Kerch oolitic iron ores and possibilities of their technological modification

The main technological development problem of Kerch brown iron ore is its poor modification by a traditional magnetic-gravitation method. We studied the oolitic varieties of «brown» ore by Mössbauer and IR spectroscopy methods using the data of chemical and thermal analysis and microprobe study from core at intervals 66-66.5 and 23.5-24 m, and products of their magnetization by medium-thermal reductive roasting in the rotary furnace. The ore was filled by predominantly amorphous, fine hydrogoethite-smectite material with small phosphate admixture. The oolites were predominantly oxyhydroxide-ferriferous and three times richer in phosphates compared with the cement predominantly filled with clay material (mol.%; 1 - cement, 2 - peas): clay substance - 1) 67 ± 10, 2) 20 ± 10; phosphate substance - 1) 3 ± 2, 2) 8 ± 3; iron oxyhydroxides - 1) 30 ± 8, 2) 72 ± 9. According to the Mössbauer spectroscopy 85% of iron in oolite and 60% of iron in cement were related to goethite of various fineness. The chemical composition of the hydrogoethite in peas and cement was almost identical, its general empirical formula - (Fe0.96-1Mn0-0.04)О(ОН). In the clay phase the iron was localized in the octahedral positions of di- and trioctahedral smectite of nantronite-ferrisaponite type mainly in the trivalent state. The smectites in the cement and oolites were not identical, in the latter the octahedral positions of Fe3+ were characterized by significantly larger quadrupole splitting: in oolites IS » 03, 0.44, QS » 0.65, 1.4 mm/s; in cement IS » 03, 0.4, QS » 0.56, 1.0 mm/s. The modification of ore in the rotary furnace in reducing conditions did not result in the change of its chemical composition, the magnetic susceptibility, and saturation magnetization were increased by two orders due to the appearance of 30-40 wt.% of magnetite. In the Mössbauer spectra of magnetized ore 40 % of magnetic superfine structure were related to the partially oxidized magnetite Fe3+[Fe2+1-0.86Fe3+1-1.09□0-0.04]O4. According to Mössbauer spectroscopy the reduction of iron to the divalent state occurred also in silicates with initially trivalent iron. The values of isomer shift (1.12 and 0.96 mm/s) and quadrupole splitting (2.6-2.7 and 2.0-2.1 mm/s) correlated with octahedral positions in the structure of the dehydration products of initial smectite. The magnetic separation of both initial and magnetized samples, using an isodynamic magnetic separator, was ineffective. To obtain the desired effect, we would probably need to adjust the conversion degree of low-magnetic iron oxides and hydroxides to magnetite.