Adsorption Characteristic and Mechanism of Cr⁶⁺ by Shrimp Shell-Derived Biochar

The adsorption properties of Cr⁶⁺ from simulated chrome solution by biochar, which was prepared with shrimp shell, was investigated. The effect of pH, Cr⁶⁺ concentration, biochar dosage and temperature on the adsorption capacity was systematically examined. Furthermore, the biochar and the concentration of the dissolved chromium in the solution were analyzed to elucidate the adsorption mechanism involved in the process. The experimental results indicated that the equilibrium adsorption capacity of the shrimp shell-derived biochar to Cr⁶⁺ was dramatically affected by pH and the dosage of biochar, as well as the initial concentration of Cr⁶⁺.The equilibrated adsorption capacity of Cr⁶⁺ could reach 73.83 mg·g^-1 under the conditions of the biochar dosage of 0.2 g·L^-1, Cr⁶⁺ concentration of 15 mg·L^-1 and pH 3.0. The shrimp shell-derived biochar adsorption process on Cr⁶⁺ could be described by the pseudo-second order kinetics model. While the equilibrium data fitted well with the Langmuir isotherm and Freundlich isotherm.The Langmuir maximum adsorption amounts were detected to be 111.0 mg·g^-1. Cr⁶⁺ adsorbed on the biochar via the electrostatic power and coordination was partially reduced to Cr³⁺.