Occurrence Characteristics Of Endogenous Heavy Metals In Biochar Produced By Giant Juncao And Its Toxicity Evaluation

In this paper,the biochar was prepared from the stems of Giant Juncao.The combined forms of endogenous heavy metals and its biotoxicity of biochar were studied after produced biochar by the Giant Juncao grown in soils with different pollution levels.Elemental analysis and specific surface area determination of three biochars were first carried out.The surface morphology of biochar was observed by scanning electron microscopy?SEM?;The surface functional groups of biochar were studied by fourier transform infrared spectroscopy?FTIR?and X-ray photoelectron spectroscopy?XPS?;X-ray diffraction?XRD?was used to study the mineral composition of biochar;electron paramagnetic resonance?EPR?was used to detect free radicals in biochar;and gas chromatography was used to study the types of polycyclic aromatic hydrocarbons in biochar.Digestion with HCl-HNO₃-HClO₄ and BCR sequential extraction was used to study the characteristics of endogenous heavy metals in biochar.Using toxicity characteristic leaching procedure to reflected the leaching toxicity of biochar.The germination rate and root elongation inhibition rate of wheat were used to reflect the biotoxicity of biochar extraction solutions.The biotoxicity of biochar was further studied by the enzymatic activity of SOD,POD and CAT of wheat roots and shoots.Considering that when biochar is exposed to the environment,it will be affected by different degrees of aging.The freeze-thaw cycle aging,drying-rewetting cycle aging,simulated acid rain aging,and microbial aging are used to simulate the aging of biochar in the environment.The morphology of heavy metal and leaching toxicity of biochar after aging were measured to compare the changes of heavy metal occurrence characteristics before and after biochar aging.The main findings and conclusions are as follows:?1?The giant juncao biochar has a high carbon content?66%-69%?,has a compact aromatization structure,a large specific surface area,and has a honeycomb-like pore structure.It has abundant surface functional groups and strong basicity?pH>10?.?2?The heavy metals Cu and Cd were detected in biochar,and the Cu content in Jiu Niu biochar was as high as 35.67 mg/kg.The content of heavy metals in biochar was positively correlated with the content of heavy metals in the raw materials.The presence of polycyclic aromatic hydrocarbons and environmentally persistent free radicals has also been detected in biochar.?3?The form of heavy metals in biochar is mainly in the oxidizable state and the residual state.The aging effect significantly increases the acid content of the biochar heavy metal acid,and increases the ratio of the acid dissolved state to the total amount,which increases the biotoxicity of the biochar.?4?The presence of heavy metals in biochar has a significant inhibitory effect on wheat growth.The acid-soluble heavy metal content and TCLP extraction state significantly affect the biotoxicity of biochar.In addition,organic pollutants in biochar and environmentally persistent free radicals also affect wheat growth.Figure[29]table[14]reference[169]...