Removal of Dyes in Aqueous Media with Hydrochar Base of Solid Tanneries Waste: Optimization Process and Application

Abstract

The Response Surface Methodology (RSM) was used to optimise the conditions of preparation of activated hydrochar from tannery solid waste by hydrothermal carbonisation (HTC). The main factors such as residence time, moisture content and final carbonisation temperature were investigated during the optimisation of hydrochar preparation conditions. The three responses investigated are hydrochar yield, iodine and methylene blue indices. The results of experimental analyses showed that the yield of hydrochar decreases with increasing final temperature, leading to the formation of micropores inside the carbonaceous solid. The optimum conditions for preparing the following hydrochar were obtained: 83.10%, 390.44 mg∙g−1 and 259.63 mg∙g−1 respectively for the hydrochar yield, the iodine and methylene blue indices. The specific surface area of prepared hydrochar is 849.160 m2/g, SEM micrographs showed a porous heterogeneous surface and particularly, the hydrochar surface also revealed external pores on the hydrochar surface which acted as a pathway to the micropores. Fourier transform infrared (FTIR), however, showed a predominance of acid functions on the surface of the carbonaceous solids. Tests were carried out to eliminate indigo carmine in aqueous media. Activated hydrochar showed a high level of activity, with the Langmuir and Freundlich isotherms giving an adsorption quantity of 354.610 mol/g and a KF constant of 468.2489, respectively. The findings of the research revealed that hydrochar produced is well adapted for dyes removal.