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TREATMENT OF RESIDUES AND PRECIPITATES OF HYDROMETALLURGICAL ZINC WINNING BY DC ELECTRIC SMELTING.

Objective

THE AIM OF THE RESEARCH IS TO DEVELOP A PROCESS FOR THE TREATMENT OF RESIDUES AND PRECIPITATES OF HYDROMETALLURGICAL ZINC WINNING IN ORDER TO RECOVER THE VALUABLE METALS AND, AT THE SAME TIME, TO PRODUCE NON-POLLUTING RESIDUES HAVING LOW HEAVY METALS CONTENT.
THE PROBLEM IS OF GREAT IMPORTANCE BECAUSE MOST OF THE ZINC METALLURGICAL PLANTS PRODUCE JAROSITE RESIDUES WHOSE DISPOSAL CAUSES ENVIRONMENTAL PROBLEMS DIFFICULT TO SOLVE.
In the treatment of residues and precipitates of hydrometallurgical zinc winning by direct current (DC) electric arc melting 2 possible process variants have become visible. These involve either the recovery of lead, zinc and silver by volatilization in a common flue dust or the production of a silver containing lead bullion and a flue dust containing only lead and zinc. Large scale tests were made to investigate which of the process possibilities is more suitable to treate the residues.

The results of the smelting tests showed that it was possible to treat jarosite in pyrometallurgical process successfully. At a temperature of 1400 C and the addition of ferrosilicon slag, flue dust and a meta phase were produced.

The flue dust was high in lead and zinc, and contained high amounts of the volatile elements. The metal phase formed during the process was high in sulphur (14%) and acted as a collector for the valuable elements like silver, germanium and indium and for arsenic.

In respect to the sulphur content of the slag, the results showed that it is necessary to produce such a metal phase because the sulphur content of the slag was directly proportional to the iron content. Even if a metal phase with such a composition was not a valuable product, there should be no problem treating this material in the sinter machine lead shaft furnace.

The energy consumption from the testwork was 2000 to 2500 kWh/t of jarosite (dry) and the electrode consumption was 8 to 15 kg/t of jarosite (dry). The values are very high, but can be expected to decrease strongly in industrial scale processes.
1.- RECONSTRUCTION OF THE EXISTING 350 KVA ARC FURNACE WITH THE MODIFICATIONS NECESSARY FOR CARRYING OUT THE TESTS (LARGER BATH DEPTH, SEALING OFF THE FURNACE LID ETC...)

2.- PROVISION OF TEST MATERIALS IN FORM OF MIXTURES OR PELLETS AS: JAROSITE PB-AG-MUD, MIXTURE OF BOTH, NEUTRAL LEACH RESIDUES, RETORT ASHES (BY BUDELCO AND PREUSSAG)

3.- RECOVERY OF AMMONIA BY VOLATILISATION AND CONDENSATION UNDER CONTROLLED CONDITIONS

4.- MELTING PELLETS OF DIFFERENT FEED MATERIALS

5.- CHEMICAL ANALYSIS OF THE RESPECTIVE MELT PHASES OF THE DIFFERENT PRODUCTS AS: METALS, MATTES, SLAGS AND FLUE DUSTS

6.- EXAMINATION OF THE DISTRIBUTION AND WINNING OR RARE METALS GA, IN AND GE WHEN MELTING JAROSITE, NEUTRAL LEAD RESIDUES AND RETORT ASHES

7.- EXAMINATION CONCERNING THE MELT TREATMENT OF OTHER RESIDUES

8.- ECONOMIC FEASIBILITY STUDIES OF THE LASTLY PROPOSED PROCESS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

AACHEN UNIVERSITY OF TECHNOLOGY
Address
Templergraben 55
52056 Aachen
Germany

Participants (2)

Budelco BV
Netherlands
Address
1,Hoofdstraat
6024 AA Budel
Preussag AG
Germany
Address
Karl-wiechert-allee 4
30625 Hannover