Characterization and evaluation of magnesite ore mining by-products of Gerakini mines (Chalkidiki, N. Greece)

The qualitative and quantitative characterization of several mining by-product samples, were collected from the magnesite mine of "Grecian Magnesite SA" company (Gerakini, Chalkidiki, North Greece), was aiming to evaluate the possibility of upgrading their refractory properties by applying thermal treatment. The concentration range of main components for the selected best qualified samples was 38.7-43 wt% for MgO, 37.5-44.1 wt% for SiO₂ and 6.5-7.3 wt% for FeO. The mineralogical characterization revealed the presence of olivine, pyroxenes and serpentine, with the concentration of the latter positively correlated to LOI. Microprobe analyses clarified the presence of olivine [(Mg_1.79Fe_0.19Ni_0.01)SiO₄], consisting mainly of 90 wt% of forsterite (Mg₂SiO₄) and 10 wt% of fayalite (Fe₂SiO₄), as well as of pyroxene group minerals [(Mg_0.87Fe_0.08Ca_0.01Cr_0.01)(Si_0.98Al_0.04)O₃], consisting mainly of 91 wt% enstatite (MgSiO₃) and 9 wt% of ferrosilite (FeSiO₃), respectively. The thermal treatment of the qualified samples demonstrated that at the temperature of 650-680 °C serpentine is almost totally decomposed and at the temperature of 850 °C it has been totally recrystallized to olivine and pyroxenes. At higher temperature treatment (1300 °C), it seems that there is a recrystallization process that favors the deformation of olivine and the further formation of pyroxenes, due to the excess of Si available from the initial decomposition of serpentine, while the presence of magnesite resulted to the restriction of olivine deformation through the partial capture of available Si. For increasing the olivine percentage and, subsequently, the improvement of refractory properties of this material, at temperature > 1300°C, the ideal theoretical addition dose of wt% MgO for optimizing the formation of olivine was calculated, ranging from 7.4 to 17.5 wt%. The latter calculations are reported for the first time in the literature regarding this kind of materials.