Aluminium hydroxide

From Wikipedia, the free encyclopedia - View original article

Aluminium hydroxide
Unit cell ball and stick model of aluminium hydroxide
Sample of aluminium hydroxide in a vial
Identifiers
CAS number21645-51-2 YesY
PubChem10176082 YesY
ChemSpider8351587 YesY
UNII5QB0T2IUN0 YesY
ChEBICHEBI:33130 YesY
ChEMBLCHEMBL1200706 N
RTECS numberBD0940000
ATC codeA02AB01,
A02AB02 (algeldrate)
Jmol-3D imagesImage 1
Properties
Molecular formulaAl(OH)3
Molar mass78.00 g/mol
AppearanceWhite amorphous powder
Density2.42 g/cm³, solid
Melting point300 °C (572 °F; 573 K)
Solubility in water0.0001 g/100 mL (20 °C)
Solubility product, Ksp3×10−34[1]
Solubilitysoluble in acids, alkalis, HCl, H2SO4
Acidity (pKa)>7
Thermochemistry
Std enthalpy of
formation
ΔfHo298
−1277 kJ·mol−1[2]
Hazards
MSDSExternal MSDS
EU classificationIrritant (I) Xi
R-phrasesR36 R37 R38
S-phrasesS26 S36
NFPA 704
Flash pointNon-flammable
Related compounds
Other anionsNone
Related compoundsSodium oxide,
aluminium oxide hydroxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references
 
Jump to: navigation, search
Aluminium hydroxide
Unit cell ball and stick model of aluminium hydroxide
Sample of aluminium hydroxide in a vial
Identifiers
CAS number21645-51-2 YesY
PubChem10176082 YesY
ChemSpider8351587 YesY
UNII5QB0T2IUN0 YesY
ChEBICHEBI:33130 YesY
ChEMBLCHEMBL1200706 N
RTECS numberBD0940000
ATC codeA02AB01,
A02AB02 (algeldrate)
Jmol-3D imagesImage 1
Properties
Molecular formulaAl(OH)3
Molar mass78.00 g/mol
AppearanceWhite amorphous powder
Density2.42 g/cm³, solid
Melting point300 °C (572 °F; 573 K)
Solubility in water0.0001 g/100 mL (20 °C)
Solubility product, Ksp3×10−34[1]
Solubilitysoluble in acids, alkalis, HCl, H2SO4
Acidity (pKa)>7
Thermochemistry
Std enthalpy of
formation
ΔfHo298
−1277 kJ·mol−1[2]
Hazards
MSDSExternal MSDS
EU classificationIrritant (I) Xi
R-phrasesR36 R37 R38
S-phrasesS26 S36
NFPA 704
Flash pointNon-flammable
Related compounds
Other anionsNone
Related compoundsSodium oxide,
aluminium oxide hydroxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Aluminium hydroxide, Al(OH)3, archaically called hydrate of alumina or alumina trihydrate (Al2O3·3H2O), is found in nature as the mineral gibbsite (also known as hydrargillite) and its three, much more rare polymorphs: bayerite, doyleite and nordstrandite. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide, Al2O3, differing only by loss of water. These compounds together are the major components of the aluminium ore bauxite. Freshly precipitated aluminium hydroxide forms gels, which is the basis for application of aluminium salts as flocculants in water purification. This gel crystallizes with time. Aluminium hydroxide gels can be dehydrated (e.g., using water-miscible non-aqueous solvents like ethanol) to form an amorphous aluminium hydroxide powder, which is readily soluble in acids. Aluminium hydroxide powder which has been heated to an elevated temperature under carefully controlled conditions is known as activated alumina and is used as a desiccant, an adsorbent, in gas purification, as a Claus catalyst support, water purification, and an adsorbent for the catalyst during the manufacture of polyethylene by the Sclairtech process.

Nomenclature[edit]

The naming for the different forms of aluminium hydroxide is ambiguous and there is no universal standard. All four polymorphisms have a chemical composition of aluminium trihydroxide (an aluminium atom attached to three hydroxide groups).[3]

Gibbsite is also known as hydrargillite, named after the Greek words for water (hydra) and clay (argylles). The first compound named hydrargillite was thought to be aluminium hydroxide, but was later found to be aluminium phosphate; despite this, both gibbsite and hydrargillite are used to refer to the same polymorphism of aluminium hydroxide, with gibbsite used most commonly in the United States and hydrargillite used more often in Europe. In 1930 it was referred to as α-alumina trihydrate to contrast it with bayerite which was called β-alumina trihydrate (the alpha and beta designations were used to differentiate the more- and less-common forms respectively). In 1957 a symposium on alumina nomenclature attempted to develop a universal standard, resulting in gibbsite being designated γ-Al(OH)3 and bayerite becoming α-Al(OH)3 and nordstrandite being designated Al(OH)3. Based on their crystallographic properties, a suggested nomenclature and designation is for gibbsite to be α-Al(OH)3, bayerite to be designated β-Al(OH)3 and both nordstrandite and doyleite are designated Al(OH)3. Under this designation, the α and β prefixes refer to hexagonal, close-packed structures and altered or dehydrated polymorphisms respectively, with no differentiation between nordstrandiate and doyleite.[3]

Properties[edit]

Gibbsite has a typical metal hydroxide structure with hydrogen bonds. It is built up of double layers of hydroxyl groups with aluminium ions occupying two-thirds of the octahedral holes between the two layers.[4]

Aluminium hydroxide is amphoteric. It dissolves in acid, forming [Al(H2O)6]3+ (hexaaquaaluminium) or its hydrolysis products. It also dissolves in strong alkali, forming [Al(OH)4] (tetrahydroxidoaluminate).

Polymorphism[edit]

Four polymorphs of aluminium hydroxide exist, all based on the common combination of one aluminium atom and three hydroxide molecules into different crystaline arrangements that determine the appearance and properties of the compound. The four combinations are:[3]

All polymorphs are composed of octahedral layers of aluminium hydroxide molecules with the aluminium atom in the centre and the hydroxyl groups on the sides, with hydrogen bonds holding the layers together. The polymorphisms vary in how the layers stack together, with the arrangements of the molecules and layers determined by the acidity, presence of ions (including salt) and the surface of the minerals the substance forms on. Under most conditions gibbsite is the most chemically stable form of aluminium hydroxide. All forms of Al(OH)3 crystals are hexagonal.[3]

Production[edit]

Virtually all the aluminium hydroxide used commercially is manufactured by the Bayer process[5] which involves dissolving bauxite in sodium hydroxide at temperatures up to 270°C. The remaining solids, which is a red mud, is separated and aluminium oxide is precipitated from the remaining solution. This red mud is damaging to the environment and highly toxic. It is usually stored in large artificial lakes, this is what led to the Ajka alumina plant accident in 2010 in Hungary, killing nine people and injuring 122. The dam holding back the red mud burst allowing it to contaminate large areas of land and waterways.[6] The aluminium oxide that is produced can be converted to aluminium hydroxide through reaction with water.

Uses[edit]

Annual production is some 100 million tonnes,[citation needed] over 90% of which is converted to aluminium oxide[citation needed] (alumina) that is used in the manufacture of aluminium metal.[citation needed]

The major other uses of aluminium hydroxide is as a feedstock for the manufacture of other aluminium compounds: specialty calcined aluminas, aluminium sulfate, polyaluminium chloride, aluminium chloride, zeolites, sodium aluminate, activated alumina, aluminium nitrate.[citation needed]

Fire retardant[edit]

Aluminium hydroxide also finds use as a fire retardant filler for polymer applications in a similar way to magnesium hydroxide and mixtures of huntite and hydromagnesite.[7][8][9][10][11] It decomposes at about 180 °C, absorbing a considerable amount of heat in the process and giving off water vapour. In addition to behaving as a fire retardant, it is very effective as a smoke suppressant in a wide range of polymers, most especially in polyesters, acrylics, ethylene vinyl acetate, epoxies, PVC and rubber.

Pharmaceutical[edit]

This compound is used as an antacid under names such as Alu-Cap, Aludrox, Gaviscon or Pepsamar. The hydroxide reacts with excess acid in the stomach, reducing its acidity.[12] This decrease of acidity of the contents of the stomach may in turn help to relieve the symptoms of ulcers, heartburn or dyspepsia. It can also cause constipation and is therefore often used with magnesium hydroxide or magnesium carbonate, which have counterbalancing laxative effects. This compound is also used to control phosphate (phosphorus) levels in the blood of people suffering from kidney failure.

Precipitated aluminium hydroxide is included as an adjuvant in some vaccines (e.g. anthrax vaccine). One of the well-known brands of aluminium hydroxide adjuvant is Alhydrogel, made by Brenntag. Since it absorbs protein well, it also functions to stabilize vaccines by preventing the proteins in the vaccine from precipitating or sticking to the walls of the container during storage. Aluminium hydroxide is often mis-called "alum" even by researchers; however, "alum" properly refers to aluminium potassium sulfate (alum).[citation needed] The aluminium hydroxide causes adsorption of antigens made of proteins, which slows the release of the antigen from the injection site (the "depot effect"), as well as causing a nonspecific irritation to the immune system.[13] Vaccine formulations containing aluminium hydroxide stimulates the immune system by inducing the release of uric acid, an immunological danger signal. This strongly attracts certain types of monocytes which differentiate into dendritic cells. The dendritic cells pick up the antigen, carry it to lymph nodes, and stimulate T cells and B cells.[14] It appears to contribute to induction of a good Th2 response, so is useful for immunizing against pathogens that are blocked by antibodies. However, it has little capacity to stimulate cellular (Th1) immune responses, important for protection against many pathogens,[15] nor is it useful when the antigen is peptide-based.[13]

Potential adverse effects[edit]

In the 1960s and 1970s it was speculated that aluminium was related to various neurological disorders including Alzheimer's disease.[16][17] Since then, multiple epidemiological studies have found no connection between exposure to aluminium and neurological disorders.[18][19][20]

The pathological persistence of aluminium hydroxide used in some vaccines has also been associated with macrophagic myofasciitis,[21] a rare muscle disease.

References[edit]

  1. ^ http://www.ktf-split.hr/periodni/en/abc/kpt.html
  2. ^ Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. ISBN 0-618-94690-X. 
  3. ^ a b c d Karamalidis, AK; Dzombak DA (2010). Surface Complexation Modeling: Gibbsite. John Wiley & Sons. pp. 15–17. ISBN 0-470-58768-7. 
  4. ^ Wells, A.F. (1975), Structural Inorganic Chemistry (4th ed.), Oxford: Clarendon Press 
  5. ^ Hind, AR; Bhargava SK; Grocott SC (1999). "The Surface Chemistry of Bayer Process Solids: A Review". Colloids Surf Physiochem Eng Aspects 146: 359–74. 
  6. ^ "Hungary Battles to Stem Torrent of Toxic Sludge". BBC News Website. 5 October 2010. 
  7. ^ Hollingbery, LA; Hull TR (2010). "The Fire Retardant Behaviour of Huntite and Hydromagnesite - A Review". Polymer Degradation and Stability 95: 2213–2225. doi:10.1016/j.polymdegradstab.2010.08.019. 
  8. ^ Hollingbery, LA; Hull TR (2010). "The Thermal Decomposition of Huntite and Hydromagnesite - A Review". Thermochimica Acta 509: 1–11. doi:10.1016/j.tca.2010.06.012. 
  9. ^ Hollingbery, LA; Hull TR (2012). "The Fire Retardant Effects of Huntite in Natural Mixtures with Hydromagnesite". Polymer Degradation and Stability 97: 504–512. doi:10.1016/j.polymdegradstab.2012.01.024. 
  10. ^ Hollingbery, LA; Hull TR (2012). "The Thermal Decomposition of Natural Mixtures of Huntite and Hydromagnesite". Thermochimica Acta 528: 45–52. doi:10.1016/j.tca.2011.11.002. 
  11. ^ Hull, TR; Witkowski A; Hollingbery LA (2011). "Fire Retardant Action of Mineral Fillers". Polymer Degradation and Stability 96: 1462–1469. doi:10.1016/j.polymdegradstab.2011.05.006. 
  12. ^ Galbraith, A; Bullock, S; Manias, E. Hunt, B. & Richards, A. (1999). Fundamentals of pharmacology: a text for nurses and health professionals. Harlow: Pearson. p. 482. 
  13. ^ a b Cranage, MP; Robinson A (2003). Robinson A; Hudson MJ; Cranage MP, ed. Vaccine Protocols - Volume 87 of Methods in Molecular Medicine Biomed Protocols (2nd ed.). Springer. pp. 176. ISBN 1-59259-399-2. 
  14. ^ Kool, M; Soullié T; van Nimwegen M; Willart MA; Muskens F; Jung S; Hoogsteden HC; Hammad H; Lambrecht BN (2008-03-24). "T-helper 1 and T-helper 2 adjuvants induce distinct differences in the magnitude, quality and kinetics of the early inflammatory response at the site of injection". J Exp Med 205 (4): 869–82. doi:10.1111/j.1365-2567.2009.03164.x. PMC 2807488. PMID 18362170. 
  15. ^ Petrovsky N, Aguilar JC. (2004). "Vaccine adjuvants: current state and future trends". Immunol Cell Biol. 82 (5): 488–96. doi:10.1111/j.0818-9641.2004.01272.x. PMID 15479434. 
  16. ^ "Alzheimer's Myth's". Alzheimer's Association. Retrieved 2012-07-29. 
  17. ^ Khan, A (2008-09-01). "Aluminium and Alzheimer's disease". Alzheimer's Society. Retrieved 2012-03-08. 
  18. ^ Rondeau V (2002). "A review of epidemiologic studies on aluminum and silica in relation to Alzheimer's disease and associated disorders". Rev Environ Health 17 (2): 107–21. doi:10.1515/REVEH.2002.17.2.107. PMID 12222737. 
  19. ^ Martyn CN, Coggon DN, Inskip H, Lacey RF, Young WF (May 1997). "Aluminum concentrations in drinking water and risk of Alzheimer's disease". Epidemiology 8 (3): 281–6. doi:10.1097/00001648-199705000-00009. PMID 9115023. 
  20. ^ Graves AB, Rosner D, Echeverria D, Mortimer JA, Larson EB (September 1998). "Occupational exposures to solvents and aluminium and estimated risk of Alzheimer's disease". Occup Environ Med 55 (9): 627–33. doi:10.1136/oem.55.9.627. PMC 1757634. PMID 9861186. 
  21. ^ Central nervous system disease in patients with macrophagic myofasciitis

External links[edit]