Study of the interactions between atrazine, diazinon and lindane with humic acids of various molecular weights

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Abstract
Kinetic, complex formation and equilibrium studies of the adsorption of atrazine, diazinon and lindane on humic acids (HA) of various molecular weights (MW) were investigated. There was evidence that on HA with MW > 300,000 daltons, Intraparticle diffusion of the adsorbate into the adsorbent particles was the rate limiting process. Complex formation of atrazine with HA was observed on HA with MW < 300,000 daltons with more atrazine being complexed at acid than at alkaline pH. This result was ascribed to the presence of more atrazine molecules in the protonated form. Ion exchange and hydrogen bonding reactions as well as electron transfer were in this case the mechanisms postulated. Equilibrium data of atrazine and lindane adsorbed on all HA fractions were explained by the Freundlich type isotherm whereas diazinon adsorption on HA with MW > 300,000 daltons followed the Langmuir type isotherm. Throughout the investigation, adsorbate-adsorbent interactions was generally higher at pH 3.7 than at 7.0.