| Potentially toxic elements such as heavy metals have become a possible threat to the ecosystem due to their carcinogenic nature.Heavy metals are one of the important pollutants in soil.Their content,accumulation,mobilization,and transformation affect the quality and safety of food directly and then pose a serious threat to human health.The immobilization,stabilization,and remediation of heavy metal pollution in soil have gained significant attention in recent research.For the remediation of heavy metal pollution,the development of suitable materials is the key to immobilizing and stabilizing heavy metals in soil.As an environment-friendly and economical carbon material with abundant functional groups and excellent pore structure,biochar has attracted extensive attention for its application in soil pollution remediation and quality improvement in recent years.Therefore,it is of great theoretical significance and practical value to prepare green,economically,and efficient biochar materials and study their mechanism for heavy metal remediation.This detailed study will help optimize the material preparation technology for improving the heavy metal remediation in soil,thus ensuring food safety.The study prepared a series of biochar using waste biomass and used the biochar as amendments for soil remediation in pot experiments.We studied the mobilization and transformation of heavy metals in contaminated soil-plant systems remediated by biochar and their effects on crop growth.The results elucidated the mechanism of heavy metal stabilization,mobilization,and transformation in soil by different types of biochar,so as to provide a reference for soil remediation and treatment.In this study,the waste biomass such as crop straw(rice husk and wheat straw)and sewage sludge were used as raw materials to prepare different biochar samples.The effect and mechanism of biochar on heavy metals remediation in the soil-plant system were studied in a series of pot experiments.The characteristics of distribution,mechanisms of mobilization,and transformation of heavy metals in the soil-plant system were discussed.The physicochemical properties of biochars,as well as the composition and structural characteristics of the experimental soils and plants were systematically characterized using Brunauer-Emmett-Teller(BET),Scanning electron microscope(SEM),Elemental analyzer,X-ray photoelectron spectroscopy(XPS),Xray powder diffraction(XRD),Fourier transform infrared(FTIR),and Electron paramagnetic resonance(EPR)and other techniques.The main achievements are as follows:1)By preparing rice husk biochar(RHB)combined with chicken manure compost(CMC),four groups of pot experiments(control,2%RHB,2%CMC,and 1%RHB+1%CMC)were conducted to study the mobility and transformation of heavy metals in contaminated soil and their influence on the growth of maize.The results showed that the bioavailability and potential toxicity of heavy metals in the groups of RHB,and CMC,especially in the group of 1%RHB+1%CMC were decreased significantly,and meanwhile,the growth of maize was also promoted.The generation of reactive oxygen species(·OH)in maize roots and shoots was investigated,revealing the complexation and adsorption of heavy metals as the prominent mechanism of heavy metal stabilization in contaminated soil with the involvement of hydroxyl,carbonyl,and carboxyl functional groups.2)Sewage sludge biochar(SSB)was prepared from sewage sludge(SS)as raw material.Four groups of pot experiments(control,SS-2%,SSB-2%,and 1%SS+1%SSB)were designed to compare the remediation effects of sludge and sludge biochar on heavy metal contaminated soil.The content of Cr,Ni,and Pb in maize roots and shoots in all experimental groups was significantly decreased,and the growth of maize with 1%SS+1%SSB was significantly increased,indicating the reduction of availability and transformation of heavy metals in the soil-maize plant system.Combined with the formation of·OH in maize,the mechanism of the stabilization and immobilization of heavy metals in soils by the functional groups of hydroxyl,carbonyl,carboxyl,and amine in SS and SSB were also revealed.3)Wheat straw biochar(WB-300,WB-500,and WB-700)was prepared at different pyrolyzing conditions(300,500,and 700℃)using wheat straw as biomass raw material.The effects of wheat straw biochars on the occurrence,mobilization,and transformation of heavy metals in soil and their impact on the growth of maize were elucidated.The results revealed that wheat straw biochar considerably decreased heavy metal mobilization and accumulation in the soil-maize plant system.The dominant mechanisms for the stabilization and immobilization of heavy metals in soil owing to the presence of hydroxyl,carboxyl,and carbonyl functional moieties in biochar were complexation and ion exchange.Moreover,the mechanism of intracellular reactive oxygen species(·OH)on plant growth and heavy metal mobility and transformation in the soil-plant system was also studied. |
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