Response And Mechanism Of Different Components Of Biochar To Soil Minerals

Biochar,as an emerging functional material with great potential for carbon sequestration,has attracted wide attention.The return of biomass to the field is expected to be an effective way to deal with global climate change.Biochar will interact with soil minerals to affect its stability.However,biochar has a heterogeneous structure,and its soluble and insoluble components have different contributions to the stability of biochar,so there are few reports on how each component interacts with soil minerals.Relevant studies have theoretical significance for improving the stability of biochar,and have guiding significance for applying biochar according to local conditions and preparing functional biochar.In order to explore the interaction between different components of biochar and soil minerals,and to reveal the stability mechanism of biochar in soil from the perspective of minerals,this study prepared a series of biochar samples using rice straw,rice husk and bamboo powder as raw materials at different carbonization temperatures（300℃,500℃and 700℃）.The effects of raw material type and carbonization temperature on physicochemical properties and soluble components of biochar were studied.Three soil minerals,kaolinite,montmorillonite and illite,were selected to carry out the interaction experiment of soil minerals with soluble and insoluble components of biochar.The main results are as follows:（1）The physicochemical properties of rice straw charcoal（RS）,rice husk charcoal（RH）and bamboo charcoal（BP）were affected by carbonization temperature.With the increase of carbonization temperature,ash content of biochar increased,yield decreased,and pore structure became richer.The thermal weight loss rate decreases and the thermal stability increases.The H/C ratio decreased and the aromatization stability increased.The physicochemical properties of biochar were also affected by the raw material type.Compared with RS and RH,BP had the lowest yield,ash content,p H and specific surface area.The ash content,p H,electrical conductivity and specific surface area of RS700 in all biochar samples were the highest,and the weightlessness rate of RS700 was the lowest（51.8%）.The order of soluble organic carbon concentration of biochar was RS>RH>BP,and decreased with the increase of carbonization temperature.RS300 had the highest soluble carbon concentration of 520.7 mg/L,while BP700 had the lowest soluble carbon concentration of 5.80 mg/L.Soluble organic substances of biochar mainly include heterocyclic amines,esters,alcohols,hydrocarbons and a small part of ketones,ethers and aldehydes.Low temperature biochar（300℃）is dominated by humic acids and small molecule neutral substances.With the increase of carbonization temperature,hydrocarbons increase,heterocyclic amines and phenols decrease.（2）Soil mineral combined with biochar soluble component adsorption experiments showed that soil mineral on biochar soluble components of adsorption capacity gradually increase with concentration of soluble carbon,illite>montmorillonite>kaolinite,adsorption mechanism mainly includes the van der Waals force,ligand exchange and Ca²⁺Bridges,but for different soil minerals,The contribution ratio of the three mechanisms is different.For kaolinite,van der Waals>ligand exchange>Ca²⁺bridge;For montmorillonite and illite,van der Waals forces>Ca²⁺bridging>ligand exchange.The binding mechanism of low temperature biochar（300℃）with montmorillonite and kaolinite is mainly by van der Waals force,and with illite is mainly by Ca²⁺bridge.Van der Waals forces were the main binding force between high-temperature biochar（700℃）and soil minerals.（3）The results of simulated culture experiments of insoluble components of soil minerals and biochar showed that the atomic ratio of insoluble components and mineral complex H/C of biochar from different materials was RS>BP>RH,indicating that the aromatic stability of soil minerals was RS<BP<RH.The aromatization stability of different soil minerals and biochar complexes is illite>kaolinite>montmorillonite.Compared with kaolinite,illite,montmorillonite and biochar insoluble components have better thermal stability.Exogenous Ca²⁺antagonizes the combination of soil minerals and insoluble components of biochar,thus weakening the stability of the combination.To sum up,biochar consists of soluble and insoluble components.Soil minerals bind to soluble components of biochar mainly through van der Waals forces,ligand exchange and Ca²⁺bridging.The insoluble components of biochar can combine with soil minerals to form complexes to enhance the aromatization stability and thermal stability of biochar,and ultimately improve the overall stability of biochar.On the basis of the effective use of biomass raw materials,biochar is prepared at the carbonization temperature of 500℃.The interaction between biochar and soil minerals can increase the stability of soluble and insoluble components of biochar,so as to better play the advantages of carbon sequestration and emission reduction of biochar.