Ponomar V. Changes in the mineral composition and properties of iron ores of various types induced by magnetizing roasting

Ukraine has large resources of low-grade iron ores and iron-containing wastes. The low-grade iron ores are mainly represented by hematite quartzites of the Kryvyi Rih iron ore basin and goethite ores of the Kerch iron ore basin. The low-grade resources of iron ore are not processing due to the lack of beneficiating technologies. An effective and versatile method of beneficiation would be the combination of magnetizing roasting and magnetic separation. Thus, the purpose of the work was to investigate the transformations of the structure and magnetic properties of synthetic magnetically ordered iron-containing minerals and iron ores of various types by external factors (reducing agents, temperature). The results of the work have shown that the magnetic properties and structure of iron minerals can be readily modified by heat treatment in the presence of carbohydrates (starch, glucose, ascorbic acid, fructose and sucrose), activated carbon and carbon monoxide. In particular, the thermal treatment of synthetic goethite and hematite and goethite and hematite, localized in iron ores, in the presence of starch leads to the formation of magnetite. The starting temperature of the conversion of goethite to magnetite varies from 260 to 400 °C, depending on the mineralogy of the initial sample. Hematite starts to reduce at temperatures close to 350 °C. After heating hematite and goethite with starch, the samples acquire ferromagnetic properties due to conversion to magnetite. The saturation magnetization is increased to 50-70 A·m2/kg. The reduction of hematite to magnetite has been studied in an atmosphere of carbon monoxide at temperatures 300 - 700 ° С for 10 - 60 min. Carbon monoxide was synthesized by the reaction of activated carbon with oxygen contained in the air. The saturation magnetization of hematite increases to 15 A·m2/kg at a temperature of 300 °С. The maximum values of saturation magnetization are found to be equal to 80-85 A·m2/kg for experiments conducted at temperatures of 500-700 ° C for 40 min. Thermal decomposition of siderite ore of the Bakal deposit led to the formation of magnesiowüstite, which then turned into highly magnetic magnesiomagnetite. In addition, it was determined that the decomposition of siderite ore led to the formation of a significant amount of carbon monoxide. Therefore, roasting hematite in the presence of siderite results in the conversion of both minerals to magnetite. Optimal conditions for the conversion included heating the mixture at 600 °C for 12 min. Under these conditions, siderite and hematite completely transformed to magnetite, since solely magnetite was detected in transformed samples. The practical application of the results of this work may be advantageous for magnetic materials production and for beneficiation of iron ores and iron-containing wastes. This method of magnetite synthesis may potentially be of interest to ore mining and processing plants as well as to industrial organizations and research institutes that generate magnetic sorbents, catalysts, and pigments.