Reuse of iron ore tailing to potassium silicate synthesis and to the production of geopolymers

Abstract

This study is based on the principles of green chemistry and circular economy and involves reusing iron mining tailings to synthesize potassium silicate and further produce geopolymer, a sustainable substitute for Portland cement. Two different routes were used to obtain potassium silicate from the dissolution of silica present in iron ore tailings (IOT), namely, the hydrothermal route (HR) and the solid route (SR). For the HR, the results showed 7.58, 7.85, and 8.82 wt% SiO₂ in the solutions after 2, 6, and 8 h of reaction, respectively, indicating that these times had the same impact on the dissolution of silica. However, when performing the reaction for 24 h, the greatest dissolution was obtained for the hydrothermal route (ca. 14.65 wt% SiO₂). In the SR, it was observed that by increasing the amount of KOH, the dissolution of silica was also increased, the final solid had a content of 35.60 wt% SiO₂. The geopolymers produced using commercial potassium silicate and those produced with silicate obtained by SR showed mechanical strengths of 24.33 and 21.12 MPa, respectively. On adding IOT to the composition as a filler, there was a decrease in resistance values. The one-part synthesis methodology produced a material with a mechanical compressive strength of 31.21 MPa. This value of mechanical compressive strength is 24.84% higher than that required by the Brazilian standard for reinforced concrete in urban areas.