Adsorption of amitraz by a river sediment: Apparent thermodynamic properties

Abstract

The adsorption/desorption of amitraz by suspended river sediment particles in an aqueous medium was studied in terms of a model which assumes the adsorption/desorption equilibrium nX + S ðí SX_n(W) ðí SX_n(sed), where X and S represent the pesticide molecule and suspended particle respectively, SX_n(w) is the pesticide‐particle complex (in suspension), and n is the number of pesticide molecules associated with a single adsorption site. According to this model the apparent adsorption/desorption equilibrium constant, K’, is given by

where [X]_ads is the concentration of X in the adsorbed state in suspension found in the sediment after settling, [X]_e is the concentration of X in solution at equilibrium, and [SX]_w is the concentration of the pesticide‐adsorption site complex in suspension at equilibrium. Values of 111”; 19, 0.26"0.03 and ‐11.6"0.5 KJmole‘¹ were obtained for K¹, n, and DG’ (the apparent adsorption/desorption free energy) for the adsorption of amitraz by the river sediment used.

Key words:

• Adsorption
• pesticide
• amitraz
• adsorption equilibrium constant
• adsorption free energy