Effect of modifiers on Cr (VI) adsorption performance of activated modified-hydrochars

Hexavalent chromium (Cr (VI)) is high toxic and solubility in aquatic systems, which has attracted severe environment issues. In this work, corn straw, as raw biomass material, was modified by citric acid, ZnCl 2 , NaOH, or (NH 4 ) 2 Fe(SO 4 ) 2 via hydrothermal carbonization process, and further activated by KOH to obtain the activated modified-hydrochars. The influence of different modifiers on the Cr (VI) adsorption performance for activated modified-hydrochars was investigated by controlling adsorbent dosages, adsorption time and different Cr (VI) concentrations at pH of 3.0 under room temperature. Among these absorbents, the activated modified-hydrochar modified by ZnCl 2 possessed the excellent microporous characteristics and a high specific surface area of 1532.904 m 2 g -1 , thus exhibiting the Cr (VI) removal rate of 99.6 wt.%. Cr (VI) was reduced to Cr (III) by -OH of activated modified-hydrochars during the Cr (VI) adsorption experiments. Due to higher R 2 (>0.99) by kinetics analysis, pseudo-second-order kinetics was confirmed and further the Cr (VI) removal for the activated modified-hydrochars was a chemical adsorption process. The regression coefficients ( R 2 ) of the Langmuir model for all activated modified-hydrochars were higher than those of Freundlich model, which meant that Langmuir monolayer chemisorption was more consistent with the Cr (VI) adsorption process in this work.