Effect Of Dissolved Organic Matter On Adsorption Of Copper By Aged Biochar

Biochar has a strong application prospect in heavy metal contaminated soil remediation due to its developed pore structure,large specific surface area,and abundant surface functional groups.The solidification of Biochar on heavy metal not only occurs on the surface of Biochar particles,but also interacts with dissolved materials（such as BDOM and the soluble inorganic minerals）.Biochar-derived dissolved organic matter（BDOM）from biochars has significant mobility after the application of biochars in the environment.The expected strong interactions between BDOM and heavy metals may enable BDOM as an effective carrier for heavy metal transport.The characteristics of BDOM are determined by the raw materials of biochars as well as the geochemical processes during their release,for example,Irrigation,rainfall and changes in the soil environment.However,BDOM characteristics as affected by geochemical processes and the effect of characteristics on the interaction of aging biochar and heavy metals were not extensively studies.In this study,biochars will be prepared from different materials,including different sources of agricultural solid waste（Corn straw Pine chips）.The pyrolysis temperature varies in the range of 200～500 ^oC.Chemical degradation experiments（H₂O₂）will be conducted for various biochars.The BDOM property change will be analyzed.Based on this,the influence mechanism of BDOM on copper adsorption in aged biochar will be systematically studied.Meanwhile,the interactions between BDOM and heavy metals will be systematically studied.BDOM-heavy metal interactions controlled by DB properties will be highlighted.The results of this study will provide a theoretical basis for systematically understanding the environmental effects of biochar and understanding the environmental significance of different organic matter components in BDOM.The main research results are as follows:（1）As the temperature of pyrolysis increases,the surface hydroxyl,phenolic hydroxyl and aliphatic groups of aged Biochar gradually decrease;the content of C and N gradually increased,while the content of O and H decreased,and the H/C,O/C and（O+N）/C gradually decreased,declaring that with the increase of pyrolysis temperature,the aromaticness of aging Biochar gradually increased,at the same time the hydrophilicity and polarity gradually decreased;The contents of C,H,O and N in the BDOM released from the aging Biochar all decreased,whereas H/C decreased and O/C and（O+N）/C increased,stating that the aromaticity,hydrophilicity and polarity of BDOM released from the aging Biochar all showed a tendency toward increased with the increase of pyrolysis temperature.H/C,O/C and（O+N）/C of aged corn biochar were lower than that of aged pine biochar,indicating that aged corn stalk biochar was more aromatic,but less hydrophilic and polar than that of aged pine biochar.The contents of C,H and O elements and H/C in the BDOM of aged corn stalk biochar were all lower than that of aged pine biochar,but（O+N）/C was higher than that of aged pine biochar,indicating that the BDOM of aged corn stalk biochar was more aromatic and more polar than that of aged pine biochar.（2）The adsorption isotherm of aged Biochar on copper demonstrated that the adsorption capacity of aged corn stalk on Cu²⁺was higher than that of aged pine Biochar.The N value of the adsorption nonlinear index of Cu²⁺in the Freundlich model for two kinds of aged biomass（pine and corn straw）and its Biochar preparation was between 0.44 and 0.89,both of which were less than 1.00,indicating that the adsorption of Cu²⁺by the two kinds of aged biomass（corn straw and pine）and its Biochar preparation had strong heterogeneity.Comparing with aged Biochar whose pyrolysis temperature is greater than 500 ^oC,protoplasm and relatively low temperature Biochar（pyrolysis temperature≤400 ^oC）have higher adsorption capacity for Cu^2+.The complexation of carboxyl and hydroxyl functional groups in aged Biochar with copper effectively promoted the adsorption of copper.（3）The results of the study on the effect of BDOM on the adsorption of copper by aged Biochar showed that the adsorption coefficient K_d value of Cu²⁺of aged Biochar increased with the increase of BDOM under either high concentration of Cu²⁺(10 mg·L^-1)or low concentration of Cu²⁺(1 mg·L^-1).The release of BDOM and the loss of inorganic minerals on the surface of aged Biochar,further leads to the increase of adsorption sites on the surface of aged Biochar and the enrichment of pore structure.（4）The complexation of BDOM to copper in aged Biochar:the results of SUVA₂₅₄ and SUVA₂₆₀ show that BDOM is a hydrophilic substance with very low aromatics.According to the Three-dimensional fluorescence spectra,there are two main kinds of BDOM in the aging Biochar:humic acid and fulvic acid,and with the increase of pyrolysis temperature,the humic acid group will gradually decompose into fulvic acid which has a smaller molecular weight.The binding capacity of BDOM to Cu²⁺in aged Biochar is affected by the surface functional groups,the types of organic matter contained in BDOM and the pyrolysis temperature.Humic acids could bind to Cu²⁺more easily than fulriic acids,and as the temperature increases,the number of fluorescent groups increases and more binding sites provided,increasing the binding capacity of BDOM to Cu²⁺.The results of titration experiment of copper ions indicated that the complexation stability constant K and binding capacity of ACD were greater than that of AWD.