Aging Effect Of Biochar On Heavy Metal Absorption In The Soil

With the rapid development of urbanization and industrialization,the pollution of heavy metal in soil is increasingly serious.Biochar is a carbon-rich product pyrolysised from biomass under hypoxic conditions.Biochar has the huge specific surface area,rich functional groups,precise pore structure and high pH value,which make it possible to repair heavy metal contaminated soil.In this study,in order to study aging effect of biochar on heavy metal absorption mechanism,after simulating the aging process experiment,the physical and chemical properties of the soil,the changes of the total contents and speciations of the various metals,the changes of the physical and chemical properties of the biochar,and the change of the adsorption capacity of the biochar on the heavy metals were measured.The purpose of this study is to explore the effect of biochar on the speciations of heavy metals and whether the adsorption capacity of biochar is changed after different aging methods,and to provide theoretical basis for further determination of biochar as a good modifier for soil heavy metal pollution.The main findings are as follows:1.Biochar is added to the soil to improve the pH value of contaminated soil at all levels,and the pH of the third-level contaminated soil is the largest.The soil pH increased with the increase of the proportion of biochar,and the pH value of the wet soil was slightly higher than that of the drying-wetting soil.The soil pH values decreased first and then increased over time.Compared with the soil without adding biochar,the contents of TC in the soil increased and the TN contents decreased.DOC is affected by soil moisture.DOC concentrations in wetting soil were larger than these in drying-wetting soil,and DOC content is decreasing over time.Biochar may activate Cu ions with time.In the secondary contaminated soil,the weak acid extracted Cu was found in the secondary contaminated soil after 150 days of drying-wetting alternation,and the weak acid extracted Cu was not detected in the control soil.Biochar can significantly affect the fractions of Zn,and different proportions of biochar can promote the transformation of Zn to stable speciations.2.The aged biochar is different from the original biochar in physical and chemical properties,different aging of the biochars are also different each other.The higher degree of soil pollution,thesmaller the p H value of biochar.The pH value of biochar in drying-weting soil is generally higher than that of biochar in the wetting soil.Compared with the control,the TC value of the biochar after aging did not show a significant difference,TN value generally decreased.Different degrees of pollution in the soil of DOC of biochars are different,the higher degree of pollution,the lower DOC contents in biochar.The infrared spectra of biochar showed that there was no difference in the surface functional groups of the aged biochar compared with the original biochar.The results of Boehm titration showed that the content of acidic functional groups decreased and the number of basic functional groups increased.The adsorption of Cu and Cd on biochar is more consistent with the first order kinetic equation.The adsorption of Zn is in accordance with the second order kinetic equation.The results of Langmuir isothermal adsorption model and Freundlich isothermal adsorption model show that some of the biochar conforms to Langmuir isothermal adsorption model and some are in accordance with the Freundlich isothermal adsorption model.For the adsorption of Zn,the Langmuir isothermal adsorption model can better describe it,and it is more suitable for Freundlich isothermal adsorption model for Cd adsorption.The pH of the solution significantly affected the biochar adsorption of heavy metals,when p H value is 2,original biochar has the maximum adsorption value.