Alum is also used to purify water

physical and chemical properties

LookcolorlessMelting point770 ° C
odorstabbingboiling point is decomposed
molar mass342.15 g / molDensity (° C) 2.71 g / cm3
Condition at 20 ° CfirmlySolubility in water (20 ° C, 1 bar)easily soluble

Manufacture and application

Aluminum sulphate is obtained technically from the hydroxide of aluminum and sulfuric acid under heat and high pressure.

It is used, among other things, in the food industry as a firming and stabilizing agent and as a component in fertilizers. It is also used as a glue in the paper industry, as a dressing agent in dyeing and as a seed dressing. It is also a component of foam extinguishers and medicines to stop bleeding. It is used as a precipitant in wastewater treatment.

Environmental impact and health

Depending on the concentration, aluminum sulphate is considered to be slightly harmful to the environment and is classified as slightly hazardous to water (WGK 1). Aluminum sulphate solution is corrosive and handling requires the usual precautionary measures.

Wastewater treatment / drinking water treatment

In the context of wastewater treatment, aluminum sulfate is often used as an aqueous solution for adsorption, e.g. for the removal of oils / fats and fine turbidity, and in particular for phosphate elimination through precipitation with combined flocculation, this step being accompanied by neutralization in the case of basic wastewater. The use of aluminum sulfate is also said to be effective in combating the bulky sludge that is undesirable in the sewage treatment plant.

It is also used as a flocculant in drinking water treatment. The use of aluminum sulfate is standardized in DIN EN 878.

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