Effects of additives on the physical properties of magnesite ore mining by-products for the production of refractories

Abstract The addition of alumina (Al2O3), chromite concentrate (CC) and ore (CO) and maghemite (Fe2O3) in the magnesite minerals enrichment wastes investigated, aiming to upgrade the refractory properties of products after thermal treatment at 1300° C. Firing shrinkage, water absorption, apparent porosity and bulk density, considered as the main relevant parameters of importance, determined accordingly for the products, and optical microscopy micrographs appropriately received, whereas the mineralogical characterization implemented by X-Ray Diffraction (XRD) measurements. The chemical analysis of microstructure also performed by using the point analysis feature of SEM-EDS and the main mineral phases at the surface of products determined, aiming to the better explanation of relevant mechanisms/transformations. Alumina is not suitable as additive for upgrading the refractory properties, due to the presence of high percentage glassy phase on the surface of respective product, higher apparent porosity levels and lower bulk density values, which attribute to the formation of spinel and proto-enstatite. The addition of maghemite showed better results, due to the increase of bulk density and better surface sintering of powdered raw materials. However, the best results were found by the addition of chromite additives (CC and CO), as the firing shrinkage levels showed a decreasing trend, with the highest reduction noticed with chromite ore, due to highest MgO content. The MgO content, maximizes the formation of forsterite at the examined firing temperature 1300 °C, resulting to the improvement of refractory properties. The aim of this research is to convert the mining wastes/by-products, produced during the magnesite ore enrichment processes, into a potentially commercial refractory product with added value, contributing to circular economy and zero waste mining production.