Recently, the use of nanoparticles in extraction columns has gained increasing attention due to their potential to enhance mass transfer processes. Most of the reported work, however, has been concerned with mass transfer enhancement in gas–liquid systems in the presence of nanoparticles, while limited studies of liquid–liquid systems have been reported. Liquid–liquid extraction is an extensively employed separation method that has taken on a substantial role in engineering and industrial applications for recovery processes. Therefore, the aim of this review article is to provide an overview of the state-of-the-art from the available literature on the effect of nanoparticles on the hydrodynamic behavior and mass transfer performance of liquid–liquid systems. Attention is also given to providing an understanding of the mechanisms responsible for the improvements in mass transfer with the use of nanoparticles. In the majority of studies, the presence of nanoparticles was found to be beneficial and to lead to improved mass transfer, although a few investigations reported a detrimental impact of nanoparticles. The literature does not clearly describe the conditions under which the addition of nanoparticles would be unfavorable. Moreover, the addition of nanoparticles always introduces potential drawbacks, such as sedimentation, accumulation, or clogging inside extraction columns, as well as the need to separate the nanoparticles at the outlets. These drawbacks have not been considered in the literature, limiting the practical employment of nanoparticles in this industry.

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