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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Analysis of charcoal blast furnace slags by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was used for the analysis of charcoal blast furnace slags. Plasma was generated by an application of a 1064 nm wavelength Nd:YAG laser beam to the surface of pellets created from the slags. The presence of Al, Ca, Fe, K, Mg, Mn, and Si was determined by identifying their characteristic spectral signatures. Multivariate analysis was performed for the quantification of these elements. The predicted LIBS results were found in agreement with the inductively coupled plasma optical emission spectrometry analysis. The limit of detection for Al, Ca, Fe, K, Mg, Mn, and Si was calculated to be 0.10%, 0.22%, 0.02%, 0.01%, 0.01%, 0.005%, and 0.18%, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2014

X-Ray Diffraction of Slag-Based Sodium Salt Waste Forms

Cementitious materials are used to solidify and stabilize aqueous based radioactive waste containing sodium salts. The types and proportions of cementitious ingredients used to treat aqueous radioactive waste streams containing sodium salts depend on the performance objectives for the waste forms and the compositions of the waste streams. Matrix phases can stabilize certain contaminants (co-precipitation, substitution, ion exchange, and / or sorption), influence processing properties, and are responsible for physical properties and durability of the cured waste forms. Consequently, characterization of the matrix (binder) mineralogy (chemical compositions and crystalline / non crystalline structures) is important for predicting contaminant leaching and evolution of the materials as a function of time and changing conditions This report documents sample preparation and x-ray diffraction results for a series of mixtures of sodium salt waste and cementitious binders. The objective of this study was to provide initial phase characterization for the CBP reference case cementitious salt waste form. This information can be used to: 1) generate a base line for the evolution of the waste form as a function of time and conditions, 2) potentially to design new binders based on mineralogy of the binder, 3) understand and predict anion and cation leaching behavior of contaminants of concern, and 4) predict performance of the waste forms for which phase solubility and thermodynamic data are available. Characterization of the mineralogy is also important for understanding the buffering effects that the waste form has on infiltrating water / leachates. More specifically, identification of hydrated phases capable of sequestering anions in the structures and crystallinity of the calcium silicate binder phases were of particular interest. The intent was to use this characterization data as a starting point for more detailed phase characterization using neutron diffraction techniques in addition to quasi-elastic neutron scattering techniques for characterization of water at the ORNL Spallation Neutron Source, Oak Ridge, TN. The initial characterization is complete. Due to extensive substitutions of cations and anions in the layered double hydroxide phases and the very fine intermixing of poorly crystalline hydrated phases in the reference case blend (10 : 45 : 45 cement : slag : fly ash), electron diffraction and transmission electron spectroscopy are recommended as the next step for characterization. In summary, the hydrated mixtures of Type II portland cement, Grade 100 ground granulated blast furnace slag (GGBFS) and carbon burn-out (CBO) Class F Fly ash contained hydrated phase assemblages which were typical of those reported in the literature. Based on x-ray diffraction results, no significant differences were detected in samples cured 2 months and 14 months in sealed containers at ambient indoor temperatures.

36 MATERIALS SCIENCE↗
NASA NTRS1996

Numerical Investigation of Slag Behavior for RSRM

It is known that the flow field of the redesigned solid rocket motor (RSRM) is very complicated due to the complex characteristics of turbulent multi-phase flow, chemical reaction, particle combustion, evaporation, breakup and agglomeration etc. It requires multi-phase calculations, chemical reaction simulation, and particle combustion, evaporation, and breakup models to obtain a better understanding of thermophysics for the RSRM design using numerical methods. Also, the slag buildup due to the molten particles is another factor affecting the performance of the RSRM. To achieve this goal, the volume of fluid (VOF) method is used to capture the free surface motion so as to simulate the accumulation of the molten particles (slag) of the RSRM. A finite rate chemistry model is used to simulate the chemical reaction effects. For multi-phase calculations, the Hermsen combustion model is used for the aluminum particle combustion analysis and the Taylor Analogy Breakup (TAB) model is used for the particle breakup analysis. An interphase mas-exchange model introduced by Spalding is used for the evaporation calculation. The particle trajectories are calculated using a one-step implicit method for several groups of particle sizes by which the drag forces and heat fluxes are then coupled with the gas phase equations. The preliminary results predicted a reasonable physical simulation of the particle effects using a simple two dimensional solid rocket motor configuration. It shows that the AL/AL2O3 particle sizes are reduced due to the combustion, evaporation, and breakup. The flow field is disturbed by the particles. Mach number distributions in the nozzle are deformed due to the effect of particle concentrations away from the center line.

Liaw, P.↗
DOE OSTI2016

Optimising Blends of Blast Furnace Slag for the Immobilisation of Nuclear Waste - 16245

The legacy of nuclear waste at the Sellafield site in the UK is an ongoing issue, and the current preferred route for the disposal of low and intermediate level waste is encapsulation in a cementitious matrix, formulated by blending Portland cement with blast furnace slag (BFS). Due to demands and economic challenges faced by the cement and steel industries, the supply of BFS to the UK nuclear industry has been inconsistent. These changes have caused the industry to move from a unique BFS powder supply with a certain specification to a combination of standard commercially available cementitious powders. The material currently used at the Sellafield site is a blend of ground granulated blast furnace slag (GGBS) and a coarser fraction of the same composition called Calumite, combined with Portland cement. This work involves future-proofing the supply of BFS for the UK nuclear industry by optimising the blend of the two fractions of BFS in order to replicate the unique specification required by Sellafield Ltd. The main emphasis is on the particle size distribution (PSD) and how this impacts the properties of the final wasteform. The study investigates the performance properties of the blended grouts such as workability, particle packing and heat evolution. Results show that the PSD of the cement powders affect both the physical and chemical properties of the cementitious matrix produced. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Effective Role of Biochar, Zeolite and Steel Slag on Leaching Behavior of Cd and Its Fractionations in Soil Column Study

Remediation of cadmium (Cd) from contaminated soils is considered a complicated task of environmental safety. A column leaching experiment was planned to estimate the influence of biochar (BC), zeolite (ZE) and steel slag (SL) at 1.5% and 3% application rate on Cd leaching behavior and chemical fractionation in contaminated soil. A sequential extraction procedure, the European Community Bureau of Reference (BCR), Toxicity Characteristic Leaching Procedure (TCLP) and NH{sub 4}NO{sub 3} were performed after leaching was completed. The soluble portion of Cd was decreased by 36.3%, 18.4% and 28.7% and Cd contents in leachate were decreased by 44.8%, 30% and 31.3% after BC, ZE and SL addition at 3% rate, respectively over control soil. The greater reduction in TCLP extractable Cd was observed by 29.6% with BC and 22.4% with ZE and 25.7% with SL at 3% application rate. Overall, biochar can be considered an efficient soil amendment to reduce Cd leaching as well as increased its stabilization within soil profile.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Irradiated FA Structural Materials Conditioning by Induction-Slag Remelting in a Cold Crucible

A method of managing one type of radwaste forming during BREST-300 reactor operation – the structural materials of FA – is described. In the module developed for reprocessing, the fissile materials losses together with all forms of waste must not exceed 0.1% of the initial amount, in connection with which the maximum admissible content of facade materials and structural materials sent into long-term storage must not exceed 0.001% by weight. Only the plutonium content may reach 0.015% by weight, which makes it necessary to perform additional purification and return fissile materials into the nuclear fuel cycle. A method of reprocessing the structural materials of irradiated fuel elements is proposed on the basis of induction-slag remelting in a cold crucible, which makes it possible to conduct purification to the desired index value. The operating regime of the melting unit and the qualitative composition of the employed flux that make it possible to reach the required level of purification by removal of fissile materials are described.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Flotation of Metallurgical Grade Silicon and Silicon Metal from Slag by Selective Hydrogen Fluoride-Assisted Flotation

Flotation experiments performed on metallurgical grade silicon have demonstrated that silicon (Si) can be floated in diluted solutions of hydrogen fluoride (HF) and a frother. The recovery was found to depend on HF conditioning time, frother type, and the concentration of both HF and frother. Although Brij 58 produced the highest recoveries of the frothers that was tested, good recoveries were also obtained for Flotanol C07. Chemical analyses showed that the flotation products were purer than the corresponding feed materials, and that most impurity elements were concentrated in the tailings. A case study on cleaning of slag containing 36 pct metallurgical silicon showed promising results concerning the recovery of silicon by flotation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Understanding the Relationship Between Structure and Thermophysical Properties of CaO-SiO{sub 2}-MgO-Al{sub 2}O{sub 3} Molten Slags

In the present work, the relationship between the microscopic structure and macroscopic thermophysical properties in a basic CaO-SiO{sub 2}-MgO-Al{sub 2}O{sub 3} quaternary system was identified using Fourier transformation infrared, Raman and {sup 27}Al magic angular spinning nuclear magnetic resonance (MAS-NMR) techniques. The Raman spectra quantitatively proved that with increasing Al{sub 2}O{sub 3} content, the concentrations of the symmetric units of Q{sup 0}(Si) and Q{sup 2}(Si) decreased, while those of the asymmetric units of Q{sup 1}(Si) and Q{sup 3}(Si) increased; consequently, the degree of polymerization of the networks increased, which resulted in an increase in slag viscosity. The {sup 27}Al MAS-NMR spectra demonstrated that three structural units of Al atoms, namely, AlO{sub 4}, AlO{sub 5}, and AlO{sub 6}, mainly existed in the networks. With increasing Al{sub 2}O{sub 3} content, the concentration of AlO{sub 4} slightly decreased, while those of AlO{sub 5} and AlO{sub 6} increased; overall, Al{sub 2}O{sub 3} acted as a network former in the present system. The increasing Al{sub 2}O{sub 3} content led to additional AlO{sub 6} and Si-NBO-Ca-NBO-Al frameworks, which replaced Si-NBO-Ca-NBO-Si in the networks (NBO: non-bridging oxygen) and induced a change in the primarily precipitated crystalline phase from Ca{sub 2}MgSi{sub 2}O{sub 7} and Ca{sub 2}Al{sub 2}SiO{sub 7} to MgAlO{sub 4}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Efficient Separation and Extraction of Vanadium and Chromium in High Chromium Vanadium Slag by Selective Two-Stage Roasting–Leaching

Vanadium and chromium are important rare metals, leading to a focus on high chromium vanadium slag (HCVS) as a potential raw material to extract vanadium and chromium in China. In this work, a novel method based on selective two-stage roasting–leaching was proposed to separate and extract vanadium and chromium efficiently in HCVS. XRD, FT-IR, and SEM were utilized to analyze the phase evolutions and microstructure during the whole process. Calcification roasting, which can calcify vanadium selectively using thermodynamics, was carried out in the first roasting stage to transfer vanadium into acid-soluble vanadate and leave chromium in the leaching residue as (Fe{sub 0.6}Cr{sub 0.4}){sub 2}O{sub 3} after H{sub 2}SO{sub 4} leaching. When HCVS and CaO were mixed in the molar ratio CaO/V{sub 2}O{sub 3} (n(CaO)/n(V{sub 2}O{sub 3})) of 0.5 to 1.25, around 90 pct vanadium and less than 1 pct chromium were extracted in the first leaching liquid, thus achieving the separation of vanadium and chromium. In the second roasting stage, sodium salt, which combines with chromium easily, was added to the first leaching residue to extract chromium and 95.16 pct chromium was extracted under the optimal conditions. The total vanadium and chromium leaching rates were above 95 pct, achieving the efficient separation and extraction of vanadium and chromium. The established method provides a new technique to separate vanadium and chromium during roasting rather than in the liquid form, which is useful for the comprehensive application of HCVS.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Transition of Blast Furnace Slag from Silicate Based to Aluminate Based: Density and Surface Tension

The effects of the Al{sub 2}O{sub 3} concentration and Al{sub 2}O{sub 3}/SiO{sub 2} ratio on the density and surface tension of molten aluminosilicate CaO-SiO{sub 2}-Al{sub 2}O{sub 3}-9 mass pct MgO-1 mass pct TiO{sub 2} slag were investigated at temperatures from 1723 K to 1823 K (1450 °C to 1550 °C) using the Archimedean method and the maximum bubble pressure (MBP) technique, respectively. The mechanism of the changes in density and surface tension with composition was analyzed from the viewpoint of the degree of polymerization in the structure and the types of oxygen species in the melts. At a fixed CaO/SiO{sub 2} ratio of 1.20, the density decreased with increasing Al{sub 2}O{sub 3} content up to 25 mass pct, subsequently increasing. Increasing the Al{sub 2}O{sub 3}/SiO{sub 2} ratio from 0.47 to 0.92 caused an increase in the density at a fixed CaO content, and the density decreased slightly when the Al{sub 2}O{sub 3}/SiO{sub 2} ratio was greater than 0.92. Based on the structural information, the density decreased when the Al{sub 2}O{sub 3} content enhanced the network structure and increased when the (Q{sub 2} + Q{sub 3})/(Q{sub 0} + Q{sub 1}) ratio and structural complexity decreased. The surface tension increased with increasing Al{sub 2}O{sub 3} content and Al{sub 2}O{sub 3}/SiO{sub 2} ratio. On the one hand, the surface-active component of SiO{sub 2} decreased; on the other hand, the concentration of [AlO{sub 4}]{sup 5−} tetrahedra and metal cations that act as charge compensators increased at the melt surface. A model based on the anionic and cationic radii and the Butler equation was employed to predict the surface tension, and an iso-surface tension diagram was obtained at 1773 K (1500 °C).

36 MATERIALS SCIENCE↗
DOE OSTI2019

Distributions of Ag, Bi, and Sb as Minor Elements between Iron-Silicate Slag and Copper in Equilibrium with Tridymite in the Cu-Fe-O-Si System at T = 1250 °C and 1300 °C (1523 K and 1573 K)

New experimental data on the distributions of silver (Ag), bismuth (Bi), and antimony (Sb) between liquid iron-silicate slag and liquid copper metal in equilibrium with tridymite in the Cu-Fe-O-Si system at T = 1250 °C and 1300 °C (1523 K and 1573 K) have been obtained. The experimental methodology involved high-temperature equilibration, rapid quenching of the equilibrated phases, followed by direct measurement of the equilibrium phases with electron probe X-ray microanalysis (EPMA) for measurement of major element concentrations and laser ablation inductively coupled plasma mass spectrometry (LAICPMS) for the measurement of minor element concentrations. The 4-point test approach was employed to confirm the achievement of chemical equilibrium in the current study. Open-system equilibration on quartz substrates in controlled gas atmospheres (CO/CO{sub 2}/Ar) and closed-system equilibration in sealed quartz ampoules were used. The new experimental data resolve significant discrepancies found in previous studies and can be used as input for the development of thermodynamic databases for copper-making processes.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Numerical Simulation of the Three-Phase Flow of a Bubble Interacting with the Steel–Slag Interface During the Secondary Refining Process

Gas stirring is an effective method for the secondary refining process of steel. The microphenomena among the phases of an argon bubble floating in steel and motion across the steel–slag interface were simulated and discussed with a sharp interface tracking method. A water-model experiment was set to validate the numerical model, and the experimental results showed agreement with the numerical model. A critical size for bubbles to pass the interface was found using the model.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Ultrasound-Assisted Leaching and Kinetic Study of Blended Copper Slag

This article deals with the dissolution of blended copper slag (flash and converter furnace) in hydrogen peroxide and acetic acid in the presence of ultrasound. The parameters that are effective on leaching efficiency, such as leaching temperature, leaching time, ultrasound power, acetic acid concentration, and hydrogen peroxide concentration, were investigated. The optimum leaching conditions for maximum copper dissolution (93 pct) and minimum iron dissolution (3 pct) were determined as follows: 2 M H{sub 2}O{sub 2}, 4 M CH{sub 3}COOH, 10 pct of ultrasound power, 65 °C of leaching temperature, 60 minutes of leaching time, and 1:25 of solid–liquid ratio. According to the Brunauer–Emmett–Teller (BET) analysis results on the original sample and leaching residue, the ultrasound caused formation of microcracks on the particle surface; however, the BET surface area increased and the mean adsorption pore width decreased. The apparent activation energy was found to be 55.35 kJ/mol, and the kinetics equations of the processes were established.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Characterisation of magnesium potassium phosphate cements blended with fly ash and ground granulated blast furnace slag

Magnesium potassium phosphate cements (MKPCs), blended with 50 wt.% fly ash (FA) or ground granulated blast furnace slag (GBFS) to reduce heat evolution, water demand and cost, were assessed using compressive strength, X-ray diffraction (XRD), scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) spectroscopy on {sup 25}Mg, {sup 27}Al, {sup 29}Si, {sup 31}P and {sup 39}K nuclei. We present the first definitive evidence that dissolution of the glassy aluminosilicate phases of both FA and GBFS occurred under the pH conditions of MKPC. In addition to the main binder phase, struvite-K, an amorphous orthophosphate phase was detected in FA/MKPC and GBFS/MKPC systems. It was postulated that an aluminium phosphate phase was formed, however, no significant Al–O–P interactions were identified. High-field NMR analysis of the GBFS/MKPC system indicated the potential formation of a potassium-aluminosilicate phase. This study demonstrates the need for further research on these binders, as both FA and GBFS are generally regarded as inert fillers within MKPC.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Phase diagrams for alkali-activated slag binders

Phase diagrams for alkali-activated slag (AAS) binders are simulated at (metastable) thermodynamic equilibrium, spanning the relevant compositional envelopes for these materials. The phase diagrams are generally consistent with experimental observations in the literature, dominated by calcium (alkali) aluminosilicate hydrate (C-(N-)A-S-H) gels and Mg-Al layered double hydroxides. Relationships between the stabilities of the predicted solid phase assemblages, pore solution compositions, and the bulk chemical composition are identified, yielding an improved understanding of AAS binder chemistry. Strätlingite is predicted at low to intermediate Si concentrations and at high Al content, while zeolites (and thus most likely also disordered alkali-aluminosilicate (hydrate) gels) tend to precipitate at higher concentrations of both Si and Al; katoite and AFm-type phases are stabilised at intermediate levels of CaO + Al{sub 2}O{sub 3} + MgO. The application of these results in designing AAS binders can enable the phase assemblages and chemical properties of these materials to be more precisely controlled.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effects of alkali dosage and silicate modulus on autogenous shrinkage of alkali-activated slag cement paste

Autogenous shrinkage of alkali-activated slag cement (AASC) paste prepared with different levels of alkali dosage and silicate modulus (M{sub s}) is investigated. The results show that autogenous shrinkage of AASC paste increases at a decreasing rate with alkali dosage, which is attributed to enhanced capillary pore pressure and syneresis of C-A-S-H gels. Autogenous shrinkage of AASC paste with a constant alkali dosage increases as M{sub s} increases from 0.5 to 1.0, followed with a reduction as M{sub s} further increases to 2.0. Increasing M{sub s} initially enhances the capillary pore pressure due to the enhanced reaction degree, and promotes the formation of saturated capillary pores and viscoelasticity, which facilitates the autogenous shrinkage of AASC paste. However, excessive silicate in the activator retards the internal moisture consumption, and subsequently decreases the autogenous shrinkage of AASC paste. Furthermore, increasing M{sub s} can also intensify syneresis of C-A-S-H gels, contributing to the early-age autogenous shrinkage of AASC paste.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Sequestration and release of nitrite and nitrate in alkali-activated slag: A route toward smart corrosion control

Intercalating the corrosion inhibitive ions in hydrotalcite is a promising approach to improve the long-term efficiency of inhibitors in corrosion protection of steel in reinforced concrete. In this work, the potential of autogenously generating nitrite- and nitrate-intercalated hydrotalcite in alkali-activated slag (AAS) is investigated. The results show that the added nitrite and nitrate ions are preferably uptaken in the interlayer structure of hydrotalcite in AAS, and the sequestered nitrite and nitrate are released upon chloride exposure in seawater and NaCl solution. The incorporation of nitrite and nitrate has little detrimental effects on the chloride binding capacity of AAS but slightly enhances the chloride ingress due to the pore coarsening effect. Similar to ordinary Portland cement (OPC), AAS is more permeable to the chloride in seawater than NaCl solution. However, unlike the release of bound chloride contributed by ettringite formation in seawater-exposed OPC, the enhanced chloride ingress in seawater-exposed AAS is primarily attributed to the aggravated pH reduction at the exposure front due to brucite formation. This study contributes to the design of alkali-activated binders with a smart inhibitor releasing ability for mitigating corrosion of steel in concrete.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Synthesis and characterisation of alites from reduced basic oxygen furnace slags

Basic oxygen furnace slags (BOFS) are by-products of the steelmaking process. Several researchers have studied the production of Portland cement clinker and metallic iron from BOFS via a reductive treatment. }In this study, we applied a carbothermal reduction of BOFS in a technical-scale electric arc furnace and characterised the clinker-like products. Those clinker-like non-metallic products (NMPs) had a chemical and mineralogical composition comparable to clinker for ordinary Portland cement (OPC) and contained large elongated alite crystals as major component. The pure NMPs reacted more slowly and achieved a lower degree of hydration compared with commercial OPC. }If the reactivity of the products can be further increased by employing specific adaptations, it can be used as a full clinker substitute for OPC. Nevertheless, it is also an option to use the material without further modifications as a cement component or concrete addition, which contributes to the strength development in both cases.

36 MATERIALS SCIENCE↗