生物炭-土壤矿物质界面结合机制及其对碳稳定性的影响

Land application of biochar can not only sequester atmospheric CO2 but also as improve soil fertility and immobilize contaminants. These environmental effects of biochar have intimate connection with its stability in soil. In this project, original biochar will be divided into undissolvable biochar and dissolvable biochar according to its existing states in wet soil. The interfacial interaction between soil minerals and these two biochar fractions will be studied, respectively. Besides, the effect of these interfacial behaviors on the stability of dissolvable and undissolvable biochar will be detected. (1) The FIB, SEM-EDS, XRD, XPS and surface activation energy will be used to reveal the connecting mechanisms of surface covering, pores/channels blocking and metal ion bridging between soil minerals and undissolvable biochar; (2) Batch of adsorption experiment, as well as AFM will be used to reveal the connecting mechanisms of metal ion bridging, ligand exchange and van der Waals attraction between soil minerals and dissolvable biochar. (3) The methods of chemical oxidation, TGA and microbial cultivation will be adopted to evaluate the stability of the minerals-biochar associations. The results obtained from this project will benefit the further understanding of biochar chemical process and the corresponding environmental behavior in soil.

将生物炭输入土壤不仅可以发挥固碳作用，同时还能改良土壤性质、控制土壤污染，生物炭诸多良好的土壤环境效应都与其自身的理化性质及其在土壤中的稳定性密切相关。本项目拟根据生物炭在土壤中的赋存形态将其分为不溶态生物炭与可溶态生物炭，并分别探讨二者与土壤的重要组分土壤矿物质的界面结合机制及其对生物炭稳定性的影响：（1）采用聚焦离子束、SEM-EDS、XRD、XPS，结合表面活化能揭示不溶态生物炭与土壤矿物质的表面包裹、孔道堵塞和金属离子架桥机制；（2）采用吸附实验，AFM揭示可溶态生物炭与土壤矿物质的金属离子架桥、配位体交换和范德华力界面结合机制；（3）采用化学氧化、TGA、微生物培养法研究与土壤矿物质的结合对不溶态生物炭、可溶态生物炭抗化学氧化性、抗热氧化性和抗微生物降解性的影响。最终为进一步深入理解生物炭的土壤环境化学过程及环境效应提供理论基础和科学依据。

本项目以花生壳和秸秆类生物质废弃物为原料，在不同热解温度下将其转化为生物炭，分离提取不溶态与可溶态生物炭。选取代表性粘土矿物高岭土、膨润土和针铁矿，以及3种代表性土壤金属离子Fe3+、Al3+和Ca2+。分别研究不溶态生物炭、可溶态生物炭与上述土壤矿物质的界面结合机制，并考察与土壤矿物质的结合对生物炭稳定性的影响。研究结果表明，可溶态生物炭被粘土矿物吸附后，抗化学氧化性增强，且3种结合机理的抗化学氧化性排序为：Ca2+架桥≈配位体交换>范德华力。Ca2+强化了膨润土和针铁矿对可溶态生物炭的吸附保护作用，但减弱了高岭土对可溶态生物炭的吸附保护作用。对于不溶态生物炭，自由Fe3+和Al3+分别在生物炭颗粒表面转化为Fe8O8(OH)8Cl1.35和AlCl3·6H2O晶体。细小的粘土颗粒能够进入并堵塞不溶态生物炭内部孔道，新生成晶体和生物炭生成Fe-O-C有机矿物复合体。在化学氧化条件下，与土壤矿物的结合使生物炭整体碳损失率降低43.0%，其中不溶态生物炭与可溶态生物炭碳损失率分别降低34.6%和8.4%；在微生物降解条件下，与土壤矿物的结合使生物炭整体碳损失率降低49.3%，其中不溶态生物炭与可溶态生物炭碳损失率分别降低48.3%和1.0%。本项目为揭示生物炭的固碳机制，充分发挥其固碳效应，以及进一步深入理解生物炭的土壤环境化学过程及环境效应提供理论基础和科学依据。