Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group iiia metal or beryllium
Reexamination Certificate
1999-09-22
2001-10-02
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group iiia metal or beryllium
C423S127000, C423S131000, C075S672000, C241S024130, C501S127000
Reexamination Certificate
active
06296817
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to a method for recycling aluminum dross, an oxide formed on the surface of the molten aluminum metal, to produce aluminum hydroxide (Al(OH)
3
) powder, useful as a material for various aluminum compounds, and castable refractories.
2. Description of Prior Arts
Because aluminum is readily apt to be oxidized, aluminum dross is always produced whether at a large or small amount when aluminum is molten. When aluminum is founded into a base metal after being melted, aluminum dross is removed. When pouring molten aluminum metal into a mold, aluminum dross still remains, in part, in a furnace or a crucible. Even during the casting of molten aluminum metal, aluminum dross is generated at molten metal runners.
Typically, aluminum-melting factories melt aluminum dross by heating and reclaim aluminum metal out of the dross, so as to reduce the amount of aluminum dross to be discarded. Generally, this waste dross is treated by burial in earth. Usually, the waste dross finally produced comprises a predominant amount of aluminum oxide, 10~30% of aluminum metal, around 10% of salts and a mixture of impurities which originally exist in aluminum scraps, such as Mg, Si, Fe and the like.
In the case of treating aluminum dross in a conventional manner, it costs a great deal. For example, a burial site must be secured or a significant amount of money must be paid to waste disposal agents.
In order to prepare aluminum hydroxide, bauxite is conventionally used according to the Bayer process. For example, bauxite is dissolved at a high temperature under a high pressure in a sodium hydroxide (NaOH) solution to lixiviate aluminum oxide out of the ore into the solution, followed by hydrolyzing the solution to prepare aluminum hydroxide.
In this conventional method, a high temperature and a high pressure are required upon the decomposition of the ore, which is usually accomplished in an autoclave. In addition, it is certain that using aluminum dross in preparing aluminum hydroxide is more economically favorable than using bauxite.
SUMMARY OF THE INVENTION
Knowledge of the amphoteric properties of aluminum allows aluminum to be reclaimed from aluminum dross as aluminum hydroxide, leading to the present invention.
As a consequence of the intensive and thorough research on the processing of aluminum dross, repeated by the present inventors, it was found that aluminum can be leached out of aluminum dross by use of an NaOH solution and aluminum hydroxide can be prepared from the solution, whereby its production cost can be considerably reduced relative to where bauxite is used as a raw material.
It was also found that the wastes dross after the preparation of aluminum hydroxide can be converted into castable refractories by oxidizing the residual metal components in the waste dross, whereby the disposal amount and cost of aluminum dross can be reduced.
Therefore, it is an object of the present invention to overcome the problems encountered in prior arts and to provide a method for reusing aluminum dross, which is economically and environmentally favorable.
Based on the present invention, the above object could be accomplished by a provision of a method for treating aluminum dross, comprising the steps of: crusing the aluminum dross into particles; dividing the aluminum dross particles according to particle sizes on the basis of 1 mm; leaching the aluminum dross particles equal to or smaller than 1 mm in size with an aqueous sodium hydroxide solution to give a leachate which contains sodium aluminate as a result of the reaction the aluminum metal of the aluminum dross particles with sodium hydroxide while re-melting the aluminum dross particles greater than 1 mm in size to recover aluminum metal; seeding a small quantity of aluminum hydroxide in the leachate; and hydrolyzing the sodium aluminate to obtain aluminum hydroxide.
In accordance with an embodiment of the present invention, the method further comprises the steps of: filtering the leachate to obtain a residue; washing, drying and roasting said residue; mixing the roasted residue with aggregate and alumina cement to give alumina castable refractories.
REFERENCES:
patent: 5135565 (1992-08-01), Gens
patent: 98/07467 (1999-05-01), None
Lee Hoo-In
Park Hyung-Kyu
Yoon Eui-Pak
Bos Steven
Nawrocki, Rooney & Sivertson P.A.
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