Effects of iron oxide on crystallization behavior and spatial distribution of spinel in stainless steel slag

Chromium plays a vital role in stainless steel due to its ability to improve the corrosion resistance of the latter.However,the re-lease of chromium from stainless steel slag(SSS)during SSS stockpiling causes detrimental environmental issues.To prevent chromium pollution,the effects of iron oxide on crystallization behavior and spatial distribution of spinel were investigated in this work.The results revealed that FeO was more conducive to the growth of spinels compared with Fe2O3 and Fe3O4.Spinels were found to be mainly distrib-uted at the top and bottom of slag.The amount of spinel phase at the bottom decreased with the increasing FeO content,while that at the top increased.The average particle size of spinel in the slag with 18wt%FeO content was 12.8μm.Meanwhile,no notable structural changes were observed with a further increase in FeO content.In other words,the spatial distribution of spinel changed when the content of iron oxide varied in the range of 8wt%to 18wt%.Finally,less spinel was found at the bottom of slag with a FeO content of 23wt%.

Effect of oxidization on enrichment behavior of TiO_2 in titanium-bearing slag

Due to the dispersed distribution of the titanium component in various mineral phases and very fine grain size, it is difficult to recover the titanium component from the slag. In order to utilize titanium resources, selective enriching and selective growing of the titanium component from the molten slag is expected. In this paper, the selection of the best titanium enrichment phase and the effect of oxidization on the enrichment of titanium by blowing air into the molten slag were studied. The results showed that through oxidizing the slag, the content of the perovskite phase increases while that of the other titanium-bearing mineral phases decreases until they disappear. Most titania resources were enriched into the perovskite phase and increase in size. The process of enrichment and growth is easily carried out.

Preparation,characterization and photocatalytic activity of sulfuric acid-modified titanium-bearing blast furnace slag

The feasibility of reducing Cr(VI)from the aqueous solution by sulfuric acid-modified titanium-bearing blast furnace slag(SATBBFS)as a photocatalyst was investigated.The photocatalysts were examined by X-ray diffraction(XRD),UV-vis diffuse reflectance spectra,thermogravimetric analysis(TG)and Fourier transform infrared spectroscopy(FTIR).The photocatalytic activities of the different catalysts were evaluated by the photocatalytic reduction of Cr(VI)under UV-vis light irradiation.The results show that the photocatalytic activities of SATBBFS catalysts are strongly dependent on CaTiO3-to-TiO2 mass ratio,adsorption capacity and surface acidity,and SATBBFS calcined at 400°C shows a higher photocatalytic activity compared with other catalysts.

Simultaneous preparation of TiO2 and ammonium alum,and microporous SiO2 during the mineral carbonation of titanium-bearing blast furnace slag

In this study,a route for simultaneous mineralization of CO2 and production of titanium dioxide and ammonium alum,and microporous silicon dioxide from titanium-bearing blast furnace slag(TBBF slag)was proposed,which is comprised of(NH4)2 S04 roasting,acid leaching,ammonium alum crystallization,silicic acid flocculation and Ti hydrolysis.The effects of relevant process parameters were systematically investigated.The re sults showed that under the optimal roasting and leaching conditions about 85%of titanium and 84.6%of aluminum could be extracted while only 30%of silicon entered the leachate.84%of Al^3+was crystallized from the leachate in the form of ammonium aluminum sulfate dodecahydrate with a purity up to 99.5 wt%.About 85%of the soluble silicic acid was flocculated with the aid of secondary alcohol polyoxyethylene ether 9(AEO-9)to yield a microporous SiO2 material(97.4 wt%)from the crystallized mother liquor.The Al-and Si-depleted solution was then hydrolyzed to generate a titanium dioxide(99.1 wt%)with uniform particle size distribution.It was figured out that approximately 146 kg TiO2 could be produced from 1000 kg of TBBF slag.Therefore,the improved process is a promising method for industrial application.

Recent progress of efficient utilization of titanium-bearing blast furnace slag

Titanium-bearing blast furnace slag(BFS)has valuable compositions and potential environmental hazardousness.Thus,developing efficient and green approaches to utilize BFS is highly desired for resource economization and environmental protection.In the past decades,many attempts have been adopted to reuse BFS efficiently,and significant advances in understanding the fundamental features and the development of efficient approaches have been achieved.This review provides a comprehensive overview of the latest progress on the efficient utilization of BFS and discusses the mechanism and characteristics of various approaches,along with their application prospects.In particular,the extraction and enrichment of titanium-bearing phases from BFS are highlighted because of the high availability of titanium resources.This systemic and comprehensive review may benefit the design of new and green utilization routes with high efficiency and low cost.

Recovery of titanium,aluminum,magnesium and separating silicon from titanium-bearing blast furnace slag by sulfuric acid curing-leaching

An energy-efficient route was adopted to treat titanium-bearing blast furnace slag(TBBFS)in this study.Titanium,aluminum,and magnesium were simultaneously extracted and silicon was separated by low temperature sulfuric acid curing and low concentration sulfuric acid leaching.The process parameters of sulfuric acid curing TBBFS were systematically studied.Under the optimal conditions,the recovery of titanium,aluminum,and magnesium reached 85.96%,81.17%,and 93.82%,respectively.The rapid leaching model was used to limit the dissolution and polymerization of silicon,and the dissolution of silicon was only 3.18%.The mechanism of sulfuric acid curing-leaching was investigated.During the curing process,the reaction occurred rapidly and released heat massively.Under the attack of hydrogen ions,the structure of TBBFS was destroyed,silicate was depolymerized to form filterable silica,and titanium,magnesium,aluminum,and calcium ions were replaced to form sulfates and enriched on the surface of silica particles.Titanium,aluminum,and magnesium were recovered in the leaching solution,and calcium sulfate and silica were enriched in the residue after leaching.This method could effectively avoid the formation of silica sol during the leaching process and accelerate the solid-liquid separation.

Antibacterial Properties of V-doped Titanium-bearing Blast Furnace Slag Prepared at Different Calcination Temperatures

Perovskite-type V-doped titanium-bearing blast furnace slag (VTBBFS) photocatalyst was prepared by high-temperature solid phase method.The influence of calcination temperature on the photocatalytic and antibacterial properties of VTBBFS was studied in details.Its composition and microstructure were evaluated by X-ray diffractometer,ultraviolet-visible absorption spectrometer,Fourier transform infrared spectrometer and scanning electron microscope.The antibacterial properties of VTBBFS to Candida albicans were investigated by flask oscillation method.The results showed that the optical absorption and antibacterial properties of VTBBFS were the best with 10%(ω) doping of vanadium,prepared at 800℃ for 2 h,and its sterilization rate was close to 100% to Candida albicans (ATCC10231).The minimum inhibitory and minimum bactericidal concentrations were 25 and 50 mg/mL.When the concentration was 0.2 μg/mL,the catalyst had the least toxic toxicity.

Novel wood-plastic composite fabricated via modified steel slag:Preparation,mechanical and flammability properties

A novel method was developed to enhance the utilization rate of steel slag(SS).Through treatment of SS with phosphoric acid and aminopropyl triethoxysilane(KH550),we obtained modified SS(MSS),which was used to prepare MSS/wood-plastic composites(MSS/WPCs)by replacing talcum powder(TP).The composites were fabricated through melting blending and hot pressing.Their mechanical and combustion properties,which comprise heat release,smoke release,and thermal stability,were systematically investigated.MSS can improve the mechanical strength of the composites through grafting reactions between wood powder and thermoplastics.Notably,MSS/WPC#50(16wt%MSS)with an MSS-to-TP mass ratio of 1:1 exhibited optimal comprehensive performance.Compared with those of WPC#0 without MSS,the tensile,flexural,and impact strengths of MSS/WPC#50 were increased by 18.5%,12.8%,and 18.0%,respectively.Moreover,the MSS/WPC#50 sample achieved the highest limited oxygen index of 22.5%,the highest vertical burning rating at the V-1 level,and the lowest horizontal burning rate at 44.2 mm/min.The formation of a dense and stable char layer led to improved thermal stability and a considerable reduction in heat and smoke releases of MSS/WPC#50.However,the partial replacement of TP with MSS slightly compromised the mechanical and flame-retardant properties,possibly due to the weak grafting caused by SS powder agglomeration.These findings suggest the suitability of MSS/WPCs for high-value-added applications as decorative panels indoors or outdoors.

Multiscale Study on Low Temperature Crack Resistance Mechanism of Steel Slag Asphalt Mixture

The objective of this paper was to study low temperature crack resistance mechanism of steel slag asphalt mixture(SAM).Thermal stress restrained specimen test(TSRST)and three-point bending test were carried out to evaluate the low-temperature crack resistance of SAM and basalt asphalt mixture(BAM).Based on the digital image correlation technique(DIC),the strain field distribution and crack propagation of SAM were analyzed from the microscopic point of view,and a new index,crack length factor(C),was proposed to evaluate the crack resistance of the asphalt mixture.The crystal phase composition and microstructure of steel slag aggregate(SA)and basalt aggregate(BA)were studied by X-ray diffraction(XRD)and scanning electron microscopy(SEM)to explore the low-temperature crack resistance mechanism of SAM.Results show that the low-temperature crack resistance of SAM is better than that of BAM;SAM has good integrity and persistent elastic deformation,and its bending failure mode is a hysteretic quasi-brittle failure;The SA surface is evenly distributed with pores and has surface roughness.SA has the composition phase of alkaline aggregate-calcite(CaCO3),so it has good adhesion to asphalt,which reveals the mechanism of excellent low-temperature crack resistance of SAM.

Synthesis of Foliar Fertilizer and Ca-S-Si Compound Fertilizer from Titanium-bearing Blast Furnace Slag

With titanium-bearing blast furnace slag, ammonium sulfate, citric acid and potassium carbonate as raw materials to produce foliar fertilizer and Ca-S-Si compound fertilizer by means of heating process for the first time, which improved the solubility of the slag and converted the nutritional elements into such ones which are prone to be absorbed by plants. The effects of process conditions on dissolution rate of titanium were mainly analyzed through the orthogonal experiment. The results showed that the optimum synthesis process conditions of foliar fertilizer from the slag were 360 ℃ for 35 min, the mass ratio of ammonium sulfate and titanium-bearing blast furnace slag was 8：1. Under these conditions more than 80% of iron, titanium, magnesium and part of silicon in titanium-bearing blast furnace slag converted into water-soluble substances and existing in foliar fertilizer. Foliar fertilizer contained nitrogen, sulfur, potassium, iron, titanium, magnesium and silicon, and pH value of foliar fertilizer was 6. Ca-S-Si compound fertilizer mainly contained calcium silicate and calcium sulfate, which existed in the form of citric acid-soluble substance and slightly soluble substance, respectively.

Recycling of Local Qatar’s Steel Slag and Gravel Deposits in Road Construction

Every year,the State of Qatar generates about 400,000 tons of steel slag and another 500,000 tons of gravel as a result of steel manufacturing and washing sand,respectively.The two materials(by-products)are not fully utilized to their best market values.At the same time,infrastructural renewal will take place in Qatar over the next ten years,and there will be a greater demand for aggregates and other construction materials as the country suffers from the availability of good aggregates.This paper presents results obtained on the use of steel slag,gravel and gabbro(control)in HMAC(hot mix asphalt concrete)paving mixtures and road bases and sub-bases.Tests were conducted in accordance with QCS-2010(Qatar Construction Specifications)and results were compared with QCS requirements for aggregates used in these applications.Based on the data obtained in this work,steel slag and gravel aggregates have a promising potential to be used in HMAC paving mixtures on Qatar’s roads,whether in asphalt base and asphalt wearing courses or as unbound aggregates in the base and sub-base pavement structure.

Sintering preparation of porous sound-absorbing materials from steel slag

Porous sound-absorbing materials were prepared from steel slag using waste expanded polystyrene（EPS） particles as pore former.The influences of the experimental conditions such as fly ash content,sintering temperature,sintering time,and pore former addition on the performance of the porous sound-absorbing materials were investigated.The results show that the porosity of the specimens can reach above 50.0%;the compressive strength and average sound-adsorption coefficient of the sintered specimens are above 3.0 MPa and 0.47,respectively.The optimum preparation conditions for the steel slag porous sound-absorbing materials are as follows：mass fraction of fly ash 50%,waste EPS particles 3.6 g,sintering temperature 1100℃,and sintering time 7.5h,which are determined by considering the properties of the sound-absorbing materials,energy consumption and cost.

Thermodynamic analysis and formula optimization of steel slag-based ceramic materials by FACTsage software

Using steel slag as a main raw material of ceramics is considered as a high value-added way. However, the relationship among the initial composition, ceramic microstructure, and macroscopic properties requires further study. In this paper, a series of ceramics with different slag ratios （0-70wt%） were designed, and the software FACTsage was introduced to simulate the formation of crystalline phases. The simulation results indicate that mullite is generated but drastically reduced at the slag ratios of 0-25wt%, and anorthite is the dominant crystalline phase in the slag content of 25wt%-45wt%. When the slag ratio is above 45wt%, pyroxene is generated more than anorthite. This is because increasing magnesium can promote the formation of pyroxene. Then, the formula with a slag content of 40wt% was selected and optimized. X-ray diffraction results were good consistent with the simulation results. Finally, the water absorption and bending strength of optimized samples were measured.

Complementation in the composition of steel slag and red mud for preparation of novel ceramics

A method for preparing novel ceramics was developed in this study. Different ratios red muds were added to steel slags to optimize the preparation of novel ceramics by a traditional ceramic preparation process. The sintering mechanism, microstructure, and performance were studied by X-ray diffraction techniques, scanning electron microscopy, and combined experiments of linear shrinkage, water absorption, and flexural strength. The results confirmed that red mud can reduce the volumetric instabilities through the complementarity of red mud and ferroalloy slag. The crystal phases in the ceramics are all pyroxene group minerals, including diopside ferrian, augite, and diopside. The flexural strength of the ceramic that contains 40 wt% red mud and was prepared at the optimal sintering temperature(1140°C) is greater than 93 MPa; its corresponding water absorption is less than 0.05%.

Effect of slag on oxide inclusions in carburized bearing steel during industrial electroslag remelting

Industrial experiments with three types of slags were performed to investigate the effect of slag on oxide inclusions during electroslag remelting(ESR) process. G20CrNi2Mo bearing steel was used as the consumable electrode and remelted using a 2400-kg industrial furnace. The results showed that most inclusions in the electrode were low-melting-point CaO-MgO-Al_2O_3. After ESR, all the inclusions in ingots were located outside the liquid region. When the slag consisted of 65.70 wt% CaF_2, 28.58 wt% Al_2O_3, and 4.42 wt% CaO was used, pure Al_2O_3 were the dominant inclusions in ingot, some of which presented a clear trend of agglomeration. When the ingot was remelted by a multi-component slag with 16.83 wt% CaO, a certain amount of sphere CaAl_4O_7 inclusions larger than 5 μm were generated in ingot. The slag with 8.18 wt% CaO exhibited greater capacity to control the inclusion characteristics. Thermodynamic calculations indicated that the total Ca and Mg in ingots were attributed from the relics in electrode and strongly influenced by the slag composition. The formation of ingot inclusions was calculated by FactSage^(TM) 7.0, and the results were basically in accordance with the observed inclusions, indicating that a quasi-thermodynamic equilibrium could be obtained in the metal pool.

Research on Hydration of Steel Slag Cement Activated with Waterglass

This paper studied the hydration and strength influence factors ofSteel Slag Cement (SSC), such as the quantity of steel slag and slagand the dosage of additive. The results show that: (a) In the processof hydration of SSC, steel slag and slag activate each other; (b)Waterglass's structure forms the preliminary skeleton of SSC, and thehydration products of SSC link or fill in the skeleton; (c) Sodium inWaterglass is the catalytic and its concentration does not change inthe process of hydration. (d) Structure of activation is asignificant factor to the property of SSC.

Methods for Improving Volume Stability of Steel Slag as Fine Aggregate

Suitable methods for enhancing the volume stability of steel slag utilized as fine aggregate were determined. The effects of steam treatment at 100 ℃ and autoclave treatment under 2.0 MPa on the soundness of steel slag sand were investigated by means of powder ratio, linear expansion, compressive and flexural strength. DTA, EDX, XRD and ethylene glycol methods were employed to analyze both the treated slags and susceptible expansion grains. Experimental results indicate that powder ratio, content of free lime and rate of linear expansion can express the improvement in volume stability of different treated methods. Steam treatment process cannot ultimately prevent specimens from cracking and decrease of strength, but mortar made from autoclave treated slag keeps integration subjected to hot water of 80℃ until 28 d and its strength do not show significant decrement. The hydration of over-burn free lime and periclase phase are the main cause for the disintegration or crack of untreated and steam treated steel slag＇s specimens. Autoclave treatment process is more effective than steam treatment process on enhancement of volume stability of steel slag.

Properties of Steel Slag and Stainless Steel Slag as Cement Replacement Materials:A Comparative Study

To enhance the understanding about the utilization of steel slags as a cementitious material, we comparatively studied the chemical, mineralogical and morphological properties of two types of steel slag; basicoxygen-furnace carbon slag(BOF C) and electric-arc-furnace stainless steel slag(EAF S). Moreover, we studied the standard consistency, setting time and the effect of the slag replacement ratios on the fluidity and compressive strength of blended cement mortar. The experimental results showed that BOF C had higher alkalinity, higher pH value and more hydraulic phases than EAF S. Both types of slag showed water reduction effect due to its high fineness. Neat BOF C paste showed flash set and acceleration in the initial setting time of blended cement especially at high slag proportions. However, EAF S prolonged the setting time of blended cement even at low slag proportions. The pH values for blended cement contained 50% BOF C or EAF S were lower than those of pure cement paste. Despite of slag type, compressive strength gradually decreased with increasing slags content. The strength of BOF C mortar was higher than that of EAF S mortar with the same replacement ratio for the same age. Slag activity index demonstrated that BOF C and EAF S conformed to the Chinese National Standard(GB/T 20491-2006) requirements for steel slag as grade one and grade two, respectively.

Effect of Fine Steel Slag Powder on the Early Hydration Process of Portland Cement

Hydration heat evolution, non-evaporative water, setting time and SEM tests were peorormed to investigate the effect of fine steel slag powder on the hydration process of Portland cement and its mechanism. The results show that the effect of fine steel slag powder on the hydration process of Portland cement is closely related to its chemical composition, mineral phases, fineness, etc. Fine steel slag powder retards the hydration of portland cement at early age. The major reason for this phenomenon is the relative high content of MgO , MnO2, P2O5 in steel slag, and MgO solid solved in C3 S contained in steel slag.

PHOSPHORUS REMOVAL USING STEEL SLAG

Steel slag is a byproduct produced in large amounts in the steel-making process. It is an important resource that can be effectively utilized. An experiment was described in which steel slag was tested as an adsorbent for the removal of phosphorus from waste water. Phosphorus removal depended on the amount of steel slag added, the pH value, the contact time, and the initial concentration. Under laboratory conditions when the added slag was 7.5g/L, the contact time 2h, and the pH value was equivalent to 6.5, over 99% of the phosphorus was removed; the experimental data on steel slag adsorption of phosphorus in the water fitted the Freundlich isotherm model. Steel slag was found to be very effective in adsorbing phosphorus.