Equilibrium and kinetic studies on Ni(II) removal from aqueous solution by Citrus Limettioides peel and its carbon adsorbent

Activated carbon has been prepared from Citrus limettioides peel (CLPC); a novel waste material by chemical modification with sulphuric acid followed by bicarbonate treatment applied for the adsorption of Ni(II) from aqueous solutions. Batch experiments have been carried out to study the effect of various parameters such as contact time, pH and adsorbent dosage on various Ni(II) concentrations along with, raw Citrus limettioides peel (CLP). The optimum pH required for the maximum adsorption of Ni(II) is found to be 4.0-9.0 and 5.0-8.0 for CLPC and CLP, respectively. The optimum contact time is found to be 4 hr in all cases of carbon and raw peel. The presence of hydroxyl and carboxylic acid groups are confirmed by FT-IR spectra. Equilibrium data agreed well with Langmuir model. Based on Langmuir isotherm the adsorption capacity is found to be 38.46 mg g for CLPC and 25.64 mg g for CLP at 300K. The kinetic data follow pseudo-second order model with film diffusion process. Similar studies have also been carried out using commercial available activated carbon (CAC) for evaluation purposes. The adsorption capacity of CAC is found to be 11.36 mg g. Hence the adsorption capacity (Qo) of CLPC and CLP is found to be 3.4 and 2.3 times greater than that of CAC. These adsorbents are also tested for the removal of Ni(II) from electroplating wastewater and found to remove 85% and 99% for CLP and CLPC respectively whereas the CAC show 75% removal only with an initial concentration of 220 mg/100 mL. The overall results indicate that carbon derived from Citrus limettioides peel (CLPC) could effectively be used to remove 99% of Ni(II) from water and wastewater.