This article presents a range of mix design formulations to obtain metakaolinbased geopolymer synthesis. Geopolymer samples were synthesized from metakaolin, a 10 M sodium hydroxide solution, and alkaline sodium silicate. These three components were mixed in different proportions to form a paste which was molded in a cylindrical shape, set at room temperature for 24 hours, and demolded. The workability of the paste, the integrity of the samples, development of efflorescence, and the presence of undissolved metakaolin particles in the microstructure of the geopolymer matrix were observed. Since sodium and water play a vital role in the geopolymerization and were added at fixed proportions, a mix design was employed based on the molar proportions of aluminum, silicon, and sodium plus water. The simplex design plot was able to separate the regions of a mix of the components that showed different behaviors according to the observed responses. The dissolution of metakaolin, condensation of orthosialate and silicate species, which are expected to interact with each other according to the model of geopolymerization of Davidovits, can explain the observed results. "Good results" (no release of white powder, no efflorescence, no shrinkage, and no cracks) after 28 days of curing at room conditions were observed for the molar proportions 0.097 < Al < 0.112, 0.120 < Si < 0.178, and 0.711 < Na+H 2 O < 0.775 (Na/H 2 O = 0.185).

The iron ore beneficiation process produces a large quantity of waste. Mining companies are looking for technologies that make it possible to dispose of their waste and transform it into raw material for the manufacture of products that can be applied in other areas, for example in the production of concrete, mortar, ceramics, blocks, and bricks. This study aimed at the feasibility of using a calcined iron ore overburden as a precursor of alkali-activated binders. For alkaline activation of the precursors, sodium hydroxide solution and sodium silicate were used in the atomic proportions Al / Na = 2 and Si / Al> 0,7. Mineralogical and microstructural characterization was carried out by X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX). Tests of compressive strength were performed for the binders with 7, 14, 21 and 28 of curing days. The results of the analyses demonstrated that the properties of the alkali-activated binders produced with the overburden were similar to the binders obtained by precursors used traditionally. It was found, therefore, that the calcined iron ore overburden, can be considered a precursor for obtaining alkaline activated binders