School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai 200093, China.
School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
J Hazard Mater. 2021 Jun 15;412:125213. doi: 10.1016/j.jhazmat.2021.125213. Epub 2021 Jan 23.
Biochar has two existing forms in the moist soil environment, free dissolvable biochar (particle size < 0.45 μm) and undissolvable particles (particle size > 0.45 μm). The release and decomposition of dissolvable biochar from bulk biochar particles is a primary C loss pathway in biochar-amended soils, which would be reduced by their interactions with soil minerals. Most previous studies focused on the effect of feedstock types and pyrolysis conditions on dissolvable biochar stability, while few studies researched the interaction between dissolvable biochar and soil components, for instance the soil minerals, and its effect on the stability of dissolvable biochar. In this study, bentonite and goethite were selected as model soil minerals because of their differences in structure and surface types: negatively charged 2:1 type phyllosilicate (bentonite) and positively charged crystalline mineral (goethite). Dry-wet cycling was conducted to determine the effect of these two minerals on the release of dissolvable biochar from walnut shell-derived biochar particles. The stability of dissolvable biochar was measured by chemical oxidation and biodegradation. Both soil minerals reduced the release of dissolvable biochar by over 34% with the presence of Ca. Mechanisms of "Ca bridging", "ligand exchange" and "van der Waals attraction" contributed to the formation of dissolvable biochar-bentonite complexes, and Ca promoted dissolvable biochar inserting into bentonite interlayer space, expanding d-spacing from 1.25 nm to 1.55 nm. However, "Ca bridging" barely formed on goethite because of charge repulsion, indicating that the dissolvable biochar was bound with goethite mainly by "van der Waals attraction" and "ligand exchange". Due to organo-mineral complexes formation, the chemical oxidation extent of dissolvable biochar was reduced by 22.8-36.5%, and the biodegradation extent was reduced by 72.7-85.0%, since the soil minerals are more effective to prevent the dissolvable biochar from being biodegraded. This study proved soil minerals and Ca were beneficial for enhancing biochar stability, these observations assisted in assessing the biochar ability for long-term carbon sequestration.
生物炭在湿润土壤环境中有两种存在形式，即自由溶解的生物炭（粒径<0.45μm）和不溶解的颗粒（粒径>0.45μm）。可溶解生物炭从大块生物炭颗粒中的释放和分解是生物炭添加土壤中 C 损失的主要途径，而其与土壤矿物质的相互作用会降低这一途径。大多数先前的研究侧重于生物质原料类型和热解条件对可溶解生物炭稳定性的影响，而很少有研究探讨可溶解生物炭与土壤成分（例如土壤矿物质）之间的相互作用及其对可溶解生物炭稳定性的影响。在这项研究中，膨润土和针铁矿被选为模型土壤矿物质，因为它们在结构和表面类型上存在差异：带负电荷的 2:1 型层状硅酸盐（膨润土）和带正电荷的结晶矿物（针铁矿）。干湿循环用于确定这两种矿物质对核桃壳衍生生物炭颗粒中可溶解生物炭释放的影响。通过化学氧化和生物降解来测量可溶解生物炭的稳定性。在 Ca 的存在下，这两种土壤矿物质都使可溶解生物炭的释放减少了 34%以上。“Ca 桥接”、“配体交换”和“范德华吸引力”等机制促进了可溶解生物炭-膨润土复合物的形成，Ca 促进了可溶解生物炭插入膨润土层间空间，将 d 间距从 1.25nm 扩展到 1.55nm。然而，由于电荷排斥，“Ca 桥接”几乎没有在针铁矿上形成，这表明可溶解生物炭主要通过“范德华吸引力”和“配体交换”与针铁矿结合。由于形成了有机-矿物复合物，可溶解生物炭的化学氧化程度降低了 22.8-36.5%，生物降解程度降低了 72.7-85.0%，因为土壤矿物质更有效地阻止可溶解生物炭被生物降解。这项研究证明了土壤矿物质和 Ca 有利于增强生物炭的稳定性，这些观察结果有助于评估生物炭长期碳固存的能力。
