The Discrepancy between Coal Ash from Muffle, Circulating Fluidized Bed (CFB), and Pulverized Coal (PC) Furnaces, with a Focus on the Recovery of Iron and Rare Earth Elements

Abstract

Coal ash (CA) is not only one of the most solid wastes from combustion, easily resulting in a series of concerns, but it is also an artificial deposit with considerable metals, such as iron and rare earth. The variation in the coal ash characteristics due to the origins, combustion process, and even storage environment has been hindering the metal utilization from coal ash. In this study, three ash sample from lab muffle, circulating fluidized bed (CFB), and pulverized coal (PC) furnace was derived for the discrepancy study from the combustion furnace, including properties, iron, and rare earth recovery. The origins of the coal feed samples have more of an effect on their properties than combustion furnaces. Magnetic separation is suitable for coal ash from PC because of the magnetite product, and the iron content is 58% in the Mag-1 fraction, with a yield of 3%. The particles in CA from CFB appear irregular and fragmental, while those from PC appear spherical with a smooth surface. The results of sequential chemical extraction and observation both indicated that the aluminosilicate phase plays an essential role in rare earth occurrences. Rare earth in CA from muffling and CFB is facilely leached, with a recovery of approximately 50%, which is higher than that from PC ash. This paper aims to offer a reference to easily understand the difference in metal recovery from coal ash.

Phosphorus Release Dynamics from Ashes during a Soil Incubation Study: Effect of Feedstock Characteristics and Combustion Conditions

“…On one hand we used ashes burned in a lab muffle (EBPR ashes) and, on the other, the pig manure ashes were produced in a biomass boiler. Consequently, it is important to mention that the results obtained from the ashes burned in the muffle may not necessarily reflect the actual conditions during a real combustion [36]. In the muffle furnace, the temperature is kept constant through the entire process, which may not be the case in a real combustion scenario where temperature fluctuations can occur as explained by Zheng et al [37] (i.e., thermal shocks by the addition of fresh material, the production of combustion by-products and fumes or external factors).…”

Bioleaching of Rare Earth Elements: Perspectives from Mineral Characteristics and Microbial Species

“…In fact, it is difficult to compare among studies, because the CFA used in each study may be different, which greatly affects the leachability of REEs. For instance, the CFA generated from a circulating fluidized bed contains more organic/sulfide and acid-soluble fractions and a lower aluminosilicate fraction than that from a pulverized coal furnace [92]. Hence, the REEs in CFA from circulating fluidized beds may be recovered more easily by acid leaching.…”

Review of the Preparation and Application of Porous Materials for Typical Coal-Based Solid Waste

“…It is the primary solid waste from coal-fired power plants. Depending on the method of boiler combustion, fly ash can be classified as either circulating fluidized bed (CFB) fly ash or pulverized coal (PC) fly ash [27].…”