[Characteristics of Biochars and Their Adsorption Performance and Mechanisms for Cr(Ⅵ)].

This study aims to understand the recycling process of by using the slow pyrolysis technology to prepare biochars under different temperatures and by characterizing the physicochemical properties of biochars. The results showed that a relatively high level pyrolysis of could be reached when the temperature was up to 400℃. The yield rate and the ash content of biochars were negatively correlated with the pyrolysis temperature, while the carbon content was positively correlated. The specific surface area of biochars was in the range of 44.54-317.82 m·g. The biochar surface was in the shape of a honeycomb and rich in oxygen-containing functional groups, such as hydroxyl (-OH) and carboxyl (-COOH) groups. The adsorption experiments revealed that the adsorption of Cr(Ⅵ) onto biochars followed the pseudo-second-order kinetics equation and Langmuir isotherm, indicating that the adsorption process was controlled by the fast reaction process and governed by monomolecular and chemical adsorption. The optimal pH for Cr(Ⅵ) adsorption onto biochars was 2 and their adsorption capabilities were in the order of BC400 > BC700 > BC600 > BC500 > BC300 (the adsorption capacity of BC400 was 4.79 mg·g). The adsorption mechanism included the electrostatic interactions between biochar and anions (HCrO and CrO) and the complexation of oxygen-containing functional groups.