Characterization of soil humic acid reacting with calcium ion and its application

Dr Baohua Xiao1, Haimin Tang1,2, Peiwen Xiao1,2

1State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China, 2University of Chinese Academy of Sciences, Beijing, China

Soil humic acid (SHA) practically defined as soluble in basic solution and insoluble in acidic solution is an important component of soil organic matter (SOM). SHA was considered as the main reagent for maintaining sound physical structures of soil and providing nutrients to living plants. SHA had drawn tons of attention, but the chemical properties of SHA, even its existing, remain controversial since of the large inconsistence of characteristics data between literature studies. Here we reported a study on reactions of calcium ion with SHA samples and the online spectroscopic characteristics of SHA during the reactions. This study has two major purposes: first, to understand the overall reaction of Ca2+ and SHA in soil and to dig out underlying mechanisms; second, to illustrate the inactivation effects of Ca2+ to SHA samples, which could be qualitatively described by spectroscopic information. To achieve these purposes, three bulk SHA samples were carefully extracted from three layers of a profile of limestone soil using the recommend extraction method of IHSS, one bulk SHA from the top layer was further divided into 5 sub-fractions according to their apparent molecular weights using a tangential flow filtration system, and a continuous on-line measurement system, including automatic potentiometric titrator, UV-visible spectrometer and three-dimensional excitation and emission matrix fluorescence (3D-EEM), was set up. The idea is to allow Ca2+ reacts with SHA gradually in the apparatus of automatic potentiometric titrator and so that the optical spectroscopic signals of SHA can be monitored continuously. The preliminary results showed that the overall reaction of Ca2+ and SHA is a combined process of complexation and adsorption, the reaction with Ca2+ can modify the spatial configuration and molecular size of SHA which may be reflected by changes in the spectroscopic signals of SHA.


Baohua Xiao is a professor researcher in the State Key Laboratory of Environmental Geochemistry at the Institute of Geochemistry, Chinese Academy of Sciences, Guiyuang China. He received his Ph.D. in Earth and Environmental Science from Drexel University (2004), M.Sc. in Geochemistry from Institute of Geochemistry, Chinese Academy of Sciences (1996), and B.Sc. in Geochemistry from University of Science and Technology of China (1993). He did postdoctoral study in Department of Environmental Science of Rutgers University (2004-2008). His research interests lie in characterization of natural organic matters and understanding interactions between metals and soil organic matters.

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