All You Need to Know About Iron Oxide Red
Red iron oxide - properly known as hematite - is a naturally occurring ore of iron with a vast array of uses beyond simply as a source of iron. From pigmentation to ceramics additives and an essential part of modern petroleum exploration, the highest quality hematite finds many applications, and is available from African Pegmatite milled to any specification.
Natural Red Iron Oxide
Natural red iron oxide has many forms but there are only two which are used as colours and pigments for industrial use. It is one of the most abundant iron ores that can be found on earth. Iron oxide red has been used by many civilizations. Different variations of hematite can be found all around the world. Hematite is iron oxide, Fe2O3, and is the primary ore of iron, mined chiefly for the production of metallic iron.
The Hematite Factor
The reddish colour of soil is actually due to the presence of oxidised iron that is found mostly in the tropics. These soils carry very little affinity to water, as they are hard and dense. The importance this carries can be seen by the fact that the recorded use of haematite dates back to the 18th and 19th centuries. Ceramics and clay structures also held immense importance in those times, with these clays containing large proportions of iron oxide. When there was no concept of blotting paper, haematite was used as ink absorbent and was known as Devonshire sand. The applications are extremely vast and can be found in bridges, paints, pottery, pavers, substitutes of graphite and polishing glass as well.
Uses Of Iron Oxide Red
Red iron oxide is known by many names such as red ochre and bloodstone. Native peoples in the Indian subcontinent and the Americas extensively paid attention to it in geology and used it for decorative purposes and images. For exhibiting body paint, it was also used as a raw material. Hematite is the first choice ore as a source of iron for manufacturing iron and steel. The purest form of hematite is referred to as ‘rouge’ and it is used to polish glass and plates - capitalising on its abrasive qualities related to its hardness and strength.
A naturally occurring iron oxide ore is thin and scaly and is called micaceous hematite. It is reported that this material is used as a substitute or in the manufacturing of stoves replacing black lead. It also holds immense importance in petroleum and natural gas industries as a lubricant, pivotal in oil drilling (see later). Iron mine tailings are rich in haematite, which is how they can be used to manufacture bricks. Recycling is required because of the high alkalinity of the tailings; thus it can be found easily in recyclable waste streams in large volumes.
One of the choices to give pottery its shiny characteristic, hematite can be used. It has been used as pottery glazing and was mixed with enough water to make it easy to apply. In earlier centuries, tiles and bricks were decorated using haematite and pastes made of hematite.
Anti-corrosion paint is also made by using red iron oxide. Hematite is inert towards ultraviolet rays, making it the perfect anti-corrosive barrier. It can be used in paints and roof tiles to make sure that there is no little to no exposure to ultraviolet rays to the structure underneath. It can also shield from harmful effects of sulphur dioxide, ammonia and other pollutants. Even when making buildings, it can be used with other coarse materials such as cement. Iron tailings can help make unfired bricks due to their characteristics of being strong and durable after being reprocessed - a popular construction method in the developing world. In optimal pressure conditions and adequate water content, iron tailings can form non-fired bricks and other miscellaneous building materials.
Used As A Pigment
Dependability, extensive opacity and permanence are some of the most important qualities that colourants should have. When it comes to alkalis, haematite is indifferent towards them, whereas it is partly soluble in acids. Hematite does not react with most organic solvents. This pigment is extremely important in colourants, dyes and pigments.
The classic example of red iron oxide is as an inclusion pigment in the production of clay ceramics, such as tiles and bricks. Inclusion pigments are when a pigment is added to a clay before it has been fired into the ceramic form, such pigments do not dissolve in the media (i.e. the clay, water and other materials), but are dispersed evenly throughout.
The traditional terracotta pottery and ceramic colour is easily achieved with a simple addition of 4 to 10% (by weight) hematite to a clay and then firing it. Deep blacks can be achieved when manganese ores are used with hematite; whereas pink colours can be achieved when moderate amounts of zirconium silicate are used alongside hematite. For normal ceramics, no more than 5% by weight is used. 6 to 7% is considered a ‘high iron ceramic’, with wildly high amounts as high as 65% being responsible for ultra vivid, low porosity, porcelains when combined with kaolin. There are virtually limitless possibilities available by combining hematite with other metals in the pre-firing mixing stage.
There are many other uses of this pigment. When applied to glass, the red colouring on the glass helps protect what’s on the other side from UV radiation. It also provides a non-leaching contaminant, making it important for beer bottles, oils, wine and pharmaceuticals. It is also used as an additive in plate glass for automotive and residential use.
Another very important use is as fillers. This means that it is used as materials that are pastes which are used to smooth out surfaces and cover imperfections. The advantages of this can be seen in removing deep scratches from cars, metal-based items and even wood. Once it is dried and sanded, it will be ready to get primed and painted.
Ceramics and Clay
For a very long time, one of the main uses of red iron oxide is making art and clay structures such as ornaments or statues. This is used to give clay the colour red or terracotta. After these are fired, these ceramics hold a very vibrant and rich colour, which is not found easily with any other material.
Due to the durability and longevity they hold, roofing tiles are the number one choice for roofing materials in America, many of which are pigmented with hematite. Concrete and other building materials can be used to make roof tiles, walls and roadways and then those are mixed with other materials and/or ceramics such as clay, to elevate their durability. It is often seen that roof tiles have the characteristic of being red in colour. This is because clay and cement are used for coating purposes after they are mixed with hematite and roof tiles are coated with them.
Fluxes For Ceramics And Glazes
One aspect often overlooked in the production of ceramics and glazes is the temperature required to fire them. Any way of lowering the temperature will result in a financial saving through a lower heating requirement. A flux is any material that lowers the melting or firing temperature of a particular body. Under reducing atmospheres, hematite/red iron oxide can behave as a flux. This provides the added benefit of producing a more fluid melt in the case of glazes. On the contrary, under oxidising conditions, hematite behaves as an antiflux, driving up the temperature requirement.
Hematite In Petroleum Production
Although not a commonly thought of use for hematite, the drilling of petroleum makes extensive use of hematite in various mud types. These muds primarily lubricate the drilling tooling, allowing for a more efficient process with fewer blowouts or production stoppages. Hematite is used as a weighting material in muds, providing much needed extra density. There are two ‘muds’ used, oil based and water based:
Hematite in oil based mud (OBM)
The defining feature of an OBM is that the continuous phases are oil based. The addition of hematite to these muds reduces wetting, as hematite is a low wetting material. Wetting is where water adheres to solids in the mud, which can cause more water to reach the drilling area, which then can lead to clumping. Clumping may mean clogging up of the drill bit and tooling, which means lower levels of process efficiency. Low wetting materials reduce the possibility of wetting taking place.
Hematite in water based mud (WBM)
Compared to OBMs, WBMs have aqueous continuous phases. Hematite is used here too as a weighting agent at an up to 20% by weight contribution. Hematite replaces borite in WBM and is responsible for less sedimentation, meaning less wear on tooling and therefore a reduced overall requirement for lubrication.
Hematite: Impact On Rheology
In the petroleum production space, the (plastic) flow of solids is crucial to consider - as a subset of rheology - the flow of matter. Adding anything to a mud intended for drilling will have an impact on it. Adding more weighting agents, for example, to make the overall mud more dense should only be done with suitably dense materials such as hematite and not lower density ones. Because solids have profound impacts on plastic flow, and this flow is proportional to applied force, a fine and consistent particle size is required to minimise flow changes - this is easily achieved with hematite.
Other Uses: Radiation Barriers
Because of hematite’s resistance to both neutron and gamma radiation, hematite finds some use as a radiation barrier, especially when it is dispersed through concrete. Hematite is very dense and therefore only moderate amounts need to be used - representing a thinner concrete pad requirement. It should be noted, however, that hematite is not immune to the alkali-silica reaction and so cannot be used for primary radiation containment in any situation. Common deployments as part of protective concrete layers include hematite at 10 to 50% by volume.
Health And Safety
In line with most other oxides of iron, hematite (red iron oxide) is not toxic to humans. Because of its use cases and non-toxic nature, it is FDA approved. The only health concern is related to lung irritation caused by powdered hematite, which is easily negated by using suitable personal protective equipment and ventilation.
- Hematite is a naturally occurring ore of iron, the most common ore of iron and the most used source of iron. It is often sold as red iron oxide
- Red iron oxide has many uses from pigments and dyes through to ceramics
- Its resistance to heat and antipruritic properties mean that it is often used for casings and coverings.
- Hematite can be used as a flux in glaze production (under reducing conditions) and as a component in radiation barriers
- Hematite is used widely in petroleum extraction as a weighting agent where, depending on use case, it is responsible for reducing wetting or wear to tooling
African Pegmatite is a leading processor and supplier of hematite - also known as red iron oxide - amongst a wide array of minerals and materials for virtually any process requirement. Combining a wealth of experience and in-house technologies, African Pegmatite is the go-to industrial partner.