EVALUATION OF LIQUID MEMBRANE SYSTEMS FOR REE EXTRACTION
Raquel Rodríguez Varela, PhD Student, raquelrv@kth.se
Kerstin Forsberg, Assistant Professor, kerstino@kth.se
Joaquín Martínez de la Cruz, Associate Professor, martinez@kth.se
Åke Rasmuson, Professor, rasmuson@ket.kth.se
Department of Chemical Engineering and Technology, KTH Royal Institute of Technology, Stockholm,
Sweden
ABSTRACT
Separation and purification of rare earth elements (REE) is of great importance due to the variety of their
technological applications. In this context, liquid membrane separation stand out as an alternative to
traditional techniques in order to selectively separate and concentrate REE. Some of the most significant
advantages of the liquid membrane technologies are the minimum liquid membrane inventory and the low
power consumption (V. S. Kislik 2010). However, membrane instability can be a significant problem for
industrial application and the mechanisms behind membrane instability are poorly understood.
This study analyses the separation of rare earth elements by means of liquid membranes with the final
objective of recovering REE from an apatite concentrate (M. Alemrajabi, 2015, M. Mohammadi, 2015). In
this study, the feed phase will consist of an aqueous phase containing REE, the membrane phase will contain
organic solvent and carrier (mainly D2EHPA and EHEHPA), and the stripping phase will be a hydrochloric
acid solution. In order to analyse the suitability of liquid membranes in the extraction of REE, a deeper
insight into the mechanisms causing instability is needed. In this study, surface tension is considered as the
key factor of Marangoni instabilities and spontaneous emulsification (A. M. Neplenbroek 1992. H-D. Zheng
2009, F. F. Zha 1995). The influence of capillary forces and the effect of mass transfer through the membrane
will be examined. Furthermore, a comprehensive evaluation of mass fluxes, separation efficiency and
membrane performance on a wide range of operating conditions will be conducted in order to optimise the
separation process. This study is expected to provide valuable information for the design of more stable and
efficient liquid membrane processes.
KEYWORDS
REE, Liquid membranes, Stability, Capillarity, Surface tension, Marangoni effect, Emulsification