Montmorillonite/Fe₃O₄/Humic Acid Composites（MFH） On The Experimental Study Of The Mechanism Of Action Of U（Ⅵ）

Low-level radioactive wastewater loyal uranium exists in the water in the form of U（VI）,and has the characteristics of high toxicity and easy migration.Adsorption method has the advantages of low cost,high efficiency,and less likely to cause secondary pollution.In order to find an efficient and recyclable adsorbent for the treatment of U（VI）-containing wastewater,this experiment prepared a composite of Fe₃O₄/humic acid（Fe₃O₄/HA）and montmorillonite/Fe₃O₄/humic acid materials（MFH）by hydrothermal method.MFH were analyzed by FTIR,SEM,BET and XRD.Based on the experimental results of thermodynamics kinetics,the adsorption mechanism of MFH on U（VI）was discussed,and the following results were obtained:（1）The effects of factors such as pH,Fe₃O₄/HA dosage,reaction time,initial U（Ⅵ）concentration,and the results show that the maximum adsorption capacity of Fe₃O₄/HA for U（VI）is 140.845 mg/g under conditions of temperature is 30℃,pH=6,the dosage of Fe₃O₄/HA was 20 mg,reaction time is 60min,etc.XRD and FTIR characterization showed that Fe₃O₄/HA was successfully synthesized and the surface contained a large number of functional groups.The adsorption process of U（Ⅵ）by Fe₃O₄/HA conforms to quasi-second-order kinetics and Langmuir model,which indicates that the main adsorption mechanism is chemical adsorption,and thermodynamic analysis shows that the adsorption process is a spontaneous endothermic reaction.After five consecutive adsorption-desorption cycles,the Fe₃O₄/HA repeated utilization rate reached 74.8%.（2）The effects of humic acid content,initial pH,the dosage of MFH,reaction time,initial concentration of U（VI）and adsorption temperature on the adsorption of U（VI）by MFH were studied.The results showed that the maximum adsorption rate of U（VI）by MFH was 97.5%under the conditions of humic acid content of 0.228 g,pH=6,the dosage of MFH is 15 mg,temperature of 30°C,and reaction time of 30 min.The maximum adsorption capacity is 267 mg/g,without Montmorillonite The maximum adsorption capacity of Fe₃O₄/HA for U（Ⅵ）is 140.845 mg/g.Fe₃O₄/HA are small particles agglomerated together,MFH has a corrugated structure and small Fe₃O₄/HA particles are distributed;BET results show that the specific surface area of MFH is 25.42 m²/g larger than that of Fe₃O₄/HA,and the pore volume increases,the pore diameter decreases.The characteristic crystal plane diffraction peaks of Fe₃O₄（311）and MMT（101）exist in XRD,and the material was successfully prepared.The adsorption process of U（Ⅵ）by MFH conforms to the quasi-second-order kinetic model;Langmuir can fit the adsorption results very well,mainly monolayer adsorption and multilayer adsorption.-OH and Fe-O are the main adsorption sites of MFH for U（Ⅵ）.U（Ⅵ）is successfully adsorbed on the surface of the material.MFH undergoes chemical reduction during the removal of U（Ⅵ）.The area of Fe²⁺decreased before and after,and the area of Fe³⁺increased.A small amount of Fe²⁺reacted with U（Ⅵ）to reduce U（Ⅵ）to U（IV）.The adsorption mechanism of MFH on U（Ⅵ）is mainly surface complexation and reduction reactions.After 5 cycles,the removal rate of U（Ⅵ）by MFH is still above 90%,which shows that MFH has good cycle regeneration performance.