Study On Adsorption Of Cadmium By Soybean Root Biochar And Stabilization Of Heavy Metals In Livestock And Poultry Manure At Different Pyrolysis Temperatures

With the rapid development of modern agriculture and industry,heavy metals are discharged into the environment,causing serious pollution.For example,in order to promote the growth of livestock and poultry,improve feed utilization efficiency and prevent livestock and poultry diseases,some feed additives containing heavy metals are widely used,resulting in high concentrations of heavy metals such as Zn and Cu in livestock and poultry feces.The biomass rich in heavy metals disposed random,the heavy metals will be re-released into the environment and cause secondary pollution.As a large agricultural country,China produces agricultural and forestry wastes every year.Converting them into biochar can not only play a role in carbon sequestration and help to achieve"carbon neutralization",but also can be used as adsorption materials to absorb heavy metals in the environment and reduce the bioavailability of heavy metals.In this study,soybean roots were pyrolyzed at different temperatures to study the effect of temperature on the properties and structure of soybean root biochar,to provide a theoretical basis for studying the absorption properties of heavy metal（Cd）.At the same time,the effect of pyrolysis temperature on the stability of heavy metals（Zn and Cu）in livestock and poultry manure（pig manure and chicken manure）was studied,and the stabilization mechanism of heavy metals was explored,in order to provide a new way for the resource utilization of agricultural and forestry wastes and a new idea for the safe and efficient treatment of biomass containing heavy metals.The conclusion obtained are as follows:1.The pyrolysis temperature has a significant effect on the structural characteristics and physicochemical properties of biochar.With the increase of pyrolysis temperature,the BET and total pore volume of soybean root biochar,livestock and poultry manure biochar tend to the formation of micropores in biochar with the increase of pyrolysis temperature.The results of elemental analysis,Raman,XPS and FTIR show that the H/C atomic ratio of biochar decreases with the increase of temperature,and the increase of pyrolysis temperature can make soybean root biochar more prone to carbonization and higher aromaticity.Increasing the pyrolysis temperature can induce the formation of aromatic flake clusters in biochar.2.The pyrolysis temperature significantly affects biochar properties and the removal mechanisms of heavy metals consequently.Based on Langmuir model,the adsorption maximum for Cd（II）was up to138.544 mg g^-1.The mechanism of Cd（II）adsorption on soybean biochar was also explored through kinetics adsorption experiments,as well as both solution and solid-phase microstructure characterization.These findings suggested that pyrolysis of soybean root at 900℃could not only be an option to control agricultural wastes but also could be of benefit in using biochar as excellent adsorbent.3.The pyrolysis temperature affects the adsorption mechanism of soybean root biochar for Cd（II）in solution.Microstructure characteristics and mechanism analysis further suggested that Cd（II）-πinteractions and combining with sulfur-containing functional groups were the main mechanisms of Cd（II）adsorption by biochar.After comparison of the characterization and evaluation of the adsorption capacity of different pyrolysis temperatures of biochars,a new perspective has been found to explain the adsorption mechanisms onto biochar adsorbents and the effects of different molecular structures and different components of biochar on the adsorption mechanism.4.Heavy metals mostly concentrated on the biochar derived from livestock and poultry manure in pyrolysis.TCLP leaching results indicated that the compared with raw materials thermal conversion could reduce the leaching of heavy metals in the biochar and the best treatment for stabilization is CM400.The speciation analysis of heavy metals indicated that heavy metals in the biochar could transform into more stable forms by pyrolysis.Combined with FTIR,XPS and organic element analysis,it is inferred that the fixed mechanism is that the original organic structure is destroyed by pyrolysis,organic components volatilize or reconstruct,and metal elements form and complex with sulfur after exposure.Overall,the pyrolysis temperature significantly affects the structural characteristics and physicochemical properties of biochar,and then affects its adsorption of heavy metals.Besides,the pyrolysis pathway can enhance the stability of heavy metals.Hence,this research could provide a helpful insight and important theoretical support for the remediation of heavy metals in water and the stabilization of heavy metals in biomass.