In the past few years, the number of studies regarding the application of ionic liquids (ILs) as alternative solvents to extract value-added compounds from biomass has been growing. Based on an extended compilation and analysis of the data hitherto reported, the main objective of this review is to provide an overview on the use of ILs and their mixtures with molecular solvents for the extraction of value-added compounds present in natural sources. The ILs (or IL solutions) investigated as solvents for the extraction of natural compounds, such as alkaloids, flavonoids, terpenoids, lipids, among others, are outlined. The extraction techniques employed, namely solid–liquid extraction, and microwave-assisted and ultrasound-assisted extractions, are emphasized and discussed in terms of extraction yields and purification factors. Furthermore, the evaluation of the IL chemical structure and the optimization of the process conditions (IL concentration, temperature, biomass–solvent ratio, etc.) are critically addressed. Major conclusions on the role of the ILs towards the extraction mechanisms and improved extraction yields are additionally provided. The isolation and recovery procedures of the value-added compounds are ascertained as well as some scattered strategies already reported for the IL solvent recovery and reusability. Finally, a critical analysis on the economic impact versus the extraction performance of IL-based methodologies was also carried out and is here presented and discussed.

Waste electrical and electronic equipment (WEEE) is the fastest growing type of waste globally and is an important challenge due to its heterogeneity, intrinsic toxicity and potential environmental impact. However, WEEE also represents an important secondary source of critical and valuable elements and must be viewed as a resource within the context of a circular economy. The use of ionic liquids (ILs) to recover metals from WEEE is reviewed with a special emphasis on the use of ILs in leaching and solvent extraction processes. The advantages of ILs as a reaction medium compared to existing conventional solvents lies in their tuneability and potential environmental benefits. Many studies have used ILs for the selective extraction and purification of metals from WEEE, particularly from waste fluorescent lamp phosphor and batteries containing rare-earth elements with promising results. However, significant barriers remain to the commercial use of ILs for treating WEEE and key barriers to progress are identified. In particular more focus is required to improve upstream collection and separation of WEEE, as this would greatly increase the potential to use selective, more efficient, ILs for metal recovery.