Geopolymerization mechanism of binder-free mine tailings by sodium silicate (original) (raw)
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The demand for low environmental impact of materials in our habitat is one of the current societal challenges. Along with other solutions of waste valorisation, alkali activation as geopolymers can be one possible solution of waste valorisation because they may allow, for instance, an alternative solution for cement-based materials in some applications and it is one contribution for circular economy. This work has focused on the development and processing of geopolymers that incorporates as a fine aggregate a high-sulfidic mining waste (mine tailing), a difficult waste to process. Rheology analysis was applied as an important step to understand not only the geopolymers behaviour but also its transition from the fresh to the hardened state. The effect of precursor binder type (metakaolin or blast furnace slag), of mine tailing content and also the effect of temperature and curing conditions of different formulations were studied in this solution. It was possible to conclude that alth...
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In this study, the alkaline solutions (NaOH) with concentrations from 1M to 18M, red mud (RM) and silica fume (SF) were used as reactors in geopolymer reactions. RM contains 7.40% SiO 2 and 13.65% Al 2 o 3 and SF has 94.50% SiO 2 , but only the active oxides can participate in the geopolymer reactions. The activity of the oxides was investigated by determining the compressive strength of the samples under different curing conditions. The characteristics of the geopolymer samples were determined by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analysis (TGA)/differential thermal analysis (DTA) and nuclear magnetic resonance analysis (NMR). The experimental results indicate that active silica mainly exists in SF. In the structure of geopolymers, the silicon can bond directly with each other (Si-Si) or be linked through 'bridging' oxygen (Si-O-Si) to form independent polymer chains, while aluminium atoms can only replace the silicon atoms in Si-O-Si polymer chains to form Si-O-Al instead.
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Cement and Concrete Composites, 2017
and 5:1 by using silica fume as silica corrector to alter Si ratios. The microstructure and strength of these geopolymers were characterized through XRD, SEM, NMR and compressive strength measurements. The dissolving rates of Al and Si species in geopolymerization were measured, and freeze-dried N-AS -H gel was characterized by FTIR spectra. Modelling and simulation were employed to calculate the binding energy of one Si atom and the total energy of geopolymers formed at various Si/Al ratios. At Si/Al ratio of 2:1, high concentrations of Si and Al species are dissolved from precursors, high contents of Si-O-T linkages are formed and the geopolymer is of high compressive strength. The mechanical strength of geopolymers at various Si/Al ratios is dependent on the formation of N-AS -H gel, rather than the zeolitic nuclei or silicate derivatives. This study might provide fundamentals for the geopolymerization of mine tailings, which usually possess high Si/Al ratios.
Geopolymers from mining tailings for more sustainable raw material supply
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For ecologic and economic reasons tailings, waste rock and water management become progressively important factors in the mining industry. The European Union funded project ‘Integrated mineral technologies for more sustainable raw material supply’ (ITERAMS) aims to (1) close the water cycle of the mineral processing plant (i.e. minimizing the release of wastewater to the adjacent environment), and (2) to use tailings (and waste rock) as raw materials for geopolymers. This will (1) enable significantly more efficient water recycling at the mining sites, (2) deliver cost savings and added income due to the valorisation of solid waste residues, and (3) minimize the overall environmental footprint of the mining industry and will therefore help improving its performance and as a consequence its social position. The developed solutions influence the total lifecycle of the mining operation, as they provide input to project planning and operational phases as well as to the closure and recul...
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This paper is based on the characterization of synthesized geopolymer binders based on either powder or solution silicate, and the amount of water contained in synthesized binders is determined to evaluate their possibility to coat a brick. The structural evolution of the formed geopolymers was investigated using FTIR spectroscopy. The mechanical properties were evaluated using compression tests. The structural evolution ensured that the solutions prepared from silicate powder or liquid had different degrees of polymerization, which modified the polycondensation reaction of the mixture. Nevertheless, the use of aluminosilicate solutions based on powder or liquid display similar behavior in a polycondensation reaction. The obtained materials show good mechanical properties, and it is possible to deposit this binder on the brick depending on the water content.
Effect of nano-silica on microstructure formation of low-cost geopolymer binder
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Influence of Nano-SiO 2 (NS) addition on properties of Geopolymer materials has been studied through measurement of physicomechanical and morphological characteristics of the hardened specimens. Alumino-silicate materials are water-cooled slag, albite, kaolin, and metakaoline. Materials were prepared at water/binder ratios in a range of 0.244:0.320 for water-cooled slag based materials, while it increased to 0.46 for albite-based mixes, whereas the used activator sodium hydroxide is 10 wt.%. The control geopolymer mix has been composed of water-cooled slag, metakaoline, and kaolin in the ratio of (4:2:1). Albite used for comparison with slag to demonstrates the possibility of producing lightweight geopolymer binder. Nano-silica was added in the range from 0:3% from the total weight with 0.5% increment. Results indicated that, compressive strengths of geopolymer mixes incorporating NS were obviously higher than those of control one, specially at early ages as well as up on using 2.5% NS with the lowest percentage of water absorption; also uses of albite instead of slag results in formation of light binder with promising mechanical characteristics.