Influence of anions on the formation of β-FeOOH rusts

The artificial β-FeOOH rusts were synthesized by oxidation of FeCl2 solutions and hydrolysis of FeCl3 solutions. Various Na salts such as sulfate, biphosphate, nitrate, and silicate were added to the starting solutions at different anion/Fe molar ratios of 0–0.05. The XRD patterns of the products showed only the diffraction peaks of β-FeOOH. The crystallinity of the products was noticeably reduced by adding SO42- and HPO42- but slightly influenced by adding NO3-. The addition of SiO32- markedly crystallized the products by the hydrolysis of FeCl3. The N2 adsorption revealed that the products with SO42- were porous particles assembled by β-FeOOH subcrystals. SO42- and HPO42- strongly coordinating to Fe(III) markedly lowered the crystallinity of the products and remained in the formed particles.