摘要
稀土元素对全球经济和新兴产业的发展具有不可替代的支撑作用,其供应短缺使科学家的目光转向从替代来源(如粉煤灰)中回收稀土元素。本文从粉煤灰中稀土元素的含量、分布与赋存以及提取等几个方面进行了综述。许多区域粉煤灰高度富集稀土元素,且部分关键稀土元素含量大于稀土矿石,极具有回收潜力。稀土元素主要分布于粒径较小和非磁性的粉煤灰组分中,其主要载体为铝硅酸盐玻璃相。本文重点分析了粉煤灰中稀土元素提取方法的原理和优缺点。机械和化学协同活化可提高粉煤灰的活性,运用酸浸、酸碱联合浸出并加以辅助技术可高效浸出稀土元素。分离过程中,沉淀法和纳滤膜法操作简单但产品纯度有待提高,溶剂萃取法、浸渍树脂法和液膜法具有连续操作、有效分离、可回收等优点,但液膜法稳定性较差。生物吸附法更加环保,是否具有普遍适用性需进一步研究。最后指出今后的研究重点应当是协同提取粉煤灰中各种有价元素,关键在于如何高效地从复杂浸出液中梯度分离有价元素,以获取高纯度产品,降低成本以实现工业化生产。
Rare earth elements were known as"industrial monosodium glutamate"and"mother of new materials"because of their excellent physicochemical properties,and played an irreplaceable role in supporting the development of the global economy and emerging industries.With the rapid development of the social economy,the consumption of rare earth elements was increasing all over the world.Due to the shortage of rare earth elements supply,scientists turned their attention to recovering rare earth elements from alternative non-conventional sources.In the foreseeable future,the status and role of coal as China′s main energy source is difficult to change.However,it was found that rare earth elements were enriched in coal and further enriched in coal fly ash after combustion.Therefore,the extraction of rare earth elements from coal fly ash had become a hot research topic.This paper reviewed the content,distribution,occurrence modes of rare earth elements in coal fly ash and their extraction.The results showed that rare earth elements were highly enriched in the coal fly ash in many regions(such as the Far East of Russia,Kentucky of the United States,Guangxi,Chongqing,and Inner Mongolia of China,etc.)and the content of some critical rare earth elements was higher than that of traditional rare earth ores,showing great recovery potential.Rare earth elements were mainly distributed in coal fly ash with small particle sizes and non-magnetic particles.Their main carriers were the aluminosilicate glass phase,and they also existed in the form of rare earth elements rich minerals such as phosphate,apatite,and zircon,and even appeared in amorphous carbon with nano-scale metal inclusions around the glass phase.In this paper,the principle,advantages,and disadvantages of the extraction methods of rare earth elements from coal fly ash were summarized.Based on the distribution characteristics of rare earth elements in coal fly ash,it was proposed that the synergistic activation of mechanical(separation and grinding)and chemical(roasting after adding alkali flux)could improve the activity of coal fly ash.Among them,the type,dosage,and temperature of alkali flux had an important influence on chemical activation.Then,acid leaching,acid-base combined leaching assisted with certain techniques(such as microwave,ultrasonic,and stirring)could extract rare earth elements efficiently.The leaching effect of rare earth elements was affected by leaching method,leaching agent,leaching time,temperature,and coal fly ash type.The most effective leaching agents were NaOH and HCl solutions,whose leaching kinetics was mainly chemical control and diffusion.In addition,bioleaching was a more environmentally friendly technology,but the leaching rate was lower.In the separation process,precipitation method,solvent extraction method,impregnation resin method,membrane separation method,and biosorption method were used to concentrate rare earth elements from complex leaching solutions.The precipitation method had a simple operation,but the lower purity and selectivity of the product should be improved.The solvent extraction method,impregnation resin method,and liquid membrane method all depended on the affinity between the organic solvent and rare earth elements.They had the advantages of continuous operation and effective separation.Among them,the solvent extraction method could reduce the waste of organic solvents by countercurrent cascade extraction.The impregnation resin method had higher stability and recoverability,which was better than the cascade extraction process.Compared with the solvent extraction method,the liquid membrane method maximized the mass transfer interface area of rare earth elements and reduced the amount of non-aqueous solvents and chelators,but the instability of the liquid membrane affected its large-scale application.Nanofiltration membrane depended on the permeation flux of the membrane,although a higher recovery effect could be achieved,the purity of the product needed to be enhanced.Compared with other methods of recovering rare earth elements,biosorption was more environmentally friendly,whether it had universal applicability needed to be further studied.The feasibility of rare earth extraction from coal fly ash depended on the efficient acquisition of high-purity rare earth metals and economic and environmental issues.Therefore,the following points should be considered in future research:(1)In the activation stage of coal fly ash,improper selection of method and alkali flux might produce a large amount of residue and toxic gas,and the leaching and separation process might cause many chemical reagents to pollute the environment and corrode the equipment.It was necessary to consider reducing the corrosion of the reaction vessel and environmental protection in the case of industrial production.(2)Considering the cost,appropriate methods and reagents should be selected to recover rare earth elements,making it more economical.(3)Coal fly ash often contained a variety of valuable metals,and collaborative extraction of valuable metals should be the main research direction.The key to comprehensively analyzing various valuable metals in coal fly ash was how to efficiently separate valuable elements stepwise from complex leaching fluids to obtain high-purity products.
作者
秦身钧
徐飞
李神勇
齐德娥
赵贵
邢静锴
Qin Shenjun;Xu Fei;Li Shenyong;Qi De’e;Zhao Gui;Xing Jingkai(College of Earth Science and Engineering,Hebei University of Engineering,Handan 056038,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2022年第8期1097-1110,共14页
Chinese Journal of Rare Metals
基金
国家自然科学基金项目(42172191)
河北省自然科学基金项目(D2021402013,D2019402181)
河北省高等学校科学技术研究重点项目(ZD2019055)资助。
关键词
粉煤灰
稀土元素
分布与赋存
提取
coal fly ash
rare earth elements
distribution and mode of occurrence
extraction
