JPS5824375B2 - Bauxite Karano Alumina - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating bauxite for alumina production by the Bayer process, and more specifically to a method for treating bauxite for producing alumina by the Bayer process.
H or Fe2O3・H2O) and alumogeteite C (
The present invention relates to an advantageous caustic extraction method for bauxite containing goethite iron such as FeAl)OOH).

Generally, in the Bayer process, when extracting alumina from bauxite, the conditions for extraction with caustic alkali are appropriately selected depending on the form of aluminum oxide contained in the bauxite.

That is, the aluminum oxide shim is Gibbsite (A120
In the case of boehmite (A1203.I(20)), a relatively high extraction temperature of 200 to 250°C is selected.

On the other hand, even if bauxite containing goethite type iron as described above is extracted at any of the above temperatures, it is difficult to separate the produced red mud from the extract.

This suggests that it is also possible to obtain satisfactory sedimentation separation of red mud using corn starch, which is commonly used to flocculate red mud, or even a more powerful synthetic flocculant such as sodium polyacrylate. However, in order to obtain a sediment with a high density of red mud, a multi-stage thickener is required to thicken it, which is extremely uneconomical in terms of equipment operation.

The present inventors have conducted extensive research in order to eliminate the above-mentioned difficulties specific to the alkaline extraction of this type of bauxite, and have extracted bauxite containing goethite-type iron such as goethite and alumogoetite from reducing organic matter such as soil or coal. By extracting the amorphous substance of the shell with caustic alkali at a temperature of 270°C or higher in the presence of humus and humic acid, the amount of alumina extracted can be increased and the sedimentation and separation of red mud can be facilitated. I found out.

In other words, the present invention uses bauxite containing goethite iron, which has conventionally had a low alumina extraction rate and difficult red mud sedimentation separation, in the presence of reducing organic substances such as natural humus, humic acid, or their derivatives. at 270℃
□ provides a method for advantageously extracting with a caustic aqueous solution at the above temperature.

The bauxite used in the present invention may contain any form of aluminum.

That is, it may be gibbsite or boehmite.

Further, the goethite type iron contained may be goethite or alumogethite.

These may be mixed, or other forms of iron such as hematite and magnetite may be mixed.

The purpose of the present invention is to reduce the solidity of extracts based on goethite iron.
It overcomes the difficulty of liquid separation, which is inherent in the presence of goethite iron.

The aqueous caustic alkali solution used in the present invention is a well-known aqueous solution capable of extracting bauxite in the Bayer method to obtain an alkaline aluminate solution as an extract, and generally an aqueous sodium hydroxide solution is used.

Further, as is generally used, it is industrially preferable to use the residual liquid after precipitating aluminum hydroxide from an aqueous sodium aluminate solution as it is or after readjusting it.

The reducing organic substance used in the present invention is preferably natural humus, humic acid, or their derivative nitrofumic acid.

Hummus generally refers to a brown to black amorphous organic carbon substance that is present in soil or coal, and an amorphous acidic organic substance that is soluble in alkali and insoluble in acids and has the same color as hummus is called humic acid.

These form the bulk of the organic and carbonaceous substances in the soil.

In the present invention, it is possible to use the soil containing these as is, but it is also possible to extract hummus and humic acid from the soil and use this extract.

Alternatively, humic acid derivatives can also be used, whether solid or liquid.

Examples of humic acid derivatives include nitrofumic acid, which is produced by oxidizing lignite or brown coal with nitric acid.

Nitrohumic acid has the following structural formula and is commercially available from Chillnight Co., Ltd. under the trade name Chillnight A.

In short, any organic substance that can reduce goethite type iron in bauxite to magnetite in a caustic alkaline solution at 270° C. or higher according to the following formula can be used in the present invention.

6 Fe2O3' H20+C→4Fe304+CO2
+6H20 Although the formation of hematite was observed in the middle of the reduction reaction from goethite to magnetite, it is significant in the present invention to transform goethite-type iron.

Since these organic substances such as humus and humic acid are originally contained in bauxite ore or its top soil, it is preferable to use them, but depending on their content and goethite content, derivatives or extracts may be added. It can be used.

Furthermore, since these organic substances are colored in the extract, there is an advantage that their concentration can be easily identified.

The amount of organic matter used varies depending on the amount of goethite iron present in bauxite, the mass of organic carbon in the extraction starting solution, the composition of organic carbon, etc., but in general, it is 10 g or less as organic carbon per 11 of the extraction starting solution. is sufficient.

Even at a higher concentration, the goethite type iron undergoes transformation, and although the effects of the present invention are achieved, the alumina precipitation rate decreases in the next alumina precipitation step, which is not preferable.

In addition, it is more effective to add the organic carbon material that causes the transformation of goethite in a solid form than in a liquid form. For example, in the case of a liquid obtained by extracting topsoil, it is necessary to add at least 3 g of carbon to the initial extraction liquid, or as a solid. In this case, it is calculated as 0.
7g711 or more is preferable.

The heating temperature used is 270° to 350°C, and the higher the temperature, the shorter the heating time.

Industrially, the preferred temperature is about 300° C., although it is appropriately selected depending on the equipment used, such as a tubular type or a tank-two extractor.

The present invention is carried out in a pressure-resistant heating container, and the heating time varies depending on the temperature and can be shortened as the temperature increases.

The time can be determined in advance for various bauxites by separating the red mud from the extract after heat treatment and subjecting it to X-ray diffraction to confirm that goethite has changed to hematite or magnetite and that no goethite is present. It is possible.

Furthermore, alumogoetite type iron is decomposed and extracted due to the high temperature of 270℃ or higher, increasing the yield of aluminum, and organic substances such as humus and humic acid are consumed as reducing agents during the reduction reaction from goethite to magnetite, and organic substances are This has the advantage that it does not accumulate in the process solution.

Since the red mud produced by the method of the present invention is mainly composed of magnetite, it has the possibility of performing solid-liquid separation using its magnetism.

In actually applying the present invention, humic acid derivatives such as nitrhumic acid are added to the starting solution of caustic alkaline extraction which does not contain organic matter, and bauxite containing goethite is extracted at 270°C or higher, or organic carbon is already extracted. A process liquid containing carbonaceous substances is used as a starting liquid, and to this, organic carbonaceous substances such as humus and humic acid, and hawkide containing goethite are supplied and extracted at 270°C or higher.

The thus obtained extract is easily separated into red mud and a supernatant alkaline aluminate solution by adding a known flocculant such as starch or sodium polyacrylate and allowing it to stand, and the red mud sedimentation rate is 1 separation. Excellent results were obtained in terms of performance and alumina extraction rate, and no accumulation of added organic carbon was observed.

The present invention will be specifically described below with reference to Examples.

Example 1 1.5 as organic matter (organic substance carbonaceous tight, C)
800 g of bauxite ore topsoil containing AA20343.7 was extracted at 150°C in a caustic soda solution (30 g/A' as concentration Na20), and after extraction, the slurry was separated into solid and liquid using a centrifugal sedimentation machine. Extraction contract 2.51 (
Effective Na2O25g/l.

AA203,30 g/lo, C,3,4g/11
) was obtained.

This extract was diluted with a small amount of water, and further added with reagent caustic soda and reagent-grade aluminum hydroxide.
138g/l, Al2O table 5g/l and 0, C3,
A circulating aqueous sodium hydroxide solution containing 0 g/l was obtained.

80011L of this aqueous solution was mixed with goethite and alumogeteite type iron to give a weight ratio of 14.2 and a weight ratio of 0. C,
It was charged into an autoflave together with 128 g of bauxite containing 0.28% Al2O3 grade 48.0% by weight.

Each extraction test was heated under autogenous pressure at the temperatures shown in Table 1 for the times indicated.

0 of sodium polyacrylate as red mud flocculant after cooling
．． After adding 13 ml of 1% aqueous solution and stirring, 97 ryal of the red mud suspended extract was collected into an 11 measuring cylinder and its sedimentation rate was measured.

The sedimentation rate was calculated by injecting 970ml of red mud suspension slurry extract into 11 measuring cylinders, measuring the depth of the supernatant 2 minutes after the start of separation into red mud and supernatant, and calculating the sedimentation rate per hour. Converted to speed.

The volume of the sediment that had been allowed to settle in the apparatus for 20 hours was measured, and the supernatant was removed as an extract. The sediment was dried, the solid matter was weighed, and this was divided by the volume of the sediment to determine the degree of concentration.

In addition, the alumina content of the solid material was analyzed to determine the extraction rate of alumina.

On the other hand, the organic matter contained in the extract was determined as organic carbon.

The results are shown in Table 1.

FIG. 1 shows a diagram plotting the relationship between settling time and volume of red mud settling for each test number of an actual case.

The number of each curve corresponds to the test number in Example 1.

In test numbers (5), (6), and (7) according to the present invention in which the treatment temperature was 270°C or higher, it was found that the sedimentation rate of red mud was extremely slow.

Furthermore, test numbers (6) (method of the present invention) and (I) (temperature 27
X of the red mud obtained by each of
A line diffraction test was performed.

As a result, it was found that the iron in the red mud obtained by Test No. (1) was goethite, but the iron in the red mud obtained by Test No. (6) was transformed into magnetite.

Example 2 Topsoil (OC; 1.
5, A120343.7), effective Na2025g/l, A120330g/l by the method of Example 1.
2.51 of an extract having a composition of 102C23.4 g/l was obtained.

This was boiled down to 0.81, and 74 g of caustic soda was added to give an effective Na2O; 150 g/1A1203:9.
1g/l, 0. C2: A composition liquid 0.81 having a concentration of 10 g/l was obtained.

This was called liquid A. The above operation was repeated several times to obtain the required amount of liquid A.

Meanwhile, caustic soda solution (150g/V as Na20)■
Add 139 g of reagent-grade aluminum hydroxide per liter and similarly dissolve at 150°C to obtain an effective Na2O concentration of 150 g/l.
, Al2O3; 91 g/l was obtained, which was designated as Solution B.

Mix liquid A and liquid B, and add various o and c in the range of 2 g/l to 10 g/11.

A concentrated extraction starting solution was prepared.

For example, Test No. 10 with O and C concentrations of 3.05 g/l was obtained by mixing and preparing A:B-〇 in the ratio of 61:1.41.

Bauxite of the same quality as in Example 1 was added to the extraction starting solution obtained in this manner at a charging molar ratio of 1.3, and extracted at an extraction temperature of 280 to 285°C for a residence time of 5 minutes. In the same manner, the sedimentation rate, Al2O3 extraction rate, and red mud production rate were determined, and the form of iron in the extracted residue was determined by X-ray diffraction.

The results are shown in Table 2.

Furthermore, the X-ray diffraction pattern of each test number is shown in FIG.

From Table 2, it was found that when the O and C concentrations in the extraction starting solution were below 3 g/l, the sedimentation properties of red mud were extremely poor and the alumina recovery rate was low.

This is thought to be because, as is clear from the X-ray diffraction patterns a and b in FIG. 2, it is difficult for goethite to transform into hematite or magnetite unless the O, C, concentration is 3 g/1 or more.

Also, magnetite is 0.0 as seen from Figure 2 e and f2g.
It starts to be produced when the C1 concentration is around 8 g 713, and 9 g
/1. Above this point, most of the iron appears to be of the magnetite type.

Example 3 A caustic alkali extraction starting solution (aluminum hydroxide dissolved in a caustic soda solution) that does not contain 0, C3 was used, and bauxite mineral layer topsoil (0, C,
Section 1,51? A120343.7) Nitrohumic acid (0, C, 33, 2) starch was added, extracted under the same conditions as in Example 2, and tested in the same manner as in Example 1. Shown in the table.

From Table 3, in order to obtain a sedimentation rate of red mud of 6 m/hr or higher and an alumina extraction rate of 98 coefficient or higher, when using topsoil, the total C in the raw material must be 0.55 coefficient or higher. When using nitrofumic acid, it is necessary to adjust the amount of TotaAO and C in the raw materials to 1.16%.

Almost no effect was observed for starch.

In addition, tests were also conducted on organic carbon such as soybean protein and coal tar, but no significant effects were found.

Example 4 An extraction test of bauxite containing goethite type iron was conducted using a plant process liquid containing hummus or humic acid.

Plant repeat process liquid (0,C.9.38 g/l,
Effective Na 20150 g/! ! ), and in addition, this plant repeated process liquid was diluted with a synthetic liquid containing no O, C, and an initial solution of 0-C-5,58 g/lt effective Na20154.8 g/l and O, C.

A starting solution containing 2 g/l of 3A and 20146.79/l of effective Na was prepared.

0. C, 0, 29 Section, A120350.2 Section, Moisture 29
．． Bauxite containing goethite type iron in Section 5 was extracted using each of the above starting solutions at different extraction temperatures and residence times, treated in the same manner as in the actual case, and conducted the same tests. Table 4 shows the results obtained. Shown below.

Table 4 shows the starting liquid at 0. It is shown that the higher the C0 concentration, the better results can be obtained with a shorter residence time.

In addition, the concentration of 0 and C6 in the extract was lower than that of the starting solution, and 0
This shows that °C1 does not accumulate.

[Brief explanation of drawings]

FIG. 1 is a red mud sedimentation curve of the bauxite extract in Example 1, and FIG. 2 is an X-ray diffraction diagram of the red mud in Example 2.

Claims (1)

[Claims] 1. In a method for extracting alumina from bauxite containing goethite iron using caustic alkali, the bauxite is treated in the presence of humus, humic acid and/or their derivatives at a temperature of 270°C or higher until the goethite iron is transformed. A method for extracting alumina from bauxite, which is characterized by extracting by retaining a caustic alkali aqueous solution.