Adsorption of Atrazine Pesticide by Different Soil Samples: Apparent Thermodynamic Properties



The adsorption/desorption of atrazine pesticide by different soil particles in an aqueous solution was studied in terms of a model which assumes the adsorption/desorption equilibrium nX+s δi SXn (w) δSXn(soil particle) where X and S represent pesticide molecule and suspended particles respectively: SXn(w) is the pesticide particle complex and n is the number of particles molecules associated with a single adsorption site.

The apparent adsorption/desorption equilibrium constant k is given by:

ln[X]ads =   ln(nk) + nln[X]e + [SXn]w

[x]ads is concentration of X in adsorbed state in suspension.[X]e is the concentration of X in solution at equilibrium.[SXn]w  is the pesticide adsorption site complex in the suspension at equilibrium. The set of values of: 0.1359, 2.3846 and -11.01 KJ/mole for the sediment; 0.1443, 3.6602 and -13.92 KJ/mole for clay; 0.4539, 1.6774 and -7.37 KJ/mole for the Kwale red were obtained for n, K and δG respectively (the apparent adsorption/ desorption free energy) for the adsorption of atrazine by the sediment, clay and Kwale red soil sample used.


Key words: Adsorption, pesticide, atrazine, adsorption equilibrium constant,

         adsorption free energy.

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