Kinetic and isotherm studies for adsorption of Pb(II) from aqueous solution onto coconut shell activated carbon

Abstract

Coconut shell (CS) was used as a neglected agricultural waste to produce the activated carbon through chemical activation process with phosphoric acid (activated coconut shell (ACS)). This process is easy and environmental friendly. The activated carbon (ACS) as biosorbent was evaluated for sorption of lead from wastewater using a series of batch adsorption experiments and compared with pyrolysis CS. The characterization results showed that this biosorbent (ACS) has high surface area and functional groups. The efficiency of adsorption process was studied at various parameters: pH, contact time, initial concentration, and competing ions for the removal of Pb(II) ions from aqueous solution. Adsorption equilibrium data were analyzed by the two parameters models (Langmuir, Freundlich, Temkin, and R–D) and the three parameters models (Generalized, Toth, Radke–Prausnitz, and Fritz–Sclunder models). The adsorption equilibrium data was well described by Langmuir and the monolayer adsorption capacities were found to be 49.92 and 26.14 mg/g onto ACS and CS, respectively, which are agreement with those obtained from the three-parameter isotherm models. The experimental kinetic data were best fitted with Bangham’s, Weber–Morris and pseudo-second-order models. The diffusion mechanism was controlled by both boundary layer and pore diffusion for the two adsorbents CS and ACS. It is noteworthy that the effect of Cd(II) and Fe(III) on the adsorption of Pb(II) is very weak, even with high concentration of Cd(II) or Fe(III), which means that the investigated adsorbents have higher affinity for sorption of Pb(II) than that of the other competing ions. The results showed that ACS can be used as a low-cost adsorbent for the removal of Pb(II) ions from aqueous solutions.