Study of olivines in the weathered crust of the kovdorsk massive as raw materials for refractories

Abstract

A reduction in the magnesia concentration is due to the increase in the contents of AI203 and P2Os. At the same time we note a direct link between the MgO content and the amounts of CaO, FeO, Fe203, and SiO 2. An increase in the Fe0 content is accompanied by a reduction in the Fe203 content. These variations and also the relationships between them are determined by the mineral composition of the ore, as shown in Table 2 (contents of apatite and nepheline are stated after recalculation from the results of chemical analysis of samples, expressed as P20s and A1203; and the amounts of the remaining minerals are shown according to microscopic data). The main mineral is olivine which is taken to be a member of a continuous series of solid solutions formed by forsterite, Mg2SiO 4, and fayalite, PemSi0~. However, in fact, its composition is much more complex. According to chemical analysis data, the olivine contains (mass): 45.5-46.5% MgO, 7.2-8.9% FeO, 40.5-41.5% Si02, 0.2-2.2% CaO, 0.4-0.5% M_nO, 2.1-4.4% Fe203. The olivine grains are coated with a thin brittle film, yellow in color, which probably consists of serpentine [3], and is hydrated in the slurry fractions (<0.05 mm). According to DTA data, the slurry is dehydrated at II0-240~ mass loss Amcalc equals 3% (such a low Amcaic value is because the slurry, in addition to hydrated iron hydroxide Fe(OH)3"nH20, contains substantial amounts of serpentine and mica). This process is accompanied by blackening of the material, and the development of magnetic properties, probably due to the formation of magemite, ~-Fe=O 3. Thermodynamic studies were made of the possible ways that calcium and maganese could be introduced into the crystal lattice of olivine. Literature data on the thermodynamic properties of minerals was used [5, 6]. The reaction products were taken to be phases whose formation is most probable according to triangulation results in the CaO-Mg0-YeO-SiO 2 system [5], and also compounds existing in oxide systems containing Mn0 [7, 8]. Since olivines are members of a continuous series of solid solutions formed by forsterite, Mg2SiO ~, and fayaiite, Fe2Si04, we examined the reaction of these minerals with calcium and manganese oxides. Calcium oxide reacts with forsterite to form montichellite CaMgSiO~ and periclase, MgO.