Sodium aluminates

Sodium aluminate (theoretical formula NaA102) has a certain industrial importance not only as an intermediate in the digestion of bauxite in the Bayer process (see Section 3.2.4.2). USA production of sodium aluminate in 1993 was estimated to be 85 10- t/a. Sodium aluminate is produced by dissolving hydrated aluminum oxide in 50% sodium hydroxide. It is utilized in water purification, in the paper industry, for the post-treatment of Ti02-pigments, for the manufacture of aluminum-containing 

---

From the sodium aluminate solution, aluminium hydroxide is precipitated by passing in carbon dioxide ... 

The s)mthesis of zeolites is traditionally performed by crystallisation from a sol-gel mixture comprising reagents such as silica, sodium aluminate, sodium hydroxide and water. Another key component of the sol-gel mixture is a base whose main role is to regulate the pH of the mixture. If an organic base is used then a templating effect may also be observed... 

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. 

The manufacture of cryoHte is commonly iategrated with the production of alumina hydrate and aluminum trifluoride. The iatermediate stream of sodium aluminate from the Bayer alumina hydrate process can be used along with aqueous hydrofluoric acid, hydrogen fluoride kiln gases, or hydrogen fluoride-rich effluent from dry-process aluminum trifluoride manufacture. 

Recovery from Bayer Liquor. The significant amount of primary gallium is recovered from the alumina industry. The main source is the sodium aluminate Hquor from Bayer-process plants that produce large quantities of alumina. Several methods have been developed to recover gallium from Bayer Hquor. 

A commercial process which uses hydrothermal leaching on a large scale is the Bayer process for production of aluminum oxide (see Aluminum compounds). This process is used to extract and precipitate high grade alurninum hydroxide (gibbsite [14762-49-3]) from bauxite [1318-16-7] ore. The hydrothermal process step is the extraction step in which concentrated sodium hydroxide is used to form a soluble sodium aluminate complex ... 

Typical gels are prepared from aqueous solutions of reactants such as sodium aluminate, NaOH, and sodium siUcate other reactants include alumina trihydrate (AI2O2 3H2O), coUoidal siUca, and siUcic acid. Some synthetic 2eohtes prepared from sodium aluminosihcate gels are given in Table 3. 

In gel-forming processes, the reactive aluminosibcate gel is first formed into a pellet which reacts with sodium aluminate solution and caustic solution. The 2eobte crysta11i2es in situ within an essentiaby self-bonded pellet, or as a component in an unconverted amorphous matrix. 

Chemically, ultramarines are complex sodium aluminates having a zeoHte stmcture. Composition varies within certain wt % ranges, ie, Na20, 19—23 AI2O3, 23-29 Si02, 37-50 and S, 8-14. 

Cryolite. Cryofite [15096-52-3] Na AlF, is the primary constituent of the HaH-Hfiroult cell electrolyte. High purity, natural cryofite is found in Greenland, but its rarity and cost have caused the aluminum industry to substitute synthetic cryofite. The latter is produced by the reaction of hydrofluoric acid [7664-39-3] HE, with sodium aluminate [1302-42-7] NaA102, from the Bayer process... 

Sodium aluminate is used in water purification, in the paper industry, for the after treatment of Ti02 pigment, and in the manufacture of aluminum containing catalysts and zeoHte. Worldwide markets are in the range of 125,000 t/yr (19). 

Commercial grades of socbum aluminate contain both waters of hycbation and excess socbum hycboxide. In solution, a high pH retards the reversion of socbum aluminate to insoluble aluminum hycboxide. The chemical identity of the soluble species in socbum aluminate solutions has been the focus of much work (1). Solutions of sodium aluminate appear to be totaby ionic. The aluminate ion is monovalent and the predominant species present is deterrnined by the Na20 concentration. The tetrahydroxyaluminate ion [14485-39-3], Al(OH) 4, exists in lower concentrations of caustic dehydration of Al(OH) 4, to the aluminate ion [20653-98-9], A10 2) is postulated at concentrations of Na20 above 25%. The formation of polymeric aluminate ions similar to the positively charged polymeric ions formed by hydrolysis of aluminum at low pH does not seem to occur. Al(OH) 4 has been identified as the predominant ion in dilute aluminate solutions (2). 

Small amounts of sodium aluminate are prepared in the lab by fusion of equimolar quantities of sodium carbonate [497-19-8] and aluminum acetate [139-12-8], A1(C2H202)3, at 800°C (4). Other methods involve reaction of sodium hycboxide with amorphous alumina or aluminum [7429-90-5] metal. Commercial quantities of sodium aluminate are made from hydrated alumina, in the form of aluminum hydroxy oxide [24623-77-6], AIO(OH), or aluminum hycboxide [21645-51 -2], Al(OH)3, a product of the Bayer process (5,6) which is used to refine bauxite [1318-16-7], the principal aluminum ore. 

Commercial grades of sodium aluminate are obtained by digestion of aluminum tnhydroxide in aqueous caustic at atmospheric pressure and near the boiling temperature (7). Digestion of the aluminum hydroxy oxide in aqueous sodium hycboxide [1310-73-2] requbes pressures of up to 1.38 MPa (13.6 atm) and temperatures of about 200°C. Dry sodium aluminate is obtained by evaporation of water. Several processes for the production of sodium aluminate are known that do not reqube the addition of water. In one process, bauxite reacts with molten sodium hycboxide at approximately 400°C (8) in... 

Gel-Based Activated Aluminas. Alumina gels can be formed by wet chemical reaction of soluble aluminum compounds. An example is rapid mixing of aluminum sulfate [17927-65-0], Al2(S0 2 XH20, and sodium aluminate [1302-42-7], NaA102, solutions to form pseudoboehmite and a... 

Gibbsite usually contains several tenths of a percent of alkaU metal ions the technical product, precipitated from a sodium aluminate solution, contains up to 0.3% Na20 wliich carmot be washed out even using dilute HQ. Several authors (1,2) suggest that these alkaU ions are an essential component of gibbsite structure. 

Chemical recovery ia sodium-based sulfite pulpiag is more complicated, and a large number of processes have been proposed. The most common process iavolves liquor iaciaeration under reduciag conditions to give a smelt, which is dissolved to produce a kraft-type green liquor. Sulfide is stripped from the liquor as H2S after the pH is lowered by CO2. The H2S is oxidized to sulfur ia a separate stream by reaction with SO2, and the sulfur is subsequendy burned to reform SO2. Alternatively, ia a pyrolysis process such as SCA-Bidemd, the H2S gas is burned direcdy to SO2. A rather novel approach is the Sonoco process, ia which alumina is added to the spent liquors which are then burned ia a kiln to form sodium aluminate. In anther method, used particulady ia neutral sulfite semichemical processes, fluidized-bed combustion is employed to give a mixture of sodium carbonate and sodium sulfate, which can be sold to kraft mills as makeup chemical. 

In the Shoe or one-shot method (4), formamide is used to coagulate sodium silicate. The silicate solution used in the Joosten method can be diluted with water to lower its viscosity. Concentrations of sodium silicate between 10—70% are used (viscosities of 2.5—50 mPa-s). Concentrations of formamide are between 2 and 30%. Other reactants such as CaCl2 and sodium aluminate are used in concentrations between 2.4—12 g/L of silicate solution. 

To effectively remove carbonyl sulfide from a gas stream, special alkaline scmbbiag Hquors are used. These contain sodium aluminate or sodium plumbite, or they are made of alkaUes with a hydrolysis catalyst based on Zn, Fe, Ni, or Cu. Diethanolamine, diglycolamine, or other alkanolamines (qv) mixed with water remove carbonyl sulfide from sour, ie, acid-gas-containing, gas streams (25,26) (see Carbon dioxide). 

To improve magnesium reduction, which also improves siHca reduction in cold process softening, sodium aluminate may be used. The sodium aluminate provides hydroxyl ion (OH ) needed for improved magnesium reduction, without increasing calcium hardness in the treated water. In addition, the hydrolysis of sodium aluminate results in the formation of aluminum hydroxide, which aids in floe formation, sludge blanket conditioning, and siHca reduction. 

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. 

Aluminum based chemicals have been used for many years in wastewater treatment applications for suspended solids removal. These include dry and liquid alum, with sodium aluminate used in activated sludge plants for phosphorus removal. 

Tonerde-hydrat, n. hydrate of alumina (aluminum hydroxide). -kali, n. potassium aluminate. -lack, m. alumina lake. -metaU, n. aluminum, -natron, n. sodium aluminate. -prMparat, n. alumina preparation, tonerderelch, a, rich in alumina, aluminous. Tonerde-galz, n. aluminum salt, -stein, m, alumina brick, -sulfat, n, sulfate of alumina... 

NaY zeolite is produced by digesting a mixture of silica, alumina, and caustic for several hours at a prescribed temperature until crystallization occurs (Figure 3-8). Typical sources of silica and alumina are sodium silicate and sodium aluminate. Crystallization of Y-zeolite typically takes 10 hours at about 210°F (100°C). Production of a quality zeolite requires proper control of temperature, time, and pH of the crystallization solution. NaY zeolite is separated after filtering and water-washing of the crystalline solution. 

---