Transformação de rejeitos da mineração de ferro e serpentinito em silicatos e outros produtos de valor agregado

Abstract

In this work, iron and serpentinite mining tailings were used to produce value-added materials: sodium silicate, magnesium oxide/hydroxide and geopolymers. Serpentine is a rock rich in the serpentine family of minerals, Mg3Si2O5(OH)4. In the first part of the work, two different routes were used to obtain magnesium oxide/hydroxide and sodium silicate from serpentinite. The first route was a hydrothermal process in which the serpentinite was mixed with 1 to 10 mol L-1 NaOH solutions and the mixture was kept in an autoclave at 200 °C for 24 hours. In this route, the best result was obtained in the reaction that used 10 mol L-1 NaOH solution, leading to a solid composed mainly of magnesium hydroxide. In the second route, named solid route, serpentinite impregnations were carried out with NaOH solutions using amounts of 30 to 140% of NaOH in relation to the serpentinite mass, and the solids obtained were calcined at temperatures from 500 to 800 °C. For this route, the best result was obtained with the use of 140% NaOH and a calcination temperature of 700 °C, which resulted in a solid composed mainly of magnesium oxide. In both routes, a liquid fraction of sodium silicate solution was obtained. In the second part of this work, iron tailings reactions with NaOH were carried out. The iron waste used consists mainly of SiO2 (70.57%) and Fe2O3 (23.29%), according to X-ray fluorescence analysis. The reactions were carried out in an autoclave at 200 °C, quantities in mass of 1:1.5 and 1:2.5 of iron waste to NaOH and reaction times of 4 and 8 hours. Using proportions of 1:2.5 of waste to NaOH and a reaction time of 8 hours, it was possible to completely dilute the silica from the solid, obtaining a solid fraction consisting mainly of hematite and a solution of sodium silicate. In the third part of this work, geopolymers with different compositions were produced using mining tailings and serpentinite as fillers (proportions of 25 and 50%), and sodium silicate solution produced from iron tailings as activating solution. The geopolymers produced showed fast curing time and very good results in mechanical compressive strength, which ranged from 32.13 to 58.28 MPa.