A Comparative Study On Biochar Properties And Cd²⁺ Adsorption Behavior Under Effects Of Different Ageing Processes Of Leaching,acidification And Oxidation

Biochars,which from agricultural and forestry wastes,can improve soil properties and control the bioavailability and migration of harmful elements,such as the adsorption and fixation of heavy metals?cadmium,copper,lead,etc.?.However,exposed to the natural environment for a long time,it will undergo a variety of epigenetic geochemical processes?including oxidation,acidification,rainfall,etc.?,which named"aging process".These aging effects will affect the physicochemical properties of biochars.At present,the effects of various aging processes on the physicochemical properties of biochars,especially on the adsorption properties and mechanisms are not clear.Therefore,this paper focuses on three aspects:the effects of leaching,acidification and oxidation on the physicochemical properties of biochar;the effects of different aging processes on the heavy metal cadmium(Cd²⁺)adsorption by biochars;the effects of aging on the Cd²⁺migration of biochars.In this paper:?1?The straw biochars are prepared and treated in different aging processes.In the meanwhile,I use various testing methods?element analysis,SEM-EDS,FTIR,XPS and zeta potential,etc.?to characterize fresh and aged biochars,and compare the properties of biochars,which with different aging effects;?2?Through batch experiments,the adsorption characteristics and mechanisms of three aged biochars on Cd²⁺were compared.At the same time,the influence of environmental factors?pH,background solution,coexisting ions?on adsorption were also confirmed.?3?Soil column leaching experiments were carried out to study the effect of biochars with different aging processes on the migration behavior of Cd²⁺.The results show that:?1?The physicochemical properties of biochars with different pyrolysis temperatures are quite different.The low-temperature biochars contain a large number of oxygen-containing functional groups,and the high-temperature biochars contain a plenty of organic components.Leaching aging process causes a large amount of soluble substances loss of biochars,while acid rain and oxidation aging processes promote the formation and accumulation of oxygen-containing functional groups on the surface of biochar;?2?high-temperature biochars have a large Cd²⁺adsorption capacity,and mineral co-precipitation plays a leading role.Aging will reduce the adsorption performance of high-temperature biochars.The Cd²⁺adsorption of low-temperature biochars depends on surface complexation and ion exchange,acidification and oxidation aging will promote the adsorption capacity of low-temperature biochars;?3?the pH of solution,coexisting ions and background liquid will affect the Cd²⁺adsorption of biochars.Acidification and oxidation aging improved the adsorption of low-temperature biochars under acidic conditions?pH=2⁴.5?,the presence of Pb²⁺and Cu²⁺would inhibit the Cd²⁺adsorption of biochar;?4?the application of biochar could significantly improve the water holding capacity and pH of soil;Biochar could effectively fix Cd²⁺in brown soil,but it would significantly increase the exposure risk of Cd²⁺in red soil.