided using Excel software. Finally, experimental data were analyzed using adsorption isotherm and kinetic equations. The results show that cadmium removal efficiency increases with an increase in the adsorbent dose and contact time and decreases with the increase in initial concentration of cadmium. Furthermore, it is observed that by raising the ionic strength of solution 30 fold, the adsorption rate is increased from 90.7% to 62.3%. Due to regression coefficient (≥0.99), the adsorption process follows Langmuir isotherms model and pseudo-second order equation. Attending to the outcomes, zinc oxide nanoparticles have proper efficiency in the removal of cadmium from aqueous solutions. So, they can be used in treatment of the wastewaters containing cadmium ions. However, its efficiency is deeply dependant on the ion strength and the interactions of other metals in wastewater.