The Laux process
The Laux process was originally used to produce aniline (C₆H₅NH₂) from nitrobenzene (C₆H₅NO₂). In 1925, chemist Dr. Laux discovered that, under specific chemical conditions, the iron oxide formed during this reaction could be used as a pigment with high tinting strength.
This process primarily produces black iron oxide, such as Bayferrox® Black 330, using cast iron turnings. It can also be used to produce yellow iron oxide, such as Bayferrox® Yellow 420. For this purpose, iron granules are used instead of cast iron turnings. A further thermal processing step can convert black iron oxide into red iron oxide pigment, such as Bayferrox® Red 110.
The process uses iron scrap as a raw material, incorporating this material into the production of iron oxide pigments.
The precipitation process
In the precipitation process, iron sulfate is oxidized with oxygen from the air in an alkaline medium to produce yellow iron oxide pigment, such as Bayferrox® Yellow 920. As in the Penniman process, yellow pigment seed particles are needed to produce high-quality yellow pigments.
The Penniman process
In the Penniman process described here, iron scrap is oxidized with oxygen from the air in a sulfuric acid medium to produce yellow iron oxide pigment. Iron sulfate acts as a catalyst. Yellow pigment seed particles are also needed to produce high-quality yellow pigments.