Comparison of nickel adsorption from electroplating rinse water by coir pith and modified coir pith

The coir pith was used as an adsorbent for nickel removal because the coir pith contains high lignin (36%) and cellulose (44%). The optimum condition for nickel removal by coir pith in a batch system was solution pH 4–7, adsorbent dosage of 5% (w/v), an equilibrium contact time of 10 min and a temperature of 30 °C. The nickel adsorption was fitted to the Langmuir and Freundlich isotherms that showed that the maximum value of nickel adsorption (qmax) by coir pith and modified coir pith were 9.5 and 38.9 mg g−1, respectively. Sodium hydroxide increased metal binding site (free O−) of modified coir pith. The mechanism of nickel adsorption by the coconut coir pith was confirmed by elution with sulfuric acid, which implied that it was chemisorption. The evidence showed that lignin and holo-cellulose are the main components in coir pith that played a major role in nickel adsorption. The main functional groups in coir pith that were involved in nickel adsorption were hydroxyl and methoxy groups. It was confirmed by X-ray adsorption spectroscopy (XAS) that the oxidation species of nickel involved in nickel adsorption by coir pith and modified coir pith was Ni(II).