Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
2000-11-20
2002-10-22
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C075S739000, C075S740000
Reexamination Certificate
active
06468327
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for processing residual substances containing at least one nonferrous metal, preferably selected from the group comprising zinc, lead, nickel, copper, and cadmium, and/or compounds thereof.
Both the production of nonferrous metals and the recycling of nonferrous-metal-containing secondary raw materials, such as residual substances from steel works, in particular dusts from steel works, involve considerable amounts of nonferrous-metal-containing products and/or residual substances (Ullmann's Encyclopedia of Industrial Chemistry, 5
th
edition, volume A28, page 512).
Particularly important in terms of quantity are the amounts of zinc-containing residual substances resulting from the production of zinc and from the recycling of residual substances from steel works. These residual substances may be subdivided into three groups:
a) sludges resulting from the electrolytic production of zinc
b) slags resulting from the pyrometallurgical production of lead and residues resulting from the pyrometallurgical production of zinc
c) dusts containing zinc and lead, mainly resulting from the processing of scrap.
The great annual charges of these residual substances-group c) alone makes up about 880,000 t per year in Europe, with the charges as well as the nonferrous-metal content tending to rise (M. Hoffmann: Die Rüickgewinnung von Zink und Blei aus Staüben der Elektrostahlerzeugung, VDI Bildungswerk, BW 43-20-04, Sep. 22 and 23, 1997)—have already at an early stage led to considerations and to the development of processes which aim at a purifying processing of the above-named residual substances.
DE-650 256 for instance describes a process for processing lead sulfate and lead-sulfate-containing material. Later, the process was also further developed with a view to the recovery of zinc from residual substances of the above-mentioned group a), and it has been used over decades (Ullmanns Enzyklopädie der technischen Chemie, 3
rd
edition, volume 19, page 99).
EP-A-0 581 995 describes a process which aims at the processing of all three groups of residual substances, a), b), and c), in particular at the processing of dusts from steel works and so-called consumer batteries. The pyrometallurgical process step of this process is based on the process rule known from DE-650 256.
Since dusts from steel works make up the biggest quantitative share of zinc-containing residual substances of groups a), b), and c), there has been a large number of considerations about subjecting this group of residual substances to far-reaching processing. Among these processes, only the so-called rolling process economically stands its ground up to now, even though also this process is technically difficult to control (Ullmanns Enzyklopädie der technischen Chemie, 4
th
edition, volume 24, page 599).
The problem of the zinc contamination of airborne dust in the off-gases of iron-scrap converters and electric furnaces is described in the metallurgical literature (F. Pawlek, Metallhüttenkunde, deGruyter, 1983, page 688).
Both in the processing according to DE-650 256 and in the rolling process, the iron of the feed material forms into slag, and it thereby completely escapes recirculation to iron processing, despite a quantitative share of up to 30% in the feed material.
There are attempts to work up dusts from steel works in a hydrometallurgical way, the object being the recycling of both the zinc and the iron-containing residue (M. Hoffmann: Die Rückgewinnung von Zink und Blei aus Staüben der Elektrostahlerzeugung, VDI Bildungswerk, BW 43-20-04, Sep. 22 and 23, 1997). Here, a solution containing ammonium chloride is used. Due to the high solubility of iron in the electrolyte and the limited possibility of recirculating the electrolyte, this process involves a considerable amount of resources used and only a limited recycling.
In Europe, all available processing capacities can process only about half of the quantities of residual substances of groups a) to c) produced every year, the processing furthermore being technically difficult to control. Only a partial recirculation of the valuable substances is achieved, so that a considerable portion of the valuable substances has to be dumped. And it simply will be impossible to manage the increases in the above-named residual substances, which are expected in the short run.
SUMMARY OF THE INVENTION
The object of the present invention is to overcome the above-identified disadvantages and difficulties and to provide a simple process for processing residual substances containing at least one nonferrous metal and/or compounds thereof, which allows a selective separation of the feed material into the various substances and fractions of valuable substances while requiring a cery limited use of technology. Moreover, the process is supposed to bear high variations in the composition of the feed materials.
In a process of the initially described kind, this object is achieved in that the nonferrous metal is extracted from the residual substances by means of an extracting agent containing a carboxylic acid and/or a substituted carboxylic acid and/or their alkali and/or ammonium salts and/or mixtures thereof.
In the residual substances the nonferrous metal may be present in metallic or oxidic form or salt-like. For the purpose of the present description, “extraction” means separation of the nonferrous metal from the residual substances, the nonferrous metal after separation from the residual substances being present in ionic form.
A Preferably, a fatty acid having 1 to 18 C atoms in the molecule, in particular acetic acid or propionic acid, is used as a carboxylic acid.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process according to the invention is very advantageously used for the processing of residual substances containing iron and nonferrous metal, in particular residual substances from steel works, and the processing of residual substances resulting from the thermal untilization of so-called consumer batteries.
The principle of the process according to the invention lies in the physicochemical interaction of nonferrous metals and, optionally, iron with carboxylic acids, substituted carboxylic acids, their alkali and ammonium salts or mixtures thereof, which interaction leads to big differences in the solubility of the various metal species as a salt in the carboxylic acid used.
The following table shows representative solubility data for various metal species in an aqueous solution, related to an extraction with acetic acid.
Solubility in Water [g/l] at
Species
Room Temperature
Zinc acetate
300
Fe-III-acetate
Traces
Lead-II-acetate
443
Nickel acetate
166
Copper-II-acetate
72
Above all, a big difference in the distribution of iron and nonferrous metals between an extract phase and a solid phase can be deduced from this list. This property corresponds to one of the basic requirements for the recycling of large quantities of feed materials having a heterogeneous composition.
This extraction process meets the demand for a technologically simple procedure in that it may be applied in both a very large range of concentration of the reactive component, i.e., the carboxylic acid, substitued carboxylic acid, their alkali and ammonium salts or mixtures thereof, in an aqueous solution and a very large temperature range up to the boiling point of the extracting agent.
This behaviour is confirmed for instance by the dissoluting behaviour of zinc in acetic acid, which is nearly independent of the concentration (Gmelins Handbuch der anorganischen Chemie, System No. 32, Zinc, Supplement, Verlag Chemie, 1956, page 584).
The concentration and composition of the extracting agent and the operating temperature are optimization parameters, which have an influence on the economic efficiency and the desired result of the separation, but not on the process rule. The composition of the extracting agent and the concentration of the reactive components can be analysed and set according to usual prior art techniques.
In
Luttenberger Hertha
Siebenhofer Matthaeus
Zapfel Wilhelm Hans
Baker & Botts L.L.P.
King Roy
Kole, Esq. Lisa B.
McGuthry-Banks Tima
VTU - Engineering GmbH
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