Regeneration of the ionic liquid tetraoctylammonium oleate after metal extraction Dries Parmentier 1,2 , Yash A. Valia 2 , Sybrand J. Metz 1 , Odne S. Burheim 1,3 and Maaike C. Kroon 2* 1 Wetsus Centre of Excellence for Sustainable Water Technology Oostergoweg 7, 8911 MA Leeuwarden, The Netherlands 2 Separation Technology Group Department of Chemical Engineering and Chemistry Eindhoven University of Technology Den Dolech 2, 5612 AZ Eindhoven, The Netherlands 3 Department of Electrical and Computer Engineering, HiST – Sør-Trøndelag University College, 7004 Trondheim, Norway * Corresponding author. E-mail: m.c.kroon@tue.nl; Phone: 31-40-2475289; Fax: +31-40-2463966.