Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1998-07-16
2000-07-04
Wyszomierski, George
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75480, 423108, C21B 1106, C22B 1900
Patent
active
060832959
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of processing finely divided materials incorporating a range of metal based constituents. The invention is applicable particularly but not exclusively to processing flue dust generated by steel making in an electric arc furnace.
BACKGROUND OF THE INVENTION
In a typical electric arc furnace or other steel making furnace, several thousand tonnes of flue dust are generated each year. The constitution of the flue dust varies with the feed material to the furnace which normally consists of or includes a wide range of scrap metal including old motor cars. The flue dust may contain about 40% of non-ferrous metallic compounds, about 50% ferrous compounds (mainly oxide) with the remainder being gangue material. The non-ferrous metallic constituents are normally predominantly lead oxide and zinc oxide but typically include some zinc chloride, copper chloride, cadmium chloride, potassium chloride, sodium chloride and cadmium oxide. Oxides of potassium and sodium may also be present. Flue dust from a basic oxygen furnace normally contains a higher proportion of ferrous compounds but there are still significant proportions of non-ferrous material.
Historically, flue dust has been dumped but this involves a substantial cash expenditure and is becoming environmentally less acceptable due to the toxicity of many of the constituents. The invention is concerned particularly with a process for reclaiming constituents from a material such as flue dust. The invention may be looked on primarily as a means for avoiding disposal of contaminants or as a means of extracting valuable non-ferrous metals or as a means of recuperating iron for re-use in the steel making process. The dominant objective depends on the circumstances.
It is already known from EP 275863A to mix flue dust with solid carbonaceous material and an organic binder, pelletize this mixture and heat the pellets. Some constituents are driven off while iron and lead are reduced to the metallic form and poured off as liquid metal. It is stated that the lead can be separated from the iron gravitationally but some lead must remain in solution in the iron. Also, very high temperatures have to be used to achieve the molten state for the iron and extracting the metal in molten form requires a facility such as tilting a rotary kiln and is not convenient for continuous operation.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method of processing flue dust or other finely divided material to separate constituents therefrom in a more practical manner.
The invention is concerned with a method of processing finely divided material incorporating a range of metal based constituents, the method comprising: pelletizing the material; drying the pellets, sintering the pellets at a temperature and residence time to produce very strong pellets at which temperature volatile first constituents are driven off from the pellets; and heating the pellets in the presence of a reductant whereby one or more second constituents are reduced to a volatile form and driven off leaving one or more reduced third constituents. The method is characterised in that finely divided material which would tend to fuse the pellets is excluded from the reduction phase whereby the pellets retain their integrity at the temperatures employed for reduction.
Avoidance of finely divided material permits a sufficiently high temperature to be selected for effective reduction without fusing the pellets together. This in turn leads to convenient handling of the material and a long life for the plant in which the method is operated.
Preferably the reduction and also the sintering take place in rotary kilns.
The pellets may be screened between the sintering and reduction stages for removal of finely divided material.
If a solid reductant such as anthracite is used, it is important to avoid finely divided reductant, for example by using washed anthracite.
The invention may be applied to flue dust from a steel making furnace in which case the principal or substantiall
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Arc Dust Processing (UK) Limited
Combs Morillo Janelle
Wyszomierski George
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