JPS6131759B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a chromium-aluminum tanning agent from an alumina hydrate containing chromate. Currently, as is well known, various tanning agents have been proposed and used, but chromium tanning agents and tannin tanning agents are mainly used. Chrome tanning agents have been used since ancient times due to their outstanding tanning effect.
Various basic chromium sulfates are known based on different basicities and chromium content differences. However, even with such effective chromium tanning agents, several drawbacks have been pointed out in line with the demands of the times. has become a major problem, and various studies are being conducted to deal with it and countermeasures are required. Countermeasures against this problem include (1) a so-called recycling method in which chromium-containing wastewater is returned to the chrome tanning process for use; (2) A so-called highly adsorbent chromium tanning method that uses a tanning agent that improves chromium adsorption. (3) A method of using the minimum necessary amount of chromium in combination with other tanning agents has been proposed and has been partially implemented. Another drawback, which is a characteristic of chromium compounds, is that the tanned leather remains colored by trivalent chromium, making it difficult to dye the leather. In view of these problems, aluminum tanning agents, zirconium tanning agents, etc. that do not use any chromium compounds have been proposed, but they have not been replaced because of their inferior tanning effect. Therefore, currently the above
Among methods (3), a chromium-aluminum tanning agent is used. One of them was developed in Poland, and is said to be a reaction product of sodium dichromate, aluminum sulfate, sodium bisulfite, and formic acid (salt), but the reaction system is extremely complex. There are many problems such as poor quality stability, and part of the sodium bisulfite decomposing during the reaction, resulting in insufficient reduction of hexavalent chromium and difficulty in adjusting basicity. On the other hand, zirconium-aluminum-
A method for producing a chromium ternary tanning agent has been proposed.
(Special Publication No. 42-471). In this, an aluminum-chromium mixture is described as a precursor,
Aluminum is present in a larger amount than chrominium, and its production not only tends to generate hydroxides, but also cannot be expected to have much of a tanning effect on its own. In view of the above facts, the present invention has discovered the most industrially advantageous method for producing chromium-aluminum tanning agents in terms of both raw materials and production, and has developed a method that is excellent in terms of quality. The invention was completed. That is, the gist of the present invention is to add an acid to hydrated alumina containing chromate to dissolve it, then add a reducing agent to reduce hexavalent chromium, and then neutralize it with an alkali agent. The present invention relates to a method for producing a chromium-aluminum tanning agent, which is characterized in that it is highly basicized. In the present invention, the alumina hydrate containing chromate, which is the starting material, is most rational and advantageous to effectively utilize by-products in the chromate production process, especially sodium chromate from chromium ore. In the manufacturing process, it is preferable that a large amount of alumina hydrate is produced as a by-product depending on the manufacturing process. In other words, this alumina hydrate generally has a high water content and contains a large amount of hexavalent chromium due to its nature, but this separation is almost impossible and there are many problems in its disposal. . In other words, sodium chromate is produced by oxidizing and roasting a mixture of chromium ore, a soda source, and a filler such as lime, and leaching it with water. Production methods based on sintering or direct melting of chromate acid and alkali in an oxidizing atmosphere have gradually come to be adopted. In these methods, a large amount of alumina in the chromium ore is dissolved as alkali aluminate along with alkali chromate during the leaching process, so a step is required to neutralize the alkali chromate leachate and insolubilize and separate the alumina content as alumina hydrate. is necessary. Therefore, the alumina hydrate produced as a by-product in this process is a precipitate containing alkali chromate, and the Cr ₂ O ₃ /Al ₂ O ₃ ratio can be adjusted appropriately by washing or adding alkali chromate. This makes it the most suitable raw material for the method of the present invention. The starting material, alumina hydrate containing chromate, has a composition with a weight ratio of 07≦Cr ₂ O ₃ /
It is desirable that Al ₂ O ₃ ≦3, and therefore, the above-mentioned alumina hydrate is used for industrially advantageous production, but in that case, the by-products from the above-mentioned chromate production process are used. It goes without saying that it can be used as is, but it can also be adjusted to the above composition range as needed. In view of the above reasons, it goes without saying that other means of preparing the starting material can be used, namely a mixture of chromate or dichromate and alumina hydrate. In the present invention, the chromate contained in the alumina hydrate means one containing one or more of alkali monochromates, alkali dichromates, and chromium trioxide. Next, an acid is added to the alumina hydrate containing the chromate to dissolve it. As an acid, sulfuric acid,
Preference is given to using hydrochloric acid. The reaction at this time can be expressed by the following equations (1) and (2), where the chromate-containing alumina hydrate is a mixture of sodium monochromate and aluminum hydroxide, and the acid is sulfuric acid. 2Na ₂ CrO ₄ +H ₂ SO ₄ →Na ₂ Cr ₂ O ₇・2H ₂ O＋Na ₂ SO ₄ (1) 2Al(OH) ₃ +3H ₂ SO ₄ →Al ₂ (SO ₄ ) ₃ +6H ₂ O (2) In this case The amount of sulfuric acid added may be the stoichiometric amount shown by formulas (1) and (2). Addition of acid is an essential condition for converting insoluble aluminum hydroxide into soluble aluminum salt. Next, after adding acid, hexavalent chromium (Na ₂ Cr ₂ O ₇ .2H ₂ O) represented by formula (1) is reduced. The reducing agent used at this time may be sulfur dioxide gas, an inorganic reducing agent such as sodium bisulfite, or an organic reducing agent such as glucose, honey, alradides, etc. In the case of sulfur dioxide gas: Na ₂ Cr ₂ O ₇・2H ₂ O＋3SO ₂ →2Cr(OH)SO ₄ +Na ₂ SO ₄ +H ₂ O (3) For glucose: 4Na ₂ Cr ₂ O ₇・2H ₂ O＋12H ₂ SO ₄ +C ₆ H ₁₂ O ₆ → 8Cr(OH ) SO ₄ +4Na ₂ SO ₄ +6CO ₂ +22H ₂ O (4) The product at this time is basic chromium sulfate, which corresponds to a chromium tanning agent with a basicity of 33.3%. Next, aluminum sulfate [Al ₂
(SO ₄ ) ₃ ] has no tanning properties and must be made highly basic by adding an alkaline agent to impart tanning properties. The alkaline agent at this time is not particularly limited as long as it neutralizes and makes it highly basic, but caustic alkali, alkali carbonate, alkali bicarbonate, sodium aluminate, etc. can be used. Among these, alkali bicarbonate is particularly good because it is preferable for operation to use an alkaline agent that is as mild as possible. For example, the reaction to obtain basicity of 33.3% using sodium bicarbonate is shown as Al ₂ (SO ₄ ) ₃ +2NaHCO ₃ →2Al(OH)SO ₄ +Na ₂ SO ₄ +2CO ₂ (5). Additionally, in order to prevent the formation of aluminum hydroxide and maintain a predetermined basicity during high basicity operation, it is desirable to add a carboxylic acid compound. As is well known, carboxylic acid compounds are used as masking agents for OH groups when forming a high base, such as formic acid, acetic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, phthalic acid, tartaric acid, citric acid, or lactic acid. etc., and they may also be alkali metal salts, alkaline earth metal salts or ammonium salts,
At least one type or two or more types are selected as appropriate. The alkaline agent is gradually added and neutralized at a temperature of room temperature to 80°C to form a high base. Next, after the addition of the alkali agent is completed, the mixture is continued to be incubated for a while, if necessary, and then spray-dried by a conventional method to form a product into granules. Product particle size can be dissolved in cold water
It is preferable to pass about 40 meshes, but the number is not limited to this. The composition of the chromium-aluminum tanning agent obtained by the present invention is often as follows (wt%): Cr ₂ O ₃ : 2 to 25%, preferably 7 to 20% Al ₂ O ₃ : 2 to 25% Preferably 5 to 16% Basicity: 20 to 55% Preferably 28 to 50% The chromium-aluminum tanning agent of the present invention thus obtained improves the heat resistance of tanned leather using aluminum tanning agent alone with chromium, and also improves the heat resistance in waste water. This method has the effect of reducing the chromium content to at least 1/8 of that of conventional methods and greatly reducing the amount of chromium contamination, and has the following advantages. The amount of chromium used can be reduced, reducing the amount of chromium in wastewater. The tanning agent has the respective characteristics of chrome tanning agent and aluminum tanning agent, that is, the heat resistance is almost the same as that of chrome tanned leather, and the color tone of the tanned leather is whiter than that of chrome tanned leather, and the dyeability is better. Become. In the end, a tanned leather is obtained that is flexible, has good grain fineness, and has excellent dyeability. The method of using the chromium-aluminum tanning agent obtained according to the present invention is basically no different from that of ordinary chromium tanning agents, and the tanning operation is not complicated at all. Thus, according to the present invention, alumina hydrate containing chromate, which is a by-product from the chromate manufacturing process and which is difficult to dispose of, can be effectively converted into valuable chromium.
This means that it can be recycled as an aluminum tanning agent. The present invention will be specifically explained below with reference to Examples and Test Examples. Example 1 Sodium chromate leachate obtained by leaching the alkaline oxidized roasted product of chromium ore with water [Na ₂ CrO ₄ 27.7%, dissolved sodium aluminate 1.7%
(as Al ₂ O ₃ )] was neutralized by adding sulfuric acid to form a precipitate of alumina hydrate, which was over-separated to obtain an alumina hydrate containing sodium chromate with the following composition. .

[Table] For 1000 kg of this hydrate, 500 kg of water and 448 kg of sulfuric acid (H ₂ SO ₄ 98%) were placed in a glass-lined reaction vessel equipped with a thermometer and a stirrer, heated to 90°C, and stirred and mixed for 60 minutes. did. After confirming that the alumina hydrate was completely dissolved, 117 kg of sulfur dioxide gas was injected to reduce all hexavalent chromium to trivalent chromium. After confirming that the hexavalent chromium content is completely eliminated by a diphenylcarbazide coloring test, add bicarbonate of soda.
217Kg was gradually added over 120 minutes to make it highly basic. After addition, the mixture was filtered according to a conventional method and then spray-dried to obtain 1107 kg of a granular product. Product composition is

[Table] The basicity was 33.3%, the Cr ₂ O ₃ /Al ₂ O ₃ weight ratio was 0.7, and the water solubility was very good. Example 2 675 kg of sodium monochromate solution (Na ₂ CrO ₄ 32.0%) was used for 1000 kg of alumina hydrate, which was the same as in Example 1.
516 kg of sulfuric acid (H ₂ SO ₄ 98%) was placed in a glass-lined reaction vessel equipped with a thermometer and a stirrer, heated to 90°C, and stirred and mixed for 60 minutes. After confirming that the alumina hydrate has completely dissolved, sulfur dioxide gas is
249 kg was injected, and all hexavalent chromium was denatured to trivalent chromium. After confirming that the hexavalent chromium content was completely eliminated by a diphenylcarbazide coloring test,
217 kg of bicarbonate of soda was gradually added over 120 minutes to make it highly basic. After addition, the mixture was filtered according to a conventional method and then spray-dried to obtain 1642 kg of granular product. Product composition is

[Table] The basicity was 33.3%, the Cr ₂ O ₃ /Al ₂ O ₃ weight ratio was 1.5, and the water solubility was very good. Example 3 For 1000 kg of alumina hydrate, which is the same as in Example 1,
250Kg of water, 631Kg of sulfuric acid (H ₂ SO ₄ 98%), thermometer,
The mixture was placed in a glass-lined reaction vessel equipped with a stirrer, heated to 90°C, and stirred and mixed for 60 minutes. After confirming that the alumina hydrate is completely dissolved,
Glucose (C ₆ H ₁₂ O ₆ 50%) was added to denature all hexavalent chromium to trivalent chromium. The glucose required at this time was 55 kg, and it was confirmed by a diphenylcarbazide coloring test that the hexavalent chromium content was completely eliminated. Next, 65 kg of sodium formate was added, and after mixing for 60 minutes, 376 kg of sodium bicarbonate was gradually added over 180 minutes to make the mixture highly chlorinated. After addition, the mixture was filtered and spray-dried according to a conventional method to obtain 1192 kg of granular product.

【table】

[Table] Basicity 50.0%, Cr ₂ O ₃ /Al ₂ O ₃ weight ratio 0.7,
HCOONa was 0.5 mol relative to Cr ₂ O ₃ +Al ₂ O ₃ and had very good water solubility. Test Example 1 Commercially available basic chromium sulfate tanning agent (Cr ₂ O ₃ 25.5
%, basicity 33.3%) were used in the usual manner using a drum at 20 rpm. As a result, _{the Cr2O3} content of the resulting tanned leather,
The heat shrinkage temperature and the Cr ₂ O ₃ content of the tanning wastewater were as follows.

[Table] Measurement of Cr ₂ O ₃ content and heat shrinkage temperature is
It was conducted in accordance with JISK6550 leather testing method. Test Example 2 Tanning was carried out in the same manner as in Test Example 1, using 8 parts by weight and 10 parts by weight of the chromium-aluminum tanning agent produced in Example 1 for 100 parts by weight of the same pickled leather as in Test Example 1. Ivy. The Cr ₂ O ₃ content, heat shrinkage temperature, and tanning wastewater of the resulting tanned leather were as follows.

【table】

[Table] Comparing with Test Example 1, (1) The heat shrinkage temperature is about the same. (2) The Cr ₂ O ₃ content in tanning wastewater has been reduced to about 1/8. These features are obvious.

Claims (1)

[Claims] 1 Add acid to chromate-containing alumina hydrate, which is a by-product from the chromate manufacturing process, to dissolve it, then reduce the hexavalent chromium in the resulting solution, and add an alkali agent to form a high base. 1. A method for producing a chromium-aluminum tanning agent.