| Biochar is rich with carbon including aromatic carbon and alphatic carbon or labile carbon.It has been perceived that biochar is inert.However,a number of studies showed that biochar applied to soil undergoes changes due to abiotic or biotic processes and ultimately mineralized as CO2,but compare to the other organic carbon or uncarbonization organic substances,it may need a long time.The changes and mineralization degree of biochar would affect the biochar fuctions for improving soil,combating climate change,and soil remediation.The changes in biochar with the aging process and the potential impacts of biochar aging on soil organic,contanminant and mineral are scarce,a comprehensive research system of the biochar aing process has not been established.To study the biochar properties and the interactions with the substances with the aging process are the theoretical basis for evaluating the short and long-time influence of biochar in the environment.Herein,We focused on studying the physichemical changes of biochar aging after naturaloxidation,chemical oxidation,aging under soil surrounding and adding the biochar in the soil,especially the composition and structural characteristics of the biocar and impacts on heavy metal adsorption.The transformation and morphology of the biochar particles were monitored by diffuse-reflectance Fourier transform infrared spectroscopy(DRIFTS),scanning electron microscopy(SEM)coupled with energy X-ray dispersive spectroscopy,and X-ray photoelectron spectroscopy(XPS).The main findings are as follows:(1)Biomass-derived biochar was produced by rice husk at 350 and 550℃,the physicochemical properties of biochar were characterized:the fresh R550 biochar sample contained higher C and ash contents than the R350 sample,although its H,N,and O contents were lower,indicating the higher-temperature biochar was carbonized more efficiently and contained more aromatic and less aliphatic matter.Within the same biochar particle,the oxidation degree of the exterior was higher than that of the interior surface during pyrolysis.There were many oxygeny-containing functions on biochar surface,such as carbonyl,hydroxyl,ether bonds,carboxylic groups etc.The R350 biochar possessed more aliphatic substances and ether bonds than the R550,while the R550 had more aromatic and ester groups(2)The rice husk-derived biochar was incubated for the desired time,we aimed to determine the physicochemical properties of biochar produced from rice husk at 350 and 550℃,to characterize changes in the biochar properties during aging and to identify the effect of aging time on these changes.To simulate different stages in the aging process,samples were incubated at a constant temperature in the dark and maintained at 60%water holding capacity for 100-300 d,at the same time,another samples were put into the fabric bag and buried into the soil under 40%water holding capacity.During the aging course,the content of a decrease in C content was found,while the O and H content were increased.An increase in hydrophilicity of the surface polar functional groups were found also during incubation.Biochars were oxidatived during the aging course,and SEM indicated that oxidation occurred close to the biochar surface rather than in the biochar particle interior.Furthermore,the DRIFTS and XPS results indicated that oxygeny-containing groups such as carboxyl,ester and ether were changed after aging.(3)Bichar aging can be accerlated by chemical agent.After oxidized by H2O2 and HNO3,a decrease in C content was accompanied by an increase in aromaticity for the R350 sample,while the polarity of the functions was increased and aromaticity decreased for the R550.Whatmore,the N content was 5.4 times that of biochar before oxidization with HNO3,the carbonyl,carboxyl groups,ether bonds were introduced while oxidizing.Introduction of-NO2 was identified when biochar was oxidized with HNO3.The oxidation caused by H2O2 was not as severe as HNO3,and the impact of higher pyrolysis biochar caused by H2O2 was more obviously than the lower pyrolysis biochar.(4)All the parameter of the two biochars after three different aging process were analysised by SPSS statistics.The mianly changes of the higher temperature biochar upon aging was oxygeny-containing groups especially carbonyl group while the aromatic condensation degree of the low-temperature biochar decreased with the oxygeny-containing groups varied after aging(5)After analysising the physichemical and adsorption behavior of biochar after different aging process,we found that an increase in the oxygen content of all biochars,the changes of oxygeny-containing groups especially the hydroxyl,carboxyl and ether groups were responsible for the adsorption behavior of biocha on Cu(II).(6)In order to study soil interaction with biochar over time,the two selected biochars were mixed with soil by1%,3%,5%for 30-240 days.The content of humus acid increased earlier and then decreased with the aging time increasing,and the dissolved organic matter decreased during the course,which may due to the activities of soil microorganism was increased by the bicahar and made the humus acid and dissolved organic matter quikly decomposed.The content changes of HA shown the same trend as humus acid.In addition,after biochar obtained under lower temperature added to the soil,the soil aromatic condensation degree decreased.However,the reverse was observed for the higher temperature biochar.In general,biochar imput improved the H/F value of soil and increased the soil polymerization degree. |
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