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    Effect of Sulfate Contamination on the Volume Change Behavior of Bentonite

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    This paper reports the influence of the principal anionic contaminant of acid rain deposition, namely sulfate ion, on the index, swelling, compressibility, and permeability characteristics of bentonite. Adsorption of sulfate ion leads to edge-to-edge bonding of bentonite particles; the occurrence of such a reaction mode throughout the clay matrix mobilizes an edge-to-edge flocculated fabric.

    The liquid limit, swelling magnitude, and swelling pressure of bentonite clay markedly increases on sulfate adsorption. It is likely that, for the anion-treated clay, besides the growth of a diffuse double layer, water is imbibed by entrapment in the large void spaces of its flocculated structure, thus explaining the higher liquid limit and swelling magnitude of the treated specimen. Further, it is considered that the higher degree of particle interference associated with the flocculated fabric of the anion-treated clay resists particle rearrangement under external stresses more effectively than the oriented array of the natural clay, accounting for the larger swelling pressure of the former specimen. The greater particle interference associated with sulfate clay presumably is responsible for its consolidation curve being positioned above that of the natural clay.

    The de/d (log p) versus pressure plots indicated higher compressions for the anion-treated clay at any given pressure increment. Possibly the anion-treated clay with a flocculated fabric undergoes greater particle reorientation under a given load, explaining its higher compressibility. The similar ranges of permeability coefficients observed for the natural and anion-treated clays suggested that the changes in clay fabric brought about by anion adsorption is not significant enough to influence the permeability of bentonite clay.


    chemical properties, clays, compressibility, industrial wastes, permeability, swelling

    Author Information:

    Sridharan, A
    Professor and research scientist, Indian Institute of Science, Bangalore,

    Rao, SM
    Professor and research scientist, Indian Institute of Science, Bangalore,

    Gajarajan, VS
    Assistant professor, J. C. College of Engineering, Mysore, Karnataka State,

    Committee/Subcommittee: D18.06

    DOI: 10.1520/STP23547S