UMMC Technical University, Verkhnyaya Pyshma, Russia:

P. A. Kozlov, Deputy Director Responsible for Research, Doctor of Technical Sciences, e-mail: p.kozlov@tu-ugmk.com

UMMC OJSC, Verkhnyaya Pyshma, Russia:

A. M. Panshin, Chief Technical Officer, Doctor of Technical Sciences

S. A. Yakornov, Deputy Chief Technical Officer Responsible for Metallurgical Production, Candidate of Technical Sciences

UMMC Technical University, Verkhnyaya Pyshma, Russia¹ ; Chelyabinsk Zinc Plant PJSC, Chelyabinsk, Russia²:

D. A. Ivakin, Head of the Metallurgy Laboratory¹, Head of the Production Control Office at the Engineering Centre², Candidate of Technical Sciences, e-mail: dai@zinc.ru

This paper describes a technique developed for processing EAF dusts and recovering zinc. The technique is based on the Waelz process without zinc sublimation and allows to obtain a product suitable for hydrometallurgical processing and clear of lead or halogens in one process stage. It would be feasible to use an alkaline hydrometallurgical process for this product as it enables a selective recovery of zinc while iron remains in the solid residue. A pyrometallurgical process is necessary to remove halogens, increase the solubility of zinc and remove lead. In the alkaline process, the latter transfers to the solution together with zinc. As part of the development procedure, the thermodynamics of lead and iron in alkaline medium was studied. For this, equilibrium diagrams were built in the Eh – рН coordinates. Findings:
– zinc can dissolve at рН > 12.7 while forming the following anions: ZnO₂^2– and [Zn(OH)_n]^2–n. A study that looked at leaching zinc ores confirms that anions of the latter type do form;
– lead can dissolve while forming [Pb(ОН)₆]^2–-type hydroxo complexes at рН > 12.5. When the solution is heated to 80 ^oС, their solubility can reach 140 g/dm³. In a hot solution hydroxo complexes form orthoplumbite and orthoplumbate ions PbО₂^2–, PbО₃^2– as a result of dehydration;
– the low solubility of all iron compounds in alkaline medium and their position in the diagram only defined by the pH range suggest that the leach solutions contain no iron ions of any type. With the temperature raised to 80 ^oС, the equilibria in the Fe – H₂O system remains unchanged in alkaline medium and no significant increase in the solubility of iron compounds is observed. The findings show that selective dissolution of products containing zinc oxides (including EAF dusts after the above mentioned pyrometallurgical process) in alkaline solutions is feasible. The zinc leaching residue was analyzed for chemical and phase composition to find possible applications for it. It is demonstrated that calcium ferrites, aluminates and alumosilicates account for 80% of the residue. This iron-calcium material can be utilized by cement industry.

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