Aluminum hydroxides precipitation

Alternatively, Rb sulfate may be obtained by treating a hot solution of rubidium aluminum sulfate (rubidium alum) with ammonia solution. Aluminum hydroxide precipitates. The product mixture is fdtered. The filtrate on evaporation crystaUizes rubidium sulfate. 

Aluminum hydroxide is a white precipitate. If I take samples from the flask that did not produce Pbb, and mix it with a sample from flask B which I know contains NaOH, I should produce the white aluminum hydroxide precipitate. 

Figure 5. Textural changes during phase transformations with APB < 1.0 in dry (I) and liquid (II) media. Scheme II corresponds to formation of aluminum hydroxide precipitated under pH = 6 at 473K.9...

The linear CO stretching frequency for the carbonylated platinum colloid while lower than that found for surface bound CO, is in the range reported for the platinum carbonyl clusters [Pt 3 (CO) 6 ] n / sind we find that the carbonylated colloid is easily transformed into the molecular cluster [Pt 12 (CO) 24 ] (10) reaction with water. The cluster was isolated in 50 yield based on platinum content of the precipitate by extraction with tetraethylammonium bromide in methanol from the aluminum hydroxide precipitated when water is added to the aluminoxane solution. The isolation of the platinum carbonyl cluster reveals nothing about the size or structure of the colloidal platinum particles, but merely emphasizes the high reactivity of metals in this highly dispersed state. The cluster isolated is presumably more a reflection of the stability of the [Pt3(CO)6]n family of clusters than a clue to the nuclearity of the colloidal metal particles - in a similar series of experiments with colloidal cobalt with a mean particle size of 20A carbonylation results in the direct formation of Co2(CO)8. 

Upon cooling, the liquor becomes supersaturated and aluminum hydroxide precipitates out in a reversal of the formation reaction. The solution is seeded with solid aluminum hydroxide to increase the precipitation rate. The hydrargillite formed is filtered off and washed. A large part of it is mashed and returned as seed for the following precipitation and the rest is carefully dried. Coarse particulate aluminum hydroxide is obtained, which can be processed by grinding and sieving to particulate particle size fractions between 10 and 100 pm. 

Derivation From bauxite. The ore is dissolved in strong caustic and aluminum hydroxide precipitated from the sodium aluminate solution by neutralization (as with carbon dioxide) or by autoprecipitation (Bayer process). 

Problem In order to present students with a cognitive conflict it is possible to precipitate a solid and to dissolve this solid by the same substance. One way is to add a small amount of sodium hydroxide solution to aluminum chloride solution aluminum hydroxide precipitates as a white solid. After that an excess of sodium hydroxide is added the white solid disappears because the soluble tetrahydroxide aluminum complex is formed. If this excess of hydroxide solution is added from the beginning, no precipitation occurs, the complex is just formed. 

The most common technique of catalyst preparation involves impregnation of the support with an aqueous solution containing salts of the catalytic metals". In other instances the support and metal precursors are coprecipitated. For example, copper is precipitated as a basic carbonate by mixing CuCNOjjj with NazCOj. By including AKNOjjj with the Cu(N03)2, an intimate copper carbonate/aluminum hydroxide precipitate is formed. Copper carbonate crystals of 20-40 nm are produced, intermixed with... 

Table II. Equilibrium Constants for Aluminum Hydroxide Precipitation Reaction, Al + 3H2O Al(OH)3C + 3H, at Temperatures Indicated...

Solutions of aluminum isopropoxide in cumene and diethylsilanediol in isopropyl alcohol were blended to give the desired ratios of silicon to aluminum. Water was added in excess of that required to hydrolyze the aluminum isopropoxide to aluminum hydroxide. The solution was distilled to remove the isopropyl alcohol and water, leaving a clear solution of reaction product in the cumene. When diethylsilanediol was omitted, the aluminum hydroxide precipitated and the decanted cumene solution contained no compound of aluminum. 

Characterization of aluminum chlorohydrate has revealed a predominance (about 88%) of Ai polymer with the balance being monomers and smaller polycations (20). The highly charged Al 3 surrounded by Q counterions is self-stabilized by repulsion forces, preventing association and subsequent aluminum hydroxide precipitation (21). Thus, aluminum chlorohydrate solutions remain clear and free of precipitate after years of storage at room temperature. Aqueous dilution or an increase in pH to 5—6, however, results in rapid degradation and formation of gibbsite [14762-49-3] an insoluble aluminum hydroxide polymorph (8). 

Aluminum hydroxide precipitated freshly, for example, when filter alum is added to water in the water treatment process of coagulation, is more soluble than the thermodynamically-stable AKOHlajs) phase, gibbsite. This material has the same composition but a different, more well-defined crystal structure. The solubility product for gibbsite is... 

II. Aluminum hydroxide precipitated in the cold with ammonia solution is covered with water in an autoclave and heated for two hours at 200°C. Pure boehmite is formed. 

Owing to aluminum s ability to form amphoteric hydroxides, the aluminum hydroxide precipitate dissolves on the further addition of dilute sodium hydroxide solution Rasa hydroxo complex is created. 

Titration of hydrochloric acid, containing a small amount of aluminum chloride, with sodium hydroxide (aluminum hydroxide precipitated)... 

In several parts of this experiment aluminum hydroxide precipitates even in acidic solution. To gain some perspective on this, calculate each of the following. 

The classical process for winning aluminum is one developed by Hall and by Herault in 1886 and 1888. Aluminum oxide (AI2O3) of high purity is mixed with cryolite (NajAlFg) in the ratio of 1 10. The mixture melts at approximately 950 °C. The preparation of the pure aluminum oxide, which is usually from bauxite, is the first step in winning aluminum. This process was developed by K.J. Bayer in 1892. The bauxite is treated with concentrated sodium hydroxide and reacted with the aluminum minerals to get sodium aluminate. After aluminum hydroxide precipitates from the aluminate solution, it is then calcinated at 1200-1300 °C. 

A good illustration of the importance of the order in which reactants are mixed is given in Figure 7.4, which shows the differences in XRD for aluminum hydroxide precipitation at pH 9 [18]. Each procedure led to a different compound microporous boehmite (aluminum nitrate added to sodium carbonate), bayerite (sodium carbonate added to aluminum nitrate), or fibrillar boehmite (simultaneous addition). 

After the aluminum hydroxide precipitate has been filtered, it is calcined in preparation for electroreduction to the metal. The solution recovered from the filtration is reconcentrated so that it can be used again. This task is accomplished by heating to evaporate water from the solution, a procedure that requires much energy and is the most costly part of the Bayer process. 

From Table 4.1, you see that Al2(S04)3 is soluble (Rule 4), NaOH and N S04 are soluble (Rule 1), and Al(OH)3 is insoluble (Rule 8). Thus, aluminum hydroxide precipitates. The balanced molecular equation with phase labels is... 

Other substances, including the iron oxides, remain undissolved and are filtered off. As the hot solution of sodium aluminate cools, aluminum hydroxide precipitates, leaving the soluble silicates in solution. In practice, the solution is seeded with aluminum hydroxide to start the precipitation. 

Goodenough (1960), with further details provided by Neipert and Bon (1967), and then by numerous investigators in many combinations (i.e., such as with ion exchange resins or other co-precipitants). Many different lithium-containing brines were also tested, such as seawater, geothermal brines from Italy, France and Japan, as well as brines from the Dead Sea, Salton Sea, the Great Salt I e and various oilfield waters. However, no commercial processes were ever developed utilizing aluminum hydroxide precipitates. 

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