Conformation and size of humic substances: Effects of major cation concentration and type,pH, salinity,and residence time |
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| Institution: | 1. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;2. School of Chemistry and Materials Science, Guizhou Normal University, Guiyang 550001, China;3. BCEG Environmental Remediation Co., Ltd, Beijing 100015, China;4. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, Guizhou, China;5. University of Chinese Academy of Sciences, Beijing 100049, China;1. Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP3), Department of Environmental Science and Engineering, Fudan University, Shanghai, 200433, China;2. College of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, China;3. Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, P.R. China;4. Shanghai Technical Service Platform for Pollution Control and Resource Utilization of Organic Wastes, Shanghai, 200438, China;1. Department of Chemical Engineering, Tennessee Technological University, Cookeville, TN 38505, United States;2. Center for the Management, Utilization and Protection of Water Resources, Tennessee Technological University, Cookeville, TN 38505, United States;3. EnviroChem Services, 224 Windsor Drive, Cookeville, TN 38506, United States |
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| Abstract: | The macromolecular structure of humic substances (HS), i.e. molecular size, shape, conformation, and weight is believed to control key physico-chemical reactions in aquatic systems. However, these properties of HS are still deeply a matter of debate. Furthermore, they are affected by solution physico-chemical parameters such as ionic strength, pH, and chemical composition, etc. To better understand aggregation processes of HS in natural waters, the effects of cation concentration and type, water composition, and pH on the size and conformation of the Suwannee River Humic Acid (SRHA) were investigated with synthetic solutions. The size and the conformation of the SRHA in NaCl and CaCl2 solutions at different concentrations (0.001–0.5 M) and pH (4.5–9.3) were determined using the photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM), respectively. In addition, dissolved organic matter (DOM) samples collected from the Adour estuary along a salinity gradient were imaged by TEM. The average size of the SRHA measured by PCS increased with pH and ionic strength. This behavior was confirmed by TEM micrographs. The increase in pH and CaCl2 engendered aggregation of the SRHA. Two aggregation steps were identified, a big increase in HS size occurred for small changes in CaCl2 concentrations in the range <0.02 M CaCl2, and a slight increase occured for higher concentrations in the range >0.02 M CaCl2. The parallel analysis of SRHA by PCS and TEM allowed overcoming the limits for both techniques.Comparable results were found for the DOM samples from the Adour estuary (South West of France). The conformation and size of the HS network of these samples varied with the salinity gradient. TEM images demonstrated that, HS have a branched open network in freshwater whereas they have a more compacted and close network with increasing salinity. |
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