Iron solubility, colloids and their impact on iron (oxyhydr)oxide formation from solution

Iron (oxyhydr)oxides play fundamental roles in geological and biological processes. They are studied in various scientific fields ranging from chemistry to medicine and used for technological applications. All these contexts require an understanding of iron solubility, its speciation in water as well as phase transformation processes from solution to solid and vice versa. We describe experimental findings and theoretical concepts of iron (oxyhydr)oxide dissolution and formation in aqueous solution: hydrolysis, nanoparticle size-dependent aspects of solubility and particle formation pathways, nucleation, growth and oriented attachment. We discuss that the existence of nanometric colloidal species affects the properties of classical models that are often overlooked due to challenges regarding their conceptual description.