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DEVELOPMENT AND OPTIMIZATION OF TECHMIQUES FOR THE REPROCESSING OF ZINCFERROUS PICKLING WASTES FROM HOT DIP GALVANISING WORKSHOPS

Objective

The aim of this project is to develop an electrolytic process which would permit iron and zinc, in the form of a cathodically precipitated metallic alloy, to be separated out from solutions and allocated for reuse.

In order to optimize the cycle, the zinc recycling will be done in imperial smelting furnaces. In addition, the residual solution will be reprocessed under environmentally acceptable conditions (eg by ion exchange, depletion electrolysis, evaporation etc) in such a way that it can repeat the pickling process in the hot dip galvanizing workshops.

The waste gas produced by electrolysis, together with its chlorine content, should either be purified by absorption (thus providing saleable or usable products), or it should be used in the oxidation to iron(3+) ions of the iron(2+) ions resulting from the pickling process. At the same time, comparisons should be made with the well known technology associated with a solvent extraction process for the separation of iron and zinc, in order to check out the economic viability of the electrolysis process. In addition, sufficiently large quantities of zinc chloride and iron(II) chloride solution from the pickling waste need to be produced in a mixer settler, in order to be able to carry out assessment and quality improvement tests on the product solutions. Wherever possible, therefore, accompanying metals and organic constituents should be removed from the iron(II) chloride solution for use in waste water treatment in clarification plants, and the diluted iron chloride solution resulting from the first stage s ould be concentrated by additional methods of treatment such as electrolysis, electrodialysis, etc. The research findings should demonstrate possible ways of putting the most economically viable pickling waste reprocessing method into practice.

A membrane electrolysis cell of variable design for the investigation of the general operating parameters for the electrolysis process (current density, bath voltage, temperature, acidity), suitable electrode materials, electrode pitch, bath agitation, anolyte composition, electrolyte control, membrane material and retention and different pickling waste feed rates will be used.

With regard to the depleted pickling waste and the anolyte, the composition will be investigated as a function of current density and residence time, chlorine gas content, mixture ratio, catholyte and anolyte, economic depletion factors, utilization of the product solutions (recycling, reduction, post treatment and reprocessing respectively).

The gas produced at the anode will be investigated with regard to purification and utilization by absorption (adsorbent, use of reagents, effectiveness, product optimization) or use of oxidation potential (iron and oxidation in pickling solutions). In all electrolysis products, their usability and the technico-economic limits will be analyzed.

Based on the information obtained, an enlarged pilot plant (with 10 m{2} electrode surface area) will be used to demonstrate the practical feasibility (cell design, gas extraction, electrolyte management, membrane and electrode retention). In addition, mass balances, energy consumption, economics and an overall concept will be determined.

For a comparison of the economics of the electrolysis process and the solvent extraction for selective iron and zinc separation from pickling waste it is necessary to perform optimizing investigations into questions of solvent extraction, and specifically into the use of the resulting product solutions, some of which are in dilute form.

Part of this application involves investigation into the use of iron(II) chloride and zinc chloride product solutions through concentration (reduction, electrodialysis, precipitation, chloridic zinc electrolysis) and, where appropriate, for post cleaning of the feed solutions.

In the case of electrolytic zinc production from zinc chloride solution, the optimum operating parameters, a suitable cell design and methods for the anode gas treatment (feedback to the direct used pickling solution electrolysis process) will be determined.

A joint comparative analysis of the economics of the use of electrolysis of used pickling acid and solvent extraction will be done.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Preussag AG
Address
Rammelsberger Straße 2
38640 Goslar
Germany

Participants (2)

Bammens Groep BV
Netherlands
Address
5,Ambachtsweg 46-48
3600 BC Maarssen
Preussag AG
Germany
Address
Rammelsberger Straße 2
38640 Goslar