Sulfur-Modified Biochar Efficiently Removes Cr(VI) from Water by Sorption and Reduction

Sulfur-modified biochar was prepared and used to efficiently remove Chromium (Cr) from water. It was found that the sulfur-modified biochar prepared from lower primary pyrolysis temperature (<400°C), higher secondary pyrolysis temperature (>400°C), appropriate secondary pyrolysis time, and S/C ratio was favorable for Cr removal. According to the response surface methodology analysis, the biochar prepared under the primary pyrolysis temperature of 350°C, secondary pyrolysis temperature of 450°C, secondary pyrolysis time of 60 min, and S/C ratio of 2:1 could achieve the maximum Cr removal (92%). The S-modified biochar prepared under the optimum condition exhibited greater capacity of adsorbing Cr(VI) or reducing Cr(VI) into Cr(III) compared with the biochar without the S modification. The enhanced Cr(VI) adsorption and reduction were likely because some of the sulfur-containing groups formed on the modified biochar could bind and interact with the Cr(VI). Besides, the enhanced surface area by the sulfur modification also played a role in prompting the removal and reduction of Cr(VI).