Natural Red Iron Oxide - Applications & Uses
Red iron oxide has a wealth of uses, from as a pigment to ensuring optimal oil drilling, and is available in the highest purity, milled to any specification, from African Pegmatite.
Haemetite, most commonly known as rust, is a chemical compound of iron and oxygen. In the industrial realm it is known as red iron oxide and is one of the most important minerals. This compound of iron and oxygen is only one of sixteen known oxyhydroxide variants. As a granulated powder it makes an excellent cost effective colourant. Red iron oxide is one of the oldest pigments to be used by every major civilization.
Naturally occurring as deposits in crystalline form, variations of haemetite can be found around the world. Even far away on Mars, red iron oxide is available naturally. On Earth, it coexists with several other minerals including chalk, clay, and quartz. Readily available in several forms, only two forms are specifically used as a colourant and can be used in the production of industrial, commercial, and household products including:
Colourant, Pigment, and Dyes
The company African Pegmatite has a large global footprint with over 170 million coloured bricks produced every year. Qualities as a colourant include permanency and dependability with extensive opacity and tinting strength. Additionally, haemetite is indifferent to alkalis, does not react with solvents, but are partially soluble in acids.
Clay and Ceramic Colouring
Classical terracotta colourations will be observed in most clays post firing, to which 4 to 10% by weight red iron oxide has been added. Alongside other pigments, the use of red iron oxide as the primary pigment can lead to a wealth of other colours and hues.
When used at 65 weight%, iron oxide alongside kaolin and sand will afford a vividly read pigment in porcelain; deep black ceramics can be produced when 10% of the hematite is replaced with powdered magnesite ore. Coral pink can be observed when the same amount of hematite/red iron oxide is replaced with zirconium silicate. Modulation of the characteristic red-brown chromophore resulting from red iron oxide by the addition of other metals will result in a wide bouquet of possibilities in terms of colour.
The red colouring provides UV protection, and provides non leeching containment which is important to products like beer, wine, pharmaceuticals, and oils, and for plate glass for residential, commercial, automotive, and architectural use.
In general, the darker the bottle colour, the better resistance to ultraviolet light, and thus the better the chance of preservation of the container glass’s contents.
A logical extension from ceramic pigments to glazes is natural with hematite/red iron oxide. When combined with silica, 10% by weight of red iron oxide is more than sufficient to produce a lustrous red glaze after firing in excess of 1000 °C - with the hematite-silica combination glaze pigment possessing enhanced levels of stability over pure hematite or silica. This reduced temperature requirement is well suited to the modern ceramic industry, which relies on fast turnarounds and maximal use of equipment. On the other hand, hematite glazes can be fired to produce blueish colourations in reducing environments, with the addition of oxides of potassium being responsible for a modulation of the blue towards green.
Crazing is reduced by the addition of red iron oxide/hematite in the glaze prior to firing in quantities exceeding 2 weight%. Such quantities may not afford colouration. Crazing is where small, hairline cracks form in a glaze due to thermal expansion of the glaze over time, even after firing.
Cement, Concrete, Pavers, and Blocks
Using only one part hematite and three parts grey cement will create a deep red cement colour, and many variations are used in modern walkways, parks, and private and public recreational areas. For concrete applications, 5 to 10% by weight of red iron oxide is used. Red iron oxide is also used with a variety of coloured pavers and blocks for creative paving of walkways, driveways, patios, firepits and masonry work.
Contemporary asphalt is a mixture of aggregates and cement, using bitumen as a binder. One issue with asphalt is its tendency to absorb heat and create ‘urban heat islands’ in built up areas, which lead to overall localised temperature increases. One method of alleviating this is to increase the reflectivity and therefore decrease the heat absorption. Red iron oxide can be added to an asphalt mixture at 5% in order to attain a temperature reduction of ca. 3 °C relative to undyed asphalt(1). Additional benefits include stronger mechanical strength and an increase in reflectivity of 18.8% compared to the control.
Best suited to indoors for homes and industrial use, red oxide flooring is very cost efficient, durable, and appealing for its’ luxurious shine that ages well.
For durability, red iron oxide pigment roofing tiles are a great choice. They are weather durable and this type of roof can last well in excess of 15 to 30 years, and does not need to be sealed or re-sealed. Depending on the base material, such as concrete or clay, some red iron oxide roofs can last 50 to 100 years.
Plastics And Rubber
Hematite is a known additive in a range of plastics, acting as a binder and providing durability benefits for applications such as:
- PVC, Polyolefins, PS, ABS, engineering polymers,
- Silicone items
- Rubber items in a vast array, such as gaskets, stoppers and playground balls.
Polishing And Buffing
Although not a major use, red iron oxide finds use as a mild abrasive, used especially for high-value cleaning and finishing applications, such as:
- Powder – usually mixed with an emollient and used for polishing fine silver.
- Waxes and greases – used for polishing metals, antiques and reproductions.
- Jeweller’s rouge – light abrasive used with a soft cloth for final polishing on fine metals in jewelry and lenses.
Emulsions And Coverings
Perhaps as a natural extension of being a wide ranging pigment for ceramics, red iron oxide is used in paints and coverings to provide both colouration and other benefits:
- Paints – acrylic, tempura, fresco, watercolors, oil based, and rust-hindering versions.
- Primer for metal and wood – creates a solid layer to hinder rust and bleed-through.
- Glazes – for ceramics to provide all shades and tints of pink to maroon.
- Stains – used for wood and plaster applications.
- Fingernail polish
One example of where red iron oxide is used as a coating is in that for steel. In standard conditions, steel will weather and rust. A coating is therefore needed to protect it, and paint may not be the best solution owing to it also degrading in weather conditions. A coating based on castor oil, polyethylene glycol and red iron oxide has been developed(2). The in situ generated polyurethane coating containing the oxide was found to have excellent performance in laboratory conditions, with enhanced adherence to the steel below compared to polyurethane based coatings without the iron oxide inclusion.
One of hematite’s major applications is in the drilling space, particularly for oil and gas. Hematite lends itself to be included in drilling muds where its properties mean that wetting is reduced and enhanced flow properties may be observed. Drilling tends to proceed via the addition of muds, as below, and hematite acts in many scenarios as a weighting material - i.e. a material that increases the mud’s density.
Hematite In Oil Based Mud (OBM)
OBMs have oil based continuous phases and are particularly susceptible to wetting, which is where water adheres to the solids in the mud, which then may cause excess water to reach the drilling area, and this can result in clumping of the solids. Excess solids will lead to inefficiencies in the drilling process, a poorer extraction of the resource and likely degradation of the drill bit and associated tooling. Hematite is a low-wetting material, and therefore the use of this over other weighting materials will reduce the likelihood of wetting taking place(3).
Hematite In Water Based Mud (WBM)
In WBM scenarios, hematite can be used in quantities of up to 20% by weight in the mud which has an aqueous continuous phase, with a notable decrease in sedimentation relative to commonly used borite due to the high iron oxide content(4), this lower sedimentation paradigm reduces wear on the tooling and therefore a lower requirement for lubrication.
Hematite And Rheology
Rheology is the flow of matter, and of significance in the drilling space, the plastic flow of solids. Plastic flow is a movement proportional to an applied force, and in petroleum exploration, a shape or phase change resulting from such a force. Solids have profound impacts on rheological performances of muds, and so adding red iron oxide will have an effect. Consistent particle size is easily achievable with red iron oxide and highly important in terms of rheology. Across many studies, hematite has been shown to have higher density values, better gelling ability and higher plastic viscosity than the commonly used barite(5), with excellent performance at deep boring depths, therefore providing for more stable bore holes and more stable drilling.
Fluxes For Ceramics And Glazes
In the ceramic glazing space, a flux is a material that ensures a lower temperature is required to make the ceramic glaze or bulk ceramic material, prior to firing, thereby reducing the overall energy requirement. Under reducing atmospheres, red iron oxide behaves as a flux, also affording the benefit of a more fluid melt. Under non-reducing (i.e. oxidising) conditions, red iron oxide behaves as an antiflux in a glaze melt and therefore provides a stiffer melt.
As A Food Safe Additive
‘Red 101’ is a United States Food and Drug Administration-approved additive for food and other products which will not cause harm when used at low quantities, and is used in applications as diverse as:
- Dental composites,
- Cosmetics and beauty & personal care goods, where red iron oxide has been used since the 1990s. Highly sought for cosmetics for being non-toxic, moisture resistant and not known to cause allergic reactions (even in those with sensitive skin). Adding titanium oxides, many shades of lighter red to pink are created. Used in many products including lip gloss, lipstick, blush, eye shadow, soaps, lotions, creams, powders, soaps, facial and body masks, and scrubbing salts. As an additive in cosmetics, red iron oxide has been shown - alongside zinc and titanium oxides - to be effective at blocking the transmission of high energy visible light(6). Such light may be damaging to skin after prolonged exposure. Red iron oxide is added at less than 10% by weight.
- Tattoo inks. Although not a primary pigment, the use of iron oxide is regarded as acceptable, but it may not afford the longest lasting colour.
- Red iron oxide has been used as a ‘pearlescent’ dye for foodstuffs(7), with their unique nanostructures being attributable for such light scattering behaviour. Iron oxides carry the European food label of E172.
Used in a paste style materials for smoothing out imperfections and deep scratches on cars, wood, or metal-based items. Once dried and sanded, can be primed and painted to perfection.
The nanoparticle form can be used in unique applications for medical purposes using its paramagnetic properties such as reverberation imaging, marking carcinogenic tissues, attractively controlled delivery of pharmaceuticals, and thermotherapy.
Used in nanoparticle form, for the processing and data storage in tape form. In the field of electrochemical cells, various forms of iron have long been used in electrodes. One modern application is that which uses red iron oxide co located within a carbon fibre electrode. When used as such, produced by a simple calcination process, the red iron oxide/carbon fibre electrode produced promising results when deployed in a lithium ion battery cell as the anode(8), displaying a specific capacity of 1138 mAh g−1, with excellent cycling capabilities.
Although not used as a primary containment method due to the alkali-silica reaction, as hematite is not immune to this reaction, hematite is used as part of concrete and ceramic radiation barriers used around nuclear power plants and other radiative environments. Hematite is resistant to neutron and gamma radiation over long periods of time, at elevated temperatures, especially when as part of a concrete slab. Hematite is typically used at concentrations of 10 to 50 volume%. Because of hematite’s high density, less of it needs to be used, meaning a thinner concrete/ceramic is required overall.
High Heat-Resistance Coatings
Used for boilers, flues, and ovens for temperatures up to 90 Celsius. Can be used on the interior or exterior surfaces.
Used for boilers, flues, and ovens for temperatures up to 90 Celsius. Can be used on the interior or exterior surfaces.
As A Catalyst
Iron is one of the most prevalent metals used in catalysts today, for example the iron catalyst that is essential to the Haber Bosch process of making ammonia. A more contemporary challenge is the splitting of water to afford oxygen and hydrogen - an energy intensive process. Once annealed at 600 °C, red iron oxide has been shown to have some potential as a catalyst for the electrocatalytic splitting of water(9). In rocketry, red iron oxide is used as a propellant modifier, where it modulates the rate of burning of fuels(10). Researchers note that iron oxide is rarely used above concentrations of 5 weight%, and that insufficient facts are known about exactly its mode of action. Overall, with regards to catalytic applications of which these are just two, the complex surface chemistry is often cited as the reason why iron oxide is a good and widely performing catalyst. Naturally, many more complex catalysts based on iron oxide have been developed and are now amongst some of the most exciting species around.
As mentioned above, hematite is non-toxic. The only potential hazard is lung irritation that comes from inhaling excess amounts of fine dust. Mitigation is via careful mixing of the iron oxide powder when used and to use appropriate personal protective equipment.
- Hematite is a naturally occurring ore of iron, and is often sold as red iron oxide
- Primarily used as a source of iron, red iron oxide has many other uses
- Red iron oxide is used as a pigment/dye/colourant for many materials including ceramics, glasses, glazes and even food
- Its resistance to heat and antipruritic properties mean that it is often used for casings and coverings. Additionally, red iron oxide is used as a flux in ceramic and glaze production
African Pegmatite is a leading miner, miller and processor of the highest quality red iron oxide for a wealth of applications. Available in any quantity and processed to the exacting specifications of a customer, African Pegmatite is the go to industrial partner for the supply of red iron oxide and a wide variety of other minerals for the most demanding projects.
1 P. R. B Torres et al., Case Studies in Construction Mater., 2023 18, 1709
2 S. M. M. Morsi et al., Process Org. Coatings, 2019, 136, 105236
3 J. T. Cline et al., Wettability Preferences of Minerals Used in Oil-Based Drilling Fluids, in: SPE International Symposium on Oilfield Chemistry, Houston, 1989
4 P. Ranjan and A. Dutta, Int. J. Dev. Res., 2017, 7, 16806
5 P. O. Ogbeide and S. A. Igbinere, FUTOJNLS, 2016, 2, 68
6 A2 P. Boland et al., J. Cosmet. Dermatol., 2020, 20, 532
7 B. Hetzer et al., Food Additives and Contaminants, Part A, 2022, 39, 1933
8 H.-S. Kim et al, J. Ind. Eng. Chem., 2021, 104, 22
9 J. Mayandi et al., Catalytic and Magnetic Properties of Yellow and Red Iron Oxide for Water Splitting, in: The International Conference on Advanced Materials for Clean Energy and Health Applications, Jaffna, Sri Lanka, 2019
10 F. Maggi et al., Acta Astronautica, 2019, 158, 416