Obtenção de silicato de potássio a partir de rejeito de mineração de ferro para produção de geopolímeros

Abstract

The iron mining is one of the most important activities in Brazil. The iron ore beneficiation process is responsible for generating a large volume of two types of tailings: sandy and mud tailings. Both are directed and stored in containment dams. The sandy tailings have high levels of SiO2 in their composition and, when reacting with an alkaline base, can be extracted as silicate from the corresponding alkali metal, producing a product of high added value. In this work, two different routes were used to obtain potassium silicate from iron mining tailings (RM), the hydrothermal route (HR) and the solid route (SR). For the hydrothermal route, the reaction was carried out at different times (4, 6, 8, and 24 hours) and different amounts of KOH (12, 15, and 18 g), using 12 g of mining tailings. In the solid route, for the same RM mass, only the amount of KOH used (12, 15, and 18 g) was varied. The SiO2 and K2O contents of the products obtained in each of the routes were quantified by titration. X-ray Diffraction (XRD), Mössbauer Spectroscopy, Infrared Absorption Spectroscopy (IR-ATR), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) were performed to understand the transformations that occur in the quartz and iron phases after the reactions. The results obtained by the characterization techniques showed the fragmentation of quartz particles present in the RM, indicating that the methodologies used were effective. Potassium silicates produced through the hydrothermal processes carried out at 2, 6, 8, and 24 hours showed 7.58, 7.85, 8.82 and 14.65 wt% SiO2, respectively. When the procedure was performed by varying the base concentration, 14.08, 14.65 and 13.27 wt% SiO2 were obtained using 12, 15, and 18 g of KOH, respectively. The SR, which used 18 g of potassium hydroxide, produced a material with K2O and SiO2 contents of 45.88 and 35.60 wt%, respectively. This material was used in the preparation of an activator solution for the production of geopolymers in different formulations, using iron mining tailings as filler (25 and 50% proportions). The materials presented results of mechanical resistance to compression that vary between 9.64 and 21.12 MPa, after 7 days of curing. In addition, a new proposal for geopolymer synthesis was carried out starting from solid potassium silicate and without the previous preparation of an activating solution. After 7 days of curing, the material showed a compressive strength of 31.21 MPa. The resistance results presented are close to those described in the literature.