Aluminium sulfate

Aluminium sulfate, alternatively spelled either aluminum or sulphate.
Other names: Cake alum, Filter alum, Papermaker's alum, Alunogenite.

Empirical formula (anhydrous) : Al₂(SO₄)₃
Molar masses :
Al₂(SO₄)₃ = 342.15 g·mol^-1(anhydrous)
(O = 56,11 %, S = 28,12 %, Al = 15,77 %)
Al₂(SO₄)₃, 18 H₂O = 666.42 g·mol^-1 (octadecahydrate)
Al₂(SO₄)₃, 14 H₂O = 594 g·mol^-1

Aluminium sulfate is sometimes referred to as a type of alum. Alums are double sulfate salts, with the formula AM(SO₄)₂·12H₂O, where A is a monovalent cation such as potassium or ammonium and M is a trivalent metal ion such as aluminium. 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.

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

It is available in various solid forms (depending on the manufacturer):

• powder, current size of 0.1 to 2.5 mm
• granulated, "nutty", with a particle size between 2 and 12 mm or 3 and 35 mm
• Crushed pieces of 10 cm wide and about 1 cm thick
• 8.25% aqueous solution of aluminum oxide (Al2O3)

Main features :

	Solid (anhydrous)	Solid "nutty"	Solution
% Al2[SO4]3	>99.8	99.2	27.7
% Al2O3	18	17 (minimum)	8,25
Volumetric mass density ( 20 °C)	2.672 kg/m3	1690 kg/m³ (±7)	1200 kg/m³ (±10)
pH	-	-	2,2
Acidity (pKa)	3.3-3.6	-	-

Solubility in water (soft water) in relation of température (g / L) :
(g/L = g as Al₂(SO₄)₃ per liter of solution)

The insoluble portion is maximum 0.3% (w / w).
The solutions are to be stored (preferably) above 0 ° C.

Chemical action.
The chemical action of conventional coagulants gives:

• decrease in the TAC
• increase in free CO2
• adding water SO4 sulfate and / or chloride, for example Cl.

A formulation for water treatment.
Aluminium sulfate react with dissolved calcium bicarbonate.
12 Al₂[SO₄]₃,14H₂O...+ ...3 Ca[HCO₃]₂ .............>>>>>>.... 2 Al[OH]₃ ...+ ...6CO₂.....+....3CaSO₄
........(342+252)=594.................(3x162)=486 or 30°F as TAC v ...........(2x78)=156............(6x44)=264.........(3x96 as SO4)=288

Par mg/L aluminium sulfate added there (30/594) = 0.05 °F lower Alkalinity (TAC), and is formed (264/594) = 0.444 mg of free CO2, and is also formed (156/594) = 0.263 mg of aluminum hydroxide (as insoluble flocs), and (288/594) = 0.485 mg of dissolved sulphate.

Standardization.
Standard products used for the production of drinking water: Official French Bulletin - Aluminium sulfate : NF EN 878.

Uses.

• Aluminium sulfate is used in water purification and as a mordant in dyeing and printing textiles. In water purification, it causes impurities to coagulate which are removed as the particulate settles to the bottom of the container or more easily filtered. This process is called coagulation or flocculation.
• 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 the Hydrangea macrophylla. The gardener can add aluminium sulfate to the soil to reduce the pH level which in turn will result in the flowers of the Hydrangea turning a different color.
• Aluminium potassium sulfate and another form of alum, aluminium ammonium sulfate are the active ingredients in some antiperspirants; however, beginning in 2005 the US Food and Drug Administration no longer recognized it as a wetness reducer.
• Aluminium potassium sulfate is usually found in baking powder, where there is controversy over its use due to concern regarding the safety of adding aluminium to the diet.
• In construction industry it is used as waterproofing agent and accelerator in concrete. Another use is a foaming agent in fire fighting foam.
• It is also used in styptic pencils, and pain relief from stings and bites.
• It can also be very effective as a molluscicide, killing spanish slugs.

Safety.

• respiratory problems and irritation of the mucous
• irritation to the skin
• serious irritation to the eyes

Alzheimer's disease:
There have been studies that have found an association between exposure to and long-term use of antiperspirants and Alzheimer's disease, however the studies also have shown that the association is negligible (less than 1%). There is no adequate evidence that exposure to aluminium in antiperspirants leads to progressive dementia and Alzheimer's disease.

Breast cancer:
The International Journal of Fertility and Women's Medicine found no evidence that certain chemicals used in underarm cosmetics increase the risk of breast cancer. Ted S. Gansler, MD, MBA, the director of medical content for the American Cancer Society, stated "There is no convincing evidence that antiperspirant or deodorant use increases cancer risk".

The European Journal of Cancer Prevention stated "underarm shaving with antiperspirant/deodorant use may play a role in breast cancer. "The journal Breast Cancer Research proposed a link between breast cancer and the application of cosmetic chemicals in the underarm, including aluminium, with oestrogenic and/or genotoxic properties. Personal care products are potential contributors to the body burden in aluminium and newer evidence has shown that more aluminium is deposited in the outer regions than the inner regions of the breast. But whether differences in the distribution of aluminium are related to higher incidence of tumours in the outer upper region of the breast remains unknown.

Effects on the environment.
Aluminum sulfate may decrease the pH of stream, thus representing a potential threat to aquatic fauna and flora (stream, river, groundwater).

Sources : personal and Wikipedia, the free encyclopedia.

---

(use your browser)