Effects Of Silicon-riched Biochar On Silicon And Cadmium Forms In Soil And Uptake By Rice

In recent years,biochar,as a new type of environmental functional material,has been widely used in greenhouse gas emission reduction,soil improvement and other polluted environment remediation due to its highly stable physical and chemical properties.It is not difficult to find that the previous research on biochar focused more on the impact of biochar carbon on environmental change and restoration and other fields,while the research on siliceous in biochar ash has not attracted people′s attention.Therefore,the research on silicon in biochar has theoretical and practical guiding significance.In this study,various biochars with different silicon contents were prepared by using bamboo leaves,rice husks and wood as raw materials at different pyrolysis temperatures and by KOH alkali-enhanced method.:charcoal（BW3）prepared at 300°C,rice husk biochar（BH3）prepared at 300°C,bamboo leaf biochar（BB3）prepared at 300°C,rice husk biochar（BH5）prepared at 500°C,bamboo leaf biochar（BB5）prepared at 500°C,and 700°C rice husk biochar（BH7）prepared at 700℃,bamboo leaf biochar（BB7）prepared at 700℃,KOH alkali-enhanced rice husk biochar（AH）prepared at 550℃and KOH alkali-enhanced bamboo leaf biochar（AB）prepared at 550℃.Biochars with different silicon contents were screened out through elemental analysis and structural characterization of biochars;biochars with different silicon contents（BW3,BH7,BB7,AH,AB）were taken as the research objects to explore the effect of silicon in biochars.Dissolution and its effect on soil silicon balance and its mechanism of action;Based on the physicochemical characteristics of silicon content in silicon-riched biochar,the removal mechanism of Cd in aqueous medium was studied by means of SEM-EDS,FTIR,BET and XRD.Using pot experiments,the remediation effects of higher silicon content of biochars（AH,AB）and lower silicon content of biochars（BW3）on Cd-contaminated soils were studied,and the effects of different silicon content biochars on soil chemical properties,cadmium forms and rice cadmium uptake in reddish paddy soil were clarified..In addition,pot experiments were used to analyze the effects of biochars with different silicon content（BW3,BH7,BB7,AH,AB）on soil silicon forms,rice yield and silicon absorption in reddish paddy soil.The purpose is to provide a scientific basis for silicon-riched biochar to remediate Cd-contaminated soil and rice production.The main research results are as follows:（1）Elemental analysis and structural characterization of biochar were carried out by elemental analyzer,SEM,FTIR and other techniques.The results showed that:under the same biomass conditions,the yield,H,O,N element content decreased with the increase of temperature,The content of C and ash increased with the increase of temperature;with the increase of temperature,the aliphatic functional groups in biochar decreased,and there was the conversion of carbonyl carbon and phenolic hydroxyl to aromatic bridge carbon.The change trend of total silicon and avaiable silicon of biochar is basically similar,and the content of alkali-enhanced biochar（AH,AB）is relatively higher.（2）In the process of silicon release of biochars with different silicon contents,the higher silicon content of biochar（AB）is the most obvious,and the p H reach the maximum value;the cumulative dissolution of various types of silicon increases with time,and the overall The rule of higher silicon content of biochar is greater than that of medium silicon biochar is greater than that of lower silicon content of biochar,namely:AB>AH>BB7>BH7>BW3;the release of silicon from biochar prepared at different temperatures,the cumulative release of the total silicon also varies with the pyrolysis temperature increases and increases,and the whole is consistent with the C-Si model;The results of variance analysis showed that the type and amount of silicon-riched biochar had extremely significant effects on the available silicon,organically bound silicon,iron-manganese bound silicon,and amorphous silicon in acidic soil（p<0.01）,and the difference between the two was significant.The interaction was extremely significant（p<0.01）,and the addition of silicon-riched biochar could change the existing forms of various silicon in the soil（3）Through the removal mechanism of Cd²⁺in the water phase by silicon-riched biochar,combined with scanning electron microscope SEM-EDS,FTIR,XRD and other techniques,the adsorption characteristics of silicon-riched biochar for Cd²⁺were characterized.The results show that:when p H=6,the removal efficiency and adsorption capacity of silicon-riched biochar on Cd²⁺reached the maximum value;by analyzing the fitting results of Langmuir and Freundlich models of silicon-riched biochar,lower silicon content of biochar（BW3）and medium silicon content of biochar（BH7,BB7）could it fits the Langmuir model better,while the higher silicon content of biochar（AH,AB）can fit the Freundlich model better,and the adsorption of biochar has strong heterogeneity.By thermodynamic parameter calculation,the adsorption process of lower silicon content of biochar（BW3）,medium silicon content of biochar（BB7）and higher silicon content of biochar（AB）is an endothermic reaction,while the adsorption process of medium silicon content of biochar（BH7）and higher silicon content of biochar（AH）is an exothermic reaction;through the removal of inorganic components of low-silicon organisms,the changes of functional groups detected by FTIR before and after the reaction,and the change of ion concentration before and after the reaction,it can be seen that the complexation and ion exchange of functional groups are the lower silicon content of biochar to remove water.Two important mechanisms of Cd²⁺in the phase,while chemical precipitation and ion exchange may be two important mechanisms for the removal of Cd²⁺in the aqueous phase by medium silicon and higher silicon content of biochars,and silicon crystals were also detected on the surface of medium silicon and higher silicon content of biochars.Precipitation of Cd₂Si O4 provides a good basis for the removal of heavy metal Cd blocking in soil by silicon-riched biochar.（4）The results of the pot experiment showed that the proportion of exchangeable and reduced cadmium in the soil decreased with the addition of silicon-riched biochar,while the proportion of oxidizable and residual cadmium increased.Compared with CK,the addition of biochar significantly reduced the cadmium content in various parts of rice,and the treatment with 0.4%higher silicon content of biochar AB had the most obvious reduction effect,which was 66.85%lower than CK;Compared with CK,the addition of silicon-riched content of biochar significantly reduced the cadmium enrichment coefficient（BCF）of rice by 14.52%-36.32%;The changes of transfer coefficients TF1（root to straw）and TF2（root to grain）were significantly smaller than those of CK with high or low addition of silicon-riched biochar.Treatment（p<0.05）,the decrease rates were50.64%-57.39%,48.87%-56.05%,31.39%-47.67%,29.06%-45.34%,respectively.（5）The results of the pot experiment showed that after adding silicon-riched biochar to the reddish paddy soil,the contents of soil available silicon,organically bound silicon and iron-manganese bound silicon were significantly increased.Compared with CK,the available silicon,organically bound silicon and iron manganese bound silicon increased by 184.23%,59.53%and117.54%respectively;when the addition amount（0.8%）,the grain yield of rice increased significantly.The increase is 4.18%～44.28%.