Premium
Adsorption of Sulfate by Kaolinite and Amorphous Iron Oxide in the Presence of Organic Ligands
Author(s) -
Inskeep William P.
Publication year - 1989
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq1989.00472425001800030024x
Subject(s) - tannic acid , chemistry , adsorption , sulfate , humic acid , gallic acid , oxalic acid , citric acid , inorganic chemistry , nuclear chemistry , kaolinite , ascorbic acid , organic chemistry , mineralogy , antioxidant , fertilizer , food science
The ability of soils to adsorb SO 4 is an important factor in determining the effect of acidic deposition on the transport of H + and cations in terrestrial ecosystems. However, the role of soluble organic acids and humic substances on the adsorption of SO 4 is poorly understood. Consequently, this study was conducted to determine the effects of soluble organic ligands on the adsorption of SO 4 by amorphous iron oxide (AIO) and kaolinite (KGa‐2). Adsorption experiments were conducted by titrating 50 m M K 2 SO 4 with suspensions of KGa‐2 (146‐583 m 2 L −1 ) or AIO (324 m 2 L −1 ) in 0.01 M KCl, at pH 4.3 and 25 °C. Sulfate adsorption was studied over a range in total SO 4 of 0.01 to 2.5 m M in the absence and presence of organic ligands including Seward humic and fulvic acid, tannic acid, citric acid, oxalic acid, and gallic acid. Sulfate adsorption capacities in the absence of organic ligands were 3.5 and 1.3 µ mol c m −2 at 324 m 2 L −1 AIO and 583 m 2 L −1 KGa‐2, respectively. Humic and tannic acid present at 1.4 to 3.6 m M total soluble C reduced SO 4 adsorption by KGa‐2 at total SO 4 levels below 0.12 mM. Humic, tannic, citric, gallic, and oxalic acid were all effective at inhibiting SO 4 adsorption by AIO. In several cases the percent of SO 4 adsorbed was reduced from near 100 to zero at total SO 4 levels below 0.12 m M . The amount of inhibition was related to the quantity of oxygen‐containing functional groups added rather than the total soluble C. These results indicate that organic acids compete for SO 4 adsorption sites and that the presence of organic acids in soil solutions will influence SO 4 adsorption capacities.