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1.2 Aluminium sulphate
1.2.1 General <strong>information</strong>
1.2.1.1 Introduction
With a worldwide production of 2.9 million tonnes in 1982, aluminium sulphate is <strong>the</strong> most
important aluminium compound after aluminium oxide and hydroxide, <strong>the</strong>se latter compounds
are already covered in <strong>the</strong> Non-Ferrous Metals BREF.
The most important producers are <strong>the</strong> US (with 1.1 million tonnes in 1984 on <strong>the</strong> basis of 17 %
Al2O3, Western Europe (with 0.9 million tonnes per year) and Japan (with 0.8 million tonnes per
year on <strong>the</strong> basis of 14 % Al2O3) [48, W. Buchner et al, 1989].
Aluminium sulphate is a substance essentially used in water treatment as a flocculating agent
and in <strong>the</strong> paper industry. Aluminium sulphate is also <strong>the</strong> starting material for o<strong>the</strong>r aluminium
compounds [13, EIPPCB, 2000]. The commercial product is ei<strong>the</strong>r a solid hydrated salt, whose
formula is typically Al2(SO4)3 . 13 to 15 H2O. It is shipped in flakes, powder or blocks, or as an
8 % (as Al2O3) solution in water [6, CEFIC, 2002].
Aluminium sulphate is industrially produced by <strong>the</strong> reaction of aluminium hydroxide (or o<strong>the</strong>r
aluminium raw materials such as bauxite or kaolin) with sulphuric acid. In Europe, <strong>the</strong> largest
part of aluminium sulphate is produced by <strong>the</strong> reaction of sulphuric acid with wet or dry
aluminium hydroxide according to <strong>the</strong> following reaction:
6
2Al(OH)3 + 3 H2SO4 F Al2(SO4)3 + 6H2O
This reaction is <strong>the</strong> common trunk of all processes, and it is typically carried out in a stirred
batch reactor at a temperature of 110 – 120 °C and under atmospheric pressure. The resulting
solution is treated differently according to <strong>the</strong> shipment mode:
for shipment as a solution, <strong>the</strong> Al2O3 concentration of <strong>the</strong> mixture leaving <strong>the</strong> reactor is
simply adjusted, and <strong>the</strong> resulting solution is clarified (by filtration). This process only
generates minor air and water emissions
for shipment as a solid, <strong>the</strong> mixture leaving <strong>the</strong> reactor is sent ei<strong>the</strong>r to a crystalliser, a flaker
or a solidification box according to <strong>the</strong> shape required. Fur<strong>the</strong>r treatments may include
crushing, milling, sieving before packaging. This process generates almost clean waste
water from <strong>the</strong> concentration steps and air emissions containing particulate from solid
handling.
O<strong>the</strong>r feedstocks e.g. bauxite or clays, are industrially used, but as <strong>the</strong>y are not as pure as
aluminium hydroxide, <strong>the</strong>ir processing ei<strong>the</strong>r leads to a less pure aluminium sulphate (e.g.
containing soluble iron sulphate or suspended solids) or generates solid wastes. Also, spent
aluminium salts solutions (e.g. from aluminium surface treatment activities) can be a source of
small amounts of aluminium sulphate used for <strong>the</strong> local markets [6, CEFIC, 2002].
1.2.1.2 <strong>Information</strong> on aluminium sulphate – inorganic coagulants
The substances covered are all based on aluminium sulphate in a solid or liquid pure form or
containing additives, mainly iron, in <strong>the</strong> form of iron sulphate. In both <strong>the</strong> solid and liquid form,
<strong>the</strong> categories can be split into three groups:
iron free
low iron
iron blends.