Characteristics of Some Selected Methods of Rare Earth Elements Recovery from Coal Fly Ashes

The article covers the issues related to the characteristics, application, and some methods of rare earth elements (REEs) recovery from coal fly ashes. REEs are elements with growing demand and a very wide range of application, especially when it comes to modern technologies. The conducted analysis and price forecast proved the existing upward tendency, and this confirmed the need to search for new REE sources, among industrial waste (proecological effect). The development of the REE recovery technology would involve solving several problems related to REE speciation, optimization of factors controlling their extractivity and selection of the REE separation method from obtained extraction solutions with a very extreme pH and complicated composition. The paper presented advantages and disadvantages of usually used methods of REE separation from coal fly ashes, like physical and acid–base leaching. It was also presented alternative REE recovery techniques in the form of membrane and biological methods and based on ion liquids (ILs) or chelating agents. The directions of further modifications, which will allow the efficient REE recovery were presented. The aim of this article was to propose specific solutions based on the creation of appropriate multistage method of REE recovery. It will be a combination of magnetic and size separation, acid–base leaching (including roasting in justified cases), removal of matrix elements with ILs (Al, Si, and Fe), and finally REE membrane separation, allowing one to obtain the appropriate process efficiency.

Immobilization of Powdered Coal Fly Ashes (CFAs) into CFA Beads and Column Studies on Color Removal from Pulp Mill Effluents Using These CFA Beads

In this study, immobilization process of the three (3) powder CFAs was studied. The major results on immobilization process were briefly presented. A total number of fifteen (15) column studies from the combination of the five (5) types of CFAs beads and the three (3) PMEs samples were performed. In each column study, a set of aggregate parameters of flow rate, empty bed contract time, operational time, and throughput volume was studied, and the data was fitted to existing modeling of breakthrough curves. The overall operational time was 12–24-hour, color removal efficiencies were 40–90%, and throughput volume of treated PMEs was 10–14 bed volume. For the column study, the correlation coefficient R2 value for each combination indicated that the Thomas model had a better fit with the observed data than the Adams-Bohart model, and the color adsorption capacities of CFA beads varied in a wide range of 0.31–28.23 mg/g.