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 Title: Effects of structural iron oxidation state on the hydraulic conductivity and potassium fixation of smectite clays and soils Author(s): Shen, Siyuan Doctoral Committee Chair(s): Stucki, Joseph W.; Boast, C.W. Department / Program: Agriculture, AgronomyMineralogyChemistry, Agricultural Discipline: Agriculture, AgronomyMineralogyChemistry, Agricultural Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Agriculture, Agronomy Mineralogy Chemistry, Agricultural Abstract: Changes in oxidation states of structural Fe in smectites altered the physicochemical properties of the minerals, which is of great importance to agriculture and environment because the permeability of soils and availability of plant nutrients depends in large degree on these properties of clays.Two smectites (SWa-1 and API 25) and the clay fraction of Batestown till with different saturating cations (Na$\sp+$, K$\sp+$, and Ca$\sp{2+}$) were reduced by sodium dithionite (Na$\sb2$S$\sb2$O$\sb4$) or sulfide (Na$\sb2$S), both in suspension and in situ after consolidation. The results indicated structural Fe reduction altered the hydraulic conductivity of the clays. The changes in hydraulic conductivity depended on both the oxidation state and consolidation history of the clay, and the choice of reducing agents and saturating cations.The swelling of K-saturated SWa-1 was determined and compared with the swelling of Na-smectite at various Fe oxidation states. The results indicated that the swelling of oxidized K-smectite was much less than that of oxidized Na-smectite. Structural Fe reduction decreased the swelling of Na-smectite, but increased the swelling of K-smectite. The swelling of reduced K- and Na-smectite was similar.The two smectites, one illite (Fithian), and the clay fractions from the A horizon of three Illinois soils were studied by different methods and techniques. The results indicated that the structural Fe reduction altered the distribution of K between exchangeable and fixed states. In smectites, Fe reduction increased K fixation without changing the amount of exchangeable K. In Illite, the reduction treatment released K to the surrounding solution. The behavior of soil clays is thus largely dependent on the type of clay minerals and the original fixed K content. Redox cycling increased the amount of residual Fe(II), and also altered the fixed K in the clays. Issue Date: 1994 Type: Text Language: English URI: http://hdl.handle.net/2142/23486 Rights Information: Copyright 1994 Shen, Siyuan Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9512547 OCLC Identifier: (UMI)AAI9512547
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