Hydrothermal carbonization of vegetable-tanned leather shavings (HTC-VTS) for environmental remediation: optimization of process conditions.

Herein, the response surface methodology (RSM) has been used to study simultaneously the effects of carbonization temperature, residence time and moisture content on the activated hydrochar preparation-based vegetable-tanned leather shavings (VTS) using hydrothermal carbonization method (HTC). Owing to the desirability chosen, three responses were analysed, namely: the hydrochar yield, iodine and methylene blue numbers. The analysis of experimental results revealed that the hydrochar yield was decreased with increase in carbonization temperature which led to micropores formation inside the hydrochar network. The optimal preparation conditions retained were: 83.10%, 390.44 mg g-1 and 259.63 mg g-1 for the hydrochar yield, iodine and methylene blue number respectively. The hydrochar micrograph showed the presence of external pores, whereas the FTIR analysis recorded the presence of acidic functional groups found on hydrochar surface. The findings revealed that the VTS is a good precursor for the hydrochar preparation useful in the removal of organic and inorganic pollutants in aqueous media.

Removal of metallic trace elements (Pb2+, Cd2+, Cu2+, and Ni2+) from aqueous solution by adsorption onto cerium oxide modified activated carbon.

The equilibrium and kinetic studies of removal of Pb2+, Cd2+, Ni2+, and Cu2+ metal ions were carried out using activated carbon prepared from palm kernel shell and doped with CeO2 (Ce/AC). The obtained material carbon was characterized by XRD which showed some crystalline traces of CeO2, SEM displaying the porous texture with spherical pores and the determination of pH of point of zero charge (pHPZC) which was found to be equal to 6. The contact time and adsorbate were thoroughly investigated. The maximum adsorption depends inversely on the hydrated metal radius. This observation was confirmed by calculating the formation energies (ΔH(M(OH)2)) of M(OH)2. The metal ionic radii were acting on calculated sorption capacity and that sorption efficiency related to ionic radii of metal was as follows: R(Ni2+) ≤ R(Cd2+) < R(Cu2+) < R(Pb2+). The texture and morphology of the material after sorption were affected by the metallic ion nature as observed by SEM. The kinetic studies showed that the rate constant (k2) of pseudo-second-order model decreased with the increase of the hydrated cations radii, while the rate constant of intraparticle diffusion increased with the increase of the ionic radii. The Freundlich isotherm model best fit the experimental sorption data for all the metallic ions.