Precipitate, aluminium hydroxide

Pour 50 ml of an aluminium chloride solution into a 100-ml beaker and precipitate aluminium hydroxide by adding an ammonia solution with stirring. How can the completeness of precipitation be determined Filter off the aluminium hydroxide on a funnel with a filtering bottom and without removing the hydroxide from the filter, pass a solution of methylene blue through it. How can the vanishing of the colour of the solution be explained ... 

In nature aluminium oxide is mostly mined as the minerals bauxite and laterite, but these as extremely impure. Most bauxite is purified according to the Bayer process which removes the oxides of iron(III), silica and titanium. This takes place by autoclaving the bauxite with sodium hydroxide and sodium carbonate. The precipitated aluminium hydroxide is subsequently heated, or calcined. Calcination involves a heat treatment of a powder as a result of which the latter breaks down ... 

Garcia Gutierrez [19] has described an azo coupling spectrophotometric method for the determination of nitrite and nitrate in soils. Nitrite is determined spectrophotometrically at 550 nm after treatment with sulfuric acid and N-1 -naphlhylclhylcnediamine to form an azo dye. In another portion of the sample, nitrate is reduced to nitrite by passing a pH 9.6 buffered solution through a cadmium reductor and proceeding as above. Soils were boiled with water and calcium carbonate, treated with freshly precipitated aluminium hydroxide and active carbon, and filtered prior to analysis by the above procedure. 

Vegetables were boiled with water and calcium carbonate, treated with freshly precipitated aluminium hydroxide, and filtered prior to analysis as above. 

Precipitate aluminium hydroxide by adding ammonium hydroxide to a solution of alum. Wash the precipitate free from acid, and add a slight excess of concentrated hydrochloric acid. 

Precipitation was achieved by adding 3.5 dm of Al2(S04)3 solution to NaOH solution of the same volume. Precipitated aluminium hydroxide was rinsed with water, and had the excess of ions removed using an ion-exchange process. A measure of aluminium hydroxide activity was the maximal exchange capacity towards 8303 ions at pH = 7. 

The temperature of the solution may influence solid phase precipitation. Aluminium hydroxide precipitation is an exothermic process. The percipitation temperature was changed from 289 to 309 K. However a statistical analysis of the data obtained indicated that the exchange capacity of the precipitate produced was not influenced by the temperatures within the above range. 

The time taken to add Al2(S04)3 is a very important factor in process scale-up. To find this relationship, four experiments were run with four different dosage times 2, 10, 20 and 40 sec. Statistical analysis of the data showed that the dosage time, while the solution is not mixed, does not influence the exchange capacity of precipitated aluminium hydroxides. 

Whilst excess of hydrochloric acid is necessary to ensure that diazotization will be complete, coupling will not take place if the pH is too low. Sodium acetate is therefore added to the liquor to convert free hydrochloric into acetic acid, after which the pH should be about 4-5. Coupling will also be retarded if the liquor becomes alkaline, and this can occur easily on account of the sodium hydroxide which may be left in the cotton after it has been impregnated with the naphthol derivative. Excess of alkali can be neutralized by adding acetic acid, sodium bicarbonate, or aluminium sulphate. Aluminium sulphate should not be used in a package-dyeing machine because it gives rise to a certain amount of precipitated aluminium hydroxide and this will be retained by filtration. Some loss of lustre of mercerized cotton can also be caused by aluminium sulphate. 

Aluminates are for the most part crystalline, soluble compounds, obtained by the action of metallic oxids or hydroxids upon alumina. Potassium aluminate, KaAlaOa-fSAq, is formed by dissolving recently precipitated aluminium hydroxid in potash solution. It forms white crystals very soluble in HaO, insoluble in alcohol caustic and alkaline. By a large quantity of HaO it is decomposed into aluminium hydroxid, and a more alkaline salt, KgAltOa. 

The aluminium oxide formed in this process has a complex form. It is partially hydrated and has a two-layer structure. At the surface of the metal there is a thin (perhaps 0.025 jum), compact boundary layer and then there is a porous overlayer. The latter has a very open structure and structural techniques (see Fig. 7.13) show it to consist of a collection of parallel tubes perpendicular to the surface. After the anodic oxidation the metal is dipped into a caustic soda solution to precipitate aluminium hydroxide in the pores and hence produce a more robust layer. 

Coloured or turbid waters should be shaken out with chloride-free, freshly precipitated aluminium hydroxide or chloride free washed activated charcoal, and filtered. Organic substances are destroyed in a weakly alkaline solution with KMnOz, heating gently. Excess KlVlnO is eliminated with H2O2, the hydrated manganese oxides are filtered off and washed, chloride-free. 

Martinal aluminium hydroxide based mineral additives from Martinswerk are claimed to be enviromnentally fiiendly and have processing temperatures of up to 200 °C. For use in thermosetting plastics and elastomers, products with a medium particle size are recommended. These grades are produced by grinding coarsely precipitated aluminium hydroxide. 

After milling, the ore is first broken down using an Al-containing NaOH solution which is seeded to precipitate aluminium hydroxide Al(OH)3. This is dehydrated at about 1100 °C according to 2Al(OH)3 —> AI2O3 -I-3H2O. 

Data on the mechanism of lithium sorption from liquors with freshly precipitated aluminium hydroxide are limited and contradictory. For example, Goodenough reports on the isolation of lithium-aluminate complex [17]. Some authors [11] suggest that lithium is adsorbed on the surface of aluminium hydroxide, and high adsorption coefficient is provided by the presence of salt background which prevents aluminium hydroxide from crystallization when the temperature of the process is raising. Other authors assume that lithium coprecipitation with aluminium hydroxide leads to intercalation of lithium into the structure of the latter and to the formation of lithium-containing aluminium hydroxide characterized by pseudo-boehmite structure [12]. The authors of [13] conclude that the overall interaction of lithium with amorphous aluminium hydroxide can be represented by the following scheme ... 

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