Influence of the origin and nature of humic substances on atrazine adsorption onto powdered activated carbon
Though the subject was copiously and oldly studied, this work is bringing a new contribution to the study of the influence of the origin and the nature upon their properties and in particular with atrazine, the more used herbicide these fast years. In order to study this influence of the origin and nature of various humic substances upon the removal of atrazine by adsorption onto powdered activated carbon (PAC), humic substances were obtained from different sources : - Natural aquatic fulvic (F1) and humic (H1) acids isolated from Beaune Lake (Limoges, France). - Natural aquatic fulvic (F2) and humic (H2) acids extracted from hydroxyde sludges of the water treatment plant of La Bastide (Limoges, France). - Soil fulvic acids (F3) extracted from a canadian top soil horizon. - Commercial humic acids (Aldrich. H4 and Jansen H5) obtained from commercial sodium humates. The results of adsorption test of humic acids, fulvic acids and atrazine (alone or together) onto powdered activated carbon (PAC) at three different pH (5,6 ; 7,0 ; 8,8) were expressed by Freundlich's and Langmuir’s models and permitted us to note that : - According to the increasing of water solubility of humic substances with basic pH, their adsorption was better in acidic medium. - Natural aquatic humic substances (H1, H2, F1, F2) were more adsorbed onto PAC than humic substances tram soil (H3) or commercial origines (H4, H5). - Atrazine adsorption capacity was 260 mg.g-1 according to Langmuir's model. - Atrazine adsorption decreased with F1 for all pH ; the same result was also observed with the other natural aquatic humic substances. - Commercial humic acids didn’t importantly affect atrazine adsorption. These differences appeared to be derived from the nature and the origin of fulvic and humic acids. The rose of atrazine on the humic substances adsorption showed a difference between humic and fulvic acids whose adsorption was not influenced by atrazine even humic acids only presented an increasing of adsorption. All these results showed the importance of the selection of humic substances to evaluate the interaction SH-Pesticides during adsorption onto PAC and let us think to a competitive adsorption between fulvic acids and atrazine onto PAC.