Effect Of Aging On Physicochemical Properties And Pb(?) Adsorption Capacities Of Biochar

Biochar is beneficial for soil amendment,but further research is still required on changes in its physicochemical properties during aging,especially in oxygen-containing functional groups and associated adsorption behaviors.Here,we investigated the changes in the physicochemical properties of the biochars before and after aging treatments by using natural aging,freeze-thaw cycles,dry-wet cycles,and chemical oxidation methods.We measured the scanning electron microscope,specific surface area and other indicators of biochar before and after aging.We studied the changes in the physicochemical properties of biochar over time before and after natural aging.We analyzed the physicochemical properties of biochar before and after three different types of artificial aging.We also studied the changes in the adsorption capacity of biochar to Pb???after three types of artificial aging,and we discussed the adsorption mechanism combined with the changes of physicochemical properties.The results are as follows:?1?Five years after the application of biochar to typical loess soil under field conditions,the SSA of the biochar did not consistently decline or increase but fluctuated over time.This fluctuation was due to the destruction and blockage of the pore structure and the formation of micropores.The increases in the surface O content and oxygen-containing functional group content over the 5 years suggest that the aging of the biochar is initiated at the surface and is mainly a surface phenomenon characterized by alterations in the interfacial properties.In addition,the stability of the C over time illustrates the feasibility of biochar as a C sequestration technique,and the increases in the oxygen-containing functional groups and specific surface area over time are responsible for the process of nutrient adsorption.?2?The aging of biochar changes its physicochemical properties,and these changes differ for different types of biochar and treatments.In our study,the p H values of apple tree branch biochar and maize stalk biochar after three aging treatments all showed a downward trend.Moreover,the acidity and alkalinity of the two types of biochar after chemical oxidation treatment changed,which was caused by the increase of the content of acidic oxygen-containing functional groups.Apple tree branch biochar and maize stalk biochar all showed a decrease in C content and an increase in O content and O/C atomic ratio after three different treatments,and the change trend of O content and O/C atomic ratio was the most significant after chemical oxidation treatment,which was caused by the oxidation of H₂O₂.In addition,apple tree branch biochar and maize stalk biochar showed different trends in the changes of the functional groups after the three aging treatments due to the different types of biochar and aging methods.Among them,the increase of oxygen-containing functional groups and other data in our test results are mutually corroborating,indicating that biochar has undergone oxidation during the aging process.?3?The aging of biochar changes its Pb???adsorption behavior,and these changes differ for different types of biochar and different treatments.Changes in specific surface area affect the number of binding sites,thereby affecting the Pb???adsorption capacity of biochar.An increase in O-containing functional group content enhances the Pb???adsorption capacity of biochar via complexation of carboxyl and hydroxyl functional groups with Pb???,and other mechanisms.In our study,the Pb???adsorption capacity of all the biochar samples was due to the complexation of surface free carboxyl and hydroxyl functional groups with Pb???and van der Waals forces between the adsorbate and adsorbent greatly.Limited metal precipitation also occurred during the adsorption process.Our research in this area will offer insights regarding the implications of biochar aging on contaminant behavior.