Adsorption of Cu2+ and Cd2+ from aqueous solution by mercapto-acetic acid modified orange peel. 
The present article describes the adsorption behaviors of Cu2+ and Cd2+ on mercapto-acetic acid modified orange peel.  The prepared adsorbents were characterized using Malvern Zetasizer, infrared spectrophotometer and infrared C-S analyzer.  The effect of various parameters like solution pH, contact time, and initial metal ion concentration on adsorption efficiencies of these two metals were studied systematically by batch experiments.  Adsorption isotherms of Cu2+ and Cd2+ on orange peel and mercapto-acetic acid modified orange peel were obtained and analyzed with Langmuir and Freundlich isotherm models.  The rates of adsorption of Cu2+ and Cd2+ on both adsorbents were found to follow a pseudo-second order equation, indicating their chemical adsorption.  Maximum adsorption capacities of Cu2+ and Cd2+ on the mercapto-acetic acid modified orange peel were found to be 70.67 and 136.05 mg/g, respectively.  Adsorption-desorption studies showed that the mercapto-acetic acid modified orange peel could be used more than five cycles.  This study demonstrated that, the waste orange peel after simple chemical treatment could be used as a potential adsorbent for toxic metals such as Cu2+ and Cd2+.