Mechanochemical Activation of Lignite-Coal Ash from Thermal Power Plants as a Method for Increasing the Extraction of Rare Earth and Dispersed Elements

Rare earth (REE) and rare elements (RE) are important materials for high-tech industries. To date, coal and coal ash have been recognized as a promising, economically profitable alternative source of rare earth elements, however, the implementation of their extraction process requires the development of new approaches to concentration and leaching. In this work, waste from large lignite-coal thermal power plants in Novosibirsk was studied as sources of rare earth and rare elements. The morphology and phase composition of the samples were analyzed, as well as elemental analysis by inductively coupled plasma mass spectrometry (ICP-MS). It was found that the studied samples are characterized by an increased gallium content. The effect of preliminary mechanochemical activation (MCA) of ash on the degree of extraction of target elements has been studied. MCA was performed in the presence of various complexing reagents (etidronic acid, carbamide, EDTA, humic acids and their salts). The composition of the aqueous extracts from the treated samples was analyzed in detail. It has been shown that the highest degree of gallium extraction is achieved when using sodium humate as a complexing agent.