Aluminium sulfate

Last updated
Aluminium sulfate
Aluminium sulfate.jpg
Names
IUPAC name
Aluminium sulfate
Other names
  • Aluminum sulfate
  • Aluminium sulphate
  • Cake alum
  • Filter alum
  • Papermaker's alum
  • Alunogenite
  • aluminium salt (3:2)
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.110 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 233-135-0
E number E520 (acidity regulators, ...)
PubChem CID
RTECS number
  • BD1700000
UNII
  • InChI=1S/2Al.3H2O4S/c;;3*1-5(2,3)4/h;;3*(H2,1,2,3,4)/q2*+3;;;/p-6 Yes check.svgY
    Key: DIZPMCHEQGEION-UHFFFAOYSA-H Yes check.svgY
  • InChI=1/2Al.3H2O4S/c;;3*1-5(2,3)4/h;;3*(H2,1,2,3,4)/q2*+3;;;/p-6
    Key: DIZPMCHEQGEION-CYFPFDDLAS
  • [Al+3].[Al+3].[O-]S(=O)(=O)[O-].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O
Properties
Al2(SO4)3
Molar mass 342.15 g/mol (anhydrous)
666.44 g/mol (octadecahydrate)
Appearancewhite crystalline solid
hygroscopic
Density 2.672 g/cm3 (anhydrous)
1.62 g/cm3 (octadecahydrate)
Melting point 770 °C (1,420 °F; 1,040 K) (decomposes, anhydrous)
86.5 °C (octadecahydrate)
31.2 g/100 mL (0 °C)
36.4 g/100 mL (20 °C)
89.0 g/100 mL (100 °C)
Solubility slightly soluble in alcohol, dilute mineral acids
Acidity (pKa)3.3–3.6
−93.0×10−6 cm3/mol
1.47 [1]
Structure
monoclinic (hydrate)
Thermochemistry
-3440 kJ/mol
Hazards
NFPA 704 (fire diamond)
NFPA 704.svgHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
0
0
NIOSH (US health exposure limits):
PEL (Permissible)
none [2]
REL (Recommended)
2 mg/m3 [2]
IDLH (Immediate danger)
N.D. [2]
Related compounds
Other cations
Gallium sulfate
Magnesium sulfate
Related compounds
See Alum
Supplementary data page
Aluminium sulfate (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Aluminium sulfate is a salt with the formula Al 2 (SO4) 3. It is soluble in water and is mainly used as a coagulating agent (promoting particle collision by neutralizing charge) in the purification of drinking water [3] [4] and wastewater treatment plants, and also in paper manufacturing.

Contents

The anhydrous form occurs naturally as a rare mineral millosevichite, found for example in volcanic environments and on burning coal-mining waste dumps. Aluminium sulfate is rarely, if ever, encountered as the anhydrous salt. It forms a number of different hydrates, of which the hexadecahydrate Al2(SO4)3·16H2O and octadecahydrate Al2(SO4)3·18H2O are the most common. The heptadecahydrate, whose formula can be written as [Al(H2O)6]2(SO4)3·5H2O, occurs naturally as the mineral alunogen.

Aluminium sulfate is sometimes called alum or papermaker's alum in certain industries. However, the name "alum" is more commonly and properly used for any double sulfate salt with the generic formula XAl(SO
4
)
2
·12H
2
O
, where X is a monovalent cation such as potassium or ammonium. [5]

Production

In the laboratory

Aluminium sulfate may be made by adding aluminium hydroxide, Al(OH)3, to sulfuric acid, H2SO4:

2 Al(OH)3 + 3 H2SO4 → Al2(SO4)3 + 6 H2O

or by heating aluminium metal in a sulfuric acid solution:

2 Al + 3 H2SO4 → Al2(SO4)3 + 3 H2

From alum schists

The alum schists employed in the manufacture of aluminium sulfate are mixtures of iron pyrite, aluminium silicate and various bituminous substances, and are found in upper Bavaria, Bohemia, Belgium, and Scotland. These are either roasted or exposed to the weathering action of the air. In the roasting process, sulfuric acid is formed and acts on the clay to form aluminium sulfate, a similar condition of affairs being produced during weathering. The mass is now systematically extracted with water, and a solution of aluminium sulfate of specific gravity 1.16 is prepared. This solution is allowed to stand for some time (in order that any calcium sulfate and basic iron(III) sulfate may separate), and is then evaporated until iron(II) sulfate crystallizes on cooling; it is then drawn off and evaporated until it attains a specific gravity of 1.40. It is now allowed to stand for some time, and decanted from any sediment. [6]

From clays or bauxite

In the preparation of aluminium sulfate from clays or from bauxite, the material is gently calcined, then mixed with sulfuric acid and water and heated gradually to boiling; if concentrated acid is used no external heat is generally required as the formation of aluminium sulfate is exothermic. It is allowed to stand for some time, and the clear solution is drawn off.

From cryolite

When cryolite is used as the ore, it is mixed with calcium carbonate and heated. By this means, sodium aluminate is formed; it is then extracted with water and precipitated either by sodium bicarbonate or by passing a current of carbon dioxide through the solution. The precipitate is then dissolved in sulfuric acid. [6]

Uses

Sediment core sampled from a Minnesota lake. Aluminium sulfate flocs are depicted as white clumps near the sediment surface. Aluminum Sulfate Floc in Lake Sediment.png
Sediment core sampled from a Minnesota lake. Aluminium sulfate flocs are depicted as white clumps near the sediment surface.

Aluminium sulfate is sometimes used in the human food industry as a firming agent, where it takes on E number E520, and in animal feed as a bactericide. In the United States, the FDA lists it as "generally recognized as safe" with no limit on concentration. [7] Aluminium sulfate may be used as a deodorant, an astringent, or as a styptic for superficial shaving wounds.[ citation needed ] Aluminium sulfate is used as a mordant in dyeing and printing textiles.

It is a common vaccine adjuvant and works "by facilitating the slow release of antigen from the vaccine depot formed at the site of inoculation."[ citation needed ]

Aluminium sulfate is used in water purification and for chemical phosphorus removal from wastewater. It causes suspended impurities to coagulate into larger particles and then settle to the bottom of the container (or be filtered out) more easily. This process is called coagulation or flocculation. Research suggests that in Australia, aluminium sulfate used in this way in drinking water treatment is the primary source of hydrogen sulfide gas in sanitary sewer systems. [8] An improper and excess application incident in 1988 polluted the water supply of Camelford in Cornwall.

Aluminium sulfate has been used as a method of eutrophication remediation for shallow lakes. It works by reducing the phosphorus load in the lakes. [9] [10]

When dissolved in a large amount of neutral or slightly alkaline water, aluminium sulfate produces a gelatinous precipitate of aluminium hydroxide, Al(OH)3. In dyeing and printing cloth, the gelatinous precipitate helps the dye adhere to the clothing fibers by rendering the pigment insoluble.

Aluminium sulfate is sometimes used to reduce the pH of garden soil, as it hydrolyzes to form the aluminium hydroxide precipitate and a dilute sulfuric acid solution. An example of what changing the pH level of soil can do to plants is visible when looking at Hydrangea macrophylla . The gardener can add aluminium sulfate to the soil to reduce the pH which in turn will result in the flowers of the Hydrangea turning a different color (blue). The aluminium is what makes the flowers blue; at a higher pH, the aluminium is not available to the plant. [11]

In the construction industry, it is used as waterproofing agent and accelerator in concrete. Another use is a foaming agent in fire fighting foam.

It can also be very effective as a molluscicide, [12] killing spanish slugs.

Mordants aluminium triacetate and aluminium sulfacetate can be prepared from aluminium sulfate, the product formed being determined by the amount of lead(II) acetate used: [13]

Al
2
(SO
4
)
3
+ 3 Pb(CH
3
CO
2
)
2
→ 2 Al(CH
3
CO
2
)
3
+ 3 PbSO
4
Al
2
(SO
4
)
3
+ 2 Pb(CH
3
CO
2
)
2
Al
2
SO
4
(CH
3
CO
2
)
4
+ 2 PbSO
4

Chemical reactions

The compound decomposes to γ-alumina and sulfur trioxide when heated between 580 and 900 °C. It combines with water forming hydrated salts of various compositions.

Aluminium sulfate reacts with sodium bicarbonate to which foam stabilizer has been added, producing carbon dioxide for fire-extinguishing foams:

Al2(SO4)3 + 6 NaHCO3 → 3 Na2SO4 + 2 Al(OH)3 + 6 CO2

The carbon dioxide is trapped by the foam stabilizer and creates a thick foam which will float on top of hydrocarbon fuels and seal off access to atmospheric oxygen, smothering the fire. Chemical foam was unsuitable for use on polar solvents such as alcohol, as the fuel would mix with and break down the foam blanket. The carbon dioxide generated also served to propel the foam out of the container, be it a portable fire extinguisher or fixed installation using hoselines. Chemical foam is considered obsolete in the United States and has been replaced by synthetic mechanical foams, such as AFFF which have a longer shelf life, are more effective, and more versatile, although some countries such as Japan and India continue to use it.[ citation needed ]

Related Research Articles

<span class="mw-page-title-main">Sulfuric acid</span> Chemical compound (H₂SO₄)

Sulfuric acid or sulphuric acid, known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, and hydrogen, with the molecular formula H2SO4. It is a colorless, odorless, and viscous liquid that is miscible with water.

<span class="mw-page-title-main">Iron(II) sulfate</span> Chemical compound

Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula Fe SO4·xH2O. These compounds exist most commonly as the heptahydrate (x = 7) but several values for x are known. The hydrated form is used medically to treat or prevent iron deficiency, and also for industrial applications. Known since ancient times as copperas and as green vitriol (vitriol is an archaic name for sulfate), the blue-green heptahydrate (hydrate with 7 molecules of water) is the most common form of this material. All the iron(II) sulfates dissolve in water to give the same aquo complex [Fe(H2O)6]2+, which has octahedral molecular geometry and is paramagnetic. The name copperas dates from times when the copper(II) sulfate was known as blue copperas, and perhaps in analogy, iron(II) and zinc sulfate were known respectively as green and white copperas.

<span class="mw-page-title-main">Lead(II) sulfate</span> Chemical compound

Lead(II) sulfate (PbSO4) is a white solid, which appears white in microcrystalline form. It is also known as fast white, milk white, sulfuric acid lead salt or anglesite.

<span class="mw-page-title-main">Calcium sulfate</span> Laboratory and industrial chemical

Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO4 and related hydrates. In the form of γ-anhydrite (the anhydrous form), it is used as a desiccant. One particular hydrate is better known as plaster of Paris, and another occurs naturally as the mineral gypsum. It has many uses in industry. All forms are white solids that are poorly soluble in water. Calcium sulfate causes permanent hardness in water.

<span class="mw-page-title-main">Potassium alum</span> Chemical compound

Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound: the double sulfate of potassium and aluminium, with chemical formula KAl(SO4)2. It is commonly encountered as the dodecahydrate, KAl(SO4)2·12H2O. It crystallizes in an octahedral structure in neutral solution and cubic structure in an alkali solution with space group P a −3 and lattice parameter of 12.18 Å. The compound is the most important member of the generic class of compounds called alums, and is often called simply alum.

<span class="mw-page-title-main">Potassium sulfate</span> Chemical compound

Potassium sulfate (US) or potassium sulphate (UK), also called sulphate of potash (SOP), arcanite, or archaically potash of sulfur, is the inorganic compound with formula K2SO4, a white water-soluble solid. It is commonly used in fertilizers, providing both potassium and sulfur.

<span class="mw-page-title-main">Ammonium sulfate</span> Chemical compound

Ammonium sulfate (American English and international scientific usage; ammonium sulphate in British English); (NH4)2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen and 24% sulfur.

<span class="mw-page-title-main">Aluminium nitrate</span> Chemical compound

Aluminium nitrate is a white, water-soluble salt of aluminium and nitric acid, most commonly existing as the crystalline hydrate, aluminium nitrate nonahydrate, Al(NO3)3·9H2O.

<span class="mw-page-title-main">Beryllium hydroxide</span> Chemical compound

Beryllium hydroxide, Be(OH)2, is an amphoteric hydroxide, dissolving in both acids and alkalis. Industrially, it is produced as a by-product in the extraction of beryllium metal from the ores beryl and bertrandite. The natural pure beryllium hydroxide is rare (in form of the mineral behoite, orthorhombic) or very rare (clinobehoite, monoclinic). When alkali is added to beryllium salt solutions the α-form (a gel) is formed. If this left to stand or boiled, the rhombic β-form precipitates. This has the same structure as zinc hydroxide, Zn(OH)2, with tetrahedral beryllium centers.

A nitrate test is a chemical test used to determine the presence of nitrate ion in solution. Testing for the presence of nitrate via wet chemistry is generally difficult compared with testing for other anions, as almost all nitrates are soluble in water. In contrast, many common ions give insoluble salts, e.g. halides precipitate with silver, and sulfate precipitate with barium.

<span class="mw-page-title-main">Mercury(II) sulfate</span> Chemical compound

Mercury(II) sulfate, commonly called mercuric sulfate, is the chemical compound HgSO4. It is an odorless salt that forms white granules or crystalline powder. In water, it separates into an insoluble basic sulfate with a yellow color and sulfuric acid.

Indium(III) sulfate (In2(SO4)3) is a sulfate salt of the metal indium. It is a sesquisulfate, meaning that the sulfate group occurs 11/2 times as much as the metal. It may be formed by the reaction of indium, its oxide, or its carbonate with sulfuric acid. An excess of strong acid is required, otherwise insoluble basic salts are formed. As a solid indium sulfate can be anhydrous, or take the form of a pentahydrate with five water molecules or a nonahydrate with nine molecules of water. Indium sulfate is used in the production of indium or indium containing substances. Indium sulfate also can be found in basic salts, acidic salts or double salts including indium alum.

<span class="mw-page-title-main">Ammonium alum</span> Chemical compound

Ammonium aluminium sulfate, also known as ammonium alum or just alum (though there are many different substances also called "alum"), is a white crystalline double sulfate usually encountered as the dodecahydrate, formula (NH4)Al(SO4)2·12H2O. It is used in small amounts in a variety of niche applications. The dodecahydrate occurs naturally as the rare mineral tschermigite.

In ore deposit geology, supergene processes or enrichment are those that occur relatively near the surface as opposed to deep hypogene processes. Supergene processes include the predominance of meteoric water circulation (i.e. water derived from precipitation) with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary (hypogene) sulfide ore minerals and redistribute the metallic ore elements. Supergene enrichment occurs at the base of the oxidized portion of an ore deposit. Metals that have been leached from the oxidized ore are carried downward by percolating groundwater, and react with hypogene sulfides at the supergene-hypogene boundary. The reaction produces secondary sulfides with metal contents higher than those of the primary ore. This is particularly noted in copper ore deposits where the copper sulfide minerals chalcocite (Cu2S), covellite (CuS), digenite (Cu18S10), and djurleite (Cu31S16) are deposited by the descending surface waters.

<span class="mw-page-title-main">Iron(III) sulfate</span> Chemical compound

Iron(III) sulfate (or ferric sulfate), is a family of inorganic compounds with the formula Fe2(SO4)3(H2O)n. A variety of hydrates are known, including the most commonly encountered form of "ferric sulfate". Solutions are used in dyeing as a mordant, and as a coagulant for industrial wastes. Solutions of ferric sulfate are also used in the processing of aluminum and steel.

<span class="mw-page-title-main">Sodium alum</span> Inorganic compound

Sodium aluminium sulfate is the inorganic compound with the chemical formula NaAl(SO4)2·12H2O (sometimes written Na2SO4·Al2(SO4)3·24H2O). Also known as soda alum, sodium alum, or SAS, this white solid is used in the manufacture of baking powder and as a food additive. Its official mineral name is alum-Na (IMA symbol: Aum-Na).

<span class="mw-page-title-main">Ammonium iron(III) sulfate</span> Chemical compound

Ammonium iron(III) sulfate, NH4Fe(SO4)2·12 H2O, or NH4[Fe(H2O)6](SO4)2·6 H2O, also known as ferric ammonium sulfate (FAS) or iron alum, is a double salt in the class of alums, which consists of compounds with the general formula AB(SO4)2 · 12 H2O. It has the appearance of weakly violet, octahedrical crystals. There has been some discussion regarding the origin of the crystals' colour, with some ascribing it to impurities in the compound, and others claiming it to be a property of the crystal itself.

<span class="mw-page-title-main">Antimony(III) sulfate</span> Chemical compound

Antimony sulfate, Sb2(SO4)3, is a hygroscopic salt formed by reacting antimony or its compounds with hot sulfuric acid. It is used in doping of semiconductors and in the production of explosives and fireworks.

Barium permanganate is a chemical compound, with the formula Ba(MnO4)2. It forms violet to brown crystals that are sparingly soluble in water.

References

Footnotes

  1. Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN   0-07-049439-8
  2. 1 2 3 NIOSH Pocket Guide to Chemical Hazards. "#0024". National Institute for Occupational Safety and Health (NIOSH).
  3. Global Health and Education Foundation (2007). "Conventional Coagulation-Flocculation-Sedimentation". Safe Drinking Water is Essential. National Academy of Sciences. Archived from the original on 2007-10-07. Retrieved 2007-12-01.
  4. Kvech S, Edwards M (2002). "Solubility controls on aluminum in drinking water at relatively low and high pH". Water Research. 36 (17): 4356–4368. Bibcode:2002WatRe..36.4356K. doi:10.1016/S0043-1354(02)00137-9. PMID   12420940.
  5. Austin, George T. (1984). Shreve's Chemical process industries (5th ed.). New York: McGraw-Hill. p. 357. ISBN   9780070571471. Archived from the original on 2014-01-03.
  6. 1 2 Chisholm 1911, p. 767.
  7. 21 CFR 182.1125, 2020-04-01, retrieved 2021-02-22
  8. Ilje Pikaar; Keshab R. Sharma; Shihu Hu; Wolfgang Gernjak; Jürg Keller; Zhiguo Yuan (2014). "Reducing sewer corrosion through integrated urban water management". Science. 345 (6198): 812–814. Bibcode:2014Sci...345..812P. doi:10.1126/science.1251418. PMID   25124439. S2CID   19126381.
  9. Kennedy, Robert H.; Cook, G. Dennis (June 1982). "Control of Lake Phosphorus with Aluminum Sulfate: Dose Determination and Application Techniques". Journal of the American Water Resources Association. 18 (3): 389–395. Bibcode:1982JAWRA..18..389K. doi:10.1111/j.1752-1688.1982.tb00005.x. ISSN   1093-474X.
  10. Martyn, Huser, Brian J. Egemose, Sara Harper, Harvey Hupfer, Michael Jensen, Henning Pilgrim, Keith M. Reitzel, Kasper Rydin, Emil Futter (2016). Longevity and effectiveness of aluminum addition to reduce sediment phosphorus release and restore lake water quality. Uppsala universitet, Limnologi. OCLC   1233676585.{{cite book}}: CS1 maint: multiple names: authors list (link)
  11. Kari Houle (2013-06-18). "Blue or Pink - Which Color is Your Hydrangea". University of Illinois Extension. Retrieved 2018-09-03.
  12. Council, British Crop Protection; Society, British Ecological; Biologists, Association of Applied (1994). Field margins: integrating agriculture and conservation : proceedings of a symposium organised by the British Crop Protection Council in association with the British Ecological Society and the Association of Applied Biologists and held at the University of Warwick, Coventry on 18–20 April 1994. British Crop Protection Council. ISBN   9780948404757.
  13. Georgievics, Von (2013). The Chemical Technology of Textile Fibres – Their Origin, Structure, Preparation, Washing, Bleaching, Dyeing, Printing and Dressing. Read Books. ISBN   9781447486121. Archived from the original on 2017-12-05.

Notations