Solvent extraction removal of iron from zinc process solutions using organophosphorus extractants

摘要

In order for solvent extraction technology to be acceptable as an alternative to existing jarosite precipitation circuits, iron must be cleanly separated and concentrated into a feed stream suitable for downstream iron by-product recovery whichmeets market specifications and economics. Ten years ago, significant progress was made in a joint McGill University/CANMET project that involved iron extraction with mono(2-ethylhexyl) phosphoric acid and stripping with HCI. Our iron solvent extractionresearch was reactivated recently by looking into this and other members of the organophosphorus extractant family. Our research focuses on the mechanisms and control of anion (SO{sub}4{sup}(2-)/C1{sup}-) transport across the various phases(Raffinate/Organic/Strip), iron build-up in the strip liquor, and extractant stability/selectivity. In this paper, these issues along with some other performance parameters are discussed using data derived from an extensive search of the two commerciallyavailable and best known members of the organophosphorus family, di-2-ethylhexyl (D2EHPA) and mono-2-ethylhexyl (M2EHPA) phosphoric acid. Further in this discussion, the challenges lying ahead in the development of SX systems that overcome thedeficiencies of D2EHPA and M2EHPA are outlined. In particular, the necessity of considering secondary separation technologies that can further concentrate iron values in the chloride strip liquor to levels economically attractive for the production ofsaleable iron oxide by pyrohydrolysis is addressed.