Treatment Of Blast Furnace Slag Research Articles

Synergistic treatment of blast furnace slag and basic oxygen furnace slag for efficient recovery of iron: Phase transformation and oxidation mechanisms

In light of the steel industry's rapid advancements, the availability of high-quality mineral resources is diminishing. Therefore, the recovery of iron from BOF slag is of great significance to the sustainability development. Considering the compositional characteristics of BOF slag, the transformation of the iron-containing phase into (Mn,Mg)yFe3-yO4 is the key step. Thus, a novel process for recovering iron resources by synergistic treatment of blast furnace slag (BFS) and BOF slag was proposed. This research employed FactSage thermodynamic simulation, XRD, SEM-EDS, XPS, and EPMA to analysis the impact of BFS addition (10–50 %), cooling methods (from water-cooling to furnace-cooling), and temperature (1400–1600 °C) on phase transformation and the RO oxidation mechanism, and the conditions of (Mn,Mg)yFe3-yO4 generation and enrichment was obtained. The results show that at BFS addition of 30 %, reaction temperature 1400 °C and furnace-cooling, the iron-containing phase (Ca2Fe2O5 and RO) was almost completely transformed into (Mn,Mg)yFe3-yO4. The oxidation mechanism of RO was formation of (Mn,Mg)yFe3-yO4 by cation diffusion. Under optimal conditions, the iron recovery rate and the grade reached 65.74 % and 32.07 %, respectively, which can be used as raw material for ironmaking. Meanwhile, the main phase of the tailing slag was β-Ca2SiO4, without f-CaO, which has the potential to be used in the cement and concrete industries with the advantages of both low cost and eco-friendly. Therefore, the process with green, efficient and low cost was provided, which is a feasible idea for the comprehensive utilization of industrial solid waste.

Effects of blast furnace slag on the immobilization, plant uptake and translocation of Cd in a contaminated paddy soil

The potential toxicity of Cd to soil and rice plant severely threaten human health. This study was conducted to investigate the remediation effects of blast furnace slag (BFS) on the bioavailability of Cd in a contaminated paddy soil from a perspective of soil solution chemistry. Batch experiments, pot culture experiments, and principal analysis (PCA) were used to study the effects and mechanisms of BFS addition changing Cd chemical behavior and Cd toxicity. Results indicated that BFS facilitated Cd adsorption in soils, increased pH, Eh, and EC values in soil solution, whereas reduced dissolved Cd content. BFS amendment was efficient in decreasing root Cd intake and Cd upward transport in rice plant, with the Cd translocation factor in brown rice decreased by ∼ 75% (BFS treatment, 6‰ wt) relative to Cd treatment, which in turn increased rice biomass and grain yield. PCA indicated that the dissolved Cd concentration had a close relationship with soil pH and metal concentration in soil solution. Results from this study indicated that BFS had potential ability for either immobilization or remobilization of Cd in soils, and the findings have important implications for Cd-polluted soil remediation or other resource utilization with slag-based materials.

Enhancement of coal gangue performance by surface micro-crystalline glaze derived from mineral powder

Coal gangue is a waste derived from coal mining, and its unreasonable disposal usually causes serious land occupation and environmental pollution. Using coal gangue as a substitute for natural aggregate is an effective recycling approach, however, the high water absorption and high crushing rate of coal gangue seriously weaken its performance. This study proposed a novel strategy to decrease the water absorption and crushing rate of coal gangue by co-calcining with mineral powders, including K-feldspar, wollastonite, blast furnace slag and fly ash, meanwhile clarified the improvement mechanisms. Results showed that after calcining with mineral powders, the crushing rate of coal gangue decreased from 16.8 % to 16.1–13.2 %, and water absorption decreased from 5.29 % to 2.74–3.90 %, among which the coal gangue treated by K-feldspar and blast furnace slag had the lowest water absorption (2.74 %), reducing by 48.2 % compared to raw coal gangue. Underlying mechanisms were that during calcination, mineral powders generated micro-crystalline glaze on gangue surface, which improved the pore size distribution of coal gangue and strengthened its hardness. Specifically, as for pores with 1–1000 nm diameter, the pore volume percentage decreased from 88.5 % to 43.2–71.3 %. Vickers hardness of coal gangue increased from 0.29 GPa to 6.37–6.79 GPa, and the fracture toughness increased significantly to 41.9–67.6 MPa m1/2. Under K-feldspar and blast furnace slag treatment, the approximate thickness of micro-crystalline glaze was about 32 μm. The main component of micro-crystalline glaze was silicate lattice derived from SiO2 and Al2O3, and abundant Fe2O3 and Fe3O4 crystalline were sealed in the glaze. This study provides an innovative approach to strengthen the performance of coal gangue, which is important to expand the resource utilization of coal gangue and control the environmental pollution.

Mechanical properties and interfacial interactions in oleyl titanate‐treatedblast furnace slag/polypropylene composites

AbstractIn this study, the effect of oleyl titanate coupling agent (oTi) treatment of blast furnace slag (BFS) on the thermal and mechanical properties and especially on the interfacial interactions in BFS filled polypropylene (PP) composites was investigated. The crystallinity of the composites decreases with increasing oTi‐treated BFS loading. Fourier transform infrared spectroscopy results show an effective surface modification of BFS particles. Energy dispersive X‐ray spectroscopy measurements and scanning electron microscopy confirm good interfacial interactions between oTi‐treated BFS and PP matrix. Elongation at break and elastic modulus are significantly increased up to 70% and 22%, respectively. These results are emphasized by a half‐debonding angle of 37.61° which indicates strong interfacial adhesion between oTi‐treated BFS particles and PP matrix. These results clearly show that oTi treatment significantly improves the compatibility between BFS particles and PP matrix. These results will encourage the recycling of BFS and reducing the cost of PP composites used in many industries.

Experimental study on particle flow characteristics of three-dimensional moving bed

The disorderly treatment of blast furnace slag has caused huge energy waste. To tackle this issue, moving bed are continuously attracting worldwide attention. In this paper, the in-depth analysis of the flow characteristics of blast furnace slag-like particles in a solid-solid heat transfer moving bed is carried out. The particle flow pattern and velocity in the moving bed with different tube numbers, configurations and spacings are vividly recorded. Significantly, a quantitative formula of the mass flow rate including the opening width, the bed layer height, the tube number and spacing, the particle size and distribution was built for this solid-solid heat transfer model. Furthermore, it is found that the longitudinal velocity distribution of the particles renders obvious peaks and valleys along the width direction. This study provides theoretical guidance for the optimization of the structure and operational parameters of the solid-solid heat-exchange moving bed.

Immobilization of Cr (VI) in stainless steel slag and Cd, As, and Pb in wastewater using blast furnace slag via a hydrothermal treatment

The immobilization of hexavalent chromium in stainless steel slag using blast furnace slag as the immobilizing agent and by performing a hydrothermal treatment was investigated. The results showed that there was no immobilization in the absence of the blast furnace slag. On the other hand, the hexavalent chromium in stainless steel slag could be immobilized through the hydrothermal reaction when blast furnace slag was used at 250 °C for 24 h. A leaching test was performed to evaluate the degree of immobilization of hexavalent chromium in the products formed by the hydrothermal reaction. It was found that the degree of immobilization was very high. Based on the results obtained, the immobilization mechanism of hexavalent chromium in stainless steel slag, resulting from the hydrothermal treatment of blast furnace slag, could be elucidated. Finally, the immobilization of cadmium, lead, and arsenic using blast furnace slag as the immobilization agent was also studied while focusing on the effects of the hydrothermal treatment.

Analogue experimental study on centrifugal-air blast granulation for molten slag

Blast furnace slag is a by-product in iron and steel production process which has a high yield with extremely high discharge temperature. Aiming at energy and water saving as well as emission reduction, dry granulation technique appears to be a good application for the treatment of blast furnace slag. In this study, a granulation technique combining a high-speed rotating cup with air blast is proposed. The performance of this design was investigated by adopting a mixture of rosin and paraffin wax as the analogue of blast furnace slag. The effects of rotating speed of the atomizer, liquid flow rate and blast air flow rate on particle size, particle mass distribution and fiber mass fraction were studied. The effect of the function of air blast on the granulation performance was particularly discussed. The results showed that at a higher rotating speed and a smaller liquid flow rate, smaller particles can be easily obtained, yet the fiber mass fraction also increases. However, the increasing blast air leads to the increase of particle size and fiber mass fraction. For the operating conditions tested in this study, over 60% of total mass of particles fall within the size range of 0.5–1 mm, which means that the present system has a good performance in centrifugal granulation.

Hydrothermal preparation of tobermorite from blast furnace slag for Cs+ and Sr2+ sorption

Al-substituted 11Å-tobermorite was formed by alkaline hydrothermal treatment of blast furnace slag with sodium silicate added at 180°C for 2–48h. Effects of the hydrothermal treatment time were characterized by XRD, SEM, and isothermal adsorption of N2. Sorption characteristics of the obtained samples were examined for Cs+ and Sr2+. The sample obtained by hydrothermal treatment for 48h (HT-48h) consisted of calcium silicate hydrate (C–S–H), and Al-substituted 11Å-tobermorite. The HT-48h showed the highest performance for Cs+ and Sr2+ selectivity in the presence of Na+. The interlayer Na+ of Al-substituted 11Å-tobermorite and surface Ca2+ played an important role in selective Cs+ and Sr2+.

Use of Two Industrial Wastes as Soil Amendments: Effect on Dissolved Reactive Phosphorus in Runoff

To control the dissolved reactive phosphorus (DRP) concentration in a soil solution, a number of soil amendments were tested. In the current study, Blast Furnace Slag (BFS) and Water Treatment Residues (WTR) were tested on bare soil under two rainfall intensities and two soil roughness levels. The soil was fertilized with P (KH2PO4) at a rate of 400 kg ha−1 while BFS and WTR were applied at a rate of 5 g per 100 g of soil. Two soil roughness levels were exposed to artificial rainfall intensities of 30 and 65 mm h−1. Three rainfall events were performed on each treatment. The runoff water generated over an area of 0.5 m2 with a slope of 8% was collected at different time intervals and analyzed for DRP, Al, Fe, and K concentrations. The results showed that, regardless of rainfall intensity and soil roughness, the concentration of DRP in the runoff water increased with increasing runoff time from the unamended plots. However, in the BFS- and WTR-amended soils, the DRP concentration decreased with runoff time. Dissolved reactive P and DRP loads were the lowest from the WTR-amended plots, followed by the control and the BFS treatment plots. Water treatment residues reduced the mean DRP concentration by 27.3% and the DRP load by 32% compared to unamended plots. The two rainfall intensities significantly affected the DRP concentration and load. Under the low rainfall intensity, the DRP concentration and load were higher compared to the high rainfall intensity. The overall DRP concentration was not affected by changes in soil roughness. However, the DRP loads were higher from the plots with low soil roughness levels, especially during the first and second runs. Both the BFS and WTR were also effective in reducing the DRP concentrations in the drain water collected during the runoff events. The concentrations of Al, Fe, and K in the runoff water were not affected by the soil amendments. However, the electrical conductivity and pH readings were higher from the BFS-amended plots.

Effect of Microwave Irradiation on Hydrothermal Treatment of Blast Furnace Slag

The effect of microwave irradiation on the hydrothermal treatment of blast furnace (BF) slag was investigated using a 2.45 GHz microwave irradiation system. The comparison of the features of a microwave-hydrothermal (M-H) reaction with those of a conventional hydrothermal (C-H) reaction showed that in both these reactions, tobermorite (Ca5Si6O16(OH)2·4H2O) was formed as the major phase in the treated samples. When the BF slag was hydrothermally treated by the C-H reaction, tobermorite was formed in the vapor state as the major phase at 200°C after a holding time of 48 h; in the M-H reaction, tobermorite was rapidly formed within 3 h at the same temperature. It was elucidated that microwave irradiation promoted the hydrothermal reaction to a significant extent.Furthermore, effects of microwave irradiation on BF slag subjected to hydrothermal hot-pressing were investigated. After microwave irradiation, the compressive strength of the slag compact and rate of porosity in the compact after treatment increased and decreased, respectively, in comparison with those before treatment. Moreover, microwave irradiation was advantageous over conventional heating at the same temperature in that it enhanced the compressive strength of the BF slag.

Evaluation of Hydrothermal Treatment to Immobilize Hexavalent Chromium in Wastewater Using Granulated Blast Furnace Slag

The immobilization of hexavalent chromium in wastewater using blast furnace slag as the immobilizing agent was investigated by using hydrothermal treatment. The results showed that immobilization was not attained without a hydrothermal treatment, while hexavalent chromium in solution could be immobilized through the process of hydrothermal treatment with the blast furnace slag at 250°C for 18 h. In particular, the reducing condition was attributed to the presence of sulfur in the blast furnace slag, which indicated that the sulfur could plays key role in the immobilization of hexavalent chromium in the present study. In addition, the leaching test was carried out to evaluate the level of immobilization of hexavalent chromium in the products after the hydrothermal treatment, and it was found that the degree of immobilization was very high. Based on the results obtained in the present study, the immobilization mechanism of the hydrothermal treatment of blast furnace slag in wastewater was elucidated.

Reaction Mechanisms of Blast Furnace Slag in Liquid and Vapor Dominated Hydrothermal Systems

In order to develop an efficient process for the treatment of waste slag, the behavior of hydrothermal reaction of blast furnace slag has been investigated. For blast furnace slag, an experiment was conducted under various hydrothermal conditions with a liquid and vapor phase in the presence of saturated water steam pressure using an autoclave.The results indicated that calcium silicate hydrate (C-S-H) and tobermorite (Ca5Si6O16(OH)2·4H2O) were the major phases formed in the treated samples. It was also confirmed that the hydrothermal reaction process was strongly affected by the hydrothermal conditions. In particular, the hydrothermal reaction proceeded more rapidly in vapor phase than in liquid one. Accordingly, the reaction mechanism of the hydrothermal treatment of blast furnace slag has been clarified.