JP2000178663A - Treatment of aluminum dross - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treating method by which aluminum dross can be treated with high efficiency, the residues after the treatment are stable, the amt. thereof can also be reduced, and, moreover, aluminum can effectively be recovered. SOLUTION: Aluminum dross is incorporated with an aq. soln. of caustic alkali or alkali aluminate, and they are brought into reaction to form a liq. phase contg. soluble contents and a solid phase composed of insoluble contents. This liq. phase and solid phase are separated. The liq. phase is incorporated with the seed crystals of aluminum hydroxide to recover aluminum in the liq. phase as aluminum hydroxide. The Si contents in the liq. phase are precipitated as silicate by adding a zeolite group silicate mineral to the liq. phase and are separated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten metal residue generated when aluminum metal is melted in processes such as aluminum rolling, extrusion, casting, die casting, and secondary alloy production, and a residue obtained by squeezing and recovering a metal component from the residue. The present invention relates to a new method for treating ash (both are collectively referred to as dross).

[0002]

2. Description of the Related Art The amount of dross generated increases with the increase in demand for aluminum, and about 400,000 tons of dross are generated annually in Japan. This dross is not only metal aluminum but also aluminum compounds such as oxidized alumina and nitrided aluminum nitride, and various metal elements and their oxides added during the production of aluminum alloys.
It contains chlorides and carbides, and although some are effectively used as slag-making agents for steel, most of them are landfilled as industrial waste. However, metal aluminum and aluminum nitride contained in dross react with water (mainly rainwater) and generate hydrogen and ammonia as shown in the following formula, so that it is difficult to perform large-scale and batch processing. In addition, since the reaction occurs even in the storage place before the treatment, the dross treatment has a difficulty in handling at each stage of the storage, transportation and treatment. As a method for preventing this, a water treatment method has been adopted in which dross is immersed in water in advance, the reaction is terminated, and then discarded (Light Metal, Vol. 48, No. 4, (1998), 199-203). 2Al + (3 + n) H ₂ O → Al ₂ O ₃ .nH ₂ O
+ 3H ₂ ↑ 2AlN + (3 + n) H ₂ O → Al ₂ O ₃ .nH ₂
O + 2NH ₃ ↑

[0003]

Although the above-mentioned method can prevent the generation of gas after the treatment, the amount of the residue after the treatment cannot be reduced. Issues remain in terms of ensuring security. In addition, the reaction between metal aluminum and aluminum nitride and water has a slow reaction rate, and a large-capacity apparatus is required to maintain a residence time for completing the reaction. For this reason, it was practically difficult to process the generated dross in large quantities.
From these facts, the dross treatment method, which balances the reduction of the residue itself and the stability of waste, is also compact in terms of equipment,
There has been a demand for a method with high reaction efficiency, and more desirably, a method for recovering aluminum from dross. The present invention aims to solve these problems.

[0004]

As a result of various studies on the reactivity of dross, the present inventors have found that the above object can be achieved by treating dross with a caustic alkali solution or an alkali aluminate solution. The present invention has been reached. That is, the present invention comprises the following items. (1) A treatment of aluminum dross, wherein a caustic alkali or alkali aluminate solution is added to aluminum dross and reacted to form a liquid phase containing a soluble component and a solid phase, and the liquid phase and the solid phase are separated. Method. (2) A method for treating aluminum dross, wherein aluminum hydroxide serving as a seed crystal is added to the liquid phase separated in (1) above, and the aluminum compound dissolved in the liquid phase is recovered as aluminum hydroxide. . (3) A zeolite group silicate mineral is added to the liquid phase separated in the above (1) to precipitate a Si component dissolved in the liquid phase to form a liquid phase and a solid phase, and the liquid phase and the solid phase are separated. A method for treating aluminum dross. (4) In step (3), the Si component is precipitated to form a liquid phase and a solid phase. After the liquid phase and the solid phase are separated, aluminum hydroxide serving as a seed crystal is added to the liquid phase and dissolved in the liquid phase. A method for treating aluminum dross, wherein the aluminum compound is recovered as aluminum hydroxide. (5) The above (2), wherein the remaining liquid phase from which the aluminum hydroxide is recovered in the above (2) or (4) is circulated and used as a caustic or alkali aluminate solution to be added to the aluminum dross. Alternatively, the method for treating aluminum dross according to the above (4). As the caustic or alkali aluminate solution used in the above (1) to (5), a solution produced in a buyer process for producing alumina can be used.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. As the dross used in the present invention, those generated from the above-mentioned various steps can be used, and the components thereof are not particularly limited. However, since the Si component is consumed by reacting with the caustic alkali or the alkali aluminate, the From the viewpoint of reducing the amount used, the content of the Si component in the dross is small. For example, the Si element is preferably 2% by weight or less.

The alkali of the caustic alkali solution or the alkali aluminate solution used in the present invention is not particularly limited. However, sodium hydroxide, potassium hydroxide or potassium hydroxide is preferred from the viewpoint of industrial availability and low cost. It is desirable to use sodium aluminate and potassium aluminate. When the concentration of these solutions is low, the amount of solution required for processing the same amount of dross relatively increases,
In general, the concentration is set in the range of 1 to 10N, preferably in the range of 3 to 6N, because the solid-liquid separation after the reaction becomes difficult and the residue becomes difficult to clean. I do. In the case of an alkali aluminate solution, this concentration is represented by the total concentration of free caustic in the solution and caustic forming a compound as alkali aluminate.

The mixing ratio of dross to the caustic alkali or alkali aluminate solution is determined by the molar ratio of soluble aluminum (Al) such as metallic aluminum or aluminum nitride and alkali metal (denoted as M) in the mixed solution. (Al / M) is preferably 1 or less, and more preferably 0.7 or less. When alkali aluminate is used in the above, soluble aluminum includes aluminum in alkali aluminate, and the amount of alkali metal (M) is the total amount described above. When the above molar ratio is 1
If the temperature exceeds the limit, the precipitation of aluminum hydroxide starts from the initial stage of dissolution, and if the temperature exceeds 0.7, the once dissolved aluminum easily precipitates as aluminum hydroxide, and the liquid phase and the solid phase containing aluminum as a soluble component are separated. Becomes difficult. The reaction temperature of the dross with the caustic alkali or aluminate solution is preferably 60 ° C. or higher because the reaction rate is low if the reaction temperature is low, and the upper limit can be up to the boiling point of the solution at normal pressure.

[0008] Soluble aluminum such as metallic aluminum and aluminum nitride in dross is mainly converted into an aluminum compound such as alkali aluminate by a reaction, and is dissolved in the liquid phase. Insoluble matter such as alumina in the dross becomes a solid phase. After completion of the reaction, the liquid phase and the solid phase are separated. Separation can be performed by filtration, centrifugation, or the like. The separated solid phase is a stable compound such as an oxide, enables effective use, and can be discarded as it is. Aluminum hydroxide can be recovered from the separated liquid phase by a conventional method. Since aluminum is mainly dissolved in the liquid phase as alkali aluminate, aluminum hydroxide is added to this as a seed crystal, and aluminum of alkali aluminate is precipitated as aluminum hydroxide and collected. The amount of seed crystals to be added is usually 100 alkali aluminates.
It may be about 50 to 200 parts by weight based on parts by weight.

Si in dross is an element in aluminum alloy
Or in the form of an oxide or the like,
Si is caustic or alkali aluminate in dross
When the solution is added and reacted, sodium silicate is formed and
Dissolve in The generated sodium silicate is formed by dissolution of Al
Reacts with sodium aluminate in the liquid
Certain sodalite (Nasoda)_Two O ・ Al_Two O_Three 
・ 2SiO_Two )_Three Na _Two X ・ nH_Two Forms O and
Will be discarded. This series of reactions is described below.
It is. 2Si + 4NaOH + 2H_Two O → 2Na_Two SiO_Three +4
H_Two ↑ 2Al + 2NaOH + 2H_Two O → 2NaAlO_Two + 3H
_Two ↑ 6NaAlO_Two + 6Na_Two SiO_Three + MH_Two O → (Na
_Two O ・ Al_Two O_Three ・ 2SiO_Two )_Three Na_Two X ・ nH_Two O
+ 12NaOH Sodalite Na in the formula_Two X of X represents the anion in the liquid
In the case of pure sodium aluminate solution,_Two O_Four ^2- Becomes
However, if sulfates, carbonates, etc. are present, their anions correspond
I do. This sodalite formation reaction is relatively slow,
If the reaction time is not sufficient, Si remains in the solution at a high concentration.
The remaining Si becomes an impurity during aluminum hydroxide precipitation
The quality of aluminum hydroxide
You. Therefore, the Si dissolved in the liquid must be removed in advance.
Is desirable.

According to the invention (3) in the present invention, dross is reacted by adding a caustic alkali or alkali aluminate solution to form a liquid phase and a solid phase. The two are separated, and a zeolite group mineral is added to the liquid phase. The dissolved Si component is precipitated by being added to form a liquid phase and a solid phase, and these are separated. The Si component is usually dissolved in the form of sodium silicate (Na ₂ SiO ₃ ). Zeolite minerals are Na ₂ O, Al ₂ O
₃ , containing SiO ₂ , various types are known depending on the composition ratio, and are also used in detergents and the like. The above-mentioned sodalite is one such mineral and can be used in the present invention. The zeolite mineral acts as a seed crystal for the dissolved Na ₂ SiO ₃ , and by its addition, Na ₂ SiO ₃ precipitates as a solid phase and can be separated from the liquid phase. The amount of this seed crystal added was Na ₂ SiO ₃
It may be about 50 to 500 parts by weight based on 100 parts by weight.

From the liquid phase from which the Si component has been removed, aluminum hydroxide can be recovered by adding seed crystals in the same manner as described above. Thereby, highly pure aluminum hydroxide can be obtained. The dross is treated with caustic or the like, and a seed crystal is added to the separated liquid phase or the liquid phase from which the above-mentioned Si component has been removed to precipitate aluminum hydroxide, and the separated solution contains caustic alkali. . This solution can be recycled by adding it to dross to be subsequently processed.

When producing alumina from bauxite by the Bayer method as the caustic alkali or aluminate solution used in the present invention, a solution obtained in the process may be used. As this solution, a solution (mother liquor) obtained by precipitating and separating aluminum hydroxide can be used.

[0013]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples. (Example 1) 1,000 ml of a 2N KOH solution heated to 80 ° C. was put into a 2,000 ml beaker, 100 g of dross having the composition shown in Table 1 was gradually added thereto with stirring, and the whole amount was added for 1 hour after completion. The stirring was maintained while continuing. After separating the solid and liquid by vacuum filtration using qualitative filter paper,
The residue was washed and dried to determine the weight and composition (% by weight). The results were as shown in Table 1.

[0014]

[Table 1] When the Al / K molar ratio of the filtrate was measured, it was 0.69, and the solution was stable even after standing overnight.

Example 2 5 liters of a 6N NaOH solution was collected in a 10 liter wide-mouthed polyfluoroethylene (Teflon) container, and the temperature was maintained at 60 ° C. on a hot water bath.
To this, 1.5 kg of dross having the composition shown in Table 2 was gradually added with stirring, and after completion of the addition, the mixture was kept for 2 hours while continuing stirring.
Thereafter, the solid and liquid were separated by vacuum filtration using a qualitative filter paper, and the residue was washed and dried to determine the weight and composition (% by weight). The results were as shown in Table 2.

[0016]

[Table 2] On the other hand, the above-mentioned filtrate and the washing solution were mixed to obtain a liquid having an Al / Na molar ratio of 0.58, all of which was collected in a 10-liter wide-mouthed plastic container, kept at a temperature of 60 ° C. in a hot water bath, and stirred. 10 g of aluminum hydroxide seed crystals having an average diameter of 5 μm
One liter was added and kept stirring for 48 hours. Thereafter, the suspension was washed by filtration and dried to obtain 688 g of aluminum hydroxide powder.

Example 3 Aluminum from bauxite ore
Bauxite dissolution in the buyer process
A solution (mother liquor) having the composition shown in Table 3 used for
0m^Three 10m in the tank ^Three And the composition (% by weight) shown in Table 4
Of dross was gradually added with a quantitative feeder. Addition
After completion, the mixture was kept under stirring at 80 ° C. for 2 hours. After a while
The whole amount is processed with a horizontal belt filter, and the solid content is washed by filtration.
After the purification, the residue was dried with a paddle type dryer to obtain 584 kg of a residue.
Table 4 shows the composition (% by weight). Next, the solid content is
Combine the filtrate separated by filtration with the solid washing solution (filter washing
Liquid), residual trace solids with a pressurized leaf filter
15m after removing the object^Three To the precipitation tank with a stirrer
150 μm of aluminum hydroxide having an average diameter of 150 μm
kg and kept at 60 ° C. for two days and night with stirring. Scold
After that, the whole amount is treated with a horizontal belt filter, and the solid content is filtered.
After overwashing, dry with a paddle dryer and aluminum hydroxide
1.16t was obtained. Aluminum hydroxide by the above filtration
Combine the filtrate from which the system was separated with the aluminum hydroxide washing solution.
(Called washing solution), bauxite dissolution in buyer process
Returned to process. Filtration liquid, composition of filtration liquid, Al / N
Table 3 also shows the molar ratio of a.

[0018]

[Table 3]

[0019]

[Table 4]

(Comparative Example 1) 8 in a 2,000 ml beaker
1.000 ml of purified water heated to 0 ° C. was added, 100 g of dross used in Example 1 was added thereto with stirring, and the whole amount was added. After completion, stirring was maintained for 6 hours. Thereafter, solid-liquid was separated by vacuum filtration using a qualitative filter paper, and the residue was dried, and then the weight and composition (% by weight) were measured. The results are shown in Table 5. As shown in Table 5, unstable components such as aluminum metal and aluminum nitride remained, and the weight of the residue increased rather than that of the Examples, although the treatment was performed for a longer time.

[0021]

[Table 5]

[0022]

According to the present invention, (1) a soluble aluminum component in dross can be recovered as a valuable resource. (2) The amount of solid residues that require final disposal can be reduced. (3) The solid residue is chemically stabilized to enable effective use. (4) The efficiency of the apparatus can be improved as compared with the existing stabilization method (hydration method). It has very good effects.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shunichi Hijikata 224, Kaiyamacho, Sakai-shi, Osaka Showa Aluminum Co., Ltd. (72) Inventor Akira Sakamoto 8-8 Ebisucho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture Showa F-term (reference) in Yokohama Plant of Electric Works 4D004 AA44 BA05 CA13 CA34 CB44 CC11 CC12 DA03 DA10 4G076 AA02 AA10 AB22 AB28 BA26 BB04 BC07 BC08 CA02 DA30 FA01 4K001 AA02 BA13 DB08 DB25

Claims (7)

[Claims] 1. An aluminum dross characterized by adding a caustic alkali or alkali aluminate solution to aluminum dross and causing it to react, forming a liquid phase containing a soluble component and a solid phase, and separating the liquid phase and the solid phase. Processing method. 2. A process for treating aluminum dross, wherein aluminum hydroxide serving as a seed crystal is added to the liquid phase separated in claim 1, and an aluminum compound dissolved in the liquid phase is recovered as aluminum hydroxide. Method. 3. A zeolite group silicate mineral is added to the liquid phase separated in claim 1, and a Si component dissolved in the liquid phase is precipitated to form a liquid phase and a solid phase. A method for treating aluminum dross, which comprises separating. 4. The method according to claim 3, wherein the Si component is precipitated to form a liquid phase and a solid phase. After separating the liquid phase and the solid phase, aluminum hydroxide serving as a seed crystal is added to the liquid phase. A method for treating aluminum dross, wherein a dissolved aluminum compound is recovered as aluminum hydroxide. 5. The method according to claim 2, wherein the remaining liquid phase from which the aluminum hydroxide has been recovered in claim 2 or 4 is recycled as a caustic alkali or alkali aluminate solution to be added to aluminum dross. The method for treating aluminum dross according to claim 4. 6. The method for treating aluminum dross according to claim 1, wherein the alkali aluminate solution is a solution produced in a Bayer process for producing alumina. 7. The molar ratio (Al / M) of soluble aluminum (Al) to alkali metal (M) in a solution obtained by adding a caustic alkali or alkali aluminate solution to aluminum dross is 1 or less. A method for treating aluminum dross according to claim 6.