A new synthesis route from spent sulfuric acid pickling solution to ferrite nanoparticles

This paper describes a new synthesis route to magnetic ferrite nanoparticles, in which the dissolved ferrous iron(II) in spent pickling solutions is used as a starting material for the ferrite preparation. Firstly, the iron(II) in the spent pickling solution was microbially oxidized to iron(III) by using the acidophilic thermophilic microbe Acidianus brierleyi. Secondly, the iron(III) in the oxidized pickling solution was separated into the organic monocarboxylic acid solution by solvent extraction. Finally, the carboxylate solutions of iron(III) and other metal (nickel) were hydrolyzed with water at 190 °C for 20 min and gave crystalline nickel ferrite nanoparticles with an average diameter of 31 nm. In addition to the synthesis of nickel ferrite, a heat treatment of the iron(III) carboxylate at 245 °C for 60 min resulted in the preparation of crystalline magnetite nanoparticles with an average diameter of 48 nm.