Biochar aging: Properties, mechanisms, and environmental benefits for adsorption of metolachlor in soil

Abstract

Biochar (BC) will gradually age over time after its application to soil due to the effects of environmental factors, such as long-term oxidation and acid rain. The changes in the physical and chemical properties and structure of BC after aging are not well understood. In this study, soil burial (S), oxidation (O), and acidification (A) methods were used to simulate the aging of walnut shell BC based on comparisons with fresh BC (F-BC). The differences in the physicochemical properties and structure of the BC before and after aging were studied using an elemental analyzer, scanning electron microscopy, and Fourier transform infrared spectroscopy. We found that the hydrophilicity of BC increased after aging whereas the aromaticity decreased. The surface pore structures were severely damaged on O-BC and A-BC compared with F-BC. Many clay particles were attached to the surface of BC. The adsorption performance of S-BC was not significantly lower than that of F-BC. According to the Langmuir model, the Q 0 values for F-BC, S-BC, O-BC, and A-BC were determined as 33.78 mg g − 1 , 32.47 mg g − 1 , 18.62 mg g − 1 , and 19.12 mg g − 1 , respectively. Finally, based on the three types of aging processes, we analyzed the adsorption mechanism for BC after aging in its natural state and evaluated the environmental benefits of BC aging. Our results provide a theoretical basis for practical applications of BC aging in soil. • The adsorptive ability of MET on aged BC were investigated. • The adsorption isotherms of MET on F-BC were compared with S-BC, O-BC and A-BC. • Mechanisms were explained for MET adsorption. • Environmental benefits of BC aging under natural state were evaluated.