Cr(VI) heavy metal adsorption from aqueous solution by KOH treated hydrochar derived from agricultural wastes

Abstract

Chromium is widely present on earth’s crust. The removal of wastewater from processing industries using chromium has been an emerging and challenging research field these days as it causes several health problems. In this study, hydrochars were generated from eucalyptus sawdust (ESD), corn straw (CS) and corncob (CB) via microwave- assisted hydrothermal carbonization (HTC) of waste biomass. The carbonized material was further treated by different alkali modifications (KOH N 0.01, KOH N 0.05 and KOH N 0.1), targeting the efficient removal of Cr (VI) from aqueous solution. Microwave-assisted hydrothermal carbonization (HTC) temperature was kept at 220 °C. Adsorption parameters such as pH, temperature, hydrochar quantity and reaction time were optimized. Adsorption experiments were carried out for Cr(VI) removal where: pH 2, 25 °C, and 2.5 g/L hydrochar quantity were found as optimum conditions. Adsorption capacity (mg/g) at equilibrium conditions was found as 34.07mg/g, 30.15 mg/g, 29.46 mg/g for ESD, CS and CC, respectively, which were compared with commercial activated carbon as a control. SEM, BET and FTIR analysis were carried out to determine the surface morphology, surface BET area and functional groups of the hydrochars. These results indicated that hydrochars (from waste biomass) modified by KOH treatment have the efficiency to remove Cr(VI). The findings of this study suggested that the hydrochars from waste biomass could be considered as the low cost adsorbents for Cr(VI) removal and this would help in environmental applications for heavy metals removal.