Adsorption Of Uranium From Radioactive Wastewater By Phosphoric Acid Modified Carbon Material

With the rapid development of the modern nuclear energy industry,the amount of radioactive uranium-containing wastewater is increasing,and the types and sources of uranium-containing wastewater are also extremely extensive.Therefore,whether it is from the perspective of sustainable development of nuclear energy,ecological environment protection and human health,the removal of uranium from radioactive wastewater has important practical significance.The adsorption plays an important role in the purification of uranium-containing wastewater due to its large amount of advantages,including high efficiency,ease of operation,low cost and wide applicability.The carbonaceous adsorbent has excellent properties such as large specific surface area,good pore structure,high mechanical strength,strong resistance to heat and radiation damage,and exhibits great potential in the purification of radioactive wastewater.To this end,this thesis uses phosphoric acid as an activator to prepare a cheap and efficient phosphoric acid modified carbonaceous adsorbent by high temperature activation and hydrothermal method.The effects of various environmental factors on the adsorption performance of U(VI)on the above adsorbents were systematically studied by static batch experiment.At the same time,the microscopic analysis technology is used to deeply explore the adsorption mechanism of U(VI)on the obtained adsorbent materials:(1)Phosphoric acid activated peanut shell by heat activation methodPhosphoric acid activated peanut shell was prepared through heat activation method at 200-800?,which used peanut shell as carbon source and phosphoric acid as activator.The effects of pH values,ionic strength,contact time and reacting temperature on the removal of U(VI)by the adsorbent were investigated.The results showed that the adsorption performance of U(VI)on PACs was significantly improved compared with peanut shell powder.In addition,the adsorption capacity depends on solution pH,and the ionic strength can promote the adsorption of U(VI).According to the linear correlation coefficient R~2 value,the U(VI)adsorption on PACs follows the pseudo-second-order kinetic equation and the Langmuir model.According to the Langmuir fitting results,PAC-800 exhibited the highest adsorption capacity of120.90 mg/g.The adsorption process is an endothermic spontaneous process.The increasing U(VI)adsorption could be attributed to C=OOH groups and delocalized?electrons as sorption sites react with U(VI)by surface complexation and ion exchange.(2)Phosphoric acid modified medium activated carbon by hydrothermal methodAlthough PACs prepared through heat activation method in phosphoric acid can introduce phosphorus-containing functional groups,their adsorption capacity of U(VI)are still in the middle position compared with similar carbon materials.Therefore,phosphoric acid modified coal-based activated carbon(AC-PHs)was prepared by hydrothermal treatment of coal-based activated carbon in phosphoric acid solution.Similarly,the effects of hydrothermal temperature and various environmental factors in aqueous solution on the removal of U(VI)by AC-PHs were investigated by static adsorption experiments.The results indicated that AC-PHs exhibit excellent adsorption capacities for U(VI),and the adsorption process can be better fitted by pseudo-second-order kinetic equation and the Langmuir model.The maximum adsorption capacity of U(VI)on AC-PH was 228 mg/g at 298K,pH=4.0?0.1.XPS analysis showed that the-OH,-COOH and phosphoric acid functional groups on the adsorbent surface reacted with U(VI)during the adsorption process.This is the adsorption mechanism of U(VI)removal by AC-PHs.