Slag Components Research Articles

Ethanol production from kelp slag hydrolysates using genetically engineered Escherichia coli KO11

Kelp slag refers to industrial waste produced during sodium alginate extraction from kelp. The chemical components of kelp slag were analyzed in this study. The kelp slag contained large amounts of cellulose (25.88 %) and hemicellulose (12.52 %) with minimal acid-insoluble lignin content, making it an ideal raw material for ethanol fuel production. The saccharification and ethanol transformation of kelp slag by Escherichia coli KO11 were evaluated. When glucose or xylose was used as the fermentation substrate, theoretical ethanol yields of 82.35 % (glucose) and 84.78 % (xylose) were obtained. Xylose was not used until the glucose content was below 1 % when mixed sugars were fermented. Sulfuric acid pretreatment at 121 °C for 1 h was performed before enzymatic hydrolysis. The maximum rate of enzymatic hydrolysis was 93.32 % after dilute sulfuric acid (0.2 M) pretreatment and enzymatic hydrolysis by cellulase (50 °C, pH 4.8, 16 h). Separate hydrolysis and co-fermentation (SHCF), simultaneous saccharification and co-fermentation (SSCF), and non-isothermal simultaneous saccharification and co-fermentation (NSSCF) were also performed in this study. NSSCF (co-fermentation began after enzymatic hydrolysis for 6 h) was the most effective process for kelp slag fermentation where ethanol yield reached 0.45 g g−1.

Research on algorithm for self-absorption correction based on multi-particles LIBS spectra

In order to overcome the influence of self-absorption on quantitative analysis, the optimizing process of very fast simulated annealing algorithm was studied. According to basic theory of plasma emission spectrum, a new algorithm for self-absorpton correction based on multi-particles spectra was proposed, and the algorithm flowchart was given. With the self-absorption correction algorithm mentioned above, the spectra of refining slag and blast furnace slag were corrected. The effect of self-ab sorption correction on the quantitative analysis results was analyzed based on calibration free method. Comparison of Boltzmann plots before and after self-absorption correction indicated that the plasma temperatures calculated with spectra after self-absorption correction tended to be uniform, and remained stable around 11,600 K. The Boltzmann plots constructed with plasma spectra of the same particle after self-absorption correction indicated that the intercepts were almost the same except for one group data. With calibration free method and spectra after self-absorption correction, the contents of components in slag were analyzed. For refining slag, quantitative analysis precision of MgO was low. If ignoring the existence of MgO, the relative errors of quantitative analysis results of CaO, Al2 O3 and SiOs were much smaller. For blast furnace slag in which the content of MgO was 8.49%, the relative error of quantitative analysis result of Al2 O3 was 2.38%, which was the smallest. And the relative error of quantitative analysis result of MgO was 28.27%, which was still the biggest.

Manufacturing of magnetic steel by electroslag remelting: thermodynamic conditions

A study was conducted of the thermodynamic conditions for manufacturing magnetic steel (∼3% Si) by the ESR process, using electrodes made of cement steel. An examination was carried out of the influence of the following variables on the silicon content of the ingot: percentage of Si in the electrode, rate of deoxidation with Ca–Si, SiO2 activity, CaO activity, etc. By calculating the thermodynamic activities of the reactive components of the slag, it was possible to establish the conditions for manufacturing magnetic steels of uniform composition. One of the conditions is that CaO activity should not drop too much during remelting, because that would lead to segregation of the Al in the ingot.

Study on the Dephosphorization of Semi-Steel in Ladle

Combined with converter semi-steel component of Chengde steel plant, the main components of 100t ladle dephosphorization slag were calculated to propose the initial ratio of dephosphorization slag composition. The dephosphorization slag composition was then further improved by induction furnace dephosphorization. Analysis of dephosphorization rules has been done. The results show that: the dephosphorization effect reaches the best when the percent content of CaO is 35%, the amount of slag is 20kg/t, oxygen flow rate is 4L/min, oxygen blowing time is 4min, and dephosphorization efficiency can reach 56.9%; the order of the elements influencing dephosphorization rate is as follows: oxygen flow rate > slag > CaO > oxygen blowing time. From the experiment, dephosphorization in the ladle can reach the expected effect, which is the new method of hot metal pre-dephosphorization for iron and steel plant using vanadium titanium magnetite.

Study on quantitative analysis of slag based on spectral normalization of laser-induced plasma image

To reduce the influence of laser-induced breakdown spectroscopy (LIBS) experimental parameter fluctuations to quantitative analysis of slag components, a normalization method using integral intensity of plasma image was proposed and a series of experiments with slag samples were performed. Mg II 279.55 nm, Ca II 396.85 and Ca I 422.67 nm were selected as analytical lines, and analytical curves of reference mass fractions versus spectral line intensities were established. With the increment of set threshold for edge extraction of plasma image, the determination coefficients and relative standard deviations of analytical curves were improved gradually and reached the optimum values when the threshold was equal to 10 000. Comparing with the results without normalization and normalized by whole spectrum area, the relativity between spectral line intensity and mass fraction can be enhanced efficiently after normalized by integral intensity of plasma image. The verification experiments with Ti alloy samples further confirmed the conclusions mentioned above.

Calcium leaching from waste steelmaking slag: Significance of leachate chemistry and effects on slag grain mineralogy

Accelerated carbonation of alkaline wastes such as steelmaking slag offers the potential to combine waste valorisation with climate change mitigation by utilising carbon dioxide (CO2). One method of achieving this is through an indirect carbonation process to produce a marketable precipitated calcium carbonate (PCC), using ammonium salts to selectively extract calcium from steelmaking slag. Two unaddressed design parameters for a slag based plant differing from that of a traditional PCC plant are the effect of mineralogy on extraction efficiency when using a multicomponent, heterogeneous feed such as slag and the challenges raised by the resulting leachate chemistry. This paper presents petrographic textural observations on the effect of calcium leaching via ammonium chloride on individual grains of dicalcium silicate in three different widely unutilised steelmaking slags. These observations are then interpreted in conjunction with measured changes in solution leachate chemistry. The results indicate that although silica enriched regions form at the reaction front, the reaction continues into the core of the particle due to fracture propagation caused by volume reduction as calcium is extracted. Co-leaching of sulfur alongside calcium and the formation of precipitate in the leachate highlights potential engineering challenges when the process is scaled up due to fouling of process equipment. The main mineral phases in all untreated slags were found to be calcium silicates, predominantly dicalcium silicate (Ca2SiO4). This was followed by a complex mixture of calcium/magnesium-wustite (CaFeMnMg)O type phases and srebrodolskite (Ca2Fe2O5(Ti, V)). Results indicate that calcium silicate is the more reactive component of BOS slag, while lime bound as (CaFeMnMg)O is most reactive in HMD and SS slags. Selectivity of the ammonium chloride solvent was high at 95–97% and efficiency of calcium extraction ranged between 25% and 39%.

Corrosive Interaction between MgO-C Refractories and Vanadium-Recovery Slag

The interaction mechanisms between resin-bonded MgO-C bricks and vanadium-recovery slag by a static crucible slag test are investigated. Oxidation of carbon is observed, which results in pores, cracks and voids for the penetration of the vanadium-recovery slag. Periclase grains are seriously infiltrated by the slag, which leads to the disintegration and removal of MgO subgrains from the slag. Forsterite is formed and EDS confirmed that it has some FeO and MnO content. EDS confirms that there are few vanadium-containing compounds, and most vanadium exists in the form of glassy phases, which are liquid at high temperature. More low-melting point species are formed in the slag or as the result of the reaction of slag and refractory components, which is deleterious to slag resistance. Furthermore, the diffused FeO content in periclase gradually decreases from the hot face into the inner area. No diffused MnO is detected in periclase.

Characteristics and catalytic actions of inorganic constituents from entrained-flow coal gasification slag

The morphology, mineralogy, and elemental distribution of inorganic constituents from two entrained-flow coal gasification slags were mainly investigated to understand the physico-chemical characteristics of the two slags. The fully molten and partly molten inorganic components in the coarse slag tend mainly to co-exist in the overlapping bulk of lumps and agglomerates, whereas the two ones in the fine slag almost tended to be discretely presented in spherical particles and agglomerates, respectively. The trace elements (Pb, As and Zn) with great volatile behaviors were easily concentrated into the fine slag. Summarily, the inorganic constituents in gasification slags predominantly contained crystalline components (silicates, aluminosilicates, and Ca–Fe and Fe oxides) and vitreous components (Ca–Fe-aluminosilicate glass). Simultaneously, a rough distribution model for main ash-forming elements in gasification slags was proposed. Also, the catalytic actions of inorganic constituents in the two gasification slags were assessed using a thermo-gravimetric analyzer. It was found that the inorganic constituents in gasification slags can take a distinct catalytic action on the carbon gasification, mainly due to the predominant presence of these catalytic components (Ca–Fe and Fe oxides). A higher gasification reactivity of the coarse slag was mainly ascribed to a higher content of its catalytic components, compared to the fine slag.

Characterization of Process Conditions in Industrial Stainless Steelmaking Electric Arc Furnace Using Optical Emission Spectrum Measurements

Emission spectroscopy is a potential method for gaining information on electric arc furnace (EAF) process conditions. Previous studies published in literature on industrial EAF emission spectra have focused on a smaller scales and DC arc furnaces. In this study emission spectrum measurements were conducted for 140t AC stainless steelmaking EAF at Outokumpu Stainless Oy, Tornio Works, Finland. Four basic types of emission spectra were obtained during the EAF process cycle. The first one is obscured by scrap steel, the second is dominated by thermal radiation of the slag, the third is dominated by alkali peaks and sodium D-lines and the fourth is characterized by multiple atomic emission peaks. The atomic emission peaks were identified by comparing them to the NIST database for atomic emission lines and previous laboratory measurements on EAF slag emission spectra. The comparison shows that the optic emission of an arc is dominated by slag components. Plasma conditions were analyzed by deriving plasma temperature from optical emissions of Ca I lines. The analysis suggests that accurate information on plasma conditions can be gained from outer plasma having a plasma temperature below 7000 K (6727 °C).

Analysis of Arc Emission Spectra of Stainless Steel Electric Arc Furnace Slag Affected by Fluctuating Arc Voltage

Control of chromium oxidation in the electric arc furnace (EAF) is a significant problem in stainless steel production due to variations of the chemical compositions in the EAF charge. One potential method to control chromium oxidation is to analyze the emission spectrum of the electric arc in order to find indicators of rising chromium content in slag. The purpose of this study was to determine if slag composition can be gained by utilizing electric arc emission spectra in the laboratory environment, despite electric arc voltage fluctuations and varying slag composition. The purpose of inducing voltage fluctuation was to simulate changes in the industrial EAF process. The slag samples were obtained from Outokumpu Stainless Oy Tornio Works, and three different arc currents were used. The correlation analysis showed that the emission spectra offer numerous peak ratios with high correlations to the X-ray fluorescence-measured slag CrO(x)/FeO(x) and MnO/SiO2 ratios. These ratios are useful in determining if the reduction agents have been depleted in the EAF. The results suggest that analysis of laboratory-scale electric arc emission spectra is suitable for indicating the high CrO(x) or MnO content of the slag despite the arc fluctuations. Reliable analysis of other slag components was not successful.

Activity Calculation Model for Oxygen Converter Final Slag

In this paper the activity calculation model for SiO2-Al2O3-CaO-MgO-FeO-MnO slag system has been established according to the molecule-ion coexistence theory. From that the activity of each component in the converter slag at steelmaking temperature can be calculated and then provides the basis for analyzing the equilibrium distribution of element between slag and steel, as well as thermodynamics analysis related to the activity.With the increasing of FeO mass fraction, the activity of 3CaO.SiO2 shows a significant decreasing trend and the activity of MnO.SiO2 and 2MnO.SiO2 increases slowly. The activity of 3CaO.SiO2 increases at first then decreases, with the increasing of basicity. When the basicity w(CaO)/w(SiO2)=3, the activity of 3CaO.SiO2 reaches its maximum value. The activities of MnO.SiO2 and 2MnO.SiO2 decrease gradually.

Dissolution Behavior of Platinum in Na<sub>2</sub>O–SiO<sub>2</sub>-Based Slags

With the aim of minimizing the loss of platinum into slags by controlling the slag composition during the high-temperature recycling process, the effects of representative slag components, namely, Al2O3, MgO, Fe2O3, and CuOx, on the dissolution behavior of platinum into Na2O­SiO2-based slags were investigated. The solubility of platinum in the slags was measured by equilibrating the Na2O­SiO2-based slags with pure solid platinum at 1473K in air. The dissolution of platinum in the slags was found to be suppressed by the addition of Al2O3, MgO, and Fe2O3 .A l2O3 and Fe2O3 behaved as acidic oxides, whereas MgO behaved as a diluent and decreased the solubility of platinum in the slags. CuOx behaved as a weakly basic oxide and slightly enhanced the dissolution of platinum into the slags. The correlation between the platinate capacity of the slag, which is a parameter proposed in this paper, and the optical basicity enabled the content of platinum in slags at 1473K to be estimated from the slag composition. [doi:10.2320/matertrans.M2014042]

Early carbonation behaviour of no-clinker steel slag binder

The use of steel slag as a no-clinker binder was studied. Steel slag was activated by CO2 to develop strength as a cementing material for building product applications. The performance of slag paste compacts formed by low water to slag ratio was characterised by X-ray diffraction analysis, thermal analysis and field emission scanning electron microscopy analysis affiliated with energy dispersive spectrometer analysis. Results showed that the mineral components of steel slag, such as calcium hydroxide and calcium silicates (C3S and C2S), were CO2 reactive. The reaction products were strength contributing. Immediate carbonation of 2 h was capable of developing rapid early strength while promoting subsequent hydration. The reaction products of steel slag after carbonation and hydration were the combination of poorly crystalline CaCO3 intermingled with C-S-H gel, which was the characteristic of the early hardening structure of no-clinker steel slag.

Model for diffusion coefficient estimation of calcium ions in CaO–Al2O3–SiO2 slags

As a common component in metallurgical slag, CaO plays an important role in desulphurisation, dephosphorisation and absorption of non-metallic inclusions. In order to better understand the mechanism of the slag/metal reactions, the diffusion dynamics of calcium ions in CaO–Al2O3–SiO2 slags were studied. It was found that there was almost a linear relation between the logarithms of pre-exponential factor and diffusion activation energy. By combining the relation between the diffusion activation energy and the optical basicity corrected in the CaO–Al2O3–SiO2 slags, a simple model used to estimate the diffusion coefficient of calcium ion is proposed. The estimated values of the CaO–SiO2 and CaO–Al2O3–SiO2 systems agree well with the experiment data, with a mean deviation of 35·3 and 22·5% respectively.

Experimental design for optimisation of density and water absorption capacity of glass–ceramic foams prepared from silica rich wastes

The preparation of glass–ceramic foams from slag and other components including glass cullet and foaming agent (SiC) is a challenge in the development of marketable and valuable materials. Box–Behnken experimental design was used to investigate the impact of operating conditions (i.e. temperature, reaction time and foaming agent percentage) on density and water absorption capacity of glass–ceramic foams. The optimal process parameter settings to achieve a maximum water absorption capacity (71·34%) and minimum density (0·61 g cm−3) were determined. The failure mode of glass–ceramic foams occurs via layer crushing mechanism. The correlation between the process controlling parameters and the responses (density and water absorption) of the produced foams were represented by two polynomial quadratic models. The determination of main process conditions through Box–Behnken experimental design offers a technological and economic competiveness in the mass production of glass–ceramic foams with specified physical properties for a wide range of applications.

Some observations and insights on BOS refining

Selected IMPHOS heats, have been used to make observations on decarburising and dephosphorising performance, scrap melting and slag foaming characteristics during BOS refining. If it is assumed that decarburisation takes place solely in the slag/metal emulsion then maximum metal residence time in the emulsion is just under 9 seconds and at peak decarburisation time, the maximum amount of metal in the emulsion is ∼50% of the total metal content in the converter. To evaluate the effects of changes in slag component chemistry on phosphorus refining it is necessary to account for changes in slag weight, which can change substantially throughout a heat and be significantly different heat-to-heat. Dephosphorising performance depends on the thermodynamic stability of slag phases that are able to take up phosphorus and the distribution of phosphorus between these thermodynamically stable phases. The application of proprietary thermodynamic models such as MTDATA and FACTSage has helped to clarify such events. Skull build-up on the scrap pile is at a maximum when the bulk bath temperature is ∼1460°C. At this time, the solid scrap and skull component of the bulk bath makes-up just over 60% of all the metal charged to the converter. All scrap and skull is melted out at a bulk bath temperature of ∼1610°C. The stability of the foamy slag/metal emulsion changes over the period of the blow. Slag height increases with an increase in FeO(tot)wt-% and decreases with a decrease in decarburisation rate and the collapse of the foamy slag.

Retainment, Recovery and Recycling: A Swedish Success Story of ECO-Steelmaking

With a view to optimize the environmental aspects of steelmaking, the Swedish Steel Producers Association took the initiative to start a national project on ECO-steelmaking with financial support from Swedish Foundation for Strategic Environmental Research. The Division of Materials Process Science at the Royal Institute of Technology has an important part of the project, viz. “Retention, Recovery and Recycling”, with emphasis on the retention of metal values in the steel bath without loss to the slag or gas phases, to recover the metal values that are lost to the slag phase by the development of new or optimized process concepts and aim at a total recycling of the metal values as well as the slag components within or outside the steel sector. The present paper describes the optimization of existing process concepts as well as evolving newer concepts to meet the above project goals. The use of CO2–O2–Ar gas mixtures for the decarburization of high-alloyed steels, development of a low cost precursor for the addition of molybdenum to steel in EAF, direct alloying in EAF are some of the concepts initiated in the present work. Successful recovery of iron and manganese values by oxidation of the slag and separation of the magnetite or manganese ferrate by electromagnetic separation formed part of the recovery part. As part of the project, a salt extraction process was developed by which the metal values in slags could be extracted into a chloride phase followed by electrolysis in fused chloride medium. This method was found to be successful in the recovery of metal values from slags. This process could be extended to the recovery of a variety of metal values from a variety of secondary sources. The salient features of the process designs and the results are presented in this paper.

Observations on BOS Refining

Selected IMPHOS (IMproving PHOSphorus refining) heats ([1], [2]: Millman et al. in Proc. Scanmet 3, 2008; and Millman et al. in Ironmak Steelmak 38:499, 2011), have been used to make observations on decarburizing and dephosphorising performance characteristics during BOS refining. If it is assumed that decarburization takes place solely in the slag/metal emulsion then maximum metal residence time in the emulsion is just under 9 sec and at peak decarburisation time, the maximum amount of metal in the emulsion is ~ 50 % of the total metal content in the converter. To evaluate the effects of changes in slag component chemistry on phosphorus refining it is necessary to account for changes in slag weight, which can change substantially throughout a heat and be significantly different heat-to-heat. Dephosphorising performance depends on the thermodynamic stability of slag phases that are able to take-up phosphorus and the distribution of phosphorus between these thermodynamically stable phases. The application of proprietary thermodynamic models such as MTDATA and FACTSage has helped to clarify such events. The stability of the foamy slag/metal emulsion changes over the period of the blow. Slag height increases with an increase in FeO (tot) wt% and decreases with a decrease in decarburisation rate and the collapse of the foamy slag.

Preparation of Ti-rich material from titanium slag by activation roasting followed by acid leaching

A method of activation roasting followed by acid leaching using titanium slag was introduced to prepare Ti-rich material. The effects of H3PO4 dosage, roasting temperature, and roasting time on TiO2 grade were investigated. A Ti-rich material containing 88.54% TiO2, 0.42% (CaO+MgO) was obtained when finely ground titanium slag was roasted with 7.5% H3PO4 at 1000 °C for 2 h, followed by a two-stage leaching in boiling dilute sulfuric acid for 2 h. The XRD patterns show that the product is titanium dioxide with a rutile structure. Mechanism studies show that structures of anosovite solid solution and silicate minerals are destroyed in the roasting process. As a result, titanium components in titanium slag are transformed into TiO2 (rutile) while impurities are transformed into acid-soluble phosphate and quartz.

Effects of metakaolin, silica fume and slag on pore structure, interfacial transition zone and compressive strength of concrete

The pore structure and interfacial transition zone (ITZ) of concrete incorporating slag, silica fume and metakaolin were analyzed in this study. Some techniques such as mercury intrusion porosimetry (MIP), microhardness testing and scanning electronic microscopy (SEM) were employed to characterize the effects of slag, silica fume and metakaolin on the pore structure, microhardness and morphology of the ITZ at 28 and 180days. The traditional properties such as compressive strength were experimentally evaluated in relation to pore characteristics and ITZ. Meanwhile, the influence of silicon, as the major component of slag, silica fume and metakaolin, on thermodynamic stability of hydrate phases was further investigated. The experimental results show that mineral admixtures have positive impact on pore refinement and ITZ enhancement of concrete especially at later curing stages. The effect of the mineral admixtures on microstructure is in the sequence: metakaolin>silica fume>slag. The development of the compressive strength is related to the evolution of the pore structure and ITZ. Thermodynamic stability analysis indicates that if mineral admixtures are added to the CaO–Al2O3–CaSO4–H2O system, the phase assemblage of C6AsH32 and C3AS0.8H4.4, which represents a member of the solid solution series Ca3Al2(SiO4)3−x(OH)4x, has a lower Gibbs free energy of reaction and is therefore thermodynamically more stable than monosulfoaluminate at temperatures from 1 to 99°C.