 | |
| Names | |
|---|---|
| IUPAC name Aluminium sulfate | |
Other names
| |
| Identifiers | |
| |
3D model (JSmol) | |
| ChemSpider |
|
| ECHA InfoCard | 100.030.110 |
| EC Number |
|
| E number | E520(acidity regulators, ...) |
| RTECS number |
|
| UNII |
|
| |
| |
| Properties | |
| Al2(SO4)3 | |
| Molar mass | 342.15 g/mol (anhydrous) 666.44 g/mol (octadecahydrate) |
| Appearance | white 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 inalcohol, dilute mineralacids |
| Acidity (pKa) | 3.3–3.6 |
| −93.0×10−6 cm3/mol | |
Refractive index (nD) | 1.47[1] |
| Structure | |
| monoclinic (hydrate) | |
| Thermochemistry | |
Std enthalpy of formation(ΔfH⦵298) | −3440 kJ/mol |
| Hazards | |
| NFPA 704 (fire diamond) | |
| NIOSH (US health exposure limits): | |
PEL (Permissible) | none[2] |
REL (Recommended) | 2 mg/m3[2] |
IDLH (Immediate danger) | N.D.[2] |
| Related compounds | |
Othercations | Gallium sulfate Magnesium sulfate |
Related compounds | SeeAlum |
| Supplementary data page | |
| Aluminium sulfate (data page) | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Aluminium sulfate is a salt with theformulaAl2(SO4)3. It is soluble in water and is mainly used as acoagulating agent (promoting particle collision by neutralizing charge) in the purification of drinking water[3][4] andwastewater treatment plants, and also in paper manufacturing.
The anhydrous form occurs naturally as a raremineralmillosevichite, 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 differenthydrates, of which the hexadecahydrateAl2(SO4)3·16H2O and octadecahydrateAl2(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 mineralalunogen.
Aluminium sulfate is sometimes calledalum orpapermaker's alum in certain industries. However, the name "alum" is more commonly and properly used for any double sulfate salt with the generic formulaXAl(SO4)2·12H2O, whereX is amonovalentcation such aspotassium orammonium.[5]
Aluminium sulfate may be made by addingaluminium hydroxide,Al(OH)3, tosulfuric acid,H2SO4:
or by heating aluminium in a sulfuric acid solution:
The alumschists employed in the manufacture of aluminium sulfate are mixtures ofiron pyrite,aluminium silicate and variousbituminous substances, and are found in upperBavaria,Bohemia,Belgium, andScotland. These are either roasted or exposed to theweathering 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 ofspecific gravity 1.16 is prepared. This solution is allowed to stand for some time (in order that anycalcium sulfate and basiciron(III) sulfate may separate), and is then evaporated untiliron(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]
In the preparation of aluminium sulfate fromclays or frombauxite, the material is gentlycalcined, 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 isexothermic. It is allowed to stand for some time, and the clear solution is drawn off.
Whencryolite is used as the ore, it is mixed withcalcium carbonate and heated. By this means,sodium aluminate is formed; it is then extracted with water andprecipitated either bysodium bicarbonate or by passing a current ofcarbon dioxide through the solution. The precipitate is then dissolved in sulfuric acid.[6]
Aluminium sulfate is sometimes used in the human food industry as a firming agent, where it takes onE numberE520, and in animal feed as abactericide. In the United States, theFDA lists it as "generally recognized as safe" with no limit on concentration.[7] Aluminium sulfate may be used as adeodorant, anastringent, or as astyptic for superficial shaving wounds.[citation needed] Aluminium sulfate is used as amordant indyeing andprinting textiles.
It is a commonvaccineadjuvant and works "by facilitating the slow release ofantigen from the vaccine depot formed at the site ofinoculation."[citation needed]
Aluminium sulfate is used inwater purification and forchemical phosphorus removal fromwastewater. 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 calledcoagulation orflocculation. Research suggests that in Australia, aluminium sulfate used in this way in drinking water treatment is the primary source ofhydrogen sulfide gas insanitary sewer systems.[8] An improper and excess application incident in 1988polluted the water supply ofCamelford inCornwall.
Aluminium sulfate has been used as a method ofeutrophication remediation for shallow lakes. It works by reducing thephosphorus load in the lakes.[9][10]
When dissolved in a large amount of neutral or slightly alkaline water, aluminium sulfate produces a gelatinous precipitate ofaluminium 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 thepH of garden soil, as ithydrolyzes to form the aluminium hydroxide precipitate and a dilutesulfuric acid solution. An example of what changing the pH level of soil can do to plants is visible when looking atHydrangea macrophylla. The gardener can add aluminium sulfate to the soil to reduce the pH which in turn will result in the flowers of theHydrangea 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 inconcrete. Another use is a foaming agent infire fighting foam.
It can also be very effective as amolluscicide,[12] killingspanish slugs.
Mordantsaluminium triacetate andaluminium sulfacetate can be prepared from aluminium sulfate, the product formed being determined by the amount oflead(II) acetate used:[13]
The compound decomposes toγ-alumina andsulfur trioxide when heated between 580 and 900 °C. It combines with water forming hydrated salts of various compositions.
Aluminium sulfate reacts withsodium bicarbonate to which foam stabilizer has been added, producingcarbon dioxide forfire-extinguishing foams:
Thecarbon 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 atmosphericoxygen, smothering thefire. Chemical foam was unsuitable for use onpolar solvents such asalcohol, 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 portablefire extinguisher or fixed installation using hoselines. Chemical foam is considered obsolete in the United States and has been replaced by synthetic mechanical foams, such asAFFF 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]
{{cite book}}: CS1 maint: multiple names: authors list (link)