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Thread: soil science and negative charge on clay particles

  1. #1 soil science and negative charge on clay particles 
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    Dec 2008
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    What accounts for the charge on clay colloids?

    Isomorphous substitution?
    CEC?
    pH dependence?


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  3. #2  
    Universal Mind John Galt's Avatar
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    Clays are sheet minerals, with the extensive sheets composed of interlinked silicon tetrahedra and aluminium octahedra. Substitution of the silicon (tetravalent) by aluminium or other trivalent ions in the silicon tetrahedra, and of aluminium (trivalent) by calcium, magnesium, or other bivalent ions, leads to a net positive charge imbalance on the clay particle.

    This ionic substitution is possible because of the similar size of the ions involved. So, it looks like isomorphous substitution is the correct answer to your homework question.

    CEC, or Cation Exchange Capacity, is one measure of this charge imbalance.

    The concept is important in agriculture and forestry, since the CEC is an indirect measure of the fertility of the soil. Protection of aquifers or soils from pollution is related to this, as it can be a measure of the resistance to contamination. It is also important in oil exploration, since the stability of the drilled clays is related to the charge imbalance.


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