| 1. |
- Hu, Xianfeng, et al.
(författare)
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Thermogravimetric study on carbothermic reduction of chromite ore under non-isothermal conditions
- 2015
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Ingår i: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 42:6, s. 409-416
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the reduction of chromite ore by coke was investigated by means of thermogravimetric analysis under non-isothermal conditions (from room temperature to 1823 K). The fractional reduced samples were examined by SEM/EDS and X-ray diffraction analyses. The experimental results showed that the reduction of iron in the chromite ore started before that of chromium in the ore, and the reduction of chromium and iron in the ore overlapped to some degree. Chromium iron carbide (Cr,Fe)7C3, was found to be the intermediate phase during the reduction, and a chromium gradient was found in the spinel phase of the fractional reduced sample at 1673 K. A four-stage reduction process was proposed: one stage involving the reduction of iron in the chromite ore and three stages involving the reduction of chromium in the ore. The activity aspects of component FeCr2O4 and component MgCr2O4 in the chromite ore were considered. The difficulty in the reduction of the chromite ore is attributed to the fact that, as the reduction proceeds, the activity of the component MgCr2O4 in the fractional reduced ore will decrease to a very low level, which makes further reduction very difficult.
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| 2. |
- 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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| 3. |
- Engström, Fredrik, et al.
(författare)
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Crystallization behaviour of some steelmaking slags
- 2010
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Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 81:5, s. 362-371
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Tidskriftsartikel (refereegranskat)abstract
- The present study was aimed at highlighting the final properties of two different steelmaking slags which undergo different cooling rates. The experiments were conducted in laboratory scale using an induction furnace. One of the slags originates from an electric arc furnace (EAF) (high-alloyed) and the second slag from a basic oxygen furnace (BOF). The treatment of the slag included re-melting along with different cooling rates. The material collected from the tests was characterized through X-ray diffraction, scanning electron microscopy as well as thermodynamic calculations which were compared with experimental results, for confirmation. The results indicate that both the EAF and BOF slags show increased reactivity with water, as well as a decrease in crystal size when rapid cooling is applied. The wüstite-type solid solution (Mg,Fe,Mn)O varies in composition depending on the cooling conditions. Metastable Ca3SiO5 was found in the rapidly- cooled BOF slag.
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| 4. |
- Feng, Yan, et al.
(författare)
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Characterization and evaluation of the pozzolanic activity of granulated copper slag modified with CaO
- 2019
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Ingår i: Journal of Cleaner Production. - : Elsevier. - 0959-6526 .- 1879-1786. ; 232, s. 1112-1120
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Tidskriftsartikel (refereegranskat)abstract
- GCS, granulated copper slag, is currently utilized in cement and concrete with a low rate, due mainly to its low pozzolanic activity. The present study was thus performed by first mixing the GCS with CaO, and then melting and water-granulating the GCS-CaO mixtures, as to enhance the reactivity of GCS. Blended cements were formulated by replacing 30 wt. % of the cement, PC, with the modified GCS. The addition of CaO in GCS increased the release rates of heat from the early-age hydration of the blended cement pastes. The pastes with CSC20, the GCS of the highest CaO content (19.5%), acquired higher compressive strengths than those for the PC and other PC-GCS pastes at both 28 and 90 days of curing. The GCS richer in CaO consumed more calcium hydroxide for the formation of calcium silicate hydrates, with SEM micrographs showing a microstructure of more gel phases and less pores in PC-GCS paste. These results indicate that the modification by addition of CaO is an effective way to achieve a high reactivity for the GCS. It may then be possible to utilize the modified GCS as a high-quality supplementary cementitious material to enhance the sustainability for both copper and cement industries.
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| 5. |
- Feng, Yan, et al.
(författare)
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Mechanical Activation of Granulated Copper Slag and Its Influence on Hydration Heat and Compressive Strength of Blended Cement
- 2019
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Ingår i: Materials. - Basel, Switzerland : MDPI. - 1996-1944 .- 1996-1944. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- Mechanical activation of granulated copper slag (GCS) is carried out in the present study for the purposes of enhancing pozzolanic activity for the GCS. A vibration mill mills the GCS for 1, 2, and 3 h to produce samples with specific surface area of 0.67, 1.03 and 1.37 m²/g, respectively. The samples are used to replace 30% cement (PC) to get 3 PC-GCS binders. The hydration heat and compressive strength are measured for the binders and derivative thermogravimetric /thermogravimetric analysis (DTG/TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) are used to characterize the paste samples. It is shown that cumulative heat and compressive strength at different ages of hydration and curing, respectively, are higher for the binders blending the GCS milled for a longer time. The compressive strength after 90 d of curing for the binder with the longest milling time reaches 35.7 MPa, which is higher than the strength of other binders and close to the strength value of 39.3 MPa obtained by the PC pastes. The percentage of fixed lime by the binder pastes at 28 days is correlated with the degree of pozzolanic reaction and strength development. The percentage is higher for the binder blending the GCS with longer milling time and higher specific surface area. The pastes with binders blending the GCS of specific surface area of 0.67 and 1.37 m²/g fix lime of 15.20 and 21.15%, respectively. These results together with results from X-ray diffraction (XRD), FTIR, and SEM investigations demonstrate that the mechanical activation via vibratory milling is an effective method to enhance the pozzolanic activity and the extent for cement substitution by the GCS as a suitable supplementary cementitious material (SCM).
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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- Han, F.L., et al.
(författare)
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Fluorine vaporization and leaching from Mg slag treated at high temperature
- 2013
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Ingår i: Advanced Materials Research. - 1022-6680 .- 1662-8985. ; 726-731, s. 2898-2907
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Tidskriftsartikel (refereegranskat)abstract
- Pidgeon process is used by more than 300 plants in China to produce magnesium (Mg) metal. Fluorite, ranging 2-3%, is often mixed in raw materials to catalyze the Mg production. The Mg slag from the production then contains F of several mass percent. When the Mg slag is used in construction or treated for recycling, possible F pollutions are of concerns. The present study used slag samples containing F of 0.98-2.15% from an Mg factory in northwest China. Both treatments at 1000-1400°C and leaching tests before and after the treatments were conducted for the slag samples. The study results show influences of the treatments on mineral compositions of the samples, which controlled F contents in both the slag samples and leachates. The results are reported and discussed. Some suggestions are also presented to minimize fluorine pollutions and to improve environmental performances of the Pidgeon process
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| 10. |
- 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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