JP3870400B1 - Method for refining aluminum hydroxide sludge - Google Patents

Abstract

The present invention provides a purification method for removing metal harmful substances and various metal compounds from amorphous aluminum hydroxide sludge containing metal harmful substances and various metal compounds.
SOLUTION: An amorphous aluminum hydroxide sludge 1a containing a metal harmful substance and a metal compound is dissolved in a caustic soda solution 3a having an adjusted alkali concentration to produce a sodium aluminate solution 7a. The sodium aluminate solution The hazardous metal and metal compound are removed from 7a by solid-liquid separation. Further, the solution 8a from which the metal harmful substances and metal compounds have been removed from the sodium aluminate solution 7a is neutralized to elute aluminum hydroxide, and the neutralized solution 12a is solid-liquid separated to obtain an amorphous state. Aluminum hydroxide is purified.
[Selection] Figure 1

Description

  The present invention relates to a method for refining aluminum hydroxide sludge, and more particularly to a method for refining amorphous aluminum hydroxide sludge discharged from an aluminum or aluminum alloy plant.

  Amorphous cotton-like aluminum hydroxide generated from aluminum-containing waste liquid discharged from aluminum or aluminum alloy processing plants has various metal compounds, organic polymer compounds (flocculating agents), silicates, etc. as impurities. Contains. This is subjected to a dehydration step by filtration, and the like, and an amorphous cotton-like aluminum hydroxide sludge having a water content of about 75% is obtained.

  Such aluminum hydroxide has cohesiveness with various metals, silicates, organic compounds, etc. and contains a lot of impurities, so there is almost no effective utilization method, and waste treatment is carried out at a large expense. . Strictly speaking, it is only used as a raw material for "sulfuric acid band" as a flocculant for drainage.

  Since aluminum hydroxide sludge has a moisture content of about 75%, the transportation cost is considerably high in the state where moisture is transported. Moreover, it is a difficult-to-handle product. In order to cope with this, various investigations such as weight reduction by dehydration by filtration and the like have been made. However, amorphous, cotton-like aluminum hydroxide sludge is in the form of clay and imposes a considerable load on the machine. Although pressure filtration is the majority, it takes a considerable amount of time for filtration. Also, if the pressure is too strong, the operation is difficult, such as curing.

  In order to solve this problem, a drying method by incineration has been proposed. In this method, unless the incineration temperature is generally maintained at 800 ° C or higher, the moisture content is 10% or less because the properties are amorphous. I could n’t.

  In this case, the sludge melts into a sandy clinker state, becomes difficult to handle, and uses are considerably limited. Moreover, since a large amount of heat is used, it is not economically suitable.

In order to solve this problem, after pulverizing amorphous aluminum hydroxide in an amorphous shape, it is dispersed in a high-speed hot air stream to instantaneously evaporate water in the aluminum hydroxide. In which the water content is reduced to the same level as that of crystalline aluminum hydroxide while maintaining its solubility in caustic and amorphous. (For example, refer to Patent Document 1).
Japanese Patent No. 2665183

  In Patent Document 1 described above, the method is aimed at precipitating aluminum hydroxide, and is not aimed at removing harmful metal substances.

  As described above, there is a method of producing a “sulfuric acid band” by reacting this aluminum hydroxide sludge with sulfuric acid. However, due to the cohesiveness of aluminum, chromium, iron, copper contained in aluminum alloys and the like, and nickel, which is a harmful substance used for the surface treatment of aluminum sashes, are collected.

  Due to these effects, the product of “sulfuric acid band” not only becomes green or brown, but also its use is limited to wastewater treatment in factories because of its low purity. Recently, since various metal compounds are included, it is becoming difficult to trade “sulfuric acid band” products.

  In addition, the “sulfuric acid band” produced in this way has a high aluminum hydroxide sludge moisture content, so the aluminum oxide concentration in the industry standard (JIS standard) is thin, the product value is low, and it is collected at low cost. It has been.

Accordingly, the present invention aims at providing a purification process for removing the removal target impure material from aluminum hydroxide sludge amorphous containing a metal harmful substances and various metal compounds as a removal target impurities.

To achieve the above object, the purification method of the aluminum hydroxide sludge according to the present invention, nickel is a metal harmful substances, chromium, lead, cadmium and compounds thereof as well as iron, copper, manganese, zinc and its compounds A first step of generating a sodium aluminate solution by dissolving amorphous aluminum hydroxide sludge containing impurities to be removed in an alkaline caustic soda solution matched to the sludge so that the pH value is constant , It is characterized by comprising a second step of removing the solid-liquid separating the removal target impure product from the sodium aluminate solution.
Further, in the present invention, in addition to the above steps, a third step of eluting the aluminum hydroxide to neutralize the solution the removal target impure product was removed from the sodium aluminate solution, the aqueous aluminum oxide A fourth step of purifying the amorphous aluminum hydroxide by solid-liquid separation of the solution.
Hereinafter, the present invention will be described.
Aluminum in aluminum hydroxide sludge that is amorphous or amorphous is very reactive with caustic soda. Aluminum hydroxide reacts with caustic soda and dissolves as “sodium aluminate (soda)”.

However, the above removal target impure product may have different solubility by alkali concentration of caustic soda. Since aluminum hydroxide has a high reaction rate with caustic soda, it can be carried out in either scum after waste water treatment or sludge after dehydration. In addition, it is conceivable that the reaction temperature is raised in engineering.

Therefore, in the present invention, the concentration of caustic soda is kept constant according to the sludge, and amorphous aluminum hydroxide is added thereto. For example, aluminum hydroxide sludge is supplied so that the alkali concentration is measured by the pH value and becomes constant.

Various metal harmful substances and metal materials and their compounds specified In exclude impurities thereof can be performed proportional automatic control to the pH value constant.

  As described above, when the sludge of amorphous aluminum hydroxide is dissolved in the caustic soda solution, the aluminum reacts with the caustic soda to form a compound of sodium aluminate to be in a solution state.

Additional removal target impure substances contained in the sludge of amorphous-like aluminum hydroxide, depending on the caustic soda concentration, since the separated in insoluble state, and removed the insoluble matter was filtered off.

Sodium aluminate obtained by such a method has aluminum dissolved in an alkaline solution. When this solution is neutralized with an acidic solution such as sulfuric acid and subjected to solid-liquid separation, amorphous aluminum hydroxide is eluted.
The removal of such metal harmful substances and metal compounds could be achieved up to the properties of commercially available industrial product aluminum hydroxide. Aluminum hydroxide produced by refining the sludge of amorphous aluminum hydroxide is a compound purified by “elution” pH by neutrality, and is in an amorphous state.
Commercially available industrial aluminum hydroxide was obtained by the “crystallization method”. Differentiated from aluminum hydroxide with a crystalline structure. In other words, amorphous aluminum hydroxide, which is obtained by a method in which a commonly used alkaline solution is supersaturated, and seeds are added and precipitated to a saturated solution, is different from amorphous aluminum hydroxide in terms of reactivity and solubility. It is very excellent and is not expected to be widely used.

  As the sulfuric acid for neutralization, it is possible to use “waste sulfuric acid solution” discharged from the anodized film forming bath of the aluminum anodized processing plant.

  The composition of the waste sulfuric acid solution is generally [free sulfuric acid content: about 17%, aluminum sulfate content: 11%].

  Not only can it be used as a sulfuric acid solution for neutralization, but also aluminum sulfate can be recovered as an amorphous aluminum hydroxide product. The waste sulfuric acid has no recycling method and is collected as industrial waste.

By removing the impurities to be removed contained in the aluminum hydroxide sludge, the amorphous aluminum hydroxide is superior in whiteness compared to the crystalline aluminum hydroxide obtained by the precipitation method. Crystalline aluminum hydroxide obtained by the precipitation method has a yellowish light brown color, without removing the same trivalent cation iron as aluminum.

  Since the amorphous aluminum hydroxide excludes iron as various metals, the whiteness can be further increased. This is an amorphous aluminum hydroxide compound that can be sufficiently used for high-grade products such as “ceramics” and “zeolite”.

  Hereinafter, an embodiment of the method for purifying aluminum hydroxide sludge according to the present invention will be described with reference to the purification equipment shown in the drawings.

Step S1: An aluminum hydroxide sludge 1a having an amorphous shape is charged in an aluminum sludge hopper 1 with 250 kg (water content 73%).

Step S2: 76.9 kg of amorphous aluminum hydroxide sludge 1a is added to the sludge dissolution tank 3 by the sludge conveyor 2.

Step S3: The sludge dissolution tank 3 used an indirectly heated stainless steel container with a stirrer. The caustic soda solution 3a was prepared by adding 24.4 kg of industrial caustic soda flakes to 218 kg of tap water and dissolved therein, and this was mixed with aluminum hydroxide sludge in the sludge dissolution tank 3.

  Further, the caustic soda solution 3a and the aluminum component of the amorphous aluminum hydroxide sludge 1a were stirred and reacted at 80 ° C. for 1 hour in order to completely dissolve them in the sludge dissolution tank 3. The stirring speed is constant at 100 rpm.

Step S4: The solution (sodium aluminate) in the sludge dissolution tank 3 is introduced into the first filtration tank 6 by the pump 4 and stored.

Step S5: The filtrate (sodium aluminate) 7a stored in the first filtration tank 6 is sent to the first filter 8 by the pump 7.

  The liquid state of the filtrate 7a at this time is as shown in the specifications of the stock solution in Table 1 below.

第1濾過機8では、濾過液7a中で不溶解の各種金属有害物質及び各種金属類を固液分離法により除去する。この第1濾過機8は、濾過板21とバー22とシリンダ23と脚24とで構成されており、シリンダ23の油圧を解除することにより濾過板21がフリーになるので、手動でケーキをホッパー25に落とす。このケーキ26が上記除去対象不純物を含んでいるので、第1濾過機8からの濾液8a（pH13.7）であるアルミン酸ナトリウム濾液には上記除去対象不純物が除去されていることになる。

In the first filter 8, various metal harmful substances and various metals that are insoluble in the filtrate 7a are removed by a solid-liquid separation method. The first filter 8 is composed of a filter plate 21, a bar 22, a cylinder 23, and a leg 24. By releasing the hydraulic pressure of the cylinder 23, the filter plate 21 becomes free. Drop to 25. This cake 26 contains the removal target impurities, so that the removal target impurities have been removed to the sodium aluminate filtrate filtrate is 8a (pH 13.7) from the first filtration device 8.

  The composition of the cake 26 obtained from the hopper 25 is as shown in Table 2 below.

  The first filter 8 employs a method of reducing both the press-fitting and pressing pressure for the purpose of obtaining a sludge dissolution tank (clarified liquid). Since the filtrate was cloudy at the initial stage of press-fitting and during pressing, a method was adopted in which it was recovered so as not to enter various insoluble harmful substances and various metals by returning it.

The filtration rate of the clarified filtrate was 137 l / m ² h. The thickness of the cake 26 was as thin as 3 to 5 mm. This is because the aluminum compound was dissolved as much as possible at a reaction temperature of 80 ° C., and most of the cake 26 was made into various insoluble harmful substances and various metals.

Step S6: The filtrate 8a obtained by the first filter 8 is sent to the filtrate tank 9 and stored.
Step S7: The filtrate in the filtrate tank 9 is sent to the second filtration tank 11 by the pump 10 and neutralized to obtain purified aluminum hydroxide. Here, 5% sulfuric acid 11a was added to the filtrate 8a (pH 13.7) for neutralization, and aluminum hydroxide (pH 8) was eluted. As the second filtration tank 11, a stainless steel drum with a stirrer was used.

Step S8: The aluminum hydroxide solution (neutralized solution) 12a obtained in the second filtration tank 11 is sent to the second filter 13 as a filtrate. In the second filtering device 13, using the filter plate 21 × 4 room 360 mm ^□.

  Since the purpose of the filtrate 12a was to obtain high-purity aluminum hydroxide, a cake washing test was conducted.

  The cake washing water used was industrial water (electric conductivity 9 ms / m) heated to 40 ° C. The cake washing water was used twice as much as the stock solution to confirm the washing water washing effect.

As a result, the filtrate 13a is substantially equivalent to industrial water. Also, the non-crystalline product 28 obtained from the hopper 27 is shown as “refined aluminum hydroxide” in Table 2 above. As can be seen, N i, Cr, Cd, various metals harmful substances and various metal compounds such as Pb has been largely removed, such a low content of it can be seen that there is no commercial product and inferior.

Step S9: The filtrate 13a is discharged outside the factory via the discharge tank 14. Table 3 below shows the operating state of each filter.

It is the systematic diagram which showed the process which implements the purification method of the aluminum hydroxide sludge which concerns on this invention.

Explanation of symbols

1 Sludge hopper
1a Aluminum hydroxide sludge
2 Sludge conveyor
3 Sludge dissolution tank
3a Caustic soda solution
3b level meter
4 Pump
5 Flow meter
6 First filtration tank
7 Pump
7a Filtrate
8 First filter
8a filtrate
9 Filtrate tank
10 Pump
11 Second filtration tank
11a Sulfuric acid
12 Pump
12a Filtrate
13 Second filter
13a filtrate
14 Discharge tank
21 Filter plate
22 bar
23 cylinders
24 legs
25 cake hopper
26 cakes
27 Product hopper
28 products (refined aluminum hydroxide)

Claims (2)

Nickel is a metal harmful substances, chromium, lead, cadmium and compounds thereof as well as iron, copper, manganese, amorphous aluminum hydroxide sludge containing zinc and its compounds as the removal target impurities, the pH value is constant A first step of producing a sodium aluminate solution by dissolving in an alkaline caustic soda solution matched to the sludge,
A second step of removing the solid-liquid separating the removal target impure product from the sodium aluminate solution,
A method for purifying aluminum hydroxide sludge, comprising: In claim 1,
A third step of eluting the aluminum hydroxide to neutralize the solution the removal target impure product was removed from the sodium aluminate solution,
A fourth step of purifying amorphous aluminum hydroxide by solid-liquid separation of the aluminum hydroxide solution;
A method for purifying aluminum hydroxide sludge, comprising:

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