Structure, morphology and magnetic properties of hematite and maghemite nanopowders produced from rolling scale

The work is devoted to development of cost-efficient method of processing of metallurgical waste – oily rolling scale formed during hot-rolled steel strip mechanical cleaning in descaling mills. The most significant parameters of chemical metallurgical process for producing expensive and highly marketed products – α-Fe 2 O 3 and γ-Fe 2 O 3 nanopowders – have been experimentally determined. The properties of initial materials and nanodispersed products were studied by X-ray diffractometry, energy dispersive spectroscopy, scanning and transmission microscopy, and Mossbauer spectrometry. Temperature and field dependences of powders magnetization were built according to vibration magnetometer measurements. It is shown that rolling scale consists of three main phases: wustite, magnetite and hematite in a ratio of 6:8:7 by weight, respectively. The initial scale was activated in magnetic mill in stream of hydrogen and dissolved in mixture of hydrochloric and nitric acids. The resulting solutions were used to obtain α-Fe 2 O 3 nanocrystalline hematite by chemical-metallurgical method, the main stages of which were hydroxide precipitation with alkali at constant p H , washing, drying, and dehydration. γ-Fe 2 O 3 maghemite was obtained from hematite in two stages. At the first stage, hydrogen reduction was carried out, and at the second stage, the magnetite obtained was oxidized in air. Particles of synthesized nanodispersed oxide powders are in aggregated state. Particles of α-Fe 2 O 3 are spherical, and γ-Fe 2 O 3 are rod-shaped. According to Mossbauer spectroscopy, the lattices of both oxides contain magnesium, aluminum, silicon, chromium, and manganese that have passed from the initial scale. These elements determine magnetic properties of α-Fe 2 O 3 and γ-Fe 2 O 3 nanopowders. Set of properties of nanodispersed hematite and maghemite powders obtained from metallurgical waste (rolling scale) allows us to recommend their application as catalysts, in industrial wastewater heavy metal ions treatment systems, and in production of blood analysis markers.