Effects of biochar underwent different aging processes on soil properties and Cd passivation.

This study aims to determine the efficacy of biochar underwent different aging process including freeze-thaw cycling aging (FB), acidified aging (AB), and microbial aging (MB) on soil physicochemical properties and Cd passivation. The Cd-contaminated soil (3 mg·kg-1) amended with the three kinds of aging biochar (at 4% w:w) were subjected to 56-day incubation. The application of FB and MB in soil increased the soil pH (0.82-1.04, 0.27-9.36), CEC (1.06-2.53 cmol·kg-1, 1.66-2.59 cmol·kg-1), and organic matter content (2.28-4.67 g·kg-1, 3.70-5.48 g·kg-1). FB performed best in stabilizing Cd (17.06-23.65%). On the contrary, AB decreased the soil pH and CEC by 0.82-1.04 and 1.32-2.40 cmol·kg-1 and activated Cd by 11.6-19.24%. In conclusion, the efficacy of biochar on soil remediation and Cd passivation varied with aging method and cycle, and freeze-thaw treatment is an effective approach to improve the performance of biochar.

Comparison of adsorption behavior studies of Cd2+ by vermicompost biochar and KMnO4-modified vermicompost biochar.

Cd2+ pollution in aquatic environments can pose a serious threat to human health. Biochar can remove Cd2+ from aquatic environments, but the Cd2+adsorption capacity of conventional biochar is low, therefore, we focused on exploring the Cd2+ adsorption capacity of modified biochar. In this study, KMnO4 was used to modify vermicompost biochar (VBC), and static adsorption tests for Cd2+ were carried out. The biochar properties and its adsorption efficiency toward Cd2+ before and after modification were studied by kinetics and isotherm model fitting, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Additionally, an adsorption mechanism was discussed. The results showed that the KMnO4-modification resulted in a successful loading of the vermicompost biochar with MnO2, which greatly improved its adsorption capacity for Cd2+. The adsorption of Cd2+ by VBC and MVBC was a spontaneous, endothermic, and monolayer chemical adsorption process. Mineral precipitation mechanism accounted for the largest proportion, and CdCO3 was the main precipitate. After modification the proportion of surface precipitation and other mechanisms (π-electron coordination and the inner/outer sphere surface coordination) increased，while adsorption via cation exchange, oxygen-containing functional groups, physical adsorption and electrostatic attraction reduced. Hence, KMnO4 modification has a significant effect on the Cd2+ adsorption behavior of vermicompost biochar.

Soil aggregates stability and storage of soil organic carbon respond to cropping systems on Black Soils of Northeast China.

Monoculture and improper management may reduce soil fertility and deteriorate soil structure in Black soils (Mollisols) of Northeast China. The experiment was carried out from 2015 to 2016 in Black Soils comprising five cropping systems: continuous corn (CC), soybean-corn rotation (SC), corn-soybean rotation (CS), fallow-corn (FC), and fallow-soybean (FS). Our results showed that CS and FS treatments significantly increased mean weight diameter (MWD) and fractal dimension (D) in mechanical stability aggregates (MSAs), and increased MWD and geometric mean diameter (GMD) in water-stable aggregates (WSAs) compared with CC treatment. These two treatments were also significantly increased water-stable aggregates stability rate (WSAR), but decreased percentage of aggregates destruction (PAD) than CC treatment. Meanwhile, CS and FS treatments exhibited a higher carbon accumulation than CC treatment in bulk soils. Soil organic carbon (SOC) concentration in WSA0.106-0.25,WSA2-5 mm and WSA0.5-1 mm had a dominant effect on aggregate stability. Simutaneously, SOC in WSA>5 mm affected SOC concentration in bulk soils. As a whole, the CS and FS treatments can increase the percentage of macro-aggregates, enhance aggregate stability, as well as increase SOC concentration in bulk soils and all soil aggregate sizes.