Separation And Extraction Of Rare Earth Elements From Fly Ash By Supercritical CO₂ Fluid Complex Extraction

With the development of science and technology,rare earth elements have been widely used in many traditional industries and other high tech fields due to their unique optical,electrical and magnetic properties.Therefore,it has the reputation of "industrial vitamins".Although China has many rare earth resources,due to the large-scale exploitation of rare earth minerals,the rare earth resources in China have been drastically reduced.In order to meet demand of the high-tech industry,the protection of rare earth resources,and the search for new sources of rare earth have become major tasks in China.Fly ash is an inevitable product of thermal power generation.Fly ash is rich in useful elements and has a huge output.Based on the huge fly ash production,the extraction and comprehensive utilization of useful elements in fly ash avoids waste of resources and metal recovery.In the technique of extracting rare earth elements from fly ash,the supercritical CO2 fluid complex extraction method is a novel extraction method,which not only reduces the amount of acid and other chemicals,but also has a high extraction rate.Therefore,this paper first studied the extraction ratio of supercritical CO2 fluid extraction and acid leaching extraction.The results show that the supercritical CO2 fluid can improve the extraction rate of rare earth elements in fly ash.The extraction rates is different for different coal types.Fly ash of bituminous coal,the extraction rate is about 20%to 40%.Fly ash of lignite,the extraction rate can reach 40%to 60%.The extraction rate is also different for different rare earth elements.The extraction rates of La and Gd are high in these six fly ash.This may because of the rare earth element itself and the state of occurrence in the fly ash.And then studied the effects of time and acid concentration on the supercritical CO2 fluid extraction method.The results shows that for supercritical CO2 extraction methods.the extraction rate is improved with the increase of temperature.Temperature is a very important factor affecting the extraction rate.Therefore,it is possible to increase the extraction by increasing the temperature.And the extraction rate is greatly improved with the increase of reaction time.Time is a very important factor affecting the extraction rate.Therefore,it is possible to increase the extraction by increasing the reaction time,and reduce the amount of acid and the pressure and temperature can be lowered,which facilitates the industrialization of the technology.The extraction rate is also improved as the acid concentration is increased,but the effect on the extraction rate is relatively small.Increasing the acid concentration will increase the amount of acid,and cause environment pollution and corrosion to equipment.