Study On Release Behavior And Mechanism Of Biochar Colloid In Aqueous Solution

In recent years,the formation of biochar colloids in the environment has attracted more and more attention.It is an important process of biochar physical decomposition and has an important impact on pollutant migration.However,fundamental studies on the release behavior and the influencing factors of biochar colloid in the aqueous solution are scarce,and the current understanding of the mechanisms of biochar colloid release is rather limited.Therefor firstly we explored the pathway and intrinsic mechanism for the formation of biochar colloid from rice straw in aqueous sloutions and the role of main influencing factors?i.e.pyrolysis temperature,initial particle size and chemical property?,and the stability of biochar colloid in the aqueous solutions.Then we systematically explored the effects of pyrolysis temperature?300-700??and solution ionic strength?0.1-10 mM?on the yield of biochar colloids from bulk biochar prepared from wheat straw and peanut shell.The results of this study will provide a new understanding of the physical decomposition and trend of biochar in the environment,which beneficial to people understanding of the stability of biochar,providing necessary theoretical support for the sustainability and environmental benefits of biochar storage.The main research results were as follows:?1?The results of the study on biochar from rice straw showed that,the pyrolysis temperature determined the abrasive resistance of biochar and had a significant effect on the yied of biochar colloid.We found a positive correlation between the yield of biochar colloid and the content of submicron fragments.At the same pyrolysis temperature,the yield of biochar colloid after ball milling was above 4 times higher than that without ball milling?100 mesh?.The order of yield of biochar colloid was BC400?pyrolysis temperature was 400??>BC70?pyrolysis temperature was 700??>BC200?pyrolysis temperature was 200??when solution ionic strength?1 mM.With the exception of BC200,increasing the solution ionic strength and reducing pH significantly reduced the yield of biochar colloid.The yield of biochar colloid influenced by both solution ionic strength and pH.Overall two dominant processes involved in the formation of biochar colloid,release and sedimentation,of which release was more susceptible to prevailing solution chemistry.DLVO interactions properly explained the effect of ionic strength on the yield of BC400 and BC700 biochar colloid.It was proposed that the steric resistance of dissolved organic carbon?DOC?in BC200 could be responsible for the yield of BC200 still high at higher ion strength?20-50 mM?.CCC_NaClaCl of BC400 colloid was 273 mM,and CCC_NaClaCl of BC700 colloid was 127 mM.The yield and stability of biochar colloid were high in three kinds of soil aqueous solutions and two kinds of surface water.?2?The results of the study on biochar from wheat straw and peanut shell showed that,the content of biochar submicron fragments decreased with increasing of pyrolysis temperature,the abrasive resistance of biochar from wheat straw and peanut shell increased with increasing of pyrolysis temperature?300-700??.The content of submicron fragments of biochar from wheat straw and peanut shell positively correlated with O content,O/C and?O+N?/C,but negatively correlated with C content?p<0.05?.For wheat straw biochar,the content of submicron fragments also negatively correlated with ash content.The yield of biochar colloid from wheat straw and peanut shell positively correlated with the content of submicron fragments?p<0.05?for the same solution ion strength.The yield of biochar colloid significantly affected by feedstock and pyrolysis temperature.The yield of biochar colloid friom peanut shell was lower than that from wheat straw biochar,and the yied of bicoahr colloid of high pyrolysis temperature??600??was significantly lower than that of medium and low pyrolysis temperature for the same solution conditions and pyrolysis temperature.When the solution ion strength?1 mM,the yield of biochar colloid from wheat straw and peanut shell little affected by the ion strength;when the solution ionic strength increased from 1 mM to 10mM,the yied of wheat straw and peanut shell biochar colloid decreased significantly,and the degree of decrease varied according to the pyrolysis temperature of biochar,which the yield of bicohar colloid at medium and high pyrolysis temperature??500??decreased by 60.0–97.2%,while the yield of bicohar colloid at the low pyrolysis temperature?300??decreased 11.1–11.2%,which may be related to the content of DOC.