Influence of pre-treatment methods on the adsorption of cadmium ions by chestnut shell

摘要

In this work the use of chestnut shell as an adsorbent of the cadmium ions present in some industrial wastewaters was studied. Various pre-treatments were performed to increase the sorption capacity of the material and simultaneously avoid the coloration of the water due to soluble polyphenols. The effect of the pre-treatments was evaluated using the pre-treated material to adsorb Cd~(2+) ions under specified conditions. The influence of the pre-treatment agent (water, sodium hydroxide, sulphuric acid, formaldehyde and sodium chloride) and of the operating conditions (temperature and time) on the sorption capacity of the pre-treated material was analysed using the pseudo-second order kinetic model. Equilibrium sorption capacities from 2.50 to 7.11 mg Cd~(2+)/g oven-dried shell were achieved. The optimal results were obtained by pre-treating the shell with a 4% NaOH aqueous solution for 24 h at room temperature. Under these conditions an adsorption percentage of 98.6% was obtained and 80% of the maximum sorption capacity was reached in less than 1 h. X-ray photoelectron spectrometry (XPS) surface measurements were performed to compare the chemical composition of the pre-treated materials. Additionally, FTIR and XPS were used to analyze the functional groups involved in Cd binding.