Alum

An alum (/ˈæləm/) is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula XAl(SO
4
)
2
·12H
2
O
, where X is a monovalent cation such as potassium or ammonium.[1] By itself, "alum" often refers to potassium alum, with the formula KAl(SO
4
)
2
·12H
2
O
. Other alums are named after the monovalent ion, such as sodium alum and ammonium alum.

The name "alum" is also used, more generally, for salts with the same formula and structure, except that aluminium is replaced by another trivalent metal ion like chromium(III), and/or sulfur is replaced by other chalcogen like selenium.[1] The most common of these analogs is chrome alum KCr(SO
4
)
2
·12H
2
O
.

In some industries, the name "alum" (or "papermaker's alum") is used to refer to aluminium sulfate Al
2
(SO
4
)
3
·nH
2
O
. Most industrial flocculation done with "alum" actually uses aluminium sulfate. In medicine, "alum" may also refer to aluminium hydroxide gel used as a vaccine adjuvant.[2]

AlumCrystal
Bulk potassium alum KAl(SO
4
)
2
·12H
2
O
.

History

In antiquity and the Middle Ages

Alum found at archaeological sites

The western desert of Egypt was a major source of alum substitutes in antiquity. These evaporites were mainly FeAl
2
(SO
4
)
4
·22H
2
O
, MgAl
2
(SO
4
)
4
·22H
2
O
, NaAl(SO
4
)
2
·6H
2
O
, MgSO
4
·7H
2
O
and Al
2
(SO
4
)
3
·17H
2
O
.[3]

The production of potassium alum from alunite is archaeologically attested on the island Lesbos.[4] This site was abandoned in the 7th century but dates back at least to the 2nd century CE. Native alumen from the island of Melos appears to have been a mixture mainly of alunogen (Al
2
(SO
4
)
3
·17H
2
O
) with potassium alum and other minor sulfates.[5]

Alumen in Pliny and Dioscorides

A detailed description of a substance called alumen occurs in Pliny the Elder's Natural History.[6]

By comparing Pliny's description with the account of stupteria given by Dioscorides,[7] it is obvious the two are identical. Pliny informs us that a form of alumen was found naturally in the earth, and calls it salsugoterrae.

Pliny wrote that different substances were distinguished by the name of alumen, but they were all characterised by a certain degree of astringency, and were all employed in dyeing and medicine.[6] Pliny says that there is another kind of alum that the Greeks call schiston, and which "splits into filaments of a whitish colour",[6] From the name schiston and the mode of formation, it appears that this kind was the salt that forms spontaneously on certain salty minerals, as alum slate and bituminous shale, and consists chiefly of sulfates of iron and aluminium. One kind of alumen was a liquid, which was apt to be adulterated; but when pure it had the property of blackening when added to pomegranate juice. This property seems to characterize a solution of iron sulfate in water; a solution of ordinary (potassium) alum would possess no such property. Contamination with iron sulfate was greatly disliked as this darkened and dulled dye colours. In some places the iron sulfate may have been lacking, so the salt would be white and would be suitable, according to Pliny, for dyeing bright colors.

Pliny describes several other types of alumen but it is not clear as to what these minerals are. The alumen of the ancients then, was not always potassium alum, not even an alkali aluminum sulfate.[8]

Alum described in medieval texts

Alum and green vitriol (iron sulfate) both have sweetish and astringent taste, and they a had overlapping uses. Therefore, through the Middle Ages, alchemists and other writers do not seem to have discriminated the two salts accurately from each other. In the writings of the alchemists we find the words misy, sory, and chalcanthum applied to either compound; and the name atramentum sutorium, which one might expect to belong exclusively to green vitriol, applied indifferently to both.

Modern understanding of the alums

In the early 1700s, Georg Ernst Stahl claimed that reacting sulfuric acid with limestone produced a sort of alum.[9][10] The error was soon corrected by Johann Pott and Andreas Marggraf, who showed that the precipitate obtained when an alkali is poured into a solution of alum, namely alumina, is quite different from lime and chalk, and is one of the ingredients in common clay.[11][12]

Marggraf also showed that perfect crystals with properties of alum can be obtained by dissolving alumina in sulfuric acid and adding potash or ammonia to the concentrated solution.[13][14] In 1767, Torbern Bergman observed the need for potassium or ammonium sulfates to convert aluminium sulfate into alum, while sodium or calcium would not work.[13][15]

The composition of common alum was finally determined by Louis Vauquelin in 1797. As soon as Martin Klaproth discovered the presence of potassium in leucite and lepidolite,[16][17] Vauquelin demonstrated that common alum is a double salt, composed of sulfuric acid, alumina, and potash.[18] In the same journal volume, Jean-Antoine Chaptal published the analysis of four different kinds of alum, namely, Roman alum, Levant alum, British alum and alum manufactured by himself,[19] confirming Vauquelin's result.[13]

Production

Some alums occur as minerals, the most important being alunite.

The most important alums – potassium, sodium, and ammonium – are produced industrially. Typical recipes involve combining aluminium sulfate and the sulfate monovalent cation.[20] The aluminium sulfate is usually obtained by treating minerals like alum schist, bauxite and cryolite with sulfuric acid.[21]

Types

Potassium alum octahedral like crystal
Crystal of potassium alum

Aluminium-based alums are named by the monovalent cation. Unlike the other alkali metals, lithium does not form alums; a fact attributed to the small size of its ion.

The most important alums are

Chemical properties

Aluminium-based alums have a number of common chemical properties. They are soluble in water, have a sweetish taste, react acid to litmus, and crystallize in regular octahedra. In alums each metal ion is surrounded by six water molecules. When heated, they liquefy, and if the heating is continued, the water of crystallization is driven off, the salt froths and swells, and at last an amorphous powder remains.[13] They are astringent and acidic.

Crystal structure

Alums crystallize in one of three different crystal structures. These classes are called α-, β- and γ-alums.

Solubility

The solubility of the various alums in water varies greatly, sodium alum being readily soluble in water, while caesium and rubidium alums are only sparingly soluble. The various solubilities are shown in the following table.[21]

At temperature T, 100 parts water dissolve:

T Ammonium alum Potassium alum Rubidium alum Caesium alum
0 °C 2.62 3.90 0.71 0.19
10 °C 4.50 9.52 1.09 0.29
50 °C 15.9 44.11 4.98 1.235
80 °C 35.20 134.47 21.60 5.29
100 °C 70.83 357.48    

Uses

Aluminium-based alums have been used since antiquity, and are still important in many industrial processes.

The most widely used alum is potassium alum. It was used since antiquity as a flocculant to clarify turbid liquids, as a mordant in dyeing, and in tanning. It is still widely used in the treatment of water, in medicine, for cosmetics (in deodorant), in food preparation (in baking powder and pickling), and to fire-proof paper and cloth.

Sodium alum is used in substitution to potassium alum in baking powders. Ammonium alum has a few niche uses. Other alums have mostly research interest.

In traditional Japanese art, alum and animal glue were dissolved in water, forming a liquid known as dousa (ja:礬水), and used as an undercoat for paper sizing.

Alum in the form of potassium aluminium sulphate or ammonium aluminium sulfate in a concentrated bath of hot water is regularly used by jewelers and machinists to dissolve hardened steel drill bits that have broken off in items made of aluminum, copper, brass, gold (any karat) and silver (both sterling and fine). This is because alum does not react chemically to any significant degree with any of these metals, but will corrode steel. When heat is applied to an alum mixture holding a piece of work that has a drill bit stuck in it, if the lost bit is small enough, it can sometimes be dissolved / removed within hours.[22]

Related compounds

Kristall med
Chrome alum crystal

Many trivalent metals are capable of forming alums. The general form of an alum is XM(SO4)2·nH2O, where X is an alkali metal or ammonium, M is a trivalent metal, and n often is 12. The most important example is chrome alum, KCr(SO
4
)
2
·12H
2
O
, a dark violet crystalline double sulfate of chromium and potassium, was used in tanning.

In general, alums are formed more easily when the alkali metal atom is larger. This rule was first stated by Locke in 1902,[23] who found that if a trivalent metal does not form a caesium alum, it neither will form an alum with any other alkali metal or with ammonium.

Selenate-containing alums

Selenium or selenate alums are also known that contain selenium in place of sulfur in the sulfate anion, making selenate (SeO2−
4
) instead.[24] They are strong oxidizing agents.

Mixed alums

Chromium Alum - top view
Alum crystal with small amount of chrome alum to give a slight violet color

In some cases, solid solutions of alums with different monovalent and trivalent cations may occur.

Other hydrates

In addition to the alums, which are dodecahydrates, double sulfates and selenates of univalent and trivalent cations occur with other degrees of hydration. These materials may also be referred to as alums, including the undecahydrates such as mendozite and kalinite, hexahydrates such as guanidinium (CH
6
N+
3
) and dimethylammonium ((CH
3
)
2
NH+
2
) "alums", tetrahydrates such as goldichite, monohydrates such as thallium plutonium sulfate and anhydrous alums (yavapaiites). These classes include differing, but overlapping, combinations of ions.

Other double sulfates

A pseudo alum is a double sulfate of the typical formula ASO
4
·B
2
(SO
4
)
3
·22H
2
O
, where A is a divalent metal ion, such as cobalt (wupatkiite), manganese (apjohnite), magnesium (pickingerite) or iron (halotrichite or feather alum), and B is a trivalent metal ion.[25]

Double sulfates with the general formula A
2
SO
4
·B
2
(SO
4
)
3
·24H
2
O
are also known, where A is a monovalent cation such as sodium, potassium, rubidium, caesium, or thallium(I), or a compound cation such as ammonium (NH+
4
), methylammonium (CH
3
NH+
3
), hydroxylammonium (HONH+
3
) or hydrazinium (N
2
H+
5
), B is a trivalent metal ion, such as aluminium, chromium, titanium, manganese, vanadium, iron(III), cobalt(III), gallium, molybdenum, indium, ruthenium, rhodium, or iridium.[26] Analogous selenates also occur. The possible combinations of univalent cation, trivalent cation, and anion depends on the sizes of the ions.

A Tutton salt is a double sulfate of the typical formula A
2
SO
4
·BSO
4
·6H
2
O
, where A is a univalent cation, and B a divalent metal ion.

Double sulfates of the composition A
2
SO
4
·2BSO
4
, where A is a univalent cation and B is a divalent metal ion are referred to as langbeinites, after the prototypical potassium magnesium sulfate.

See also

References

  1. ^ a b Austin, George T. (1984). Shreve's Chemical process industries (5th ed.). New York: McGraw-Hill. p. 357. ISBN 9780070571471.
  2. ^ "Alhydrogel | Alum vaccine adjuvant for research | InvivoGen". www.invivogen.com. Retrieved 2018-06-08.
  3. ^ Picon, M.; et al. (2005). "L'alun des oasis occidentales d'Egypte: researches sur terrain et recherches en laboratoire". In Borgard P.; et al. L'alun de Mediterranée.
  4. ^ Archontidou, A. (2005). "Un atelier de preparation de l'alun a partir de l'alunite dans l'isle de Lesbos". In Borgard P.; et al. L'alun de Mediterranée.
  5. ^ Hall, A. J.; Photos-Jones, E. (2005). "The nature of Melian alumen and its potential for exploitation in Antiquity". In Borgard P.; et al. L'alun de Mediterranée.
  6. ^ a b c Pliny the Elder (77 CE). "Alumen, and the several varieties of it; Thirty-eight remedies". Naturalis Historia [Natural History]. Perseus Digital Library (in Latin and English). Tufts University. book 35, chapter 52. Retrieved 27 December 2011. Check date values in: |year= (help)
  7. ^ Dioscorides (c. 60 CE). De Materia Medica [On Medical Materials] (in Greek and Latin). book 5, chapter 123. Check date values in: |year= (help)
  8. ^ Chisholm 1911, pp. 766-767.
  9. ^ George Ernst Stahl (1703), Specimen Beccherianum. Johann Ludwig Gleditsch, Leipzig. From p. 269: "CVII. Vitriolum, Creta præcipitari potest, ut omissa metallica sua substantia, aluminosum evadat." (107. Sulfuric acid [and] chalk can [form a] precipitate, as its liberated metallic substance, alum, escapes.)
  10. ^ George Ernst Stahl (1723), Ausführliche Betrachtung und zulänglicher Beweiss von den Saltzen, daß diesselbe aus einer zarten Erde, mit Wasser innig verbunden, bestehen (Detailed treatment and adequate proof of salts, that they consist of a subtile earth intimately bound with water) Wäysenhaus, Halle From p. 305: " … wie aus Kreide und Vitriole-Spiritu, ein rechter Alaun erwächset: … " ( … as from chalk and sulfuric acid, a real alum arises: … )
  11. ^ Johann Heinrich Pott (1746), Chymische Untersuchungen, welche fürnehmlich von der Lithogeognosia oder Erkäntniß und Bearbeitung der gemeinen einfacheren Steine und Erden ingleichen von Feuer und Licht handeln [Chemical investigations which primarily concern lithogeognosia or knowledge and processing of common simple rocks and earths as well as fire and light]. Potsdam, (Germany), Christian Friedrich Voss, volume 1, p. 32. From p. 32:] "Concentrirt man hingegen diese solution gelinde, und läßt sie crystallisiren, so schiessen harte und mercklich adstringente und hinter her etwas süßliche crystallen an, die allen Umständen nach in der Haupt-Sach nichts anders sind als ein formaler Alaun. Diese Entdeckung ist in der physicalischen Chymie von Wichtigkeit. Man hat bishero geglaubt, die Grund-Erde des Alauns sey eine in acido Vitrioli solvirte kalckige … Erde, … " (On the other hand, if one gently concentrates this solution, and lets it crystallize, then there precipitate hard, noticeably astringent crystals with a somewhat sweet aftertaste, which in all circumstances are mainly nothing other than a form of alum. This discovery is of importance to chemistry. One had hitherto believed [that] the fundamental earth of alum is a calcareous … earth dissolved in sulfuric acid, … )
  12. ^ Andreas Sigismund Marggraf (1754), "Expériences faites sur la terre d'alun" (Experiments made on the earth of alum), Mémoires de l'Académie des sciences et belles-lettres de Berlin, pp. 41-66.
  13. ^ a b c d Chisholm 1911, p. 766.
  14. ^ Marggraf (1754) "Expériences qui concernent la régénération de l'alun de sa propre terre, l'après avoir séparé par l'acide vitriolique ; avec quelques compositions artificielles de l'alun par moyen d'autres terres, et dudit acide" (Experiments that concern the regeneration of alum from its own earth, after having separating it by sulfuric acid ; with some artificial compounds of alum by means of other earths and the aforesaid acid), Mémoires de l'Académie des sciences et belles-lettres de Berlin, pp. 31-40.
  15. ^ Torbern Bergman (1767), "IX. De confectione Aluminis". In Opuscula physica et chemica, I. G. Müller, Leipzig, 1788), volume 1. On pp. 306-307, after noting that Marggraf had noticed that potash caused alum to crystallize from a solution of alumina and sulfuric acid, Bergman adds "Notatu quoque dignum est, quod hoc cristallisationis obstaculum alcali volatili aeque tollatur, non vero alkali minerali et calce." (It is significant as well that by [use of] the volatile alkali [i.e., ammonia] this obstacle to crystallization is similarly removed, but not [in the cases of] mineral alkali [i.e., sodium carbonate] and lime.)
  16. ^ Martin Heinrich Klaproth (1797), Beiträge zur Chemischen Kenntniss Der Mineralkörper (Contributions to [our] chemical knowledge of mineral substances). Decker and Co., Posen, and Heinrich August Rottmann, Berlin; pp. 45-46 and p. 193.
  17. ^ Martin Heinrich Klaproth (1801), Analytical Essays Towards Promoting the Chemical Knowledge of Mineral Substances. T. Cadell, Jr. & W. Davies, London. His finding of potassium in leucite appears on pp. 353-354.: "On the contrary, I was surprised in an unexpected manner, by discovering in it another constituent part, consisting of a substance, the existence of which, certainly, no one person would have conjectured within the limits of the mineral kingdom … This constituent part of leucite … is no other than pot-ash, which, hitherto, has been thought exclusively to belong to the vegetable kingdom, and has, on this account, been called VEGETABLE ALKALI. — This discovery, which I think of great importance, cannot fail to occasion considerable changes in the systems of natural history, … .". The discovery of potassium in lepidolite is mentioned on p. 472.
  18. ^ Vauquelin (1797) "Sur la nature de l'Alun du commerce, sur l'existence de la potasse dans ce sel, et sur diverses combinaisons simples ou triples de l'alumine avec l'acide sulfurique". In Annales de Chimie et de Physique, 1st series, volume 22, pages 258-279.
  19. ^ Jean-Antoine Chaptal (1797), "Comparée des quatre principales sortes d'Alun connues dans le commerce; et Observations sur leur nature et leur usage". In Annales de Chimie et de Physique, 1st series, volume 22, pages 280-296.
  20. ^ Otto Helmboldt, L. Keith Hudson, Chanakya Misra, Karl Wefers, Wolfgang Heck, Hans Stark, Max Danner, Norbert Rösch "Aluminum Compounds, Inorganic" in Ullmann's Encyclopedia of Industrial Chemistry 2007, Wiley-VCH, Weinheim.doi:10.1002/14356007.a01_527.pub2
  21. ^ a b Chisholm 1911, p. 767.
  22. ^ Nancy Lee (6 August 2013). The Complete Idiot's Guide to Making Metal Jewelry. DK. p. 114. ISBN 978-1-61564-370-7.
  23. ^ J. Locke (1902). "On some double suphates of thallic thallium and caesium". American Chemical Journal. 27: 281.
  24. ^ Bell, Chichester H. (1887). Summarizing original article by C. Fabre (Compt. rend., 105, 114–115). "Selenium Alums". Abstracts of chemical papers. Inorganic chemistry. Journal of the Chemical Society. LII. Part II.: 1014. Retrieved 2017-08-19.
  25. ^ Halotrichite on Mindat.org
  26. ^ Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford: Butterworth-Heinemann. ISBN 0-7506-3365-4.

External links

  • Media related to Alum at Wikimedia Commons
2007 Alum Rock earthquake

The 2007 Alum Rock earthquake occurred on October 30 at 8:04 p.m. Pacific Daylight Time in Alum Rock Park in San Jose, California. It measured 5.6 on the moment magnitude scale and had a maximum Mercalli intensity of VI (Strong). The event was then the largest in the San Francisco Bay Area since the 1989 Loma Prieta earthquake, which measured 6.9 on the moment magnitude scale, but was later surpassed by the 2014 South Napa earthquake. Ground shaking from the Alum Rock quake reached San Francisco and Oakland and other points further north. Sixty thousand felt reports existed far beyond Santa Rosa, as far north as Eugene, Oregon.

Adjuvant

An adjuvant is a pharmacological or immunological agent that modifies the effect of other agents. Adjuvants may be added to a vaccine to boost the immune response to produce more antibodies and longer-lasting immunity, thus minimizing the dose of antigen needed. Adjuvants may also be used to enhance the efficacy of a vaccine by helping to modify the immune response to particular types of immune system cells: for example, by activating T cells instead of antibody-secreting B cells depending on the purpose of the vaccine. Adjuvants are also used in the production of antibodies from immunized animals. There are different classes of adjuvants that can push immune response in different directions, but the most commonly used adjuvants include aluminum hydroxide and paraffin oil.

Alam Hajji Baqeri

Alam Hajji Baqeri (Persian: علم حاجي باقري‎, also Romanized as ‘Alam Ḩājjī Bāqerī, ‘Alam-e Ḩājjī Bāqer, ‘Alam-e Ḩājjī Bāqerī, and ‘Alam Ḩājī Bāqerī; also known as Alam-e Hājī Bāqer, Deh ‘Alam, and Deh Alum) is a village in Chupanan Rural District, Anarak District, Nain County, Isfahan Province, Iran. At the 2006 census, its existence was noted, but its population was not reported.

Alum Bay

Alum Bay is a bay near the westernmost point of the Isle of Wight, England, within close sight of the Needles rock formation. Of geological interest and a tourist attraction, the bay is noted for its multi-coloured sand cliffs. The waters and adjoining seabed form part of the Needles Marine Conservation Zone and the shore and heath above are part of the Headon Warren and West High Down Site of Special Scientific Interest.

Alum Creek, West Virginia

Alum Creek is a census-designated place (CDP) in Kanawha and Lincoln counties along the Coal River in the U.S. state of West Virginia. It had a population of 1,749 at the 2010 census.The community was named after nearby Alum Creek.

Alum Creek State Park

Alum Creek State Park is a 4,630-acre (1,870 ha) Ohio state park in Delaware County, Ohio, in the United States. Alum Creek Lake was constructed from 1970 to 1974 as part of the Flood Control Act of 1962. Alum Creek Dam was constructed on Alum Creek, a tributary of Big Walnut Creek, which drains into the Scioto River. Alum Creek Reservoir holds 3,387 acres (1,371 ha) of water and is open to fishing, boating, ice fishing, ice boating and swimming. The park is just north of the state capital of Columbus and contains the remnants of a settlement by freed slaves that arrived in Ohio from North Carolina.

Alum Rock, Birmingham

Alum Rock (known locally as "The Rock") is an inner-city suburb of Birmingham, England, located roughly 2 miles east of Birmingham city centre. The area is officially a division of Saltley. Rockwood Academy is a secondary school located in the area.

Alum Rock, San Jose

Alum Rock () is a neighborhood and census-designated place in San Jose, California, in East San Jose. The CDP, which excludes all annexed areas, had a population of 15,536 at the 2010 census. It is home to Alum Rock Park, the oldest municipal park in California and one of the largest in the United States.

Formerly a separate town, much of the community is unincorporated surrounded by incorporated San Jose; neighborhoods between White Road and Capitol Avenue are part of a city/county agreement for annexation. James Lick High School, Mt. Pleasant High School, and William C. Overfelt High School (which are part of the East Side Union High School District), Joseph George Middle School, Ocala Middle School, and other schools in the Alum Rock Union School District serve the neighborhood. Near the center of the community is a small neighborhood commercial strip along Alum Rock Avenue at White Road.

Alum Rock Park

Alum Rock Park, in the Alum Rock district of San Jose, California, is California's oldest municipal park, founded in 1872. Located in a valley in the Diablo Range foothills on the east side of San Jose, the 720 acre (2.9 km2) park offers 13 miles (21 km) of trails, varying from fairly level along Penitencia Creek to sharp switchbacks climbing to the ridges to the South Rim Trail and the North Rim Trail. The narrow floor of the valley includes a visitor center, a small museum/animal rehab facility, picnic areas, playgrounds, lawns, sand volleyball pits, mineral springs, lush plant life, woodlands, creek play opportunities, and occasional group camping.

The ridge trails offer views of Santa Clara Valley and of the valley in which the park is located. Some trails in the park are a part of the Bay Area Ridge Trail; the Todd Quick trail connects with the Santa Clara Valley Open Space Authority's 1,600-acre Sierra Vista Open Space Preserve.

Equestrians and mountain bikers have access to some of the park's trails, while others are reserved for hikers only. Cross-country teams from high schools around North San Jose, such as James Lick High School and Independence High, use the park for training and for meets.

Alum Rock Transit Center

Alum Rock Transit Center is a light rail and bus station operated by Santa Clara Valley Transportation Authority (VTA). This station is served by VTA's Alum Rock–Santa Teresa line.

The station was opened in 2004 as part of VTA's Capitol light rail extension.

Alum Rock station

Alum Rock/28th Street station is a proposed underground Bay Area Rapid Transit station in the Little Portugal neighborhood of San Jose, California. It would be located north of East Santa Clara Street between North 28th Street and U.S. Route 101, behind Five Wounds Portuguese National Church. Preceded by the Berryessa/North San Jose BART station, it would be the first station of the Phase II portion of the Silicon Valley BART extension. The station would have direct service to Santa Clara, Richmond, and San Francisco/Daly City. The proposed station is named after Alum Rock, a neighborhood to the northeast.

Alum Rock–Santa Teresa (VTA)

Alum Rock–Santa Teresa is a light rail route operated by Santa Clara Valley Transportation Authority (VTA). The Alum Rock–Santa Teresa route is one of three existing VTA light rail routes. The other two light rail routes are the Mountain View–Winchester line and the Ohlone/Chynoweth–Almaden line. On system maps, the line is represented as the Blue Line, however VTA primarily uses its name and Line 901 in their documents.

Alum Springs, West Virginia

Alum Springs is a ghost town in Greenbrier County, West Virginia, United States. Alum Springs was 2 miles (3.2 km) east of Maxwelton. Alum Springs appeared on USGS maps as late as 1923.

Aluminium sulfate

Aluminium sulfate is a chemical compound with the formula Al2(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 and waste water treatment plants, and also in paper manufacturing.

The anhydrous form occurs naturally as a rare mineral millosevichite, found e.g. 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(SO4)2·12H2O, where X is a monovalent cation such as potassium or ammonium.

Ammonium aluminium sulfate

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.

Hex key

A hex key, Allen wrench or Allen key, is a tool used to drive bolts and screws with hexagonal sockets in their heads.

The Allen name is a registered trademark, originated by the Allen Manufacturing Company of Hartford, Connecticut circa 1910, and currently owned by Apex Tool Group, LLC. Its genericised use is discouraged by this company. The standard generic name used in catalogues and published books and journals is "hex key".

Potassium alum

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 cubic structure 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.Potassium alum is commonly used in water purification, leather tanning, dyeing, fireproof textiles, and baking powder as E number E522. It also has cosmetic uses as a deodorant, as an aftershave treatment and as a styptic for minor bleeding from shaving.

Santa Clara Valley Transportation Authority light rail

VTA Light Rail (reporting mark SCCT) is a light rail system serving San Jose, California and its suburbs in Silicon Valley. It is operated by the Santa Clara Valley Transportation Authority, or VTA, and consists of 42.2 miles (67.9 km) of network comprising two main lines and a spur line on standard gauge tracks. Originally opened in 1987, the light rail system has gradually expanded since then, and currently has 62 light rail stations in operation on the three lines. VTA operates a fleet of 99 Kinki Sharyo Low Floor Light Rail Vehicles (LFLRV) to service its passengers. The system's average weekday daily ridership as of Q3 2018 is 28,800 passengers; the greatest daily average recorded over a month was 37,536 in June 2008.

Sodium aluminium sulfate

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.

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.