Fluoride removal from Double Leached Waelz Oxide leach solutions as alternative feeds to Zinc Calcine leaching liquors in the electrolytic zinc production process

The most important limitation of leached Waelz Oxide from the pyrometallurgical treatment of Electric Arc Furnace Dust (EAFD) is its high fluorine content. This work deals with the reduction of the harmful effects of the Double Leached Waelz Oxide fluorine content in the hydrometallurgical process for electrolytic zinc production process when it is used as raw material directly in the leaching stage. The resulting process is a purification treatment of Double Leached Waelz Oxide leach solution to remove the dissolved fluoride in this unpurified zinc liquor. Leached fluorides from this liquor are precipitated in order to reduce their concentration until the specified values, avoiding cathode corrosion in the electrowinning cells. In this paper a selective precipitation process to maximize the fluoride removal and to minimize the zinc losses is presented, achieving the industrially specified solution composition when the Zinc Calcine is the used raw material. The formation of aluminium-fluoride complexes and the variation of their solubilities with the pH evolution are the basis of the proposed treatment. In addition, this fluoride removal has also been improved and optimized in order to be integrated in the overall industrial hydrometallurgical process and the obtained results are presented and discussed proving the viability of this improved stage. (C) 2016 Elsevier B.V. All rights reserved.