Interaction Between Humic Acid, Iron Oxides And Kaolinite, And Their Characteristics

Humic acids, oxides, and clay minerals distribute widely in natural environment, and commonly they were combined to form organo-mineral complexes, which serve as a basic component and absorbent in soils and sediments. The characterization of complexes is also found to be an internal factor determining the soil quality by controlling soil phase activities and affecting the physical, chemical, and biological processes in soil. In this study, complexes of Fe oxides, kaolinite, and humic acid at different reaction conditions were successfully achieved. Their complexion mechanisms, and their structure and surface properties were studied by XRD, SEM, IR, BET, TG1. The interaction between Fe oxides and kaolinite. The results from XRD and SEM indicate Fe oxides in Fe oxide-kaolinite complex featured a weak crystallinity probably due to the inhibitive effects from kaolinite. The characteristic absorption peaks of kaolinite significantly decreased compared to that from pure kaolinite, indicating Fe oxides were coated homogeneously on the surface of kaolinite in the complex. The absorption peaks in FTIR spectra of complexes clearly indicate that hydrogen bond was formed between kaolinite and goethite during interaction.2. PAHA adsorption by minerals. The ability of PAHA adsorption varies significantly among different minerals: goethite > complex > kaolinite > compound. The adsorption capacity increased with the increase of the specific surface area (SSA) and positive charges on the surface of minerals. Adsorption isothermal curve fitted well with Langmuir equation evidently; the adsorption constant and maximum adsorption value were consistent with experimental adsorption data. An increase of pH value was observed during the PAHA adsorption and found to be positively related to the amount of adsorption, indicating that the adsorption process was determined by the ionic exchange between anions in humic acid and -OH on minerals surfaces.3. Interaction between humic acid, Fe oxide, and kaolinite: IEP values of Fe oxide, kaolinite and their complexes reduced after the adsorption of PAHA, and SSA of Fe oxide, kaolinite increased after the adsorption of PAHA. The increased intensity of infrared absorption was observed for all complexes after the adsorption of PAHA, indicating hydrogen bond was formed between minerals and PAHA. The differences between thermal stabilities of the minerals before and after the PAHA adsorption were insignificant, based on the TG and DTG analysis.