CS243897B1 - Aluminium hydroxide production method in granular good filtered form - Google Patents

Abstract

A method for producing aluminum hydroxide in granular, well-filterable form, which is an important intermediate for the production of high purity alumina for single crystal cultivation and the preparation of materials with significant physical properties, e.g., luminescent, prepared by decomposition of crystalline aluminum ammonium sulfate by the action of ammonia gas by the pH of the reaction mixtures containing aluminum hydroxide, ammonium sulfate, water and ammonia are adjusted to pH = 5.5 to 8 before or during washing with water, by addition of hydrochloric, acetic or carbonic acid.

Description

Author of the invention PERNER BOHUMIL ing. CSc., FOUNDRY, 'QUAPIL JIŘÍ ing. DrSc. ;

CSAP., TURNOV / HILGER HELENA, OVER (54) Method of production of aluminum hydroxide in granular, well filterable form

A process for the production of aluminum hydroxide in a granular, well filterable form, which is an important intermediate for producing high purity alumina for the cultivation of single crystals and the preparation of materials with significant physical properties, eg luminescent substances prepared by decomposing crystalline aluminum ammonium sulphate by ammonia gas by pH mixtures containing aluminum hydroxide, ammonium sulphate, water and ammonia are adjusted to pH = 5.5 to 8 before or during the water-washing step by addition of hydrochloric, acetic or carbonic acid.

The invention relates to a process for the production of aluminum hydroxide in a granular, well filterable form.

Aluminum hydroxide prepared by the decomposition of crystalline aluminum sulphate by ammonia gas is an important intermediate for the production of alumina by annealing at 700 to 1,400 ° C according to the desired form of alumina, of high purity, intended for mono-crystal cultivation and other materials with outstanding physical properties. such as luminescent substances.

In the conventional process for the preparation of aluminum hydroxide, the reaction mixture containing aluminum hydroxide, ammonium sulfate, water and excess ammonia is washed with distilled or deionized water until the reaction to sulfate ions in the wash water after filtration disappears.

The pH of the initial ammonia saturated reaction mixture is high - more than 9 - and therefore contains dissolved aluminum in aluminate form. At the same time, the increased concentration of ammonium ions in the mixture decreases the solubility of the ammonium sulfate, which must be thoroughly washed out of the mixture.

Gradual washing with water leads to a slow drop in pH while slow precipitation of aluminum hydroxide from the dissolved aluminate. This slowly precipitated aluminum hydroxide has a very fine form, containing grains of aluminum hydroxide formed by a topochemical reaction between alum crystals and ammonia. The grains are combined by a fine form of aluminum hydroxide into larger aggregates that also enclose ammonium sulfate.

This mechanism produces, after drying, a coarse-grained structure of aggregated aluminum hydroxide containing 0.1 to 0.5% ammonium sulfate, which decomposes on further heat treatment to form harmful sulfur dioxide. Washing of the thus formed aluminum hydroxide takes up to 100 hours at a dose of about 2 kg of aluminum hydroxide.

The above drawbacks in the production of aluminum hydroxide in a granular, well-filterable form can be remedied according to the invention in that acetic, hydrochloric or carbonic acid is gradually added to the reaction mixture prior to or during the initial wash so as to reach the final pH values ranging from 5.5 to 8.

This eliminates aluminum hydroxide from the aluminate solution in a coarser form at the same time, so that it does not combine the grains of previously precipitated aluminum hydroxide into large aggregates, and on the other hand the solubility of ammonium sulfate is improved. As a result, the washing filtration is significantly accelerated for 3 to 6 hours for a 2 kg dose of aluminum hydroxide, the product obtained has a fine-grain structure and contains almost no ammonium sulfate, so that during further heat treatment the sulfur dioxide exhalation is completely negligible.

This method makes it possible to use centrifugation or pressure filtration in filtration, since the filter cloth does not become clogged with fine particles and thus substantially speed up the washing of the aluminum hydroxide.

He did

The starting reaction mixture containing 2.5 kg of aluminum hydroxide, 7 kg of ammonium sulfate and an excess of ammonia had a pH = 10.8. The mixture was stirred with 6 L of distilled water and the water was filtered off. An additional 6 L of distilled water was added and the pH of the mixture was 9.7. Next, 5% hydrochloric acid was added with stirring until pH = 6. After filtration, the reaction mixture was further washed with distilled water for five cycles until the reaction to sulfate ions disappeared. The aluminum hydroxide so washed was dried at 120 ° C and had a free-flowing fine-grained form. At annealing at 800 ° C, it was converted to alumina in free-flowing, fine-grained form, virtually avoiding leakage of sulfur dioxide emissions. The total wash time was £ 8 hours.

Example 2

The starting reaction mixture of the composition of Example 1 had a pH of 11.3. The mixture was stirred with 8 L of distilled water and after filtration, the filtrate was again mixed with 6 L of distilled water. The pH was 9.5. Next, 10% acetic acid was added to the mixture with stirring until pH = 7.5. After filtration and further addition of 8 L of distilled water, the pH was adjusted to 6.5 by addition of acetic acid. Washing with distilled water was continued until the reaction to sulfate ions disappeared. The further procedure and the result was similar to Example 1. The total washing time was 8 hours.

Example 3

The starting reaction mixture had a composition similar to that of Example 1 and pH = 11.5. The rinsing was carried out with demineralized water saturated with carbon dioxide at 20 [deg.] C. by first adding 10 liters of water, after stirring and filtering another 8 liters of water, filtered again and the aluminum hydroxide pellet was transferred to the scrubber. There was washed successively 6x8 1 more water. After each wash, the sediment was centrifuged and the pH of the filtrate was checked. This gradually decreased until the total fourth water was pH = 7.

Claims (1)

3 243897 was stirred with 8 L of distilled water and after filtration the filtrate was again stirred with 6 L of rain water. The pH was 9.5. Next, 10% acetic acid was added to the mixture with stirring until pH = 7.5. After filtration and further addition of 8 L of distilled water, the pH was adjusted to 6.5 with the addition of acetic acid. Further, washing with distilled water was continued until the reaction to sulfate ions disappeared. The next procedure and result was similar to Example 1. The total wash time was 8 hours. Example 3 The starting reaction mixture was similar in composition to Example 1 and pH = 11.5. Demineralized water saturated at 20 ° C with carbon dioxide was used to wash, adding 10 L of water first, after stirring and filtering an additional 8 L of water, filtering again and transferring the aluminum hydroxide sediment to the washer. There it was washed successively with another 6x8 1 of water. After each wash, the sediment was centrifuged and the pH of the filtrate was checked. The pH dropped down to a total of fourth water. The obtained aluminum hydroxide had a fine-grained form, the particles did not aggregate during drying and no sulfur dioxide escaped practically when calcined at 800 ° C. SUBJECT MATTER OF A method of producing aluminum hydroxide in a granular, well-filterable form by reaction between ammonium aluminum ammonium sulfate and ammonia gas, characterized in that the pH of the reaction mixture containing aluminum hydroxide, ammonium sulfate, water and ammonia is adjusted by addition of hydrochloric or acetic acid or carbonic acid to 5.5 to 8.