Aluminum hydroxide reactions

Fig. 9.8 Examples of mental models concerning the aluminum hydroxide reaction [9]...

At the anode, a chemical oxidation reaction is bound to take place. In normal fixers, sulfite (SOj ) is oxidized and acid (H ) is released as a consequence of this oxidation. Due to the decrease of the sulfite concentration and the decrease in the pH, the fixing solution becomes unstable and sulfur precipitation starts to occur when the pH of the fixer decreases below 4.0. In the case of hardening fixers, there is also an upper limit to the pH, since aluminum-hydroxides starts to precipitate when the pH exceeds 5.0. 

Aluminum. All primary aluminum as of 1995 is produced by molten salt electrolysis, which requires a feed of high purity alumina to the reduction cell. The Bayer process is a chemical purification of the bauxite ore by selective leaching of aluminum according to equation 35. Other oxide constituents of the ore, namely siUca, iron oxide, and titanium oxide remain in the residue, known as red mud. No solution purification is required and pure aluminum hydroxide is obtained by precipitation after reversing reaction 35 through a change in temperature or hydroxide concentration the precipitate is calcined to yield pure alumina. 

Molten aluminum reacts violently with water [7732-18-5] and the molten metal should not be allowed to touch damp tools or containers. In finely divided powder form, aluminum also reacts with boiling water to form hydrogen and aluminum hydroxide [21645-51 -2], this reaction proceeds slowly in cold water. 

Aluminum fluoride is also made by the reaction of fluosiUcic acid [16961 -83-4] H2SiFg, a by-product from phosphoric acid production (see Phosphoric ACID AND THE PHOSPHATES), and aluminum hydroxide from the Bayer process. 

The class of compounds identified as basic aluminum chlorides [1327-41 -9] is used primarily ia deoderant, antiperspirant, and fungicidal preparations. They have the formula Al2(OH)g where x = 1 5, and are prepared by the reaction of an excess of aluminum with 5—15% hydrochloric acid at a temperature of 67—97°C (18). The same compounds are obtained by hydro1y2ing aluminum alkoxides with hydrochloric acid (19,20) (see Alkoxides, METAl). Basic aluminum chloride has also been prepared by the reaction of an equivalent or less of hydrochloric acid with aluminum hydroxide at 117—980 kPa (17—143 psi) (20). 

Aluminum iodide [7884-23-8] AIL, is a crystalline soHd with a melting poiat of 191°C. The presence of free iodine ia the anhydrous form causes the platelets to be yellow or brown. The specific gravity of this soHd is 3.98 at 25°C. Aluminum iodide hexahydrate [10090-53-6] AIL -6H20, and aluminum iodide pentadecahydrate [65016-30-0], AIL -15H20, are precipitated from aqueous solution. They may be prepared by the reaction of hydroiodic acid [10034-85-2], HI, with aluminum or aluminum hydroxide. 

Pure nordstrandite has been prepared (5) by reaction of aluminum, aluminum hydroxide gel, or hydrolyzable aluininum compounds with aqueous ethylenedianiine [107-15-3j. However, no commercial production or uses have been reported. 

Aluminum chloride hydroxide [1327-41 -9] [10284-64-7], AlQ(OH)2 [14215-15-7], AlQ2(OH), products, commonly known as polyaluminum chlorides (PAG), are used for a wide variety of industrial appHcations. Other names for PAG are basic aluminum chloride, polybasic aluminum chloride, aluminum hydroxychloride, aluminum oxychloride, and aluminum chlorohydrate. The presence of polymeric, aluminum-containing cations, the distribution of which can differ gready, typifies PAG products. Although the formation of polynuclear aluminum species in solution has been studied for over a century, there is stiU much controversy concerning aluminum polymerization reactions and the resulting product compositions. 

Many of the reactions of nitric acid are those associated with all strong acids. For example, dilute (6 M) nitric acid can be used to dissolve aluminum hydroxide... 

We can tell from the ionization energy of aluminum that this atom holds its second and third valence electrons rather firmly. With this fact in mind, we can see why aluminum hydroxide, Al(OH)3, would not be as strongly basic as are the hydroxides, NaOH and Mg(OH>2. Aluminum hydroxide has extremely low solubility in neutral aqueous solutions but does react with strong acids according to the reaction... 

Strong Alcoholic Beverages. Products such as whiskey, cognac, brandy, etc. cause undesired reactions with unprotected aluminum. The attack causes pitting corrosion and formation of a floculent precipitate of aluminum hydroxide while the beverage itself becomes discolored, and the flavor is also affected (22). The action of liqueurs is not so... 

Aluminum sulfate, A12(S04)3 H20, is the commonest alum used. Hydration is typically 14 to 16 H20. It hydrolyzes and polymerizes in water and typically is used within a narrow window of pH levels of 5.5 to 6.5 to minimize the solubility of aluminum in the treated water. If alkalinity is present (say, due to calcium bicarbonate), the following reaction occurs, producing insoluble aluminum hydroxide [Al(OH)3]. 

The enhanced aqueous solubility of aluminum hydroxide in the presence of an acid or alkali is an example where neutralization reaction plays a part. In pure water, the solubility of aluminum hydroxide is low which is very well reflected in the following equation ... 

This way a neutralization reaction can lead to an enhancement of the solubility of an otherwise insoluble or sparingly soluble material. Because of its ability to dissolve both in acid and alkali, aluminum hydroxide is known as an amphoteric hydroxide. 

It will be seen from the various types of leaching reactions given in Table 5.2, that the dissolution of aluminum hydroxide essentially belongs to the chemical process category. The dissolution of the hydroxide in acid or alkali occurs by a mechanism involving neutralization. 

Diffuse reflectance spectroscopy was used to screen the possible interactions between a large number of adjuvants and several dyes [23]. It was concluded that supposedly inert excipients (such as starch or lactose) were capable of undergoing significant reactions with the dyes investigated (Red No. 3, Blue No. 1, and Yellow No. 5). For adjuvants containing metal ions (zinc oxide, or calcium, magnesium, and aluminum hydroxides), the degree of interaction could be considerable. It was concluded from these studies that dye-excipient interactions could also be responsible for the lack of color stability in certain tablet formulations. 

In Table 5.4 the contributions of the individual weathering reactions were assigned and combined in such a way as to yield the concentrations of Ca2+, Mg2+, Na+, K+, and H+ measured in these lakes the amounts of silicic acid and aluminum hydroxide produced and the hydrogen ions consumed were calculated stoichiometrically from the quantity of minerals assumed to have reacted. Corrections must be made for biological processes, such as ammonium assimilation and nitrification and the uptake of silicic acid by diatoms. Some of the H4Si04 was apparently lost by adsorption on aluminum hydroxide and Fe(III)(hydr)oxides, but the extent of these reactions was difficult to assess. 

The initial reaction (1) consumes NaOH and produces both hydrogen gas and an aluminate byproduct. Upon reaching its saturation limit, the aluminate compound decomposes (2) into sodium hydroxide and a crystalline precipitate of aluminum hydroxide. This process is similar to the reactions inside an aluminum battery. 

The pharmacogenomics analysis of samples from a clinical study with an aluminum hydroxide-adsorbed vaccine (diphtheria-tetanus-acellular pertussis/polio/ Haemophilus influenzae) in infants is described. These instructions can easily be adapted to clinical studies of other vaccines with changes to the type of administered vaccine, administration route, vaccination ages, and so on. This method is therefore also suitable for assessing vaccine responses in adults and to study the cellular reactions in clinical subjects who have experienced adverse reactions. 

Almost all rocks contain some aluminum in the form of aluminum silicate minerals found in clays, feldspars, and micas. Today, bauxite is the major ore for the source of aluminum metal. Bauxite was formed eons ago by the natural chemical reaction of water, which then formed aluminum hydroxides. In addition to the United States, Jamaica and other Caribbean islands are the major sources of bauxite. Bauxite deposits are found in many countries, but not all are of high concentration. 

The reaction of complex hydrides with carbonyl compounds can be exemplified by the reduction of an aldehyde with lithium aluminum hydride. The reduction is assumed to involve a hydride transfer from a nucleophile -tetrahydroaluminate ion onto the carbonyl carbon as a place of the lowest electron density. The alkoxide ion thus generated complexes the remaining aluminum hydride and forms an alkoxytrihydroaluminate ion. This intermediate reacts with a second molecule of the aldehyde and forms a dialkoxy-dihydroaluminate ion which reacts with the third molecule of the aldehyde and forms a trialkoxyhydroaluminate ion. Finally the fourth molecule of the aldehyde converts the aluminate to the ultimate stage of tetraalkoxyaluminate ion that on contact with water liberates four molecules of an alcohol, aluminum hydroxide and lithium hydroxide. Four molecules of water are needed to hydrolyze the tetraalkoxyaluminate. The individual intermediates really exist and can also be prepared by a reaction of lithium aluminum hydride... 

Alumina forms hydroxide in aqueous alkaline solution. The reaction is slow. The products, aluminum hydroxides (hydrated aluminas), contain hexacoordinated aluminohydroxide anion ... 

Rubidium acid salts are usually prepared from rubidium carbonate or hydroxide and the appropriate acid in aqueous solution, followed by precipitation of the crystals or evaporation to dryness. Rubidium sulfate is also prepared by the addition of a hot solution of barium hydroxide to a boiling solution of rubidium alum until all the aluminum is precipitated. The pH of the solution is 7.6 when the reaction is complete. Aluminum hydroxide and barium sulfate are removed by filtration, and rubidium sulfate is obtained by concentration and crystallization from the filtrate. Rubidium aluminum sulfate dodecahydrate [7488-54-2] (alum), RbA SO 12H20, is formed by sulfuric acid leaching of lepidolite ore. Rubidium alum is more soluble than cesium alum and less soluble than the other alkali alums. Fractional crystallization of Rb alum removes K, Na, and Li values, but concentrates the cesium value. Rubidium hydroxide, RbOH, is prepared by the reaction of rubidium sulfate and barium hydroxide in solution. The insoluble barium sulfate is removed by filtration. The solution of rubidium hydroxide can be evaporated partially in pure nickel or silver containers. Rubidium hydroxide is usually supplied as a 50% aqueous solution. Rubidium carbonate, Rb2C03, is readily formed by bubbling carbon dioxide through a solution of rubidium hydroxide, followed by evaporation to dryness in a fluorocarbon container. Other rubidium compounds can be formed in the laboratory by means of anion-exchange techniques. Table 4 lists some properties of common rubidium compounds. 

Agitation is continued for 30 minutes after all the chloride has been introduced, and the excess hydride is then destroyed by the careful, dropwise addition of water to the stirred and cooled reaction mixture. The hydrolysis is accompanied by the formation of a white curdy mass of aluminum hydroxide, and... 

Iron(III) oxide or alumina is refined from bauxite. Approximately 175 million tons of bauxite are mined annually worldwide, with virtually all of this processed into alumina. Alumina is a white crystalline substance that resembles salt. Approximately 90% of all alumina is used for making aluminum, with the remainder used for abrasives and ceramics. Alumina is produced from bauxite using the Bayer process patented in 1887 by Austrian Karl Josef Bayer (1847-1904). The Bayer process begins by grinding the bauxite and mixing it with sodium hydroxide in a digester. The sodium hydroxide dissolves aluminum oxide components to produce aluminum hydroxide compounds. For gibbsite, the reaction is Al(OH)3 + NaOH —> Al(OH)4 + Na+. Insoluble impurities such as silicates, titanium oxides, and iron oxides are removed from the solution while sodium hydroxide is recovered and recycled. Reaction conditions are then... 

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