Biosorptive removal of lead from aqueous solutions onto Taro (Colocasiaesculenta(L.) Schott) as a low cost bioadsorbent: Characterization, equilibria, kinetics and biosorption-mechanism studies

Taro (Colocasiaesculenta(L.) Schott) was studied as a biosorbent to remove lead(II) from water. The biosorbent was characterized with scanning electron microscopy (SEM), energy dispersive X-ray measurements (EDX), Fourier transformation infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) technique. Its structural and morphological characterizations indicate that it has potent adsorptive functional groups, high surface area (20.8 m(2) .g(-1)), flaky stratified structure and huge porosity (pore size: 0.80 nm, pore volume: 0.006 cm(3) g(-1)). Optimum biosorption occurred at pH 5.5-7.00 with a particle size of 0.150 mm and the maximum adsorption capacity of Pb(II) was 291.56 mg .g(-1). The effective biosorption dose was estimated to be 0.9 g .L-1. The ion exchange mechanism is primarily a biosorption process. The biosorption exhibited a high tolerance towards various other ions. The study of Langmuir, Freundlich and Tempkin isotherms implied the involvement of a complex biosorption process. The biosorption followed a pseudo-second-order kinetic model with significantly fast rate and the intra-particle-diffusion-process was the prime rate-controlling factor. For 100 mg Taro, the regeneration was carried out using 5 mL of 0.1 M nitric acid as an eluent and five times regenerated Taro could be efficiently reused. The biosorbent along with developed biosorption procedure was successfully applied to remove Pb(II) from river water.