Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group iiia metal or beryllium
Reexamination Certificate
1999-11-15
2001-10-09
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group iiia metal or beryllium
C423S121000, C423S127000
Reexamination Certificate
active
06299846
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for producing aluminum hydroxide from an alumina-containing ore. Specifically, the present invention relates to a process for producing aluminum hydroxide wherein aluminum hydroxide can be obtained economically at a high yield, with little contamination by silica and with a little loss of an alkaline component, in a so-called Bayer Process for producing aluminum hydroxide.
BACKGROUND OF THE INVENTION
The Bayer Process is well-known and commonly employed for producing aluminum hydroxide from alumina-containing ore such as bauxite. This process usually comprises the steps of:
(i) treating bauxite with an alkaline solution such as an aqueous sodium hydroxide solution or an aqueous mixture solution of a sodium hydroxide solution and a sodium carbonate solution to obtain a slurry (bauxite-dissolving step),
(ii) extracting alumina contained in bauxite as sodium aluminate (extraction step),
(iii) separating insoluble residues (dissolution residue) such as iron oxides, silicates and titanium oxides from the slurry to obtain a sodium aluminate solution (red mud-separation step),
(iv) adding seeds of aluminum hydroxide into the sodium aluminate solution so that aluminum hydroxide is precipitated at a temperature from 50° C. to 70° C. and the precipitated aluminum hydroxide is separated from the sodium aluminate solution (precipitation step), and
(v) recycling a portion of the separated aluminum hydroxide as seeds in the precipitation step and recovering the rest of the separated aluminum hydroxide as a product, while the sodium aluminate solution remaining after the recovery of the aluminum hydroxide is recycled as it is or after condensation for the use in the bauxite-dissolving step.
Bauxite usually contains an alkali-soluble silica (hereinafter, referred to as a reactive silica), a content thereof being dependent on a place where it is mined. Therefore, in the above extraction step, the reactive silica contained in bauxite is dissolved as well as the alumina component.
When an extract solution (sodium aluminate solution) containing the reactive silica dissolved therein is used for the precipitation step to obtain aluminum hydroxide, the silica in the solution is also decomposed and precipitated together with aluminum hydroxide, which causes deterioration of the quality of aluminum hydroxide obtained. To avoid the deterioration, the reactive silica in the extract solution is allowed, prior to the precipitation step, to react with a portion of the alumina component and a portion of the alkaline component in the extract solution, so as to precipitate as sodalite or zeolite which is alkali-insoluble (desilication step), and be separated and discarded together with the other insoluble substances such as the iron oxides and the titanium oxides in the red mud-separation step.
In this process, the reactive silica is precipitated by consuming a large amount of the alumina component and the alkaline component in the extract solution and, therefore, a large amount of losses of these components can not be avoided and the process is not economical.
For suppressing the losses of alumina and the alkaline components, Japanese Patent Laid-Open Publication No. 5-193931-A (corresponding to U.S. Pat. No. 5,545,384) discloses a process for producing aluminum hydroxide from an alumina-containing ore described wherein:
(i) the alumina-containing ore is mixed with an alkaline solution to obtain an alumina-containing slurry,
(ii) the alumina-containing slurry obtained in step (i) is mixed with a preheated alkaline aqueous solution, to obtain an alkaline aqueous mixture,
(iii) alumina is extracted as sodium aluminate from the alkaline aqueous mixture obtained in step (ii) at a temperature of 120° C. to 160° C. within 10 minutes, to obtain a mixture of an extract solution of sodium aluminate and a dissolution residue of a reactive silica,
(iv) the dissolution residue is separated from the mixture obtained in step (iii), to obtain the extract solution of sodium aluminate,
(v) the extract solution of sodium aluminate obtained in step (iv) is desilicated, to obtain a mixture of a desilication product and a desilicated-extract solution,
(vi) the desilication product is separated from the mixture obtained in step (v), to obtain the desilicated-extract solution and
(vii) seeds of aluminum hydroxide are added to the desilicated-extract solution obtained in step (vi), to precipitate aluminum hydroxide.
With the process in the JP-5-193931-A, the losses of alumina and alkaline components is quite suppressed and aluminum hydroxide is produced from an alumina-containing ore at a high yield and with little contamination by silica. However, the suppression of the losses of alumina and alkaline components is not sufficient, and the yield of aluminum hydroxide is not sufficient, either and, therefore, a more improved process has been desired.
SUMMARY OF THE INVENTION
In view of the above-described situation, the inventors of the present invention have made extensive studies for a process of producing aluminum hydroxide from an alumina-containing ore such as bauxite, wherein losses of alumina and alkaline components can be much suppressed and aluminum hydroxide can be produced with little contamination by silica and at a much higher yield from an alumina-containing ore, and have thereby accomplished the present invention.
Thus, the present invention provides a process for producing aluminum hydroxide, which comprises the steps of:
(a) mixing a first portion of an alumina-containing ore with a first alkaline solution to obtain a first alumina-containing slurry,
(b) mixing the first alumina-containing slurry obtained in step (a) with a preheated alkaline aqueous solution, to obtain a first alkaline aqueous mixture,
(c) extracting alumina as sodium aluminate from the first alkaline aqueous mixture obtained in step (b), to provide a mixture of an extract solution of sodium aluminate and a dissolution residue of a reactive silica,
(d) separating the dissolution residue from the mixture provided in step (c), to obtain the extract solution of sodium aluminate,
(e) mixing the extract solution of sodium Li aluminate obtained in step (d) with a second alumina-containing slurry obtained by mixing a second portion of an alumina-containing ore with a second alkaline solution, to obtain a second alkaline aqueous mixture,
(f) extracting alumina as sodium aluminate from the second alkaline aqueous mixture obtained in step (e), to obtain a mixture comprising an extract solution of sodium aluminate,
(g) desilicating the mixture comprising the extract solution of sodium aluminate obtained in step (f), to provide a mixture containing a desilication product and a desilicated-extract solution,
(h) separating the desilication product from the mixture provided in step (g), to obtain the desilicated-extract solution, and
(j) adding seeds of aluminum hydroxide to the desilicated-extract solution obtained in step (h), to precipitate aluminum hydroxide.
With the process of the present invention, aluminum hydroxide is produced from an alumina-containing ore at a higher yield, while the alumina component and the alkaline component is consumed in a very small amount and the contamination by silica in aluminum hydroxide obtained is very little.
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Harato Takuo
Ishida Takahiro
Ogawa Toru
Birch & Stewart Kolasch & Birch, LLP
Bos Steven
Sumitomo Chemical Company Limited
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