Exploring the Potential for Yttrium Recovery from Secondary Sources: (Bio)hydrometallurgical and Solvometallurgical Routes.

Yttrium is one of the lesser-known critical elements, but it has recently gained significant market attention due to a dramatic price increase of up to 1400% in Europe. Although its primary application is in phosphors (e.g., in LEDs), modern society heavily depends on these technologies, making yttrium indispensable. However, the limited availability of yttrium raises concerns about its long-term supply. Therefore, there is a need for efficient techniques to recover yttrium from secondary materials to ensure a stable supply. While the wastes contain only trace amounts of yttrium and often have complex elemental compositions, they are more readily available than primary sources. The yttrium content ranges from a few percent in spent phosphors to several hundred ppm in red mud, around a few dozen ppm in phosphogypsum, and up to several ppm in coal and coal fly ashes. Although conventional hydrometallurgical methods are commonly used, they lack selectivity for yttrium recovery. In contrast, unconventional solvometallurgical and bioleaching approaches currently play a relatively minor role in recovery applications. This review discusses a range of methods investigated for yttrium recovery from different types of secondary resources, including pretreatment (where applicable), leaching, and subsequent yttrium recovery from the resulting leachates. Although the chemical and phase compositions of yttrium-bearing waste materials differ substantially, necessitating tailored treatment strategies, acid leaching remains the predominant extraction route and is most commonly followed by solvent extraction and/or oxalate precipitation. Most studies reported to date have been conducted at the laboratory scale. Despite progress and the development of promising recovery concepts, the efficient separation of high-purity yttrium from other rare earth elements and co-existing impurities continues to represent the key obstacle to commercial-scale application.