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Coal fly ash (CFA) as a potential resource for rare earth elements and yttrium (REY) has attracted extensive attention over the past few years. This paper focuses on studying microwave systems for the leaching of REY from CFA. Leaching parameters including hydrochloric acid (HCl) concentration, microwave heating time, microwave heating rate, and temperature were assessed. The optimal recovery of 74.91% REY, 86.77% light rare earth elements (LREY), and 34.79% heavy rare earth elements (HREY) are obtained at the conditions of 3 M HCl, T = 220°C, heating rate 39°C/min, and leaching time 30 min. The closed microwave system produces hydrogen chloride fluid or hydrogen chloride gas that is easier to react with CFA than hydrogen ions. It was revealed by the analysis of XRD, particle size, porosity, and SEM that fracture development benefits the entrance of leaching reagents into the inner layer of CFA. A positive linear correlation was found between leaching efficiency and REY3+ ionic radius. The stability of the REY-O bond also remains consistent with the ionic radius, leading to behavior differences during the leaching. This work was targeted to provide a theoretical and technological foundation for microwave-assisted HCl leaching for the extraction of REY in CFA.

As an important long-term task in the field of dam engineering, the maintenance and reinforcement (MAR) are of great significance for ensuring the safety of the project and prolonging the service p...

Coal fly ash is regarded as a potential alternative source of rare-earth elements and has gained much attention over the past few years. However, the majority of rare-earth elements in coal fly ash...

Coal fly ash (CFA) in some areas contains higher levels of rare earth elements (REEs), which can be seen as a potential substitute for rare earth resources. As an effective method of hydrometallurg...

Using satellite imaging of the Earth at night, we quantitatively assess the rapid growth of urban areas and investigate its impact on long-term surface warming at 214 medium and large cities over eastern China. Urban growth intensity is measured using the size of the area experiencing fast night-time light increase and the distance to temperature-observation sites. Surface warming, related closely to city size, also exhibits a strong association with urban growth. A rapid increase of surface temperature is observed mainly for cities undergoing rapid urbanization (RU). Such a relation is evident over Central, South, and Northwest China, but it is weak over Northeast China, implying regional variation of temperature responses to urban growth. Satellite-derived land-surface temperature analysis suggests that cities experiencing RU are more subject to the effects of urban heat island expansion, which explains the variations of warming rate among cities within the same region. These results underscore that sur...