Reduction Of Slag Research Articles

Direct reduction of copper slag-carbon composite pellets by coal and biochar

ABSTRACT As a renewable resource of reducer, biochar prepared by pine sawdust is proposed for direct reduction of copper slag in this paper. Combined with thermodynamic analysis, effects of reduction time, temperature and CaO addition ratio on solid copper slag reduction characteristics are discussed. The oxides of iron in copper slag are Fe3O4 and 2FeO·SiO2. The reduction processes were carried out step by step for Fe3O4 and 2FeO·SiO2, respectively: Fe3O4 → FeO → Fe and 2FeO·SiO2 → Fe. The porous structure of biochar exhibits higher reduction reactivity and reaction rate than that of coal. CaO reduced the Gibbs free energy of reduction reactions and facilitated the reduction of 2FeO·SiO2 with C and CO. When CaO was added, separation reaction of FeO and SiO2 took place and α-SiO2 and β-SiO2 were produced. When the addition ratio of CaO is above 0.3, CaO·SiO2 and 2CaO·SiO2 are produced. The reduction process of copper slag was established as follows: (a) dehydration and fast pyrolysis; (b) reduction of iron oxides by C and CO; and (c) sweating metallic iron outflows from cracks in pellet. Besides, direct reduction reaction mechanism and transport process of Cu are established based on reduction experiments, XRD and SEM-EDS analysis.

Engineering performance evaluation of mortar with EOS (electric arc furnace oxidizing slag) as fine aggregate

Electric arc furnace oxidizing slag (EOS), in the fine aggregate form, can effectively be utilized as a construction material. However, its engineering properties vary with the manufacturing processes employed and the producing district, thereby causing observed differences in material performance. In this study, EOS was obtained from steel manufacturing plants in South Korea, and engineering properties of standalone EOS, as well as in combination with cement mortar were separately evaluated. Test results demonstrate that EOS primarily comprises CaO, SiO2, and FeO in combination with 18.2% larnite, which possesses β-C2S crystal structure with a similar cement mineral. The EOS mortar combination demonstrated increasing compressive strength with an increase in EOS content due to the effect of a considerable amount of β-C2S present in EOS. The EOS-based mortar with electric arc furnace reduction slag (ERS) demonstrated unsatisfactory results in accordance with a criterion set for the length rate of change. This implies that more consideration is required toward the use of mixed ERS and EOS in cement mortars due to the swelling effect of ERS on dimensional stability.

Magnetite reduction in copper converter slag using biodiesel produced from waste cooking oil

ABSTRACTIn copper smelting process, oxygen-enriched smelting leads to the enrichment of magnetite and increase of slag viscosity, which is not conducive to the sedimentation and separation of copper. Therefore, it is necessary to reduce magnetite in order to improve the recovery rate of copper. In this work, biodiesel produced from waste cooking oil was used to replace carbon and diesel, which should be more economical and environment-friendly. Effects of temperature and reaction time on biodiesel pyrolysis, magnetite reduction and slag viscosity were studied. It was found that the main products of biodiesel pyrolysis were carbon monoxide, hydrogen, methane, and carbon. Because methane will decompose to carbon and hydrogen at 823 K, the main reducing agents during magnetite reduction were hydrogen and carbon. With increasing reduction time and temperature, the magnetite phase in the copper slag gradually decreased, while the fayalite phase gradually increased. After injecting biodiesel into molten copper slag at 1523 K for 4 minutes, magnetite was reduced from 31.6% to less than 0.6% and the viscosity decreased from 1.43 poise to 0.68 poise. This low viscosity is beneficial for separation and recovery of copper from the molten slag.

Development of the Molten Slag Reduction Process -1 Characteristics of Closed Type DC arc Furnace for Molten Slag Reduction

Development of the Molten Slag Reduction Process -1 Characteristics of Closed Type DC arc Furnace for Molten Slag Reduction

Development of the Molten Slag Reduction Process -2 Optimization of Slag Reduction Process with Molten Slag Charging

Development of the Molten Slag Reduction Process -2 Optimization of Slag Reduction Process with Molten Slag Charging

A clean metallurgical process for separation and recovery of vanadium and chromium from V-Cr-bearing reducing slag

In this work, a clean metallurgical process is used to separate and recover vanadium and chromium from V-Cr-bearing reducing slag. Comparing with the traditional process, the process not only reduces the use of sulfuric acid, but also saves the cost of wastewater purification. The process consists of four procedures: low temperature sulphating roasting, reduction leaching, selectively oxidizing and the oxides of vanadium and chromium preparing. Among these, the reduction leaching and selectively oxidizing are the key steps. Low temperature sulphating roasting is used to strengthen the decomposition of V-Cr-bearing reducing slag, Na2SO3 is used for the reduction of vanadium from V(V) to V(IV) or V(III), CrO3 is used to selectively oxidize the vanadium in the leached solution, (NH4)2SO4 is used to make the vanadium precipitated in the form of ammonium polyvanadate, and NaOH is used to precipitate Cr(III) from the V precipitated solution. It was found that the leaching efficiencies of Cr and V can reach 99.7% and 99.6% respectively by low temperature sulphating roasting and reduction leaching. The products of V2O5 with purity 99.1% and Cr2O3 with purity 98.9% were obtained by treating the ammonium polyvanadate and the precipitate of Cr(III), respectively.

The Influence of Sulfur Content on the Carbothermal Reduction of SiMn Slag

This article examines the influence of sulfur content on the carbothermal reduction of MnO and SiO2 in SiMn slag by carbon black. The sulfur content in the synthetic slag is varied from 0 to 1.0 wt pct. Reduction experiments are carried out in a thermogravimetric (TG) furnace at 1873 K (1600 °C) under CO atmospheric pressure. The reduction rates are measured based on the weight loss data, and the samples are characterized by SEM/EDS and ICP-MS. The wetting property of slag on carbon black is also studied with the sessile drop technique. The reaction rate on the slag-metal interface is one order higher than on the slag-carbon interface. A small amount of sulfur (0.2 and 0.44 wt pct) accelerates the slag-metal reaction rate constant by 2.2 and 4.2 times, respectively. Therefore, small amounts of sulfur in slag significantly improve the reduction of MnO and SiO2. The MnS precipitation phenomenon during slag cooling is studied by FactSage simulation and experimental verification.

Enhancement of the nickel converter slag-cleaning operation with the addition of spent potlining

The slag cleaning (or matte settling) process was experimentally investigated at 1573 K using a fayalitic nickel converter slag containing spinel and matte/alloy particles. The addition of various amounts of spent potlining (SPL) was studied in terms of its influence on matte settling and the overall metal recoveries. The slags produced were characterized by scanning electron microscopy, energy-dispersive spectroscopy, and wet chemical analysis using inductively coupled plasma optical emission spectrometry. The presence of solid spinel particles in the molten slag hindered coalescence and settling of matte/alloy droplets. Matte settling was effectively promoted with the addition of as little as 2wt% SPL because of the reduction of spinel by the carbonaceous component of the SPL. The reduced viscosity of the molten slag in the presence of SPL also contributed to the accelerated matte settling. Greater metal recoveries were achieved with larger amounts of added SPL. Fast reduction of the molten slag at 1573 K promoted the formation of highly dispersed metal particles/clusters via accelerated nucleation in the molten slag, which increased the overall slag viscosity. This increase in viscosity, when combined with rapid gas evolution from accelerated reduction reactions, led to slag foaming.

Nonisothermal Carbothermal Reduction Kinetics of Titanium-Bearing Blast Furnace Slag

The kinetics of carbothermal reduction of titanium-bearing blast furnace (BF) slag has been studied by thermogravimetric analysis and quadrupole mass spectrometry. The kinetic parameters (activation energy, preexponential factor, and reaction model function) were determined using the Flynn–Wall–Ozawa and Satava–Sestak methods. The results indicated that reduction of titanium-bearing BF slag can be divided into two stages, namely reduction of phases containing iron and gasification of carbon ( 1095°C). CO2 was the main off-gas in the temperature range of 530–700°C, whereas CO became the main off-gas when the temperature was greater than 900°C. The activation energy calculated using the Flynn–Wall–Ozawa method was 221.2 kJ/mol. D4 is the mechanism function for carbothermal reduction of titanium-bearing BF slag. Meanwhile, a nonisothermal reduction model is proposed based on the obtained kinetic parameters.

Preparation of Multi-components TiAl Based Alloy by Aluminothermic Reduction of Acid Soluble Titanium Bearing Slag

The aluminothermic reduction of high Ti acid soluble Ti bearing slag (ASTS) was carried out to prepare the multi-components TiAl based alloy. In order to control and understand the preparation of TiAl alloy, the effects of the addition of Al and CaO, and temperature were discussed. By considering materials proportioning calculations it could successfully make TiAl alloy with sound slag-alloy separation. The recovery rates of most reduced elements are high, about 95% in the all experimental conditions. The Al addition can mainly affect the composition of TiAl alloy, while CaO addition influences the slag-metal separation by varying composition of slag system. Besides, the temperature of system can increase the recovery rate and distribution ratio for most reduced elements.

Studies on steel slag as an oxygen carrier for chemical looping combustion

Chemical looping combustion (CLC) has been suggested as an energy-efficient method for clean combustion with inherent capture of carbon dioxide. The development of commercially available, less-costly, thermally-stable and good kinetics oxygen carriers is the first propriety in the CLC process. This study is the first to explore the use of steel slag, a typical metallurgical waste, as an oxygen carrier in CLC. The primary advantage of steel slag is its low cost because of its nature of the solid waste. Steel slag mainly contains two interested substances for oxygen transfer in CLC, iron oxides and calcium sulfate (after sulfation). The thermochemical analysis on pre-sulfating steel slag was conducted by the Aspen Plus software, and the experiments of the reduction of pre-sulfating steel slag were carried out using a thermogravimetric analyzer (TGA). Characterizations of used steel slag were carried out by X-ray diffraction (XRD). Results indicated that the pre-sulfating steel slag can be a proper and excellent oxygen carrier, whose reduction kinetics using model fuel gas (CO, carbon monoxide) was rapid at medium temperatures. Further investigations revealed that it is Ca-containing components (CaSO4) in pre-sulfating steel slag that was mainly involved in the redox process using CO. Moreover, the reaction rate has increased by nearly 15 times as compared to that of the pure CaSO4 at the same temperature. The conversion of CaSO4 to CaS can be nearly complete. Higher temperatures were adverse to the stability of CaSO4, leading the decomposition of CaSO4, the degradation of its oxygen transfer capability and the increase of sulfur emissions. However, the use of steel slag rationally control the optimized reduction temperature to be 750 °C, when its kinetics can be maintained rationally at 100% conversion within 30 min and a stable oxygen transfer capability at 10.63 wt% with the minimized sulfur emissions. This finally validated steel slag as a promising oxygen carrier candidate.

A clean technology to separate and recover vanadium and chromium from chromate solutions

In this work, a clean technology is introduced to separate and recover vanadium and chromium from vanadium-containing chromate solution. It was found that vanadium can be precipitated from vanadium-containing chromate solution by hydrolysis. The hydrolysate is the mixture of polyvanadic acid and sodium polyvanadate. The concentration of V in the solution can be decreased to 0.76 g/L under pH 2.0 at 95 °C. The Na in the mixture can be effectively removed by washing with (NH4)2SO4 solution as the bind of NH4-VO3 is stronger than that of Na-VO3. The V2O5 with purity 98.6% was acquired by calcining the washed mixture. The vanadium residue in precipitated solution can be completely removed by adding Fe2+ or Fe3+ to form iron vanadate under pH 3.8–4.5. The chromium in the V free solution was reduced from Cr(VI) to Cr(III) with Na2SO3, and then the precipitate of Cr2O3∙xH2O was formed under pH above 8.5 at 90 °C. At last, the Cr2O3 with purity 98.7% was obtained by the treatment of the chromic oxide hydrate. Using the process above, the generation of V-Cr-bearing reducing slag and the mixture of Na2SO4 and (NH4)2SO4 can be avoided in vanadium pentoxide production from vanadium-containing chromate solution.

Mechanism of composite additive in promoting reduction of copper slag to produce direct reduction iron for weathering resistant steel

The mechanism of composite additive in promoting reduction of copper slag was revealed. In this paper, the kinetic study of direct reduction of copper slag (CS) was studied by isothermal method, and the phase transformation and growth behaviors of metallic iron particles during reduction process were clarified by X-ray diffraction, Scanning Electron Microscopy, and Energy Dispersive X-ray Spectroscopy analyses. The results indicated that the apparent activation energy of reduction reactions of iron oxides within CS sample was decreased from 71.27 KJ/mol to 49.86 KJ/mol with the addition of 15% composite additive, and the mean particle size of metallic iron particles increased from 9.2 μm to 35.2 μm. The composite additive can promote the reduction of iron minerals and induce the adequate growth of metallic iron particles, which is beneficial for iron and copper recovery in magnetite separation process.

Thermodynamic analysis of reduction in copper slag by biomass molding compound based on phase equilibrium calculating model

Copper slag is a good valuable material resource with high iron content in the form of fayalite. Biomass as reduction reducer was proposed in this paper. For the basic research of the reduction in biomass, the biomass reducer was simplified as molding compound C, CO, H2 and CH4. The reactions of 2FeO·SiO2 with C, CO, H2 and CH4 could proceed spontaneously with the addition of CaO. The Gibbs free energy is decreased significantly by addition of CaO. The equilibrium compositions of products were calculated and analyzed combing with 19 basic reactions. Beginning temperature of C, CO, H2 and CH4 is 900, 623, 567 and 511 K, respectively The reduction degree of C, CH4, H2 and CO is 1, 0.851, 0.695 and 0.452, respectively, at 1773 K when the reducer addition ratio is 1.0 calculated by phase equilibrium calculating model. Direct reduction reaction of copper slag dominates at higher temperature, and temperature region of 700–1173 K is the transformational zone. Indirect reduction index curves are in the shape of reverse ‘S,’ and the higher temperature is in favor of indirect reduction in copper slag. There is a steady increase in reduction degree with the increase in reducer. Reduction reaction path of copper slag by C, CO, H2 and CH4 is established.

The effect of coal ratio on the high-lead slag reduction process

The effect of coal ratio on the high-lead slag reduction was reported in this article. First, the phase diagrams of the PbOFeO- SiO2-2%CaO-10%ZnO slag system at various temperatures and coal ratios were thermodynamically constructed. Next, the density, the melting temperature, the viscosity, the chemical composition and the phase transformation of the reduced slag were investigated. The thermodynamic results indicated that the variation of coal ratio could affect the chemical composition of the reduced slag, which led the physical properties of the reduced slag to change further. The experimental results illustrated that the content of lead and copper in the reduced slag decreased, while the contents of iron, silicon, calcium and zinc in the reduced slag increased as the coal ratio increased, which led the density and viscosity of the reduced slag to decrease further. The melting temperature of the reduced slag increased sharply when the coal ratio varied in the range of 1.5% to 3%. The mineralogy of the reduced slag indicated that lead mainly existed in the reduced slag in the form of metallic lead, while the iron and zinc were mainly enriched in the reduced slag in the form of a silicate phase. The industrial verification test results demonstrated that the average recovery rate of the lead exceeded 96.0%, the average lead content in the reduced slag was below 2.0% and the average fume rate was approximately 12.0%.

Extracting lithium from a lithium aluminate complex by vacuum aluminothermic reduction

The molten salt electrolysis of LiCl?KCl is presently the primary method of producing lithium, but it is costly and has environmental issues in addition to other disadvantages. Vacuum thermal reduction may be used extensively in the future because it offers low energy consumption, a high purity product and short cycle times. The present study investigated a novel process for the extraction of lithium from Li5AlO4 clinker by vacuum aluminothermic reduction. The Li5AlO4 clinker was prepared in ambient air using lithium hydroxide, alumina and calcium oxide. The results show that this process can proceed in conjunction with a lower ratio of raw materials to lithium (8.89:1) and provides lithium reduction rates in excess of 97%. In addition, the reduction slag consists mainly of 12CaO?7Al2O3, which can be used to produce aluminum hydroxide. Thus, this process represents a highly efficient and environmentally-friendly method of generating lithium.

Optimization and microstructure study of the reduction of nickel smelting slag mixed with calcium carbide slag and coke dust for recovering iron

How to treat more industrial solid waste friendly and environmental have become the global issues. In this study, direct reduction-magnetic separation (DRMS) process was employed to recovery iron from the nickel smelting slag (NSS) with calcium carbide slag (CCS) as the additive and coke dust (CD) as the reductant. Response surface methodology (RSM) approach using central composite design (CCD) was adopted for optimizing the effects of reduction temperature, reduction time and CCS dosage on the iron content of iron concentrate powder (ICP) and iron recovery. The results were modeled and the impact factors were evaluated. All the plots show that there were positive correlations between investigated impact factors and responses in a certain range but if exceeded, the positive correlations would be broken down. The overall optimization reaction conditions were converged as around 1287 oC, 2.8 h and CCS dosage of 57.19 %. Under these proven optimization reaction conditions, the iron content of ICP and iron recovery were reached up to 91.30 % and 95.44 % respectively. The micro phase of reduced samples were investigated by X-ray diffraction analysis (XRD), in reduction process, and the microstructure of reduced samples under the optimal condition were investigated by SEM for further discussion and analyzation. The experimental results and microstructure analysis suggests that utilizing CCS and CD in DRMS process were viable.

Synthesis of Titanium Oxycarbide from Titanium Slag by Methane-Containing Gas

In this study, reaction steps of a process for synthesis of titanium oxycarbide from titanium slag were demonstrated. This process involves the reduction of titanium slag by a methane-hydrogen-argon mixture at 1473 K (1200 °C) and the leaching of the reduced products by hydrofluoric acid near room temperature to remove the main impurity (Fe3Si). Some iron was formed by disproportionation of the main M3O5 phase before gaseous reduction started. Upon reduction, more iron formed first, followed by reduction of titanium dioxide to suboxides and eventually oxycarbide.

Preparation of Ti5Si3 by silicothermic reduction of titanium-bearing blast furnace slag

ABSTRACTIn the present study, the silicothermic reduction experiments of titanium-bearing blast furnace slag were carried out in argon atmosphere at different temperatures in order to prepare titanium silicide (Ti5Si3). The influences of temperature and reaction time on the reaction process were studied by X-ray diffraction and scanning electron microscope equipped with energy-dispersive spectroscopy. It was found that most of the titanium can be transformed to Ti5Si3 within a short time when the reduction temperature was higher than 1773 K. The produced Ti5Si3 particles were sintered and formed a porous skeleton structure due to its high melting point, with liquid slags filled in it. Meanwhile, it was found that high temperatures and long reaction time were beneficial for the separation of slag from Ti5Si3. This novel method of preparing Ti5Si3 may provide a route to recycle titanium-bearing blast furnace slag.

Utilization of reduction slag and waste sludge for Portland cement clinker production

The feasibility of recycling the reduction slag, limestone sludge, iron‐oxide sludge, and stone sludge produced in the manufacture of cement was investigated through compressive strength testing, differential thermal and thermogravimetric analysis, X‐ray diffraction, and 29Si nuclear magnetic resonance analysis. The major crystalline phases of ecocement clinkers, namely C3S, β‐C2S, C4AF, and C3A, were observed. C3S content decreased and β‐C2S and α‐C2S content increased in the reduction slag. The compressive strength of EcoA pastes (ecocement contain 78% of limestone sludge, 19.51% of stone sludge and 2.49% iron‐oxide sludge) was similar to that of commercial ordinary Portland cement. The Q0 (−70 ppm) species shifted to the Q1 (−80 ppm), and Q2 (−87 ppm) species during curing. The addition of stone sludge, iron‐oxide sludge, and limestone sludge had no negative effect on the hydration of the cement pastes. In contrast, the addition of reduction slag negatively affected the formation of clinker minerals. Cement samples with reduction slag content of 1–7 wt % had lower 28‐, 60‐, and 90‐day compressive strength than did the control mix. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 669–677, 2018