Sodium aluminate is an

inorganic An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemistry''. Inor ...

chemical that is used as an effective source of

aluminium hydroxide Aluminium hydroxide, , is found as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is amphoteric, i.e., it has both basic and acidic propert ...

for many industrial and technical applications. Pure

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

aluminate In chemistry, an aluminate is a compound containing an oxyanion of aluminium, such as sodium aluminate. In the naming of inorganic compounds, it is a suffix that indicates a polyatomic anion with a central aluminium atom. Aluminate oxyanions ...

(

anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...

) is a white

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

line solid having a formula variously given as NaAlO₂, NaAl(OH)₄ ( hydrated), Na₂O·Al₂O₃, or Na₂Al₂O₄. Commercial sodium aluminate is available as a solution or a solid.
Other related compounds, sometimes called sodium aluminate, prepared by reaction of Na₂O and Al₂O₃ are Na₅AlO₄ which contains discrete AlO₄⁵⁻ anions, Na₇Al₃O₈ and Na₁₇Al₅O₁₆ which contain complex polymeric anions, and NaAl₁₁O₁₇, once mistakenly believed to be β-alumina, a phase of

aluminium oxide Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several Aluminium oxide (compounds), aluminium oxides, and specifically identified as alum ...

.Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier

Structure

Anhydrous sodium aluminate, NaAlO₂, contains a three-dimensional framework of corner linked AlO₄ tetrahedra. The hydrated form NaAlO₂·5/4H₂O has layers of AlO₄ tetrahedra joined into rings and the layers are held together by sodium ions and water molecules that hydrogen bond to O atoms in the AlO₄ tetrahedra.

Manufacturing

Sodium aluminate is manufactured by the dissolution of aluminium hydroxide (Al(OH)₃) in a

caustic soda Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base and alkali t ...

(NaOH) solution. Aluminium hydroxide (

gibbsite Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide. It is often designated as γ-Al(OH)3 (but sometimes as α-Al(OH)3). It is also sometimes called hydrargillite (or hydrargyllite). Gibbsite is an important ore of aluminium ...

) can be dissolved in 20–25% aqueous NaOH solution at a temperature near the boiling point. The use of more concentrated NaOH solutions leads to a semi-solid product. The process must be carried out in steam-heated vessels of

nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...

steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

, and the aluminium hydroxide should be boiled with approximately 50% aqueous caustic soda until a pulp forms. The final mixture has to be poured into a tank and cooled; a solid mass containing about 70% NaAlO₂ then forms. After being crushed, this product is dehydrated in a rotary oven. The resulting product contains 90% NaAlO₂ and 1% water, together with 1% free NaOH.

Reaction of aluminium and alkali

Sodium aluminate is also formed by the action of sodium hydroxide on elemental aluminium which is an amphoteric metal. The reaction is highly exothermic once established and is accompanied by the rapid evolution of hydrogen gas. The reaction is sometimes written as: : 2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂ However, the species produced in solution is likely to contain the l(OH)₄sup>− ion or perhaps the l(H₂O)₂(OH)₄sup>− ion.

Uses

In water treatment it is used as an adjunct to water softening systems, as a coagulant aid to improve

flocculation In colloidal chemistry, flocculation is a process by which colloidal particles come out of Suspension (chemistry), suspension to sediment in the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The actio ...

, and for removing dissolved

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

and

phosphate Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...

s. In construction technology, sodium aluminate is employed to accelerate the solidification of

concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...

, mainly when working during frost. Sodium aluminate is also used in the

paper industry The pulp and paper industry comprises companies that use wood, specifically pulpwood, as raw material and produce pulp, paper, paperboard, and other cellulose-based products. Manufacturing process In the manufacturing process, pulp is intro ...

, for fire brick production, alumina production and so forth. Sodium aluminate solutions are intermediates in the production of

zeolites Zeolites are a group of several Microporous material, microporous, crystalline aluminosilicate minerals commonly used as commercial adsorption, adsorbents and Catalysis, catalysts. They mainly consist of silicon, aluminium, oxygen, and have the ge ...

.Alan Dyer, (1994), ''Encyclopedia of Inorganic Chemistry'', R. Bruce King (ed.), John Wiley & Sons,

Structure

Manufacturing

Reaction of aluminium and alkali

Uses

References

See also