The Spectral Characteristics Of DOM In Straw Biochar And Pig Manure Biochar And Its Complexation With Heavy Metals In Solution

In recent years,with the rapid development of industrial and agricultural modernization in China,a large number of heavy metal pollutants have emitted through the industrial"three wastes",excessive use of fertilizers and pesticides by human activities is released into the environment,which will not only destroy the water,soil and atmospheric environment,further to threat the health of human survival,influence the sustainable development of human society and ecological environment.Soil is a natural resource that human beings rely on for survival.The remediation of soil heavy metal pollution has become an urgent problem to be solved.In recent few years,biochar prepared by low-temperature oxygen-limited pyrolysis of biomass waste has been widely used to remediate of soil contaminated with heavy metals.The results showed that the characteristics of biochar,such as high p H value,large specific surface area and abundant oxygen-containing functional groups,all played an important role in the passivation of heavy metals in soil.In addition,biochar also contains dissolved organic matter（DOM）,which can affect the migration and transformation of heavy metals in soil solution or water through complexation and chelation.However,the content and components of DOM in biochar are different with pyrolysis temperature and biomass raw materials,which affect the interaction between biochar and heavy metal ions.Therefore,this study selected 350℃and 450℃pyrolysis of maize straw（MSB）,rice straw（RSB）,peanut straw（PSB）,pig manure（PMB）biochar DOM,used UV-Vis absorption spectrum and three-dimensional fluorescence spectrum combined with parallel factor analysis,research content and spectral characteristics of different raw materials,pyrolysis temperature of crop straw and pig manure biochar DOM,via the fluorescence quenching titration experiment,comparing different sources DOM and complex parameters with different kinds of heavy metals were compared to provide data support and theoretical basis in order to further understand the interaction mechanism of biochar and heavy metals.The main results of this study are as follows:（1）The content of straw biochar and pig manure biochar DOM ranged from 2.51 to26.92mg/g.At the same pyrolysis temperature,the content of PSB-DOM was higher,which was 4.97-5.84 and 2.11-3.95 times of that of other DOM,respectively.With the pyrolysis temperature increasing from 350℃to 450℃,the contents of straw biochar DOM decreased by 36.66%-63.15%.（2）The specific absorptivity(SUVA₂₅₄)of different biochar DOM ranged from 1.51 to3.77 L/mg/m,the E_ET/E_Bz ranges from 0.37 to 0.59,and the E₂/E₃ was 4.48-7.38.Except for350℃PSB-DOM,other DOM were mainly hydrophilic substances with low aromaticity,and the main constituent substance of all DOM was fulvic acid with relatively small molecular weight.At the same pyrolysis temperature,PSB-DOM has higher aromaticity,content of oxygen-containing functional groups in aromatic structure and molecular weight.With the increase of pyrolysis temperature,the aromaticity,the content of oxygen-containing functional groups in the aromatic structure and the molecular weight of PSB-DOM were significantly decreased,while that of PMB-DOM was the opposite.（3）The freshness index（β/α）,autologous index（BIX）and humification coefficient（HIX）of all DOM were in the range of 0.50-1.15,0.51-1.34,0.75-0.93,respectively.At the same pyrolysis temperature,the humification degree of RSB and PSb-DOM were higher,and the newly generated DOM and bioavailability of PMB-DOM were significantly higher than that of straw biochar DOM.MSB-DOM is the highest in straw biochar DOM.With the increase of pyrolysis temperature,the humification degree of all DOM increased,and the newly generated DOM and bioavailability of straw biochar DOM decreased,and the variation trend of PMB-DOM was opposited.（4）The biochar DOM is mainly composed of fulvic acid-like（C1）,humic acid-like（C2）with shorter wavelength and humic acid-like（C3）with longer wavelength,of which the proportions of C1,C2 and C3 were 28.8%-58.7%,28.5-55.6%and 10.8%-18.3%,respectively.When the pyrolysis temperature is 350℃,the PMB-DOM and straw biochar were dominated by C1 and C2.At 450℃,expect RSB-DOM,which was dominated by C2,the other DOM was dominated by C1.With the increase of pyrolysis temperature,the proportion of C1 in MSB,PSB and PMB-DOM increased by 6.0%-25.3%,while the proportion of C2 decreased by 8.0%-25.6%,and only the proportion of C3 in PMB-DOM increased by 2.0%.（5）The ranges of complex interaction between each component of biochar DOM components and Cu,Cd,Pb and Zn was 12.9%-61.8%,-5.0%-11.6%,-31.7%-44.4%and-20.9%-7.1%,respectively.The complex stability constants（log K_M）of C1,C2,C3 and Cu²⁺in all DOM were 3.99-5.02,3.99-5.12 and 4.51-5.13,respectively,and the fluorophore ratios（f）involved in the complexation were 0.16-0.38,0.16-0.88 and 0.19-0.59,respectively.Except 450℃MSB and PMB,C3 has a higher complexing affinity with Cu²⁺in other DOM,and the complexing ability of C2,C3 was stronger than C1.At the same pyrolysis temperature,the complexation properties of each component in PSB and MSB-DOM with Cu²⁺were higher.With the increase of pyrolysis temperature,the complexing affinity of C1and C3 in RSB-DOM,MSB and PSB-DOM decreases and the complexing ability increases.The log K_M of each component of straw biochar DOM and Pb²⁺were 4.46-5.20,4.62-4.90,4.23-4.76,and f values were 0.04-0.32,0.09-0.27,0.18-0.73,respectively.Except for 350℃MSB-DOM,C1,C2 have a higher complexing affinity with Pb²⁺in other DOM,and C3 has a stronger complexing ability in all DOM.With the increase of pyrolysis temperature,the complexing affinity of C1 and C3 in MSB-DOM decreased,but the complexing ability increased,while the change trend of C2 was opposite.The complexing affinity of each component in PSB-DOM decreased,but the complexing ability of C2 and C3 increased.The log K_M of some components in PSB and PMB-DOM and Cd²⁺were 3.56-5.06,and the f value was 0.05-0.20.Expect for 450℃PMB,the other components of DOM had a high complexing affinity with Cd²⁺,and C2 was the highest in 450℃PSB-DOM,while C1 has the highest complexing ability in PMB-DOM.With the increase of pyrolysis temperature,the complexing affinity of C2 in PSB-DOM increased,the complexing affinity of C1 and C2 in PMB-DOM decreased,and the complexing ability of C1 increased.None of the components in DOM had significant fluorescence quenching reaction with Zn²⁺,so the parameters could not be fitted by the improved Stern-Volmer equation.