Iron oxide pigments are the most often used colour pigments in the world. They are available in the primary colours yellow (FeOOH), black (Fe3O4) and red (Fe2O3), but also as a mixture in orange, beige and brown shades. The globally leading manufacturer of iron oxide pigments (Bayferrox® and Colortherm®) is our long-term business partner LANXESS with the world's largest iron oxide production facilities in Krefeld-Uerdingen (Germany), Porto Feliz (Brazil) and Shanghai (China).
Manufacturing process of iron oxide pigments
The world's largest manufacturing plant of iron oxide pigments (Bayferrox® and Colortherm®) is the Krefeld-Uerdingen-based facility of Lanxess Deutschland GmbH. Here, Lanxess operates the world's single production line of iron oxide pigments according to the sustainable Laux process. The Laux process significantly contributes to the extraordinary quality features of Colortherm® and Bayferrox® pigments made by Lanxess Deutschland GmbH. This resource-efficient process is primarily used for the production of black iron oxide, which is then further processed to convert into a red iron oxide pigment. First of all, the precipitation and the Penniman process are used for the production of yellow iron oxide pigments. The three processes to manufacture iron oxide pigments are described in detail below.
The Laux process
|Reaction of black:||9 Fe + 4 C6H5NO2 + 4 H2O||3 Fe3O4 + 4 C6H5NH2|
|Reaction of yellow:||2 Fe + C6H5NO2 + 2 H2O||2 FeO(OH) + C6H5NH2|
|Reaction of red:||2 Fe3O4 + ½ O2||3 Fe2O3|
Initially, the Laux process was exclusively used to manufacture aniline (C6H5NH2) from nitrobenzene (C6H5NO2). Only when in 1925 the chemist, Dr Laux, found out that the iron oxide, being a by-product of this reaction, could be used, subject to certain chemical conditions, as an iron oxide pigment with extremely high colour strength. This process is primarily used for black iron oxide (e.g. Bayferrox® Black 330), however, the reaction to get iron oxide yellow (e.g. Bayferrox® Yellow 420) is also possible. From black iron oxide, it is also possible to produce red iron oxide pigments (e.g. Bayferrox® Red 110) in an additional reaction stage.
The precipitation process
|2 FeSO4 + 4 NaOH + ½ O2||yellow nucleus||2 FeO(OH) + 2 Na2SO4 + H2O|
In the precipitation process, iron sulphate is oxidized to yellow iron oxide pigment (Bayferrox® Yellow 920) in an alkaline environment with atmospheric oxygen. In this case, similar to the Penniman process, a yellow nucleus pigment is necessary in order to obtain yellow pigments of a high quality.
The Penniman process
|2 Fe + ½ O2 + 3 H2O||iron sulphate||2 FeO(OH) + 2 H2|
In the Penniman process, iron scrap is oxidized to yellow iron oxide (Bayferrox® Yellow 920) in a sulphate acid medium in the presence of atmospheric oxygen. In this case, iron sulphate acts as a catalyst. As to obtain yellow pigments of a high quality, yellow nuclei are furthermore necessary.
Product properties and delivery forms of iron oxide pigments
The synthetically manufactured iron oxide pigments of the Colortherm® and Bayferrox® series are available in 5 different delivery forms, i.e. as powder, micronized powder, granules, or as liquid pigment preparations. These high-quality colour pigments are used in many different industries.
Powder pigments are always solid substances of which the simplest form is an insoluble powder. They are predominantly used in the building industry.
Micronized powder pigments
Micronized powder pigments are characterized by minimized pigment aggregates owing to a grinding process. This form of delivery is in particular advantageous for application in the paint and varnish industry due to a particularly good dispersibility in the production process.
Compact powder is a compacted low-dust, flowable pigment mainly used for the colouring of building materials.
Granules are spray-dried and dust-free pigments. Owing to the sophisticated manufacturing process of these granules with a very good flowability, discharging them from silos, big bags or paper bags is easy and convenient for the user. This also provided for better dosing.
Liquid colours are stabilised aqueous suspensions made of iron oxide powder. Due to dust-free and clean dosing, they are easy to handle for the user.