Effect of Different CO2 Treatments on the Metal Leaching in Steel Slag Binders

Carbonation is an effective method to promote the quality of the steel slag binder. In this article, two carbonation approaches, namely hot-stage carbonation and accelerated carbonation, were employed to leach the metals, and the influence mechanism on the metal sequential leachability of the binders composed of 80 wt% of EAF slag incorporating 20 wt% of Portland cement (PC) was revealed. The carbonate products, microstructures, and chemical states were investigated, and the results indicated that chromium, vanadium, and titanium gradually transformed into inactive phases after two carbonation approaches, while zinc appeared the opposite trend. The sequential leachability of chromium declined with the increase of the carbonation efficiency, in which the exchangeable chromium decreased from 1.99 mg/kg in the A2A binder to below the detection limit in the A2C binder and C2C binder. Hot-stage carbonation treatment facilitated particle agglomeration, minerals remodeling, and calcite formation. The carbonation curing of the steel slag paste resulted in the formation of amorphous CaCO3, calcite crystalline and Si-bearing hydrates that covered the pores of the matrix, and silicate structure with a higher disorder. The hot-stage carbonation and accelerated carbonation curing methods were adopted to jointly prevent the leaching of harmful metals and facilitate promising high-volume steel slag-based binders with structural densification and CO2 storage.

Fast material disintegration of cement concrete in the exterior

Over the recent years the amount of fast destruction defects of cement paste matrix has increased markedly for exposed concrete structures of highway and airport pavements. The accelerated destruction of silicate structure is unusual due to its irregular occurrence. It only occurs at 30 to 50% of newly built pavements (in continuous segments). The issue is applicable to loaded as well as unloaded pavements. Detailed diagnostics found that the probable cause is based on concurrently occurring expansive reactions in capillaries, cracks and pores in the cement paste matrix. In defect spots the presence of several expansive substances was proven, wherein the biggest question poses the unexpectedly high potassium concentration. Potassium is only contained at best in trace amounts in road concrete input components in the Czech Republic. Neither existing regulations nor standards sufficiently deal with this type of defects of cement concretes. If they mention the existence of this issue at all, they are just limited to recommendations. Since the modification of the existing commercially produced cements to pavements is still improbable, the solutions to this issue seem problematic.

Study on the Compressive Strength of Alkali Activated Fly Ash and Slag under the Different Silicate Structure

Due to its high activation efficiency, waterglass has been widely used for alkali activations in geopolymer. In this study, the n(SiO2)/n(Na2O) (Ms) of waterglass was selected as the variable to investigate the role of the silicate structure on the mechanical properties of harden pastes. Ms was changed by the addition of NaOH to obtain the different silicate group, structure and experiments were performed by employing the liquid-sate 29Si nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and gel permeation chromatography (GPC) techniques. Furthermore, selected dissolution, scanning electron microscope (SEM-EDX), X-ray photoelectron spectroscopy (XPS) and FTIR experiments were used to measure the development of the amorphous gel and other materials with different curing condition. Results show that silicate structure of the waterglass was changed via the Si-ONa+ formation and the electric charge effect of Na+. Under the lower Ms waterglass, the Q0, Q1 and QC2 structure reverted to the main structure of the silicate group, which was kind of lower seize, molecule weight, linear or circular chain lower geopolymerization degree silicon structure. It would accelerate the geopolymerization speed of prepolymer formation. In addition, higher activity degree of Q0 and Q1 were useful to increase the formation amount of the gel structure with a low Si/Al ratio and size. Thus, silicate structure of waterglass controls the amorphous gel properties to adjust the compressive strength of alkali-activated materials.

Br diffusion in phonolitic melts: Comparison with fluorine and chlorine diffusion

Bromine diffusion was measured in two natural phonolitic melts: (1) a K2O-rich (~10 wt%) one synthesized from the white pumice phase of the 79 AD eruption of Vesuvius (Italy), and (2) a Na2O-rich (~10 wt%) one corresponding to the most differentiated melt of the 12 000 BC eruption of the Laacher See (Germany). Experiments were performed at 0.5 and 1.0 GPa, 1250 to 1450 °C, at anhydrous and hydrous (2.65 ± 0.35 wt% of dissolved water) conditions. Experiments conducted with the diffusion-couple technique in the piston cylinder were performed with only bromine diffusing and with the simultaneous diffusion of a halogen mixture (F, Cl, Br) to evaluate the interactions between the halogens during diffusion. The diffusion profiles of Br were measured by X-ray fluorescence using synchrotron radiation microprobe (SYXRF), ID18F, at the European Synchrotron Radiation Facility (ESRF, France). Bromine diffusion displays Arrhenian behavior under anhydrous conditions that is similar when it diffuses alone and when it diffuses with F and Cl. The Br diffusion coefficients range between 2 × 10–12 m2/s at 1250 °C and 1.5 × 10–11 m2/s at 1450 °C for the Na-rich melt and between 3 × 10–12 m2/s at 1250 °C and 2.5 × 10–11 m2/s at 1450 °C for the K-rich melt, at 1.0 GPa. Although Br mobility is independent of F and Cl in anhydrous phonolitic melts, its behavior may be dependent on the dominant alkali in the melt, as previously observed for Cl, but not F. For hydrous experiments, although the data are scattered, the Br diffusivity increases slightly with water and the Na/K ratio seems to influence Br diffusivity. Similarly to noble gases, halogen diffusivity at a given temperature in the phonolitic melts appears related to the ionic porosity of the silicate structure. Compared to basaltic melt, Br diffusivities are approximately one order of magnitude lower in the Na-phonolite melt, because of the difference of the pre-exponential factor. Br mobility appears to be decoupled from melt viscosity, considering the results here.

Mineralogical and Geotechnical Properties of Clay Minerals in Northern Borno, Nigeria

Clay generally refers to either fine grained earth material with particle size of less than two micron (< 2 m) or group of hydrous aluminum silicate minerals that are characterized by sheet silicate structure of composite layers stacked along the C-axis. They are common deposits found in most geological setting like in fine grained sedimentary rocks such as shale, mudstone, and siltstone, in fine grained metamorphic slate and phyllite. The interest in clay deposits arises from its numerous uses of the mineral group and the behaviour of soils constituents when used as engineering soil and its resultant effects on engineering structures like roads, dams, bridges and houses. Evaluation of the soil properties of the Chad Formation indicated that the plasticity characteristics of the samples are of low to medium plasticity as indicated by matching the result with the DIN. chart. The results of free swell showed that the samples are susceptible to swelling when they absorbed water. The particle size distribution tests indicate that the percentage of fine (i.e. samples passing the 75µm sieve) is about 1.7 % implying that the grain sizes are within the texture of medium grain fraction

Molecular level nucleation mechanisms of hierarchical MFI and MOR zeolite structures via non-stochastic pathways

Non-stochastic nucleation mechanisms were constructed for a precursor silicate structure with 1D molecular order which could crystallize into the 3D unit cells of MFI and MOR frameworks through different 2D nucleation stages.

Analisis Mikrostruktur Partikel Zirkoniakalsia-silika (ZrO 2 -CaO-SiO ) Dari Pasir Zirkon Alam Indonesia Menggunakan Metode Spray Pyrolysis

Indonesian Natural Sand, Zircon, is an Indonesia’s natural resource that contains zirconia, silica, titania and alumina. In Dentistry, zirconia as one of the content in natural zircon sand, have the potential to be the material for filler composites. The purpose of this research was to analyze the Zirconia-Calcium-Silicate Particle (ZrO2CaO-SiO2) synthesized from Indonesia natural sand, zircon, in microstructural way. Methods: By synthesizing ZirconiaCalcium-Silicate particle (ZrO2-CaO-SiO2) from Indonesia natural zircon sand, using spray pyrolysis method. A precursor solution that is used consists of zirconil nitrate (Zr (NO3) 2), sodium silicate (Na2SiO3), and calcium hydroxide (Ca (OH) 2). Variations in the temperature of the reactor that are used were 4000C, 4500C, and 5000C with a feed rate of 6 L / min and a piezoelectric frequency of 1.7 MHz. Result showed that the better content in zirconia-calcium-silicate is the one that was synthesized at a temperature of 4500C, based on the results of EDS, SEM and XRD. The composition that is obtained in the zirconia-calcium-silicate particle has a ratio of 1: 14: 4 with the size of 500-1000nm, and has a tetragonal crystal zirconium silicate structure and dicalcium monoclinic silicate. From this research it can be concluded that the result that was synthesized at a temperature of 4500C is adequate to use as a filler based on the characterization result of SEM and XRD.