Separation method of goethite-containing red mud

Details Separation method of goethite-containing red mud Separation method of goethite-containing red mud

2001-10-30

2003-12-30

Hruskoci, Peter A. (Department: 1724)

Liquid purification or separation

Processes

Making an insoluble substance or accreting suspended...

C423S121000, C423S122000, C210S733000

Reexamination Certificate

active

06669852

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method for separating an extraction residue (known as red mud) generated from a goethite-containing alumina ore. More particularly, the present invention relates to a method for separating, by use of a settling agent formed of a specific water-soluble copolymer, red mud contained in a sodium aluminate solution yielded through treatment, with an alkaline solution, of an alumina ore containing goethite as an iron component.
BACKGROUND OF THE INVENTION
The Bayer process is generally employed as a method for recovering alumina from an alumina ore through extraction. In a typical manner of the Bayer process, an alkaline solution is mixed with bauxit—named after the place where it was produced—serving as an alumina ore; the mixture is wet-milled, to thereby form a slurry; the slurry is heated at high temperature in order to take up, through extraction, an alumina component contained in bauxite, to thereby obtain an alumina-component-containing extract; and a remaining bauxite residue (i.e., extraction residue, usually called “red mud” because of its red color provided from an iron hydroxide component contained therein)—an undissolved component—is separated from the liquid phase. From the resultant alumina extract (aqueous sodium aluminate solution) from which red mud has been removed, aluminum hydroxide is precipitated, and the precipitated aluminum hydroxide is fired, to thereby yield alumina.
The residue (red mud), which is an undissolved component generated from bauxite, is separated from the slurry for extraction that has been treated at high temperature while the slurry is cooled to about 100° C. under atmospheric pressure. Typically, a thickener equipped with a mud collector is employed as a separation unit. Since the residue has a particle size as small as 10 &mgr;m or less, solid-liquid separation requires a long period of time. Thus, conventionally, a water-soluble polymer flocculant is used in order to accelerate sedimentation of the residue generated from bauxite.
Polymers such as sodium acrylate and a sodium acrylate-acrylamide copolymer are employed as polymer flocculants. In addition, a settling aid such as slaked lime or starch is also used in order to improve the sedimentation rate of the residue and to enhance the level of concentration of the lower liquid of the thickener to solid and clarification of the upper liquid.
However, some of the above substances, such as polymer flocculants, slaked lime, and starch, are not effective for separation of an extraction residue generated from any type of alumina ore. For example, studies have proven that these substances are effective for accelerating sedimentation of red mud generated from bauxite produced from GOVE ore, in Australia, but are not effective for accelerating sedimentation of red mud generated from bauxite occurring in southeast Asia, particularly in Indonesia.
This is because the residue generated from bauxite, predominantly containing components such as iron, silica, aluminum, titanium, and sodium, has a crystal morphology including any of these components that varies in accordance with the type of bauxite, leading to variation in properties such as sedimentation rate, condensation to solid, and clarification.
Examples of compounds having a high sedimentation rate include hematite (Fe
2
O
3
), anatase (TiO
2
), and boehmite (&ggr;-AlOOH), and examples of compounds having a low sedimentation rate include goethite (FeO(OH)), sodalite (Na
4
ClSi
3
Al
3
O
12
), rutile (TiO
2
), and gibbsite (Al(OH)
3
) (K. Yamada, et al.
Light Metals.,
1980, p39-50).
Large amounts of alumina ores such as BINTAN ore (Indonesia) are imported to Japan. These alumina ores contain trihydrate (gibbsite) as an alumina component and FeO(OH) (goethite) as an iron component. When such ores are subjected to a typical Bayer process, settling and separating an extraction residue (red mud) by use of a customary flocculent is difficult, since the residue contains goethite having a low sedimentation rate. Thus, there have been proposed a variety of measures for improving the settling characteristic of the extraction residue generated from bauxite containing a large amount of goethite.
Among such measures, Japanese Patent Application Laid-Open (kokai) No. 50-159497 discloses a method of converting goethite contained in bauxite to magnetite (Fe
3
O
4
) through elevation of alumina extraction temperature. This method includes extraction of alumina under the conditions; i.e., in the presence of a reducing organic substance at an extraction temperature of 270° C. or higher, to thereby convert goethite to magnetite having a good sedimentation property, thus leading to improvement in sedimentation characteristics. However, the method is economically disadvantageous, because of high energy consumption and requirement of expensive apparatus and material.
Japanese Patent Publication (kokoku) Nos. 54-3838 and 58-42131 disclose extraction methods including combined use of a substance of good sedimentation property. According to these methods, a substance of good sedimentation property is added with stirring to the extraction system, to thereby alter compositional proportions of the residue, thus attaining favorable separation of a substance of poor sedimentation property. However, these methods are also economically disadvantageous, because of a requirement for constant storage of a compound of good sedimentation property, thereby complicating the process.
Japanese Patent Application Laid-Open (kokai) No. 56-92116 discloses use of a settling aid formed of starch which has been cationized to the form of quaternary ammonium. By use of this settling aid in separation of red mud generated from a goethite-containing alumina ore, the sedimentation property can be slightly improved. However, this method is still unsatisfactory for industrial-scale treatment.
As described above, in relation to separation of red mud generated from a goethite-containing alumina ore, particularly that produced in Indonesia, the ore being imported to Japan in a large amount, there has never been known a settling aid which is endowed with good settling-separation characteristics and economical advantage and attains satisfactory performance in practical use during single use thereof.
SUMMARY OF THE INVENTION
The present inventors have conducted extensive studies to solve the aforementioned problems, and have found that separation of red mud generated upon treatment of an alumna ore containing goethite as an iron component can be performed very rapidly through use, as a flocculant (settling aid), of a water-soluble polymer including, as an effective component, a copolymer containing a divalent moiety formed of a vinylhydroxamic acid compound or a salt thereof and having an average molecular weight of at least 2,000. The present invention has been accomplished on the basis of this finding.
The water-soluble polymer to be used in the present invention, containing a vinylhydroxamic acid moiety or a salt thereof as a recurring monomer component, is disclosed to be usable as a settling aid for treatment of an alumna ore (U.S. Pat. No. 4,767,540). However, this patent provides no description about effectiveness of the settling agent for separation of red mud upon treatment of an alumina ore containing goethite as an iron component. Therefore, those skilled in the art cannot easily conceive, on the basis of the description of U.S. Pat. No. 4,767,540, the present invention directed to separation of goethite-containing red mud.
Accordingly, the present invention provides the below-defined methods for separating goethite-containing red mud.
1) A method for separating goethite-containing red mud contained in a sodium aluminate solution which is obtained by heating an alumina ore containing goethite as an iron component with an alkaline solution at 110-160° C., which method comprises adding a settling aid formed of a water-soluble polymer including, as an effective component, a copolymer containing, as a monomer component, a vinylhydroxamic

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