State Key Laboratory of Water Resources and Hydropower Engineering Sciences, Wuhan University, Wuhan 430072, China.
State Key Laboratory of Water Resources and Hydropower Engineering Sciences, Wuhan University, Wuhan 430072, China.
Sci Total Environ. 2022 Nov 10;846:157393. doi: 10.1016/j.scitotenv.2022.157393. Epub 2022 Jul 14.
Instead of traditional batch and column experiments with large water-soil ratios, this study investigated the behaviors and mechanisms of Cd adsorption and immobilization by biochar in unsaturated soils, in which the soil moisture conditions were closer to those in the actual field. The transport, transformation, and immobilization of cadmium (Cd) by pristine and KMnO-modified biochars in unsaturated soils were investigated during a 48-week mild aging process. Biochar acidified with HCl solution was employed to quantify the contributions of mineral and non-mineral components in biochar to Cd adsorption and immobilization in unsaturated soils with a three-layer mesh method. The behaviors and mechanisms of Cd adsorption by biochar in unsaturated soils significantly differed from those in aqueous solutions. The equilibrium times of Cd adsorption by biochar in unsaturated soils (weeks) were much longer than those in aqueous solutions (hours). The percentages of the Cd adsorbed by pristine and modified biochar remained relatively constant relative to the total Cd in unsaturated soils, which accounted for 39.50-49.39 % and 57.35-68.94 %, respectively. The contribution of mineral components to Cd adsorption dominated in both unsaturated soils (45.00-94.09 %) and aqueous solutions (70.73-95.51 %). The process of Cd immobilization in unsaturated soils was that biochar firstly adsorbed the exchangeable Cd from the soil, and then converted it to relatively stable Cd. After aging for 48 weeks, the contributions of non-mineral components to Cd immobilization dominated in unsaturated soil with a low concentration (1.23 mg·kg), and the contributions of mineral components to Cd immobilization dominated in unsaturated soil with medium-high concentrations (4.08-51.26 mg·kg).
本研究采用非传统的大水土比批量和柱实验，研究了生物炭在非饱和土壤中对镉吸附和固定的行为和机制，其中土壤水分条件更接近实际田间条件。在 48 周温和老化过程中，研究了原始和 KMnO 改性生物炭在非饱和土壤中迁移、转化和固定镉的行为和机制。采用 HCl 溶液酸化生物炭，采用三层网法量化矿物和非矿物成分在生物炭对非饱和土壤中镉吸附和固定的贡献。生物炭在非饱和土壤中对镉的吸附行为和机制与在水溶液中的明显不同。生物炭在非饱和土壤中对镉的吸附平衡时间（周）远长于在水溶液中的吸附平衡时间（小时）。原始和改性生物炭吸附的镉百分比相对非饱和土壤中总镉保持相对稳定，分别占 39.50-49.39％和 57.35-68.94％。矿物成分对镉吸附的贡献在非饱和土壤（45.00-94.09％）和水溶液（70.73-95.51％）中均占主导地位。镉在非饱和土壤中的固定过程是生物炭首先从土壤中吸附可交换的镉，然后将其转化为相对稳定的镉。老化 48 周后，在低浓度（1.23mg·kg）非饱和土壤中，非矿物成分对镉固定的贡献占主导地位，而在中高浓度（4.08-51.26mg·kg）非饱和土壤中，矿物成分对镉固定的贡献占主导地位。
