| The amount of agricultural wastes in Xiongan New Aera is increasing day by day,but most of them are not used reasonably and are piled up at will,which not only does not make full use of its biomass energy,but also causes agricultural non-point source pollution.The agricultural wastes in Baiyang Lake and its surrounding areas are relatively concentrated,especially the reed and the agricultural straw,which are difficult to deal with because of the policy restrictions.Straw disposal is also a challenge to China’s agriculture and environment.In China,up to 900 million tons of straw are produced every year.If these wastes can not be used effectively,they will have an important impact on agricultural production and the environment.Biochar is a stable,highly aromatic porous material formed by pyrolysis of biomass at high temperature in inert environment.It has high pH value,cation exchange capacity,abundant functional groups and specific surface area,which can improve soil structure and provide soil nutrients.At the same time,biochar can be used to adsorb and fix heavy metals and other pollutants,so as to remedy polluted soil.The properties and practical application efficient of the biochar prepared under different raw materials and preparation conditions are different.At present,the preparation methods of biochar are mostly just simply investigating the factors that affect the biochar,but there is no analysis of the effect of multiple factors,and no optimization of the parameters of biochar preparation,which limits the preparation technology and engineering popularization of biochar.In this study,typical wastes such as corn and reed straw in Xiongan New Aera were used as raw materials,and moisture content of raw materials,heating rate,carbonization temperature and carbonization time were selected as the influencing factors to prepare biochar.The orthogonal experimental design was used to prepare biochar with the different treatments,and biochar yield,pH,EC,ash content,functional group composition,pore structure and specific surface area were determined respectively.Based on the analysis of the variation of the yield and properties of the biochar under the different preparation conditions,the optimum preparation conditions of the biochar were summarized from the view of process optimization.Then,the biochar was added to soil and passivated,and effects of biochar prepared under different conditions on the inactivation of heavy metals Cd and Pb in soil were investigated.The conclusions were as follows:(1)Different straw properties,such as cellulose,hemicellulose and lignin have been found to be different,which resulted in different weight loss curves of different straw during pyrolysis.The results showed that the cellulose content of reed straw was higher than that of corn straw,and the lignin content was lower than that of corn straw.So the proportion of weight loss of reed straw was higher than that of corn straw in the second stage of weightlessness,and it decomposes more easily than corn straw.(2)Biochar has been prepared by orthogonal experiment,and its properties have been measured.Variance analysis and range analysis have been performed to evaluate the effects of various factors on the yield and properties of biochar,and to judge the influence of different factors on the yield and properties of biochar in orthogonal design,thus,the optimum technological parameters for the preparation of biochar were determined.The results showed that carbonization temperature was the most significant factor affecting the preparation of biochar,which had a significant effect on the yield and main properties of biochar.Increase of moisture content of straw material could increase yield to some extent,but had little effect on the properties of the biological carbon.An increase in heating rate had also led to a decrease in yield,but ash content and specific surface area of biochar had increased.With the increase of temperature,the specific surface area,pore volume and microporosity of biochar increased at first and then decreased,while the pore diameter decreased at first and then increased.Prolonging carbonization time decreased the yield of biochar,but it had little effect on pH and ash content of biochar,and no significant effect on specific surface area of biochar within limits.Considering the influence of various factors,the optimum parameters of reed biochar/corn biochar preparation were as follows:moisture content 15%/25%,heating rate 20℃·min-1,carbonization temperature 600℃,carbonization time 0.5h,in all treatments,treatment5 was the closest to the result,when the biochar yield was overed 30%and had the best properties.(3)Different biochar was added to soil to passivation culture for a period of time.During the period,changes of soil pH and available heavy metals had been measured.After biochar was applied to soil,pH of soil increased,and heavy metals in soil were passivated to some extent.After 35 days of biochar treatment,the volume of pH in reed biochar(LWC)treatment increased by 0.50,and that of corn biochar(YMC)treatment increased by 1.07.Under the same conditions,the inactivation efficiency of LWC to available Cd and Pb in soil could reach 51%and 44%,respectively,and the passivation efficiency of YMC to available Cd and Pb in soil could reach 47%and 39%. |
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