Mechanisms of formation and transformation of Ni–Fe layered double hydroxides in image and image containing aqueous solutions Original Research Article

The oxidation of (Ni,Fe)(OH)2 suspensions in the presence of View the MathML sourceSO32− and View the MathML sourceSO42− anions can lead whether to the SO3-form or to the SO4-form of the Ni(II)–Fe(III) layered double hydroxides (LDHs). The hydroxysulphite, like the corresponding Fe(II)–Fe(III) compound, is characterised by a M(III)/M(II) ratio of 1/3 and forms from the initial hydroxide. If P =[Fe]/[Ni]=1/3, the end product is then View the MathML sourceNi6IIFe2III(OH)16SO3·nH2O. If P >1/3, the SO3-LDH still contains Fe(II) and the oxidation process goes on. The SO3-LDH tends to transform into a mixture of ferrihydrite and SO4-LDH. The hydroxysulphate, like the corresponding Fe(II)–Fe(III) compound, is characterised by a M(III)/M(II) ratio of 1/2 and obeys to the composition View the MathML sourceNi4IIFe2III(OH)12SO4·nH2O. The formation of the SO4-LDH is favoured by the oxidation of View the MathML sourceSO32− into View the MathML sourceSO42− anions, whereas the formation of ferrihydrite is the process that takes place if the initial anions are stable, e.g. Cl−.