30 research outputs found
Synthetic glass with high alkali-reactivity and near-zero RM- CO2 emissions
As cement-related CO2 emissions increase, alternatives are actively sought. Cement substitution by slag and fly ash is standard practice worldwide and while higher side stream utilization is necessary, their volumes are not adequate to significantly alter global CO2 emissions. Cement substitution by, and alkali activation of, calcined clays offer an alternative with zero raw-material-related CO2 (RM-CO2) emissions.
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Synthesis and alkali activation of Magnesium-rich aluminosilicates
Abstract
Alkali-activated materials (AAMs) are alternative cementitious materials with lower carbon footprints compared to traditional Portland cement (PC). In addition to Ca, Si, and Al, the precursors used in the preparation of AAMs can sometimes include considerable amounts of Mg, so that Mg significantly influences the structure and properties of AAMs. When compared to Ca, Si, and Al, relatively few studies have focused on the role of Mg in AAMs. This thesis deals with alkali activation of Mg-rich aluminosilicate precursors with the following objectives: 1) preparation, characterization, and estimation of alkaline reactivity of Na-Mg aluminosilicate glasses; 2) synthesis of AAMs from Na-Mg aluminosilicate glasses and their detailed characterization to understand the fate of Mg; and 3) estimation of the potential of phlogopite as a Mg-rich raw material for alkali activation.
The structural study of Na-Mg aluminosilicate glasses indicates that the higher cationic field strength (CFS) of Mg than Na makes Mg preferable as a network modifier, whereas Na acts as a charge compensator. Alkaline reactivity studies of Na-Mg aluminosilicate glasses reveal that as Mg replaces Na in glasses, the reactivity of the glasses increases initially, attains a maximum, and then drops. This trend can be explained by the interplay between glass depolymerization and optical basicity: depolymerization dictates the glass reactivity initially, while the effect of optical basicity dominates at later stages. Detailed structural study of AAMs prepared from Na-Mg aluminosilicate glasses indicates that Mg in AAMs exists as an amorphous magnesium silicate (AMS) phase, but the existence of this phase is not well documented in the literature. The driving force for AMS formation is the high CFS of Mg, which leads to effective stabilization of the depolymerized silicate species. The absence of hydrotalcite-group phases from these AAMs is due to the depletion of Al by zeolite production. The assessment of phlogopite mineral as a Mg-rich precursor for alkali activation indicates that untreated phlogopite is highly inert. However, thermal treatment could enhance the alkaline reactivity of phlogopite.TiivistelmÀ
Alkali -aktivoidut materiaalit (AAM) ovat vaihtoehtoisia sementtimateriaaleja, joilla on pienempi hiilijalanjÀlki verrattuna perinteiseen portland -sementtiin (PC). Ca: n, Si: n ja Al: n lisÀksi esiasteissa (joita kÀytetÀÀn AAM: ien valmistukseen) voi joskus olla huomattava mÀÀrÀ Mg: tÀ, ja tÀmÀ johtaa siihen, ettÀ Mg vaikuttaa merkittÀvÀsti AAM: ien rakenteeseen ja ominaisuuksiin. Verrattuna Ca, Si ja Al, on ollut suhteellisen vÀhÀn tutkimuksia, joissa keskitytÀÀn Mg: n rooliin AAM: issÀ. TÀmÀ opinnÀytetyö kÀsittelee Mg-rikkaiden alumiinisilikaattiesiasteiden alkaliaktivaatiota seuraavilla tavoitteilla: 1) Na-Mg-alumiinisilikaattilasien alkalisen reaktiivisuuden valmistelu, karakterisointi ja arviointi; 2) synteesi AAM: istÀ Na-Mg-alumiinisilikaattilasista ja niiden yksityiskohtainen karakterisointi Mg: n kohtalon ymmÀrtÀmiseksi; 3) Flogopiitin potentiaalin arviointi Mg-rikkaana raaka-aineena alkalin aktivoimiseksi.
Na-Mg-alumiinisilikaattilasien rakennetutkimus osoittaa, ettÀ Mg: n korkeamman kationisen kentÀnvoimakkuuden (CFS) takia Na: n vuoksi Mg on edullinen verkon muokkaajana, kun taas Na toimii varauksen kompensoijana. Na-Mg-alumiinisilikaattilasien alkaliset reaktiivisuustutkimukset paljastavat, ettÀ kun Mg korvaa Na: n lasissa, lasien reaktiivisuus kasvaa aluksi ja saavuttaa maksimin, minkÀ jÀlkeen se laskee. TÀmÀ suuntaus voidaan selittÀÀ lasin depolymeroinnin ja optisen emÀksisyyden vÀlisellÀ vuorovaikutuksella: depolymerointi sanelee aluksi lasin reaktiivisuuden, kun taas optisen emÀksisyyden vaikutus hallitsee myöhemmÀssÀ vaiheessa. Yksityiskohtainen rakenteellinen tutkimus AAM: ista, jotka on valmistettu Na-Mg-alumiinisilikaattilasista, osoittaa, ettÀ Mg AAM-yhdisteissÀ esiintyy amorfisena magnesiumsilikaatti (AMS) -faasina, jonka olemassaoloa ei ole hyvin dokumentoitu kirjallisuudessa. AMS: n muodostumisen liikkeellepaneva voima on Mg: n korkea CFS, mikÀ johtaa depolymeroitujen silikaattilajien tehokkaaseen vakautumiseen. HydrotaltsiittiryhmÀn faasien puuttuminen nÀistÀ AAM: ista on havaittu johtuvan Al: n ehtymisestÀ zeoliittituotannolla. Flogopiittimineraalin arviointi Mg-rikkaana esiasteena alkalin aktivoitumiselle osoittaa, ettÀ kÀsittelemÀtön flogopiitti on erittÀin inertti. LÀmpökÀsittely voi kuitenkin parantaa flogopiitin emÀksistÀ reaktiivisuutta
On the carbonation of brucite: Effects of Mg-acetate on the precipitation of hydrated magnesium carbonates in aqueous environment
Structural collapse in phlogopite mica-rich mine tailings induced by mechanochemical treatment and implications to alkali activation potential
Abstract
The alkali activation of mine tailings is of interest to diminish the impoundment storage of large waste stream from mining industry. However, most of the mine tailings, like phosphate mine tailings generated in Finland, are rather inert and need pre-treatment to induce the reactivity for alkali activation. In this work, mechanochemical treatment was conducted to improve the reactivity of phosphate mine tailings. The ground specimens were subjected to the crystal structural analysis of X-Ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermal analyses by Thermogravimetry/Differential Thermal Analysis (TG/DTA), showing the increment of amorphous content and structural degradation as a function of grinding time. The subsequent alkaline reactivity test illustrated incremental alkaline dissolution of Si, Al and K and a schematic diagram of altered phlogopite structure (sources of aluminosilicates in tailings) was also proposed. Additionally, the mineralogical composition of individual particles was carried out by mineral liberation analysis (MLA), thereby evaluating the influence of pre-treatment on the mineralogy of tailings. The results indicate profound micromorphological changes and structural cleavage of the precursor due to grinding, which strongly increase alkaline reactivity
One-part geopolymers from mining residues â effect of thermal treatment on three different tailings
Abstract
Use of mine tailings as an aluminosilicate precursor in alkali activation is becoming an interesting alternative to manage the high-volume of waste generated from mining industries. However, very few tailings have so far been studied for their mineralogical properties and alkali activation potential. This study aims at understanding the ability of mine tailings from phosphate, kaolinite and lithium mines for their efficient participation in alkali activation. Biotite, muscovite, kaolinite, albite, and quartz were found to be the major minerals present in them. The impact of variation in mineralogy on silica and alumina solubility of these tailings was analyzed. The solubility was found to be high in impure kaolinite compared to the other two. Effectiveness of thermal treatment (750âŻÂ°C and 900âŻÂ°C) on improving the reactivity of these tailings in alkaline condition was also investigated. It was observed from the results that the effect of thermal treatment on the crystalline structure and solubility of an aluminosilicate material mainly depends on the mineral structure of the material, as well as the treatment temperature. Interestingly, thermal treatment reduced the solubility of lithium tailings with albite and quartz mineral. Effort has been made to relate the strength attained by alkali activation of mine tailings to their solubility values. However, despite of the higher solubility offered by impure kaolinite, phosphate tailings gives the maximum strength improvement by 62%. This can be due to the presence of calcium compounds in phosphate tailings that resulted in additional hydration products
Immobilization of sulfates and heavy metals in gold mine tailings by sodium silicate and hydrated lime
Abstract
Gold mining produces hazardous tailings wastes with elevated sulfur content and high levels of heavy metals including oxyanion elements such as V and As. This research investigated activation of these tailings with calcium hydroxide and sodium hydroxide/sodium silicate as a way to stabilize the material and limit leaching of harmful components. The effects of thermal treatment on the reactivity of the tailings and the use of different activating solutions on the physical properties, microstructure and leaching of harmful components are reported. The effect of adding ground granulated blast furnace slag to the tailings is also assessed. The use of 5âwt % Ca(OH)â activating solution produces optimum performance increasing the immobilization efficiency of sulfates, arsenic and the other harmful elements. Heat-treating mine tailings at 900â°C slightly improves the reactivity but did not improved the immobilization efficiency. Microstructural analysis by TEM and XRD confirmed that stabilization is based on calcium sulfate and/or ettringite formation during alkali-activation. All materials achieved reasonable compressive strength after 28 days of curing and the potential for using alkali activation as a method to treat tailings from mining is discussed
On the carbonation of brucite:effects of Mg-acetate on the precipitation of hydrated magnesium carbonates in aqueous environment
Abstract
The role of organic ligands on the formation of hydrated magnesium carbonates (HMCs) has been remaining unclear. This work reports insights into the effects of Mg-acetate on the carbonation of brucite including the kinetics of reaction, the precipitation of different HMCs, and reaction mechanisms. We found that the organic ligand increases the kinetics of brucite's carbonation and alter the formation and conversion of HMCs. A relatively unknown phase (i.e., giorgiosite) precipitates in the presence of Mg-acetate with nanowire morphology. With the presence of acetate ligand, nucleation sites formed after the breakdown of Mg-acetate complexes and be replaced by the MgâCOâ bonds. These sites act as a sink for MgÂČâș to grow crystals and prevent the passivation layer of HMCs on brucite's surface. Findings reported here can enable an approach to steer pore solution chemistry in the HMC-based binder for better reaction degree, durability, and mechanical properties
Ag- or Cu-modified geopolymer filters for water treatment manufactured by 3D printing, direct foaming, or granulation
Abstract
In this work, we compared the main characteristics of highly porous geopolymer components for water treatment applications manufactured by 3D printing, direct foaming, or granulation. Furthermore, different approaches to impregnate the materials with Ag or Cu were evaluated to obtain filters with disinfecting or catalytic properties. The results revealed that all of the investigated manufacturing methods enabled the fabrication of components that possessed mesoporosity, suitable mechanical strength, and water permeability, even though their morphologies were completely different. Total porosity and compressive strength values were 28âvol% and 16âMPa for 3D-printed, 70â79âvol% and 1âMPa for direct-foamed, and 27âvol% and 10âMPa for granule samples. Both the filter preparation and the metal impregnation method affected the amount, oxidation state, and stability of Ag and Cu in the filters. However, it was possible to prepare filters with low metal leaching between a pH of 3â7, so that the released Ag and Cu concentrations were within drinking water standards
Study of synthetic titania slags demonstrating characteristics similar to high titania ilmenite slag
Abstract
The upgradation of the ilmenite ore, using a pyrometallurgy method, is performed using a carbothermic reduction of the ilmenite. A high titania slag is obtained which is used as a feedstock for the TiOâ pigment production. The slag is cooled after tapping in big molds and can take ten days to cool. This cooling method has remained the same since the inception of ilmenite smelting and recently rapid cooling through granulation has been utilized. The work presented in this paper focuses on the microstructural study of the slags that were prepared using different techniques and cooled at different cooling rates. Various analytical techniques, such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and X-ray photoelectron spectroscopy (XPS) were used to exhibit the similarity of these synthetic slags to the properties of high titania ilmenite slag. The slag consisted mostly of pseudo-brookite phase with a MâOâ
stoichiometry and smaller amounts of silicate and rutile phase. A glassy phase of silica was observed and most of the impurities were found to be present in the silicate phase. These silica phases were observed to be separate from the pseudo-brookite phase and along the phase boundaries. Micro-cracking of the slag surface, which is the characteristic of the MâOâ
phase formed in the ilmenite slag, were observed under the SEM analysis. The XPS analysis revealed that faster cooling does result in lower amount of oxidation but the difference in the TiOâ and TiâOâ composition can have larger impact on oxidation than the cooling speed