الفهرس 
1. IntroductionOnly 14 pages are availabe for public view
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Abstract
The aim of the present study was to investigate the effects of the leractions between two important soil components, clay minerals and HSs, In the sorption of heavy metals cations under laboratory conditions selected to model the soil systems. The model system used in this study consisted of clay inerals (Kaolinite and Montmorillonite) and an extracted soil humic acid (HA). admium and lead were taken as heavy metal contaminants model.
Humic acid extracted from Egyptian soil by using recommended ~rocedures by international Humic Substance Society. HA was characterized using elemental analysis and different spectroscopic methods (NMR and FTTIR spectroscopy) to obtain more information on the chemical structure and ~nction groups of the macromolecule.
Kaolinite and Montmorillonite were characterized using elemental analysis by EDAX, calculating the surface area and cation exchange capacity (CEe) value. It was found that, the Si: AI ratio of Kaolinite is 1:1, however in case of Montmorillonite it was 2:1. Moreover, Montmorillonite has higher surface area (35.2 m2/g) and CEC (85 meq/100 g) values than Kaolinite (10 and 4, respectively).
The adsorption of soil extracted HA on colloidal-sized clay minerals particles was investigated to elucidate how the solution chemistry affects the lormation and nature of organic surface coating. A systemic study of the affects of pH and ionic strength on HA adsorption was performed. Humic acid adsorption isotherm followed Langmuir- type (L) curve.
The amounts of HA adsorbed onto clay minerals (Kaolinite and Montmorillonite) at high pH and low salt concentration are in a relatively stretched form on the surface and the adsorption was low, however, at low pH and high salt concentration a substantial fraction of the adsorbed HA is collapsed on the surface, which results in a relatively high adsorbed amount.
general, the surface complexation ligand exchange is the most important sorption mechanism of HA onto the clay minerals (Kaolinite and ontmorillonite) particles regardless of solution chemistry.
By using the scanning electron microscope, the clay minerals (Kaolinite d Montmorillonite) particles were studied after adsorption of HA noted that ay minerals particles size increases, this means that HA acts as a binding ent and as nucleus in formation aggregation.
Clay minerals (Kaolinite and Montmorillonite) particles were studied by l’ IR spectroscopy in presence and abscent of HA and this explained that ~sorption of HA on clay minerals particles carried out through carboxylic roups.
The sorption results of cadmium and lead cations on native clay inerals (Kaolinite or Montmorillonite) and on clay mineral-HA complexs under Jifferent pH and ionic strength, revealed that the adsorption amount decreased medium of lower pH and higher ionic strength, this refers to the competition lfW and Na+ for the adsorption sites with Cd (II) and Pb (II).
Heavy metals (cadmium and lead) sorption isotherm can be described lS linear isotherm at pH = 5.5 but at pH= 6.5, and the adsorption isotherm bllowed langmuir- type (L) curve in Montmorillonite and Montmorillonite-humic :omplex particles, but in case of Kaolinite and Kaolinite-humic complex ~articles, sorption isotherm can be described as Langmuir- type (L) isotherm It pH = 5.5 and 6.5. Also, the results revealed that presence of HA would mhancing the adsorption of heavy metals (cadmium and lead) on clay minerals (Kaolinite and Montmorillonite) under the studied conditions. Also, the results indicated that Pb (II) was more adsorbed than Cd (II) at the same conditions on clay minerals in presence or absence of HA.