Iron oxide pigments in the use of the process or encountered problems

What problems will be encountered in the use of iron oxide pigments

The production process of iron oxide is generally like this

1) Acid is added to iron to form Fe2+ and Fe3+
2) Alkali is added to produce Fe(OH)3 and Fe(OH)2
3) Fe(OH)3 and Fe(OH)2 are calcined at high temperature to produce FeO, Fe2O3 and Fe2O3.Feo
4) Then crush into powder
Generally speaking, it is harmless to the body, but there is a certain production risk when adding acid and high temperature calcination, but it is also caused by operation, and it has nothing to do with iron