Mesopore-rich badam-shell biochar for efficient adsorption of Cr(VI) from aqueous solution

Cr(VI) is a common pollutant in wastewater and many previous studies using biochar-based materials as adsorbents for their well adsorption performance. However, the preparations of some biochars are complex, uneconomical, and with a poor reusability, which set limit on their practical application. Here, a mesoporous-rich biochar-based Cr(VI) adsorbent was easily prepared by pyrolyzing the badam-shell that in situ activated by concentrated phosphoric acid (H3PO4), with the aim of improving the removal effect of Cr(VI) in an aqueous solution. The partition coefficient (PC) was used to compare the performance of adsorbents more comprehensively, and the maximal PC value of the activated badam-shell biochar (ABSB) was 978.8 L g(-1). In addition, its maximum adsorption capacity was 276.6 mg g(-1). ABSB has a superior removal effect on the relatively low concentration of Cr(VI) (<= 50 mg L-1), and residual Cr(VI) can meet the maximum emission standard (< 0.5 mg L-1) of industrial wastewater. The specific surface area of ABSB (1359.5 m(2) g(-1)) was approximately four times that of pristine badam-shell biochar (BSB) (371.87 m(2) g(-1)). The adsorption mechanisms involved were redox, complexation, electrostatic attraction and hydrogen bonding. The removal rate of Cr(VI) on ABSB remained at 81.6% after six cycles of adsorption-desorption. In a word, our study provides a simple, economic, and environmental method in fabricating the new adsorbent, which is highly promising and will not cause secondary pollution.