Modified Zincex process: the clean, safe and profitable solution to the zinc secondaries treatment

Abstract

In the Western World, zinc is mainly used in fields as Hot Dip Galvanizing (48%), Zinc-Base Alloys (13%), Brass and Bronzes (19%), Chemicals (10%) and Others (10%). The impure residues production from these industrial activities, zinc secondary residues, is continuously increasing and its treatment is each day more necessary. The zinc contained in some of these zinc secondaries such as Galvanizing ashes (64–72%), zinc oxides from the Waelz Process (48–60%), Electric Arc Furnace Dust (EAFD) (22–37%) and Cu/Zn oxides from foundries (35–50%) is a good value for processing such zinc secondaries. Pyrometallurgy and conventional zinc recovery technology are not trouble-free processes for them. Impurities impair performance and cause environmental problems. The Modified Zincex Process is a hydrometallurgical process that takes advantage of the Zincex Process long ago used in two industrial plants. The Modified Zincex Process is a modification and simplification of the former process using atmospheric leaching, solvent extraction and conventional electrowinning, in order to resolve impurity difficulties and recover zinc ingots SHG (99.99%). This paper deals with the main results of an experimental programme aiming at the demonstration of the suitability of the process to several feed materials. Waelz Oxides, Galvanizing ashes and EAFD coming from different European sources were tested during laboratory and continuous pilot plant campaigns. High Zinc recovery, low reagents and utilities consumption and effluents meeting EC and EPA waste regulations were confirmed. The paper also includes the main results of a feasibility study of an industrial ‘base case’. A mixed raw material and 20 000 t per year of zinc ingots production were chosen. The SHG zinc recovery from secondary raw material by means of the clean, safe and profitable Modified Zincex Process has been demonstrated.