Bauxite residue (also known as “red mud”) is a by-product of the Bayer Process. The amount of residue generated, per tonne of alumina produced varies greatly depending on the type of bauxite used, from 0.3 tonnes for high-grade bauxite to 2.5 tonnes for very low grade. Its chemical and physical properties depend primary on the bauxite used and, to a lesser extent, the manner in which it is processed.

Bauxite is composed principally of the monohydrate and trihydrate forms of alumina in varying proportions. Major impurities are the oxides of iron, silica and titanium, while other elements such as zinc, phosphorous, nickel and vanadium are found in trace amounts. The residue from the alumina production contains the impurities which are not dissolved to any significant degree, plus alumina that is not extracted in the process. For various reasons, most alumina producers add lime at some point in the process and the lime forms a number of compounds that end up with the bauxite residue.

The following data gives some idea of the wide range in chemical composition that can be found in residue from different bauxites.

Fe2O3	30 - 60%
Al2O3	10 - 20%
SiO2	3 - 50%
Na2O	2 - 10%
CaO	2 - 8%
TiO2	Trace - 10%

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