Enhanced aqueous Cr(VI) removal using chitosan-modified magnetic biochars derived from bamboo residues

The purpose of this study was to fabricate a chitosan modified magnetic bamboo biochar (CMBB) for Cr(VI) detoxification from aqueous solution. Results showed that chitosan modification provided more active adsorption sites on the surface of magnetic bamboo biochar (MBB), and hence enhanced Cr(VI) removal from aqueous solution. The maximum adsorption capacities of MBB and CMBB for Cr(VI) at 25 °C were 75.8 and 127 mg g^-1, respectively. Increasing solution pH inbibited Cr(VI) adsorption by adsorbents. However, CMBB maintained a high Cr(VI) removal efficiencies over a broader pH range (2-10), and could attain 36% of the maximum adsorption (40 mg g^-1) even at a high pH of 10.0. Rising temperature enhanced the Cr(VI) removal by two adsorbents. The escalating ionic strength and coexist substances, including Na⁺, Ca²⁺, Fe³⁺, Cl^-, SO₄^2-, PO₄^3- and humate, inhibited the adsorption efficiency of Cr(VI) on adsorbents. After the fifth adsorption-desorption cycle, the adsorption efficiencies of CMBB and MBB for Cr(VI) remained above 90% and less than 50%, respectively. All these results indicated that CMBB could be a practical adsorbent that can be utilized for the detoxification of Cr(VI) ions from wastewater.