Turning Red Mud Into a Cement Ingredient Milling Bauxite Waste Until It Reacts

This application covers a way of upgrading the waste left over from making alumina, namely bauxite residue (commonly called red mud) and bauxite tailings. The claimed method dries the waste, grinds it fine, and then keeps milling it in a high energy mill until it is chemically activated, so that it can be used as a supplementary cementitious material in concrete. It was filed by Technological Resources Pty. Limited, names Santiago Alonso Barrera Ramirez as sole inventor, and is a standard patent application claiming priority from an Australian filing of 3 April 2025. It is not a divisional.

The Problem

The Bayer process turns bauxite ore into alumina by digesting it in concentrated caustic solution. What does not dissolve is discharged as bauxite residue. The specification says that every tonne of alumina produces 1 to 1.5 tonnes of it, that it is highly alkaline, and that it has to be stored carefully in lagoons or as stacked dry mud because leaching into groundwater is a health and environmental hazard. Because of the high pH and a complex mixture of oxides and minerals, only a small proportion is ever reused, and the storage facility can make up a large part of a refinery’s footprint.

A second waste stream comes from beneficiating the ore before it reaches the refinery. Impurities such as silica, iron and titanium are removed and stored as bauxite tailings, which the specification says also take up a significant part of a beneficiation plant. The applicant wants a way to extract value from both streams with less energy, ideally powered at least partly by renewable electricity.

What This Invention Does

Claim 1 is a method of upgrading a feed bauxite waste material in three steps: drying the feed to form a dried material, comminuting (grinding) the dried material to form a ground material, and subjecting the ground material to mechano-chemical activation to form an activated material. Claim 19 claims a matching system: a dryer, plus at least one mill that grinds the dried material and then puts the ground material through mechano-chemical activation.

The title, abstract and claims all line up. The specification states the claimed method is aimed at a product that can be used as a supplementary cementitious material (SCM) for the building industry, and claim 18 gets there by processing the activated coarse fraction into SCM. Iron-rich streams for the steel industry are the secondary target.

The idea of mechano-chemical activation is that energy goes in mechanically instead of as heat. After ordinary grinding has reduced the particle size as far as it will go, continuing to mill imparts extra energy that breaks bonds in the crystal structure and finally makes the particles aggregate into agglomerates. The specification divides this into three stages: mechanical reduction until the particle size stops getting smaller, activation in a high energy mill, and then agglomeration. Milling stops once agglomeration is detected, and agglomerates under 60 microns, preferably under 50 microns, are the target.

The dependent claims and body supply the numbers. The feed is first reduced to a maximum of 2 mm (claim 3) and can be blended with up to 35 per cent by weight of an additive such as kaolinitic clay (claim 4). It is dried to under 10 per cent water (claim 6), with under 1 per cent preferred, using a dryer at 105 to 150 degrees C. Dry grinding takes the particles to a maximum average size of 15 microns (claim 8), with under 5 microns preferred. Activation applies an energy input of at least 100 kW per cubic metre (claim 13) in a mill running at a circumferential speed of up to 10 m/s (claim 14), with 3 to 5 m/s preferred. A classifier separates coarse and fine fractions and recycles them back to the mills, with the coarse fraction no larger than twice the lowest fines size (claims 9, 10, 16 and 17). The spec’s reactivity target is an R3 value of at least 250 J/g of SCM, preferably above 350.

The main embodiment blends 80 per cent bauxite residue with 20 per cent kaolinitic clay, and a table of feedstock blends shows residue at 65 to 80 per cent with kaolin at about 20 to 35 per cent, kaolin purity from about 60 to 100 per cent, matched to one of five flowsheet options. The specification contains no worked example with measured results, so the R3 figure is a target, not a reported outcome.

Key Features

• Dry, low-oxygen processing. The mills run on dry material, in a gas of at least 50 per cent nitrogen and under 1 per cent oxygen, which the spec says protects the reactivity of the material and makes dry magnetic separation possible.
• Mechanical rather than thermal activation. The applicant argues that milling can be less energy intensive than thermal activation and can be partly or fully electrically powered, so it could run on renewable energy.
• Reactivity-boosting additives. If the residue lacks enough reactive silicon-bearing material, the feed is topped up with kaolinite clay or bauxite tailings, in blends of up to 35 per cent additive.
• Optional iron removal. A reducing agent such as biochar, metallic iron, aluminium, zinc, magnesium or iron (II) sulfate can convert hematite to magnetite, which a dry magnetic separator then pulls out as a separate iron-rich stream (claim 11).
• Classifier loops. Air classifiers send coarse material back to the first mill and fine activated material back to the second, so the output has a more uniform particle size distribution.
• One mill or two. The five flowsheet options cover separate grinding and activation mills as well as a single combined mill, and place the magnetic separator either before or after activation.

Who Is Behind It

Technological Resources Pty. Limited is a Rio Tinto subsidiary. The legal news site Lawyerly describes it as such in its report that Rio Tinto subsidiary Technological Resources successfully challenged an IP Australia decision on a mining patent application. The title page lists the applicant as its own agent, with an address at 120 Collins Street, Melbourne. The specification refers to “the Applicant” as having invested significant resources in recovering value from waste material from a Bayer refinery or bauxite beneficiation plant, and Rio Tinto lists aluminium among its products and alumina refineries among its operations. The specification does not name which refinery or which residue the work was done on.

On priority, the title page records Australian application 2025901132, filed 3 April 2025, so the priority country is Australia. The application itself is a standard patent application and the title page does not mark it as a divisional or a national phase entry.

Why It Matters

Bauxite residue is one of the largest waste streams in the aluminium chain, and the specification’s own figure of 1 to 1.5 tonnes per tonne of alumina shows why. Concrete is a natural destination because it is used in huge volumes and because cement makers are under pressure to replace part of the clinker, the energy intensive component of cement. Industry bodies have been studying residue in cement for years. The International Aluminium Institute, for instance, publishes a series on bauxite residue in cement that includes a part on supplementary cementitious materials.

The obstacle has been that residue is alkaline and mineralogically awkward. This method does not try to wash or neutralise the residue first. It removes the water, grinds the material to a few microns, and uses mechanical energy to make the aluminosilicate content reactive. The claim is broad, since claim 1 names no equipment, particle size or energy figure. Whether the activated product actually meets cement industry performance requirements is not shown in this document, so the case for the method rests on the stated reactivity target and the applicant’s description of lower energy use, not on test data.

Related Concepts

• Red mud – the alkaline Bayer process residue that is the main feedstock.
• Bayer process – the alumina refining route that produces the residue.
• Mechanochemistry – the field that covers using mechanical energy, such as milling, to drive chemical change.
• Metakaolin – a thermally activated clay cement additive, the kind of SCM that mechanical activation is intended to compete with.
• Fly ash – another industrial by-product widely used to replace part of the cement in concrete.
• Ball mill – the family of grinding mills that includes the planetary ball mills named in the specification.

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AU 2026202241 was published in the Australian Official Journal of Patents on 23 April 2026 and is open for public inspection. Patent applications represent inventions that are sought to be protected and do not necessarily reflect commercially available products.