Aluminium sulfate is sometimes used in the human food industry as a firming agent, where it takes on
E number E520, and in animal feed as a
bactericide. In the United States, the
FDA lists it as "
generally recognized as safe" with no limit on concentration. Aluminium sulfate may be used as a
deodorant, an
astringent, or as a
styptic for superficial shaving wounds. Aluminium sulfate is used as a
mordant in
dyeing and
printing textiles. It is a common
vaccine adjuvant and works "by facilitating the slow release of
antigen from the vaccine depot formed at the site of
inoculation." Aluminium sulfate is used in
water purification and for
chemical phosphorus removal from
wastewater. 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 called
coagulation or
flocculation. Research suggests that in Australia, aluminium sulfate used in this way in drinking water treatment is the primary source of
hydrogen sulfide gas in
sanitary sewer systems. An improper and excess application incident in 1988
polluted the water supply of
Camelford in
Cornwall. Aluminium sulfate has been used as a method of
eutrophication remediation for shallow lakes. It works by reducing the
phosphorus load in the lakes. 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
Hydrangea macrophylla. The gardener can add aluminium sulfate to the soil to reduce the pH which in turn will result in the flowers of the
Hydrangea 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. In the construction industry, it is used as waterproofing agent and accelerator in
concrete. Another use is a foaming agent in
fire fighting foam. It can also be very effective as a
molluscicide, killing
spanish slugs.
Mordants
aluminium triacetate and
aluminium sulfacetate can be prepared from aluminium sulfate, the product formed being determined by the amount of
lead(II) acetate used: : : ==Chemical reactions==