Inorganic polymer cement from Fe-Silicate glasses: Varying the activating solution to glass ratio

Large volumes of Fe-silicate glasses - slags - are produced as residues of metal production and waste treatment processes. It would be interesting if these materials could become an alternative group of precursors for the synthesis of inorganic polymer (IP) cements. This paper investigates the polymerisation of Fe-silicate glasses of composition (in wt%) SiO2: 40; FeO: 30; CaO: 15; Al2O3: 8 and an activating solution of composition (in wt%) Na2O: 15; SiO2: 13; H2O: 72. The mass ratio of the activating solution to the glass (L/S) was varied from 0.3 to 1.0 and the effect on the IP chemistry, microstructure and properties was investigated. Despite the high Fe and low Al contents of the glass, an IP cement could be synthesised, resistant to water dissolution and delivering mortars of compressive strength >52 MPa after 28 days curing at room temperature when using a L/S ratio of 0.45. Lowering the ratio from 1.00 to 0.45 results in a significant improvement in compressive strength, a lower porosity and when immersed in water, Na dissolution is decreased and water pH is lower. Microstructural investigation indicates that when the amount of activating solution is decreased, the degree of glass dissolution is lower resulting in less IP formation and a more homogeneous IP chemistry. Compared to higher L/S ratios, the IP mortar has a more densely packed microstructure of partially dissolved glass and sand aggregates bound by the IP matrix. At lower L/S ratios, the formation of micro scale shrinkage cracks in the IP matrix is strongly reduced, while at higher L/S ratios, shrinkage cracking is more pronounced and individual micro-cracks connect to form more pronounced large scale cracks. At a L/S ratio of 0.45, the IP cement is composed of 90 wt% Fe-silicate glass and only 10 wt% Na-silicate (% of powder mix) and it is indicated that this percentage can still be reduced. As 90 wt% of this IP cement is composed of a waste material and as curing is performed at ambient temperatures, its production is expected to have important ecological and economic benefits.status: publishe

Experimental investigation of hydration of ternary blended cement paste

In this paper, ternary and binary blended cement pastes as well as pure Portland cement paste were prepared by Portland cement, ground granulated blast-furnace slag (GGBFS), limestone powder and water, which were then hydrated from 1 to 91 days at 20 °C in a sealed environment. At each curing age, the hydration kinetics of cement and slag was determined by XRD/Rietveld and selective dissolution method (EDTA), respectively. The content of CaCO3 (limestone) was quantified by Thermogravimetric analysis (TGA) technique. The degree of hydration of cement clinker was distinctly accelerated by the single addition of slag or limestone within 91 days of hydration. The coexistence of slag and limestone in ternary blended cement accelerated the hydration of cement clinker within the first 14 days of hydration, but lowered the degree of hydration of cement clinker after 91 days of hydration compared with other pastes. The degree of reaction of slag in blended cement pastes was about 8% and 35% after 1 and 91 days of hydration, respectively, which was almost not influenced by the addition of limestone powder. A small amount of limestone, i.e. around 2% of the total solid raw materials, was reacted in pastes, and mainly occurred at the early age. Based on the experimental investigation, the results show that the hydration of calcium silicate phases of cement in pastes was enhanced by the presence of limestone, but hampered by slag. The hydration of calcium alumina phases of cement was greatly accelerated by the addition of slag, and also enhanced by the presence of limestone powder in binary blended limestone cement paste at early age. However, the coexistence of limestone with slag in ternary blended cement paste restrained the hydration of calcium alumina phases of cement

La Roca Mágica - Zeolite occurrence and genesis in the Late Cretaceous Cayo arc of Coastal Ecuador.

The main objective of this study was to investigate the zeolite occurrence and distribution in the Late Cretaceous Cayo Formation of Coastal Ecuador and to relate it to the local and regional geological evolution of the area, in order to understand the zeolite occurrence, distribution and the processes of zeolite genesis in the Cayo arc. A mineralogical characterization of the area was combined with an investigation of the geological processes operating on both local and regional scale. A review of the state of the art of natural zeolite investigation showed that most zeolite deposits in marine arcs are interpreted to be formed by burial metamorphism, although the presence of local volcanic centers can have an influence on the alteration patterns. Therefore, it was chosen to study the vertical variation in zeolite mineralogy through the Late Cretaceous deposits on one hand, and the alteration near the source area of these deposits on the other hand. However, an alternative model is proposed for this type of zeolitization in literature, explaining zeolite formation by the interaction of hot pyroclasts with water. Therefore, a great effort was made to understand the eruptive and depositional processes in the Cayo arc, and to relate these processes with the alteration and the variation in alteration mineralogy through depositional sequences. One of the objectives of this work was to develop a standardized method for the mineralogical characterization of the zeolitic rocks. The main technique used was powder X-ray diffraction with the application of the Rietveld refinement method. To obtain information about the chemistry of the alteration minerals, EPMA, SEM-EDX and ICP-OES methods were used. The mineralogical characterisation showed that zeolites are common through the entire stratigraphical thickness of the Cayo Formation and over its entire outcrop area, in percentages varying from <20% to 100%. Ca-heulandite and Ca-clinoptilolite are the most abundant zeolites, while mordenite and laumontite are also common. Analcime and stilbite occur locally, while thomsonite, erionite, chabazite and epistilbite are rare. Clay minerals are common and are mainly di- or tri-octahedral chlorite/smecite, with varying proportions of smectite, and celadonite. Albite is common, occurring mainly together with laumontite, while authigenic K-feldspar is rare. Quartz is common, while opal-CT was identified in only few samples and in low percentages. Prehnite and pumpellyite occur rarely. Field and petrographical analyses of the Cayo Formation lead to a renewed stratigraphy of the Late Cretaceous deposits, and a better understanding of the volcanic evolution of the area. The Calentura Formation is restricted to the fine grained beds of Middle Coniacian age. The Cayo Formation is divided into two units. The lower Río Guaraguao unit has a Middle Campanian age and is composed of andesitic breccia, thick pyroclastic flow deposits and minor intercalated epiclastic beds. These deposits originate form a submarine dacitic-andesitic volcanism which was related to an intra-oceanic subduction zone existing at the eastern edge of the Proto-Caribbean plate. The upper unit, of Late Campanian to Early Maastrichtian age, is composed of epiclastic beds, block and ash flows and in its upper part of pyroclastic flow deposits, and records an undeep marine to subaerial subduction related volcanism. The docking of the South American continent in the subduction zone from 73 Ma, resulted in the ceasing of the volcanism in the area in the Early Maastrichtian. Subsequently, a decoupling from the Caribbean plate occurred in the Maastrichtian – Early Paleocene and the Cayo arc was incorporated into the South American plate. In the Río Guaraguao section, a depth zonation was identified in the alteration mineralogy. In the upper unit of the Cayo formation, Ca-heulandite-type zeolites and minor analcime occur. In the central part of the Cayo formation mordenite is the main zeolite and it is associated by Ca-heulandite-type zeolites, and minor laumontite, albite and stilbite. In the lowermost part laumontite and albite are the main alteration minerals. Near the base of the formation traces of pumpellyite were found. The observed zonation can not be explained by burial metamorphism, because of the limited burial of the deposits. The maximum burial related temperature at the base of the Cayo Formation was estimated at 75°C, too low for the formation of laumontite, albite and pumpellyite. This is confirmed by the low maturity of organic material in the underlying Calentura Formation. In the lower unit of the Cayo Formation, a clear relation was identified between the presence of thick pyroclastic flow deposits and the presence of 4 zones of high-grade alteration through the section. These four periods of pyroclastic flow deposition alternate with periods of epiclastic deposition. In the epiclastic beds, only low-grade diagenetic alteration occurred. The northern part of the Guayaquil area is the only region of the outcrop area of the Cayo Formation where zeolites are rare. An albite-chlorite-quartz alteration zone occurs in this region and corresponds to the extension of a caldera structure present in this area. The occurrence of chlorite, albite and prehnite and the presence of quartz veins with epidote, pyrite and galena around the central intrusive in the caldera, indicate the presence of a prophylitic alteration around the intrusive. However, the alteration is limited to the extend of the caldera structure and primary zeolitization around the caldera structure is little affected. In order to understand better the early hydrothermal alteration occurring in cooling pyroclastic deposits, several depositional sequences in the lower unit of the Cayo Formation were studied. Pyroclastic flow deposits are up to several tens of meters thick and were derived from explosive gas-driven submarine eruptions. The presence of gas pockets in the rocks and the presence of agglutinated pumice clasts, demonstrate that these deposits were still hot at deposition. A regular zonation in alteration mineralogy was described through these sequences. In all cases, a mordenite – celadonite – quartz dominated assemblage at the top of the units, grades into a heulandite – C/S dominated assemblage at the base of the units and in some cases, in the thicker pyroclastic units, to a laumontite-albite dominated assemblage. From the top to the base of the sequences, subsequent replacement reactions of mordenite to heulandite and of mordenite and heulandite to laumontite occur. The latent volcanic heat in the pyroclasts is interpreted to be the dominant factor causing the alteration of the sequences. Downwards in the deposits, temperatures will remain hot for longer, infiltration of marine water is limited and higher solid/liquid ratios occur, leading to progressive replacement of metastable phases to the thermodynamically most stable assemblages.nrpages: 232status: publishe

Inorganic polymers from a plasma convertor slag: Effect of activating solution on microstructure and properties

Plasma processing of materials is a technology now also employed in the management of municipal solid wastes, often mixed with industrial residues. The specifics depend per case, but typically the process delivers energy, in the form of a gas or heat, a metal-rich fraction as well as a slag. The slag, containing mainly Si-, Fe-, Ca- and Al-oxides, is almost completely amorphous after rapid cooling and thus could possibly be used as precursor in the synthesis of inorganic polymers (IP). The latter is explored in the present work. Slag resembling the composition of refuse-derived fuel ash was mixed with various Na-silicate activating solutions, and the effect of SiO₂/Na₂O as well as H₂O/Na₂O molar ratio on the synthesis and mechanical properties of the prepared IP was investigated. It was found that for SiO₂/Na₂O molar ratios of 1.2 and H₂O/Na₂O molar ratio of 30.8, the mechanical strength of casted IP reached almost 90 MPa after 90 days. Further decrease in the SiO₂/Na₂O ratio, accompanied by decrease in the H₂O/Na₂O ratio, increased the early strength and the released reaction heat, but had no effect on the late strength. In addition to that, crack formation was pronounced. The increase of the concentration of activating solution, by means of reducing the water content level, i.e. H₂O/Na₂O, resulted in an increase of the released reaction heat as well as an increase of the mechanical strength, up to 112 MPa at 90 days. The above results are relevant to a range of metallurgical slags and other vitreous by-products and contribute towards more high added-value applications.status: publishe

ENHANCED LANDFILL MINING, THE MISSING LINK TO A CIRCULAR ECONOMY 2.0? PREFACE TO THE SPECIAL ISSUE ON RESOURCE RECOVERY THROUGH ENHANCED LANDFILL MINING

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Eruptive history and source area of 2-nd Rupelian acid phase volcaniclastics from northern parts of Dzhebel depression (Eastern Rhodopes, South Bulgaria) as inferred from the pyroclastic stratigraphy and petrography

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Influence of the chemistry of vitrified residues on the properties of blended inorganic polymers with calcined kaolinitic clay

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Desarrollo de las investigaciones en Zeolitas Naturales en el Ecuador

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Are groundwater overextraction and reduced infiltration contributing to Arsenic related health problems near the Marlin mine (Guatemala)?

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