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矾（fán）是各种金属的硫酸盐水合结晶，有时也指一大类通式为A2SO4·B2(SO4)3·24H2O（即AB(SO4)2·12H2O）的水合硫酸盐复盐（英文：Alum）。明矾（钾铝矾，KAl(SO4)2·12H2O）是最常见的矾。

大块矾晶体

[1] 当其中的三价阳离子为铝离子时，该矾根据其一价阳离子命名；反之，当其中的一价阳离子为钾离子时，该矾根据其三价阳离子命名。

化学性质

矾被用于一系列工业用途，这是由于它们具有以下一些性质：它们易溶于水，并有一种淡淡的甜味；水溶液显酸性并且能结晶为规则的八面体。当加热时它们首先会液化，然后才失去结晶水，表面起泡，最终只留下无水粉末。它们的溶液显酸性，并多具有凝血功能（胶体聚沉原理）。

用途

工业

Potassium alum is the common alum of commerce, although soda alum, ferric alum, and ammonium alum are manufactured.

Alum has been used at least since Roman times for purification of drinking water[2] and industrial process water. Between 30 and 40 ppm of alum[2][3] for household wastewater, often more for industrial wastewater,[4] is added to the water so that the negatively charged colloidal particles clump together into "flocs", which then float to the top of the liquid, settle to the bottom of the liquid, or can be more easily filtered from the liquid, prior to further filtration and disinfection of the water.

Alum solution has the property of dissolving steels while not affecting aluminium or base metals, and can be used to recover workpieces made in these metals with broken toolbits lodged inside them.[5] As considerable expense and/or effort may have gone into machining a specialist part, this can be a worthwhile excercise.

化妆品

在印度出售的作为止血剂的矾块
  • Alum in block form (usually potassium alum) can be used as a blood coagulant.[6]
  • Styptic pencils containing aluminium sulfate or potassium aluminium sulfate are used as astringents to prevent bleeding from small shaving cuts.
  • Alum may be used in depilatory waxes used for the removal of body hair or applied to freshly waxed skin as a soothing agent.
  • Alum's antiperspirant and antibacterial properties[7][8] contribute to its traditional use as an underarm deodorant.[9] It has been used for this purpose in Europe, Mexico, Thailand (where it is called sarn-som), throughout Asia and in the Philippines (where it is called tawas). Today, potassium or ammonium alum is sold commercially for this purpose as a "deodorant crystal", often in a protective plastic case.[10]

烹调

  • Alum powder, found in the spice section of many grocery stores, may be used in pickling recipes as a preservative to maintain fruit and vegetable crispness.
  • Alum is used as the acidic component of some commercial baking powders.
  • Alum was used by bakers in England during the 1800s to make bread whiter.[11] The Sale of Food and Drugs Act 1875 prevented this and other adulterations.[12]
  • In Nigeria, it is used in the removal of snail slime before cooking

阻燃剂

  • Solutions containing alum may be used to treat cloth, wood, and paper materials to increase their resistance to fire.
  • Alum is also used in fire extinguishers to smother chemical and oil fires.[來源請求]

化学絮凝剂

  • Alum is used to clarify water by neutralizing the electrical double layer surrounding very fine suspended particles, allowing them to flocculate (stick together). After flocculation, the particles will be large enough to settle and can be removed.
  • Alum may be used to increase the viscosity of a ceramic glaze suspension; this makes the glaze more readily adherent and slows its rate of sedimentation.
  • Alum is an ingredient in some recipes for homemade modeling compounds intended for use by children. (These are often called "play clay" or "play dough" for their similarity to "Play-Doh", a trademarked product marketed by American toy manufacturer Hasbro).[來源請求]

医药

  • Alum has been used as an adjuvant to increase the efficacy of vaccines since the 1920s. See adjuvant for details on the mechanism.
  • Alum can be used as a coagulant to help stop internal bleeding of organs. Its mechanism of action is believed to be due the same preservative properties for which it is used in food storage, by causing shrinkage of the pores and decreasing humoral secretions.[來源請求]

生产

以明矾石为原料

In order to obtain alum from alunite, it is calcined and then exposed to the action of air for a considerable time. During this exposure it is kept continually moistened with water, so that it ultimately falls to a very fine powder. This powder is then lixiviated with hot water and sulfuric acid, the liquor decanted, and the alum allowed to crystallize. The alum schists employed in the manufacture of alum 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 ferric sulfate may separate), and is then evaporated until ferrous 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, decanted from any sediment, and finally mixed with the calculated quantity of potassium sulfate, well agitated, and the alum is thrown down as a finely divided precipitate of alum meal. If much iron should be present in the shale then it is preferable to use potassium chloride in place of potassium sulfate.

以铝土矿等含铝矿物为原料

当使用粘土或铝土矿为原料时，原料会被小心地煅烧，再使用逐渐加热至沸腾的硫酸进行酸浸。此后，这一混合物将被静置一段时间以得到清液，再与酸化了的硫酸钾溶液按比例混合并结晶。

当使用冰晶石为原料时，它会被与碳酸钙混合在一起并加热，从而生成铝酸钠。生成的铝酸钠用水浸方式提取，氟化钙和其他杂质则留在烧渣中。然后，通过向清液内通入二氧化碳或加入碳酸氢钠的方式使铝元素以氢氧化铝的形式沉淀下来。最后，沉淀会被硫酸溶解，并加入适量的硫酸钾以析出晶体。

种类

许多三价金属都能够形成矾。矾的通式为AMIII(SO4)2·nH2O，其中A是碱金属离子或铵根离子，MIII是一个三价离子，结晶水数n通常是12。一般来说，对应的碱金属离子越大，矾越易生成。这一规则最早是由Locke在1902年提出[13]的，因为他发现如果一个三价离子不能与铯离子形成矾，那么它就不会与其它任意一种碱金属离子或铵根离子形成矾。

Double sulfates with the general formula A
2SO
4·B
2(SO
4)
3·24H
2O, are 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
3NH+
3), hydroxylammonium (HONH+
3) or hydrazinium (N
2H+
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.[14] Analogous selenates also occur. The specific combinations of univalent cation, trivalent cation, and anion depends on the sizes of the ions. For example, unlike the other alkali metals the smallest one, lithium, does not form alums, and there is only one known sodium alum. In some cases, solid solutions of alums occur.

矾可以以三种不同晶型结晶，它们分别被称为α-矾，β-矾和γ矾。

钾明矾

钾明矾晶体
主条目：钾明矾

硫酸铝钾（KAl(SO4)2·12H2O)，即常见的明矾，有着絮凝剂、媒染剂、止血剂、防腐剂等多种用途。A common method of producing potash alum is leaching of alumina from bauxite, which is then reacted with potassium sulfate.

钠明矾

Soda alum, NaAl(SO
4)
2·12H
2O, mainly occurs in nature as the mineral mendozite. It is very soluble in water, and is extremely difficult to purify. In the preparation of this salt, it is preferable to mix the component solutions in the cold, and to evaporate them at a temperature not exceeding 60 °C. 100 parts of water dissolve 110 parts of sodium alum at 0 °C, and 51 parts at 16 °C. Soda alum is used in the acidulent of food as well as in the manufacture of baking powder.

铵明矾

主条目：铵明矾

Ammonium alum, NH
4Al(SO
4)
2·12H
2O, a white crystalline double sulfate of aluminium, is used in water purification, in vegetable glues, in porcelain cements, in deodorants (though potassium alum is more commonly used), in tanning, dyeing and in fireproofing textiles.

铬明矾

这块矾中含有的少量铬离子使其染上了紫色

铬明矾，KCr(SO4)2·12H2O，是一种铬与钾的硫酸复盐，晶体呈紫色。它可用于鞣制、媒染。

含硒矾

在这类矾中，硒原子取代了硫原子的位置，使硫酸根变成了硒酸根（SeO42-）。由于硒酸根的特性，它们是强氧化剂。

硫酸铝

主条目：硫酸铝

硫酸铝，有时又被称为造纸矾（Papermaker's Alum），是一种在工业上常被误称为矾的物质。 Although reference to this compound as alum is quite common in industrial communication, it is not regarded as technically correct. Its properties are quite different from those of the set of alums described above. Most industrial flocculation done with alum is actually aluminium sulfate.

溶解度

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.

在温度为T时，100份的水可溶解的量为：
T 铵明矾 钾明矾 铷明矾 铯明矾
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    

参见

参考资料

  1. ^ Austin, George T. Shreve's Chemical process industries. 5th ed. New York: McGraw-Hill. 1984: 357. ISBN 9780070571471. 
  2. ^ 2.0 2.1 Samuel D. Faust, Osman M. Aly. Chemistry of water treatment 2nd ed. Chelsea, MI: Ann Arbor Press. 1999. ISBN 9781575040110. 
  3. ^ Bratby, John. Coagulation and flocculation in water and wastewater treatment 2. ed. London: IWA Publ. 2006. ISBN 9781843391067. 
  4. ^ Rice, J. K. The use of organic flocculants and flocculating aids in the treatment of industrial water and industrial waste water. Symposium on Industrial Water and Industrial Waste Water (ASTM International). June 1957, (207): 41–51. 
  5. ^ http://www.model-engineer.co.uk/forums/postings.asp?th=91442&p=82#PostTop
  6. ^ [1] A Woman Rice Planter: Electronic Edition. Pringle, Elizabeth Waties Allston (pseud. Pennington, Patience),(1845-1921) p.18
  7. ^ Kanlayavattanakul, M.; Lourith, N. Body malodours and their topical treatment agents. International Journal of Cosmetic Science. 1 August 2011, 33 (4): 298–311. PMID 21401651. doi:10.1111/j.1468-2494.2011.00649.x. 
  8. ^ Aguilar, T. N.; Blaug, S.M.; Zopf, L.C. A study of the antibacterial activity of some complex aluminum salts. Journal of the American Pharmaceutical Association. American Pharmaceutical Association. July 1956, 45 (7): 498–500. PMID 13345689. 
  9. ^ Alumen, and the Several Varieties of it; Thirty-eight Remedies., Pliny the Elder, The Natural History, book 35, chapter 52; on the Perseus Digital Library at Tufts University. Last accessed 27 December 2011.
  10. ^ US patent 5399364,Francis Verdan,「Cosmetic assembly defined by encased stick of alum」,发行于1995-05-21 
  11. ^ Church Pastoral-aid Society, London. Brown Bread. The Church of England magazine. January–June 1847, 22: 355. 
  12. ^ Hassall, Arthur Hill. Adulterations detected; or, Plain instructions for the discovery of frauds in food and medicine. 1857. 
  13. ^ J. Locke. On some double sulphates of thallic thallium and caesium. American Chemical journal. 1902, 27: 281. 
  14. ^ Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford: Butterworth-Heinemann. ISBN 0-7506-3365-4.

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