Thermodynamic Properties of Chromium (III) Ion Adsorption by Sweet Orange (<i>Citrus sinensis</i>) Peels

Abstract

The adsorption of Cr (III) ion from aqueous solution using orange peels as adsorbent was investigated using batch equilibrium technique. The research is significant as it’s aimed at investigating the suitability of orange peel, a waste product as adsorbent for the adsorption of Cr (III) ions from aqueous solution. Orange peel as an adsorbent is resource-saving and has an environmental friendly behavior. Adsorption envelope experiment was conducted using a constant Cr (III) ion concentration of 0.1 M, adsorbent dose of 2.5 g and a temperature of 30°C at varying solution pH of 2, 4, 7, 9 and 12 respectively with pH of 2 having the highest adsorption and therefore it was selected for use in the adsorption isotherm experiment. Adsorption isotherm experiment was conducted at varying temperatures (30°C, 40°C, 50°C, 60°C), concentration (0.1 M, 0.2 M and 0.3 M) Cr(NO 3 ) 3 . Thermodynamic parameters such as ΔG, ΔH, ΔHr, ΔA, and ΔS were calculated from the experimental data which showed that the adsorption process is feasible, spontaneous and followed physisorption mechanism 9H2O and adsorbent dosage (1 g, 1.5 g and 2 g) respectively. The experimental results were tested using Langmuir, Freundlich, Linear and Temkin adsorption isotherm models. The experimental data best fitted the Freundlich isotherm model. The experimental results revealed the suitability of orange peel which is a waste product as effective adsorbent for the sorption of chromium (III) ions from aqueous solution.