Effect of the Class C Fly Ash on Low-Reactive Gold Mine Tailing Geopolymers

Abstract

Beneficiation of industrial wastes, such as mine tailings (MTs), through development of alternative eco-friendly geopolymer binders for construction composites offers a twofold environmental benefit, as it reduces the demand for cement and it increases the sustainability of industrial processes by creating a value-added product from an industrial byproduct. While MTs have the requisite composition for use as a geopolymer precursor, they are often low-reactive. This study explored the effect of Class C Fly Ash (FAc) on the geopolymerization of low-reactive gold MTs. A 10 M sodium hydroxide (NaOH) solution was used as the alkaline activator with four different concentrations of FAc (5, 10, 15 and 20 wt.%). The results indicated that the combination of FAc with the low-reactive gold MTs improved the physicochemical stability of the final geopolymerized samples, with a 95–120% increase in compressive strength, compared to the geopolymer samples of only low-reactive gold MTs. Although some of the strength improvement could be attributed to geopolymerization of the FAc itself, the presence of the FAc also improved the reactivity of the MTs, increasing the geopolymer production of the MTs. This study documents the positive effects of the FAc on gold MTs with low-calcium content and their conversion into sustainable inorganic composite geopolymers for the construction field.

Production and Incorporation of Calcium Hydrolyzed Nano-particles in Alkali-Activated Mine Tailings

“…The EDS semiquantitative chemical composition indicates the silicon (Si) as primary element of composition in this gold mine tailings, where aluminum (Al), and iron (Fe) are the majority secondary elements, and magnesium (Mg), calcium (Ca), potassium (K), and sodium (Na) are present in minor quantities. The quantitative X-ray diffraction data from this gold MTs was also reported in a previous research work [53], the results indicates that the main crystalline mineral phase is namely quartz (SiO2) - [51,54], following by muscovite (KAl2(FOH)2 or (KF)2(Al2O3)3(-SiO2)6) [51], magnetite (Fe3O4) [36,55], albite (Na(AlSi3O8)) [51,54,56], C-A-S-H (Ca3Al(Al3SiO10)(OH)2) [53], N-A-S-H (Na17.6(Al16Si56O144)(H2O)38.4) [53]. Additionally, a percentage of amorphous phase was also identified [53].…”

“…The quantitative X-ray diffraction data from this gold MTs was also reported in a previous research work [53], the results indicates that the main crystalline mineral phase is namely quartz (SiO2) - [51,54], following by muscovite (KAl2(FOH)2 or (KF)2(Al2O3)3(-SiO2)6) [51], magnetite (Fe3O4) [36,55], albite (Na(AlSi3O8)) [51,54,56], C-A-S-H (Ca3Al(Al3SiO10)(OH)2) [53], N-A-S-H (Na17.6(Al16Si56O144)(H2O)38.4) [53]. Additionally, a percentage of amorphous phase was also identified [53].…”

“…Additionally, there is a direct increase of the amorphous content as the calcium hydrolyzed nanoparticles concentration increases in the AAMs specimens, indicating the production of more cementing binders in amorphous state [53]. These results suggest that the presence of the calcium hydrolyzed nanoparticles during the MTs alkaline activation process positively contributed to the dissolution of the aluminosilicate phases, allowing for the generation of additional binders that ultimately contribute to the strength increase in the AAMs specimens (Fig.…”

“…In addition, it is well known that the N-A-S-H phase is present in the raw MTs (section 3.1.) and it is a the zeolitic precursor [53]. However, it is possible to observe that as the calcium hydrolyzed nanoparticles content increased in the AAMs systems, the zeolite formation decreased, indicating the potential preference of these systems to generate other phases over the zeolite in presence of calcium species.…”

“…Gold MTs sample from Vitor (Arequipa, Perú) were used in this study. The geotechnical characterizations of this MTs have been reported in previous works [52,53] and a summary of their characteristics are listed as follows: (1) the mean particle size D50 = 0.086 mm with a fine's percentage equal to 41.16% and (2) a coefficient of uniformity Cu = 5.05. The MTs were classified as silty sand (SS) with low plasticity according to USCS classification standards, having a low liquid limit (23.08%), low plasticity (PI = 1.34%), and low capacity for holding water (A = 0.033) [52,53].…”