JPS59102819A - Production of aluminum hydroxide having high whiteness - Google Patents

Abstract

PURPOSE:To produce aluminum hydroxide having high whiteness simply and inexpensively, by bringing mud of aqueous salt solution into contact with an aluminate solution prepared by Bayer's process, separating and removing colored substances in the aluminate solution. CONSTITUTION:>=0.5g, preferably 0.5-30g/l mud of aqueous salt solution produced in the purifying process of aqueous salt solution of salt electrolysis industry is brought into contact with 1l aluminate solution prepared by Bayer's process and kept in contact state for about 30min-2hr, and colored substances are separated as gel precipitate. The mud of aqueous salt solution added comprises 30-60wt% calcium sulfate, 10-70wt% calcium carbonate, and 5-20wt% magnesium hydroxide, and the total amount of these contained substances is at least >=50wt% based on the total amount of the mud (dry base). The aluminate solution from which the colored substance are thus removed is treated by a conventional procedure, to give aluminum hydroxide having improved whiteness.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing aluminum hydroxide with high whiteness (1), specifically, production of aluminum hydroxide with high whiteness (aluminate liquid containing a coloring substance such as an organic substance). method).

As is well known, the production of alumina using the Bayer method or its modified method (hereinafter referred to as the Bayer method) involves treating bauxite with a hot alkaline solution, usually at a temperature of 180°C or higher, to dissolve and extract the alumina content in the bauxite. From the resulting slurry, undissolved residues such as iron oxide, chloride, titanium oxide, etc. are separated using red mud, and after the undissolved residues have been separated, aluminum hydroxide is added as a seed to the clarified aluminate solution. The precipitated aluminum hydroxide is separated from the aluminate solution, and a part of the separated aluminum hydroxide is recycled as a seed. The remaining aluminum hydroxide is removed as a product, and the aluminate solution after Ikegata decomposition is recycled to the boxide dissolution process either as is or after being concentrated.

By the way, one part of bauxite usually contains organic substances mainly composed of humic substances, and in the dissolution process, these are dissolved in a hot alkaline solution or become soluble salts and released into the aluminate solution. Furthermore, when removing the red mud residue from the mother liquor, starch, synthetic polymer flocculants, etc. are added as precipitants, so organic matter is accumulated in the aluminate solution in the first step. It comes. The organic matter in the aluminate solution exists in various forms, from polymer complexes to final decomposition products.

These organic substances co-precipitate with aluminum hydroxide in step 1 of separating and separating aluminum hydroxide from the aluminate solution. For this reason, the precipitated aluminum hydroxide is colored yellowish brown, making it unsuitable for applications that require high whiteness, such as plastics, paper, and toothpaste filling materials.

Various methods have been proposed for removing colored substances from aluminate solutions, such as a method of adsorption and removal using activated carbon at ℃, a method of oxidation treatment with oxygen or an oxygen-containing substance, and a method of oxidation treatment with oxygen or an oxygen-containing substance, as well as Japanese Patent Application Laid-Open No. 180698/1983. There are methods using kieserite, as shown in 1, and methods using oxides, hydroxides, carbonates, silica salts, etc. of Mg and Ca, as shown in Japanese Patent Application Laid-open No. 54-168799. be.

These methods involve the problem that they are uneconomical because they use expensive processing agents, resulting in high processing costs.

c) In view of the current situation, the present inventors conducted intensive research to obtain aluminum hydroxide with a high brightness using a simple and inexpensive process. In case 1, we have discovered that it is possible to obtain aluminum hydroxide which satisfies the above requirements and has a high degree of whiteness, and has completed the present invention.

The present invention is characterized by bringing a salt water mud into contact with an aluminate solution in the Bayer process, separating and removing a reaction product with the salt water mud, and precipitating aluminum hydroxide from the aluminate solution after t. The present invention provides a method for producing high whiteness aluminum hydroxide.

The method of the present invention will be explained in more detail below.

The salt water mud used in carrying out the method of the present invention is a gel-like residue separated and removed from the salt water purification process of the salt electrolysis industry, and its composition is composed of impurities contained in the raw salt,
Furthermore, it varies somewhat depending on the specific impurity removal method.
Although not uniquely determined, usually calcium carbonate,
It is sufficient that it contains components such as magnesium hydroxide, calcium sulfate, barium sulfate, etc., especially at least 50% by weight of the substances constituting the salt water mud (inversion basis).
is composed of calcium sulfate, calcium carbonate and magnesium hydroxide, and its composition is calcium sulfate 30~
It is recommended that the composition be composed of 60% military song, 10 to 70% by weight of calcium carbonate, and 5 to 20% by weight of magnesium hydroxide.

The ratio of the salt water mud added to treat the aluminate solution is 0.059 or more for 11 of the solution based on the conversion standard.
More preferably, it is used in a range of 0.5 to 30 f/l. When the amount of salt water mud added is less than 0.05 g/7+, the effect on the whiteness of the obtained aluminum hydroxide is not significant, and when added in excess of 801//l, the whiteness commensurate with the addition of C. There is no improvement in the level.

In step 1 of the method of the present invention, a salt water mud is added and the aluminate solution to be treated can be used anywhere before the step of separating and separating aluminum hydroxide from the aluminate solution. It may be an alumina extraction process that involves mixing and heating, or an aluminate solution after separating the insoluble residue, and the temperature of the aluminate solution is particularly limited from room temperature to the alumina extraction temperature in the usual Bayer process. It is not something that will be done.

The aluminate solution and the salt water mud may be brought into contact with each other while stirring for 5 minutes or more, preferably 30 minutes to 2 hours.

By this contact treatment, the colored substances in the aluminate solution are separated as gel-like precipitates, and after these are removed by filtration, aluminum hydroxide can be separated out by a conventional method.

Method I of the present invention Considering the filtration separation of the gelatinous precipitate, it is possible to add salt water mud in the first step of the alumina extraction step before separating the insoluble residue, and to separate and remove the gelatinous precipitate at the same time as the red mud. Economical.

As detailed above, the method of the present invention effectively utilizes saltwater mud as waste discharged from the salt electrolysis industry,
It is possible to obtain aluminum hydroxide with excellent whiteness easily and inexpensively without requiring any special additional operations, and its industrial value is extremely great.

Hereinafter, the method of the present invention will be explained in more detail than in Example 1.

Example l Na20 1251/l Na2O/Ad203 (
molar ratio) has a composition of -1,6, and organic matter (as organic carbon) 2
01,/l of dark brown Bayer's solution 1 salt water mud (CaS0487 wt%, CaCO322 wt%, M
f(OH)z (10% by weight) was added as shown in Table 1 on the basis of the amount of converted material, stirred for 1 hour at a liquid temperature of 70°C, and the entire precipitate was separated by filtration.

The color tone of the filtrate thus obtained was measured for light transmittance using a colorimeter with a wavelength of 600 nm, and the results are shown in Table I.

For comparison, reagent grade CaCO3, CaSO4
, Mf (OH) 2 and a mixed reagent preparation corresponding to the composition of salt water mud were used as the organic matter removing agent.The results in this case are also shown in Table 1.

Table 1 As is clear from Table 1, the salt water mud used in the method of the present invention is Ca5CJ, CaCO3, My(OH).
A comparison of the effect of adding the reagent islands alone in No. 2 and the effect of adding a preparation corresponding to the composition of the salt water mat.Even in the first case, a remarkable effect of removing organic matter was achieved.

Example 2 The additives shown in Table 2 were added to a dark brown Bayer's liquid having a composition of Na20 125y/#te Na20/A1203 (molar ratio) = 1.6 and containing organic matter (as organic carbon) 20 f/11. Add the required amount of
．． Stirring treatment was carried out for 5 hours, and the gel-like substance produced was removed by vortexing in the furnace.

The color tone of the Bayer liquid thus obtained by straining was measured using the same method as in Example 1, and the results are shown in Table 2. However, the salt water mud was the same as in Example 1.

Table 2 Example 8 Additives having the composition shown in Table 3 were added to the Bayer liquid used in Example 2, and after stirring at a liquid temperature of 220°C for 0.5 hour, the gel-like substance was removed by filtration. .

The color tone of the Bayer's solution thus obtained was measured once in the same manner, and the results are shown in Table 3.

Table 3

Claims (1)

[Scope of Claims] 1) In the Bayer method, the aluminate solution is brought into contact with a salt water mud, and after separating and removing the reaction product with the salt water mud, aluminum hydroxide is precipitated from the aluminate solution. A method for producing high whiteness aluminum hydroxide. 2) The method according to claim 1, in which 0.05 g/1 or more of salt water mud (inversion basis) is added to the aluminate solution 3) The content of calcium sulfate, magnesium carbonate, and magnesium hydroxide is At least 5 of all forces M (transfer standard)
It has a zero double star shape or more, and its composition is 30 to 60% by weight of calcium sulfate and 10 to 70% of calcium carbonate.
2. A method according to claim 1, characterized in that a brine mud comprising 5 to 20% by weight of magnesium hydroxide is used.