Leachability and adverse effects of coal fly ash: A review

Many studies have been published in recent years focusing on the recovery of rare earth elements (REEs) from coal-related materials, including coal, coal refuse, coal mine drainage, and coal combustion byproducts particularly fly ash. The scientific basis and technology development have been supported by coal geologists and extractive metallurgists, and through these efforts, the concept has progressed from feasibility assessment to pilot-scale production over the last five years. Physical beneficiation, acid leaching, ion-exchange leaching, bio-leaching, thermal treatment, alkali treatment, solvent extraction, and other recovery technologies have been evaluated with varying degrees of success depending on the feedstock properties. In general, physical beneficiation can be a suitable low-cost option for preliminary upgrading; however, most studies showed exceedingly low recovery values unless ultrafine grinding was first performed. This finding is largely attributed to the combination of small RE-bearing mineral particle size and complex REE mineralogy in coal-based resources. Alternatively, direct chemical extraction by acid was able to produce moderate recovery values, and the inclusion of leaching additives, alkaline pretreatment, and/or thermal pretreatment considerably improved the process performance. The studies reviewed in this article revealed two major pilot plants where these processes have been successfully deployed along with suitable solution purification technologies to continuously produce high-grade mixed rare earth products (as high as +95%) from coal-based resources. This article presents a systematic review of the recovery methods, testing outcomes, and separation mechanisms that are involved in REE extraction from coal-related materials. The most recent findings regarding the modes of occurrence of REEs in coal-related materials are also included.

A Comprehensive Review of Rare Earth Elements Recovery from Coal-Related Materials

Recovery potential of rare earth elements from mining and industrial residues: A review and cases studies

Recovery of Rare Earth Elements from Coal Fly Ash through Sequential Chemical Roasting, Water Leaching, and Acid Leaching Processes

A review of rare earth elements and yttrium in coal ash: content, modes of occurrences, combustion behavior, and extraction methods

Recovery of rare earth elements from coal fly ash by integrated physical separation and acid leaching.

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...

Recovery of rare-earth elements from coal fly ash via enhanced leaching

Froth image feature engineering-based prediction method for concentrate ash content of coal flotation

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...

Tiancheng Nie

Papers

Recovery of rare earth elements from coal fly ash by integrated physical separation and acid leaching.

Recovery of rare-earth elements from coal fly ash via enhanced leaching

Froth image feature engineering-based prediction method for concentrate ash content of coal flotation

Extraction of rare earth elements from coal fly ash by alkali fusion–acid leaching: Mechanism analysis

Deep learning-based ash content prediction of coal flotation concentrate using convolutional neural network