Interactions between Humic Acid and the Mineral Surface of Laterite at Different Environmental pH

Organic compounds such as humic substances in the natural environment, especially in aquatic environments, are source of environmental problems. The stability of humic compounds in the soil is due to their adsorption on colloid surfaces through reactions with cations to form organ- mineral complexes. Many parameters such as pH, ionic strength. can affect the adsorption of humic substance on mineral surfaces. This study was initiated to investigate the use of a natural geo-material such as laterite for recovery and environmental application through batch adsorption tests. Since this system is a closed and agitated system, it makes it possible to obtain the maximum conditions for adsorption. Lateritic soil are abundant in tropical soil and exhibits some specificities that could promote humic acids-soil interactions. So, the analysis of pH influence on humic acid-laterite interactions is monitores through batch adsorption tests of a commercial humic acid at different pH (4.5; 6.5 and 8.5). The adsorption kinetic yield (R) is followed at each pH. Prior to the adsoption test, the raw laterite was analysed using infrared spectroscopy. The results of the kinetics of humic acid adsorption yield at different pH (4.5; 6.5 and 8.5) showed that the adsorption yield was inversely proportional to the increase of pH. The highest yield is obtained at pH 4.5 (94.56 %). Infrared analyzes of the laterite before and after adsorption shows that the surface of the laterite has undergone modifications associated to humic acid presence in the complexe after adsorption test. However, the media most affected by adsorption were observed at pH 8.5 and pH 4.5. The changes observed are due to the interactions between the aluminum oxides of gibbsite-AH (Al(OH)2–O–R) and kaolinite-AH (Si2O5Al2(OH)3–OH–R present on the surface of materials and the bonds of carboxylic, aromatic, phenolic, etc. groups confirms the adsorption reaction between humic acid and laterite.