Mineral assemblage transformation of a metakaolin-based waste form after geopolymer encapsulation (original) (raw)
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In the present paper, bottom ashes from urban waste incineration were used as sole source material to develop geopolymers activated with alkali solution. This study intends to gather basic structural data on the synthesized materials at fixed curing times (3 h; 1, 4, 5, 7, 30 days; 20 months) by X-ray (XRD) and Fourier Transform Infrared (FTIR) analysis. Curing time affects both crystalline phase transformation and the geopolymeric gel structure. The XRD results showed the starting of geopolymerization, due to the alkali activation, already within the first 3 h of curing. New phases such as hydrated sodium carbonate and gismondine, confirming the progressive ash reactivity, appeared after 4 h and 1 day of curing respectively. Finally, after approximately 30 days curing at room temperature, the condensation process and, consequently, the formation of a stable 3D gel of aluminosilicate network occurred. FTIR showed a 40 cm À 1 displacement of the band at 980 cm À 1 during the first hours of the geopolymer formation confirming the formation of the geopolymeric network also from a matrix without metakaolin. Furthermore Scanning Electron Microscopy (SEM-EDS) analyses were performed to assess morphological characteristics and to evaluate the presence of unreacted aluminosilicate particles in the obtained geopolymers.
Rheology, Setting, Heat of Reaction, and Compressive Strength of a Geopolymer Radioactive Waste Form
Minerals
This work contributes to our understanding of the properties of geopolymers as waste forms made of three pozzolans, to be used, e.g., to immobilize liquid low-activity radioactive waste. A binary blast furnace slag and metakaolin geopolymer composition was tailored to achieve flexible rheological properties and workability for in-can mixing or mixing/pumping applications by adding fly ash, a third pozzolan. We investigated quantitatively the early stages of geopolymerization (before and after setting) of alkali-activated slag–metakaolin–fly ash pozzolans. The effect of fly ash glass particle size on material properties was studied as well. Measurements include heat of reaction, compressive strength, yield stress, plastic viscosity, rheological setting, as well as initial and final setting following the Vicat method. A rheological time of initial setting is suggested for geopolymers, in analogy to Portland cement. The results of Vicat needle and rheological measurements are compared ...
2007
This work was prepared under an agreement with and funded by the U.S. Government. Neither the U. S. Government or its employees, nor any of its contractors, subcontractors or their employees, makes any express or implied: 1. warranty or assumes any legal liability for the accuracy, completeness, or for the use or results of such use of any information, product, or process disclosed; or 2. representation that such use or results of such use would not infringe privately owned rights; or 3. endorsement or recommendation of any specifically identified commercial product, process, or service. Any views and opinions of authors expressed in this work do not necessarily state or reflect those of the United States Government, or its contractors, or subcontractors.
The stabilization/solidification (S/S) of carbon steel electric arc furnace (EAF) dust containing hazardous metals such as Pb, Cd, Cr or Zn using geopolymerization technology is described in this paper. On the basis of the results obtained in other studies about the leaching behaviour of EAF dust S/S solids, it has been decided to study in greater depth the solids prepared with different geopolymeric agents, in an effort to optimize the following variables: the amounts of metakaolin (MK) and blast furnace slag (BFS) in the mixes; the grain size of the fly ash used as main silicoaluminate precursor and the amount of potassium silicate, also considering in this case that KOH has been used in one composition to increase the potassium oxide/silicon oxide molar proportion from 0.5 to 0.8 and finally, the replacement of BFS by other slag (MS) coming from a stainless steel plant. Mixtures of EAF waste with these kinds of geopolymeric materials and class F fly ash have been processed to study the potential of geopolymers as waste immobilizing agents. A compressive strength test and different leaching tests to determine the efficiency of heavy metal immobilisation have been carried out. The amounts of potassium silicate and KOH are the most important parameters to reach a higher resistance. The best results for an acid leaching were shown in samples with a high amount of potassium silicate, however, for water leaching, the blast furnace slag is the best option.
Molecules, 2021
In this study, the role of two reactive fillers, specifically a sand from a clay washing process as an alternative to waste glass powder and a commercial metakaolin (MK), into the geopolymerization process of waste clay-based materials was assessed. Three kinds of clayey wastes from mining operations—halloysitic, kaolinitic and smectitic clays—were tested as potential precursor of geopolymeric materials in view of a potential valorisation of these by-products. A mix-design based on the addition of low percentages (20%) of these fillers or MK to improve the mechanical and chemico-physical properties of geopolymeric formulations was evaluated. All the clays were thermally treated at a temperature of 650 °C, while the geopolymeric pastes were cured at room temperature. In particular, the chemical stability in water (pH and ionic conductivity of leachate water, weight loss), the variations in the microstructure (XRD, SEM), and in the mechanical performance (compressive strength) were an...
Journal of Composites Science, 2021
The present research investigates the possibility to create a silt-waste reinforced composite through a NaOH-activated, metakaolin-based geopolymerization process. In this regard, we used thermal exo–endo analysis, X-ray diffraction (XRD), and oedometric mechanical tests to characterize the produced composites. In our experimental conditions, the tested material mixtures presented exothermic peaks with maximum temperatures of about 100 °C during the studied geopolymerization process. In general, the XRD analyses showed the formation of amorphous components and new mineral phases of hydrated sodalite, natrite, thermonatrite and trona. From oedometric tests, we observed a different behavior of vertical deformation related to pressure (at RT) for the various produced composites. The present work indicated that the proposed geopolymerization process to recycle silt-waste produced composite materials with various and extended mineralogy and chemical–physical properties, largely depending...
IOP Conference Series: Materials Science and Engineering
A combination of gasification of low and intermediate level radioactive waste (LILW) and conditioning of the resulting product within a geopolymer matrix is a potential alternative for vitrification technologies as an immobilisation method. Geopolymer matrices have demonstrated good retention capability for radionuclides in many studies and the technology has been implemented at an industrial scale in Slovakia and Czech Republic. However, the practical waste loading has been limited by the mechanical properties of the encapsulated matrix. Even a small amount of ion exchange resin (IXR) decreases the strength of the matrix and cohesion of the matrix is lost when the fraction of resin exceeds 15-20%. In this study, the potential to combine gasification as thermal treatment and various inorganic binders as encapsulation matrices was evaluated. After gasification, the mechanical properties were not similarly sensitive to the encapsulation of IXR. Gasification enabled substantially higher loading of IXR into the sample. Also, gasification of the IXR decreased matrix apparent Caesium diffusion. Very low apparent diffusion coefficients of Cs were calculated when gasified resin was encapsulated in metakaolin matrix. Theoretically, the amount of Cs within the same volume of encapsulated material could be increased by 800 times following gasification and encapsulation within an alkali-activated metakaolin (MK) binder.
Journal of Hazardous Materials, 2008
The synthesis of geopolymer matrixes from coal (co-)combustion fly ashes as the sole source of silica and alumina has been studied in order to assess both their capacity to immobilise the potentially toxic elements contained in these coal (co-)combustion by-products and their suitability to be used as cement replacements. The geopolymerisation process has been performed using (5, 8 and 12 M) NaOH solutions as activation media and different curing time (6-48 h) and temperature (40-80 • C) conditions. Synthesised geopolymers have been characterised with regard to their leaching behaviour, following the DIN 38414-S4 [DIN 38414-S4, Determination of leachability by water (S4), group S: sludge and sediments. German standard methods for the examination of water, waste water and sludge. Institut für Normung, Berlin, 1984] and NEN 7375 [NEN 7375, Leaching characteristics of moulded or monolithic building and waste materials. Determination of leaching of inorganic components with the diffusion test. Netherlands Normalisation Institute, Delft, 2004] procedures, and to their structural stability by means of compressive strength measurements. In addition, geopolymer mineralogy, morphology and structure have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), respectively. It was found that synthesised geopolymer matrixes were only effective in the chemical immobilisation of a number of elements of environmental concern contained in fly ashes, reducing (especially for Ba), or maintaining their leachable contents after the geopolymerisation process, but not for those elements present as oxyanions. Physical entrapment does not seem either to contribute in an important way, in general, to the immobilisation of oxyanions. The structural stability of synthesised geopolymers was mainly dependent on the glass content of fly ashes, attaining at the optimal activation conditions (12 M NaOH, 48 h, 80 • C) compressive strength values about 60 MPa when the fly ash glass content was higher than 90%.