Demand for non-metallurgical Bauxite has continued to increase and a set of applications have been developed. These include refractories, abrasives (including the recently development proppants), high aluminium cements, aluminium chemicals, activated bauxite and alumina.

Other uses include filters and pigments for plastics and elastomers; special calcined aluminas for ceramics, refractories, abrasives, soft burned calcined aluminas, hard burned calcined aluminas to produce alumina cements and calcium-aluminate cements.

Non-metallurgical bauxite can be presented as:

• Chemical-grade bauxite for the production of aluminium chemicals;
• Refractory-grade bauxite to produce high alumina refractories; and
• Abrasive-grade bauxite for the production of abrasives.

Calcined Bauxite

Calcined bauxite (following iron reduction) is produced by calcining (heating) high alumina containing bauxite (55% to 60% Al2O3) at at temperatures ranging from 900°C to 1200°C for 50 to 60 minutes.

Calcination removes the inert moisture and increases the alumina content by converting tri-hydrate and mono-hydrate (gibbsite and boehmite) into anhydrous aluminium oxide by expulsion of water of crystallisation – similar to a laboratory “Loss of Ignition” (LOI) test.

Uses

Calcined bauxite is used for different applications that include:

• Refractory bricks
• Grinding media (Abrasives)
• Road surfacing material
• Proppants
• Alumina cement
• Ceramics

Refractory grade calcined bauxite is produced mainly in China, India, Guyana and the USA.

The raw bauxite used for calcination should contain alumina up to 55 to 60%. Availability of this quality bauxite is limited.

Key non-metallurgical bauxite requirements are:

NB. Most of the remainder represents water of crystallisation (Loss on Ignition LOI) which is removed by calcination.

The Roskill guide states that around 1.1 million tonnes of bauxite per annum is used for refractories and around 1.2 million tonnes of bauxite for global consumption is used for abrasives.

Approximately 70% of the refractory use is in the iron and steel industries with most of the remainder being used in cement kilns and the glass industry.