Adsorption of toxic metal ions onto activated carbon: Study of sorption behaviour through characterization and kinetics

This paper presents the physico-chemical characteristics of coconut-based activated carbon of commercial grade (ACC) and the sorption behaviour and kinetics of adsorption of toxic metal ions onto ACC. The proximate and CHN analysis of the ACC showed the presence of ∼41% carbon, ∼16% hydrogen and ∼2% nitrogen in ACC. Bulk density and heating value of ACC were found to be 599.32 kg/m3 and 18.81 MJ/kg, respectively. The BET surface area was 171.05 m2/g whereas the BET average pore diameter was 31.03 Å. The meso-porous surface area was found to be 76% and the micro-porous surface area was 24% of the total pore surface area. The polar groups present on the ACC surface impart considerable cation exchange capacity to it. ACC worked as a very good adsorbent at an optimum initial pH (pH0) of 6.0 and at a dose of 20 g/dm3 for the adsorption of cadmium (Cd(II)), nickel (Ni(II)) and zinc (Zn(II)) metal ions at a concentration of 100 mg/dm3. The adsorption of metal ions onto ACC was found to be a gradual process and the quasi-equilibrium condition reached in 5 h. The adsorption followed pseudo-second-order kinetics. The effective diffusion coefficient was of the order of 10−12 m2/s.