Soda, aluminate

Sillimanite, see Aluminum silicon oxide (1/1) Smithsonite, see Zinc carbonate Soda ash, see Sodium carbonate Spelter, see Zinc metal Sphalerite, see Zinc sulflde Spherocobaltite, see Cobalt(II) carbonate Spinel, see Magnesium aluminate(2—)... 

Sodium aluminate [1302-42-7] is another source of soluble aluminum made by leaching bauxite with caustic soda. As with alum, the active species are really its hydrolysis products which depend on the chemistry of the system to which it is added. It tends to raise the pH. It is available both as a soHd and as a solution (see Aluminum compounds, aluminates). 

There are several processes available for the manufacture of cryoHte. The choice is mainly dictated by the cost and quaUty of the available sources of soda, alumina, and fluoriae. Starting materials iaclude sodium aluminate from Bayer s alumina process hydrogen fluoride from kiln gases or aqueous hydrofluoric acid sodium fluoride ammonium bifluoride, fluorosiUcic acid, fluoroboric acid, sodium fluosiUcate, and aluminum fluorosiUcate aluminum oxide, aluminum sulfate, aluminum chloride, alumina hydrate and sodium hydroxide, sodium carbonate, sodium chloride, and sodium aluminate. 

Sodium aluminate (NaA102) normally contains an excess of sodium hydroxide or soda ash to maintain a sufficiendy high pH to prevent Al(OH)2 precipitation prior to its addition to the water as a coagulant. 

Boiler compound formulations containing aluminate, silicate, and carbonate ingredients have commonly utilized various ratios of some or all of these constituents, together with caustic soda (for alkalinity control), sodium nitrate or sulfate (to prevent caustic embrittlement), sodium lig-nosulfonate (sludge conditioner), and other compounds. 

With Aluminium.—If a solution of caustic soda is brought into contact with metallic aluminium, chemical reaction takes place, with the production of sodium aluminate and hydrogen, in accordance with the following equation —... 

Carbonate of soda, Sulphate of soda, Chloride of sodium, Aluminate of soda, ... 

The higher the concentration of the caustic soda solution which is present as a liquid phase in addition to the gel (Figure 1, top), the faster the gels precipitated from sodium silicate and sodium aluminate solutions crystallize to form zeolite A. The gels which crystallized from higher NaOH concentrations give finer particles of zeolite A than do those... 

In the process to produce alumina (Fig. 1), bauxite is crushed and wet ground to 100-mesh, dissolved under pressure and heated in digesters with concentrated spent caustic soda solution from a previous cycle and sufficient lime and soda ash. Sodium aluminate is formed, and the dissolved silica is precipitated as sodium aluminum silicate. The undissolved residue (red mud) is separated from the alumina solution by filtration and washing and sent to recovery. Thickeners and Kelly or drum filters are used. The filtered solution of sodium aluminate is hydrolyzed to precipitate aluminum hydroxide by cooling. The precipitate is filtered from the liquor, washed, and heated to 980°C in a rotary kiln to calcine the aluminum hydroxide. 

Tankwater, Bright dip acid (phosphoric), Cyanide rinse bath, Pickle Liquor, Sodium Aluminate Liquor, N.S.S.C. Liquor, Kraft Liquor, Soda Liquor, Sulfite Liquor, Stillage, Corn Syrup, Gelatin, Salt, Soybean Oil, Steepwater, Sugar, Whey, Mercerizing Caustic, Nylon Salt, Rayon Spin Bath, and Sodium Sulfate. 

The removal of other species requires the addition of sodium aluminate (Na2Al204). Reduction in the concentration magnesium is only about 10%. The addition of sodium aluminate also helps with the reduction in silica, as the magnesium precipitate, magnesium hydroxide, adsorbs silica. More complete removal requires the addition of soda ash (Na2C03) and warmer temperatures, as shown in Table 8.10. 

Monosulphate is troublesome to prepare. Mylius mixed 500 ml of a supersaturated calcium aluminate solution (649 mg CaO and 969 mg Al203l ) at 18°C, with shaking, with 2924ml of saturated CH (1.25gCa01" ) and 334ml of saturated gypsum (1.93gCaS041 ). After 30 min, crystallization was complete the mixture was filtered, washed four times with a little water followed by 96% ethanol and ether, and dried over CaClj and soda lime without evacuation. Monosulphate may also be prepared hydrothermally (A8). 

The authors summarized the results of the soda reaction test as follows For the high-silica samples the reaction products were identified as nepheline and sodium aluminum silicate (3 2 4). The amount of nepheline decreased with increasing alumina content, whereas the amount of (3 2 4) compound increased. The lack of silica in the high alumina samples permits the free alumina not tied up as a sodium aluminum silicate to react with the alkali to form beta-alumina. Higher amounts of soda produce sodium aluminates. 

The 90% alumina refractory showed a sharp drop in the amount of alpha-alumina present as the temperature was increased. The depletion of alpha-alumina does not occur unless excess soda is available and the temperature is above 2000°F, or unless the amount of SiOz present is not sufficient to tie up the soda as a sodium aluminum silicate. Finally, the free alumina existent in the lower silica-containing samples is depleted by the formation of beta-alumina and alkali aluminate. 

On the other hand, the specimens with a silica/alumina ratio of 40 60 consisted largely of mullite and formed a sodium aluminate rather than a sodium silicate. First, the soda attacked the excess alumina to form a sodium aluminate. As the reaction with soda proceeded, the mullite decomposed, forming nepheline and more sodium aluminate. 

Bauxite is treated either by Deville s method or by that of Bayer, the latter being almost exclusively employed. A third method depends upon the production of aluminium nitride. This is obtained by heating bauxite in air to 1800°-1900° in an electric furnace. It is then decomposed in an autoclave in presence of soda solution, giving (i) ammonia, used as a manure in the form of its sulphate, (ii) sodium aluminate, from which commercially pure alumina can be obtained. 

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