| 1. |
- Chen, YuHong, et al.
(författare)
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Identification of Fe-containing phase in oxidation process of BOF slag
- 2017
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Ingår i: Key Engineering Materials. - Zürich : Trans Tech Publications. - 1013-9826 .- 1662-9795. ; 726, s. 564-568
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the Fe-containing phases in BOF slag were identified before and after oxidized with atmospheric air. XRD and SEM with EDS results showed that The element Fe existed in slag in the form of calcium ferrite, wustite solid solution and hematite. Mg solid solute in wustite. After oxidized, magnetite became the major mineral phase in slag and Mg+ replace the Fe2+ of magnetite crystal to form spinel
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| 2. |
- Han, Fenglan, et al.
(författare)
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Environmental performance of fluorite used to catalyze MgO reduction in pidgeon process
- 2012
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Ingår i: Advanced Materials Research. - 1022-6680 .- 1662-8985. ; 577, s. 31-38
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Tidskriftsartikel (refereegranskat)abstract
- Environmental performances of fluorite used as catalyzer for chemical reaction between MgO and Si were investigated by performing pilot scale experiments of Mg production. F amounts of 0.012-0.116 kg were added in the charged briquettes and Mg slag generated from the chemical reaction in most of the tests weighted 4.26-4.96 kg with F contents ranging 0.21-2.52%. Based on high recoveries of F, 83-100%, in the slag after the reaction, it is estimated that there are little or no F compounds leaving the retorts during the pilot tests. However, high amount of F, 72.9 mg/kg, was leached out from an Mg slag sample obtained from an Mg plant, making it necessary to decrease amount of fluorite used as catalyzer for the reaction or to improve operation conditions, thus, enhancing rate for chemical reaction between MgO and Si in Pidgeon process
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| 3. |
- Han, Fenglan, et al.
(författare)
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Fluoride evaporation during thermal treatment of waste slag from Mg production using pidgeon process
- 2012
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Ingår i: Advanced Materials Research. - 1022-6680 .- 1662-8985. ; 581-582, s. 1044-1049
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Tidskriftsartikel (refereegranskat)abstract
- Fluoride evaporation from Mg slag samples was investigated. F content in the original slag sample from an Mg factory was 1.65%, which decreases to 0.98-1.54% in the samples heated at 1000-1400°C for 3 hours. The values of F evaporation from the test samples were 6.7-40.6%. The fluorides may evaporate in the atmosphere, causing air pollution. Some suggestions were presented based on study results obtained to minimize fluoride emissions and improve environmental performances of the Mg production by using Pidgeon process
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| 4. |
- Han, Fenglan, et al.
(författare)
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Innovative utilization of a borate additive in magnesium production to decrease environmental impact of fluorides from pidgeon process
- 2013
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Ingår i: Advanced Materials Research. - 1022-6680 .- 1662-8985. ; 690-693, s. 378-389
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Tidskriftsartikel (refereegranskat)abstract
- The present authors have utilized, for the first time, H3BO3 as an additive in pilot scale experiments of Mg production using Pidgeon process. The results from the experiments revealed positive effects of H3BO3 on both quantity and quality of the Mg metal crowns. Besides acting as a catalyzer for MgO reduction, H3BO3 stabilized also β-Ca2SiO4 in the Mg slag. Based on these results, H3BO3 may be adopted as an innovative additive replacing fluorite in the Mg production, to enhance sustainability and environmental soundness for the Pidgeon process in China.
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| 5. |
- Han, Fenglan, et al.
(författare)
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Treatments of magnesium slag to recycle waste from Pidgeon process
- 2012
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Ingår i: Advanced Materials Research. - 1022-6680 .- 1662-8985. ; , s. 1657-1667
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Tidskriftsartikel (refereegranskat)abstract
- Magnesium slag powder from a local magnesium plant was treated to improve the volume stability for its application as building materials. The slag was mixed with borates, pressed into briquettes, and then sintered at high temperature. SEM studies show that at the higher temperature Ca 2SiO4 polymorphs were stabilized by Na and B ions in the added borates. The free MgO content in the slag was also decreased by the sintering treatment. The slag powder, after mixing with 0.4-0.6% of borates and sintered at 1200°C in 5-6 hours, has become volume stable aggregates. It is then possible to use the treated slag in constructions, saving valuable natural resources and decreasing the global warming impact from magnesium production via Pidgeon process
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| 6. |
- Jiang, Liang, et al.
(författare)
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Formation of Spinel Phases in Oxidized BOF Slag under Different Cooling Conditions
- 2017
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Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X. ; 88:11
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Tidskriftsartikel (refereegranskat)abstract
- To enhance utilization of wastes generated from steelmaking, a BOF slag sample from Ning Steel group in China is treated by oxidizing at 1500 °C for 30 min and then cooled by different methods. The treated samples are characterized, in combination with calculations using FactSage 6.4. XRD results show that iron oxides in BOF slag are converted largely by the oxidation to spinel phases, Fe3O4 and MgFe2O4, which also eliminates free CaO and MgO. EDS analyses show Fe element existing in di-calcium silicate and glass phase, which are Fe3+ ions formed by oxidation. An incorporation of Fe3+ ions into crystal structures has stabilized high temperature polymorph of C2S, β-C2S, and α’-C2S, in the treated slag samples. Fe3+ ions may also act as a network former to facilitate glass formation. This may make it possible for the glass and α’-C2S phase to complement each other, leading to a higher hydraulicity, while the BOF slag, after the spinel separation, is blended in cements. Some suggestions are proposed, based on the present and early studies, to enhance hydraulicity for the BOF slag, as well as grain sizes of spinel phases, which may result in economic and environmental benefits for steel and cement industries.
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| 7. |
- Jiang, Liang, et al.
(författare)
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Structural Characteristics and Hydration Kinetics of Oxidized Steel Slag in a CaO-FeO-SiO2-MgO System
- 2019
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Ingår i: High Temperature Materials and Processes. - : Walter de Gruyter. - 0334-6455 .- 2191-0324. ; 38:1, s. 290-300
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Tidskriftsartikel (refereegranskat)abstract
- Although steel slag exhibits cementitious properties, the addition of steel slag in cement is still limited due to both the presence of excess iron oxides and instability of free lime and periclase. This paper proposes a method for oxidizing molten slag in air, aiming at extraction of superfluous wustite and stabilization of free lime and periclase. Mineralogical characteristics of raw slag and modified products were examined using X-ray diffraction (XRD), scanning electron microscopy equipped with backscattered electron imaging (SEM-BEI), energy dispersive spectrometry (EDS) and thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC). Thermodynamic calculations were performed to aid to discuss the experimental results. The results indicate that non-magnetic wustite and periclase are transformed into magnetic spinel (magnetite/magnesioferrite) after oxidation. Temperature has a significant effect on the formation of spinel. The mass fraction of free lime decreases from 3.54 wt.% to 0.96 wt.% as a result of the conversion from free lime to calcium ferrite.
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| 8. |
- Wu, Laner, et al.
(författare)
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Dusting control of magnesium slag produced by Pidgeon process
- 2013
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Ingår i: Powders and grains 2013. - Melville, NY : American Institute of Physics (AIP). - 9780735411661 ; , s. 1282-1285
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Konferensbidrag (refereegranskat)abstract
- Magnesium production by Pidgeon process has been developed very fast in China since 1990's. The waste slag from magnesium production has attracted broad attention because the huge amounts of the slag. For each ton of magnesium produced, there will be 6-8 tons of the slag generated. A big part of the Mg slag exists as fine dust with particle size of D95 < 0.1mm, which may pollute air, soil and water surrounding the Mg industry. The fine particles are generated by phase transformations of dicalcium silicate C2S (2CaOṡSiO 2) during the slag cooling. There is a volume expansion of more than 10% with the transformation of β-C2S to γ-C2S phase, causing a disintegration or dusting of the Mg slag. In the present study, several chemical stabilizers were used to treat the dusting Mg slag at 1200°C, including borates, phosphates and rare earth oxides, in order to obtain volume stable slag aggregates for environmental protection and recycling of the Mg slag. The volume expanding rates of the samples were measured. XRD and SEM studies were carried out to confirm effects of the stabilizers. The results show that all of the stabilizers were effective for the stabilization of Mg slag. Some differences between the stabilizers were also described and discussed
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| 9. |
- Wu, Laner, et al.
(författare)
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Fluoride emissions from Pidgeon process for magnesium production
- 2012
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Konferensbidrag (refereegranskat)abstract
- Primary magnesium is nowadays produced in China via Pidgeon process. An important reaction in the process is silicothermic reduction of MgO from dolime near 1200ºC under pressure of 2-10 Pa to generate Mg vapor. Fluorite, ranging 2-3% (mass fraction), is usually mixed with the raw materials to catalyze the reaction. Under the process conditions, CaF2 in the fluorite may form some fluorides to vaporize, thus polluting air. The fluorides remaining in the solid process waste, the Mg slag, may be dissolved to cause water pollution.In the present study, experiments were performed by using retorts of pilot scale in a maffle furnace to simulate the Pidgeon process for primary Mg production. The test materials, briquettes of 5.6-10 kg made of dolime, ferrosilicon and fluorite, were charged in the retorts and heated under conditions similar to the industry operation. Fluoride minerals in the Mg slag from the simulation experiments were identified by XRD and SEM-EDS techniques. Quantities of some F-containing phases formed in the process under equilibrium condition were calculated by FactSage 6.2 thermodynamic package. Fluoride distributions were determined to establish an F-balance among the input and output materials. Besides, slag samples from a magnesium plant were also characterized, including leaching test according to EN 12457-2.Based on these results, fluoride impacts on the environment were evaluated and discussed. Suggestions were also presented to minimize the environmental impacts from primary Mg production using the Pidgeon process.
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| 10. |
- Yang, Qixing, et al.
(författare)
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Dissolution behavior of fluorine from AOD slag after treatments for volume stabilization
- 2014
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Ingår i: Applied Mechanics and Materials. - 1660-9336 .- 1662-7482. ; 587-589, s. 849-855
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Tidskriftsartikel (refereegranskat)abstract
- AOD slag samples from steel works of Outokumpu Stainless Company were used to study F-dissolution relating to treatments for volume stabilization. Results from the slag tests and sample characterizations indicate that the slag re-melting with or without reduction and granulation with either water or gas have rather small effects on F leaching, as well as formation of different C2S polymorphs. The chemical composition and cooling condition are the two important parameters to control F leaching from slag samples. These two parameters should be combined together in an optimum way by the steel industry to treat slags for F-immobilization.
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