Reduction Of Slag Research Articles

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

Thermodynamic analysis of thermal energy recovery and direct reduction (TER-DR) system for molten copper slag

At present, air cooling and water quenching are traditional treatment methods for molten copper slag. However, the waste heat and valuable metals cannot be recovered efficiently by these methods. Exergy efficiency (EE) of this method is only 21.0%. This paper describes a feasibility of waste heat recovery and direct reduction of copper slag. To investigate the feasibility of this new thermal energy recovery and direct reduction system (TER-DR), thermodynamic compass method was applied. Based on physical and chemical recovery methods, TER-DR1 and TER-DR2 systems are put forward. TER-DR1 system decreases the exergy loss (EXL) and improves the EE to 57.3%, and 0.489 t DRI is acquired for every ton of copper slag. Exergy of six kinds of typical endothermic chemical reactions was analyzed. The exergy of reforming reaction of CH4 by CO2 is the highest and suitable for TER-DR system. Combined with chemical method, TER-DR2 system decreases EXL further and improves the EE to 61.3%. Steam, synthesis gas and DRI are produced by this method. By TER-DR2, for every ton of copper slag, 0.489 t DRI, 67.3 m3 CO and 67.3 m3 H2 are acquired.

Separation and recovery of vanadium and chromium from acidic leach solution of V-Cr-bearing reducing slag

The separation and recovery of vanadium and chromium from an acidic V-Cr-bearing reducing slag leach solution was investigated by selective oxidation of V(IV) using manganese dioxide, followed by precipitation of V(V) and Cr(III), respectively. The potential-pH diagrams for vanadium-manganese-water systems and chromium-manganese-water systems were drawn. E(MnO2/Mn2+) is higher than E(VO2+/VO2+) but lower than E(Cr2O72−/Cr3+), which proves manganese dioxide can be used to selectively oxidize V(IV). The oxidation of V(IV) can reach 99.5% at a temperature of 95°C for a oxidation duration of 3h with the addition of 40g/L manganese dioxide, and Cr(III) cannot be oxidized. The V(V) in the oxidized solution was precipitated in the form of ammonium polyorthovanadate and Cr(III) was precipitated as chromic hydroxide. The overall recovery of vanadium and chromium from the acidic leach solution was 98.7% and 99.4%, respectively.

Effect of Temperature and Graphite Immersion Method on Carbothermic Reduction of Fayalite Slag

In this work, graphite flakes were used to reduce fayalite slag originated from the pyrometallurgical copper extraction process. Experiments were conducted with a significantly different contact area between graphite and slag at two temperatures, 1300°C and 1400°C. The process was continuously monitored via the concentration change of CO and CO2 in off-gas. Reduction rate values in experiments where 150-micron-diameter graphite flakes were submerged into the slag and left to float slowly to the top are about four times higher compared with when graphite flakes were dispersed at the top surface of liquid slag. The activation energy for instigating reduction was 302.61 kJ mol−1 and 306.67 kJ mol−1 in the case where graphite flakes were submerged into the slag and dispersed at the surface, respectively. The reduction process is characterized by two distinctive periods: an initial steep increase in the concentration of CO and CO2 controlled by the Boudouard reaction and a subsequent slow decrease of CO and CO2 concentrations in the off-gas controlled by mass transfer of reducible oxides from bulk to the gas–slag interface.

Reduction of synthetic stainless steel slags by aluminium

ABSTRACTOne of the most efficient ways to eliminate the harm of chromium oxide in stainless steel slag is to reduce chromium oxide in stainless steel slag using aluminium. In the present work, the Al reduction of synthetic CaO–SiO2–Al2O3–MgO–Fe2O3–Cr2O3 stainless steelmaking slags at different conditions, including temperature, slag basicity and Al amount was investigated to get optimal conditions for the reduction and the metal–slag separation. It was found that the agglomeration of metal droplets and metal–slag separations were improved by increasing temperature. The reduction degrees of SiO2, Fe2O3 and Cr2O3 were enhanced with increasing basicity of slag. The addition of CaF2 in slag leads to better agglomerations of metal droplets and metal–slag separations. The highest reduction degree of chromium could reach 99% in slag with basicity of 2 at 1873 K.

Metal Recovery from BOF Steel Slag by Carbo-thermic Reduction

BOF steel slag is a main by-product in steelmaking. The valorization of BOF slag is good for the industry and the environment. In the present study, the carbo-thermic reduction of BOF slag has been investigated, the reduction of Fe and P containing phases (i. e. oxide and compounds) is discussed, and the effects of Al2O3 additions on the reduction process are described. XRD and EPMA have been applied for characterizing the slag. We conclude that, by controlling the test conditions, it is possible to purify the recovered Fe.

Effect of Na2CO3 Addition on Carbothermic Reduction of Copper Smelting Slag to Prepare Crude Fe-Cu Alloy

Copper smelting slag is a useful secondary resource containing high iron and copper, which can be utilized to prepare crude Fe-Cu alloy by a direct reduction–magnetic separation process for making weathering-resistant steel. However, it is difficult to recover iron and copper from the slag by direct reduction since the iron mainly occurs in fayalite and the copper is held in copper sulfide. Therefore, enhancement reduction of copper slag is conducted to improve the recovery of copper and iron. Additives such as Na2CO3 has been proven to be capable of reinforcing the reduction of refractory iron ore. In this research, the effect of Na2CO3 on the carbothermic reduction of copper slag was investigated, and phase transformations during reduction and the distributing characteristics of iron and copper in the alloy and non-metallic phases of the reduced pellets were also studied. The results show that the metallization rate of iron and copper was increased with the addition of Na2CO3, leading to higher iron and copper recovery in Fe-Cu alloy powder. X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) results confirm that Na2CO3 is capable of enhancing the reduction of fayaltie, copper silicate and copper sulfide, which agrees well with thermodynamic analysis. Furthermore, the reduction mechanism of copper slag was demonstrated based on systematic experimental observations.

A novel technology for vanadium and chromium recovery from V-Cr-bearing reducing slag

Wastewater produced in the process of vanadium extraction from vanadium slag is treated by reduction and neutralization which produces a V-Cr-bearing reducing slag. The recovery of vanadium and chromium from this slag was investigated by a comprehensive route including sulfuric acid leaching, selective oxidation of low valent vanadium and hydrolysis precipitation of vanadium and chromium. Under the most suitable conditions including a leaching time of 4h, sulfuric acid addition of 74wt% and leaching temperature of 90°C, the leaching of vanadium and chromium reached 90.9% and 97.8%, respectively. The vanadium of low valent in leach solution was selectively oxidized by manganese dioxide with the oxidation of 96.9%, while Cr(III) was not oxidized. The hydrolysis precipitation method was used to separate and recover V(V) and Cr(III), and the recovery of vanadium and chromium reached 98.3% and 99.1%, respectively. The overall vanadium and chromium recovery was 86.5% and 96.9%, respectively.

Hydration characteristics of recycling reduction slag and waste sludge by co‐sintered treatment produced as eco‐cement

Waste materials have traditionally been discarded in landfills and often dumped directly into ecosystems without adequate treatment. However, possible reuse and recycling alternatives should be investigated and implemented. Recent environmentally friendly approaches have been aimed at achieving sustainable development by conserving natural resources and minimizing the discarding of materials. The objective of the present study was to investigate the hydration characteristics of reduction slag, limestone sludge, stone sludge, and iron‐oxide sludge for fabricating four types of eco‐cement clinkers. The compound raw materials were burned for 2 h at 1400°C to form eco‐cement clinkers. The results showed that the major components of ordinary Portland cement (OPC), namely C3S, C2S, C3A, and C4AF, were present in the eco‐cement clinkers. The compressive strength development of EcoA pastes (containing 78% limestone sludge, 19.51% stone sludge, and 2.49% iron‐oxide sludge) was similar to that of the commercial OPC products. The compressive strength of the EcoD pastes (containing 71% limestone sludge, 19.51% stone sludge, 2.49% iron‐oxide sludge, and 7% reduction slag) decreased as the amount of α‐C2S increased. Mercury intrusion porosimetry indicated that the pore volume of the pastes gradually decreased with an increase in the curing time. Furthermore, the results of physical‐mechanical tests showed that reduction slag, limestone sludge, stone sludge, and iron‐oxide sludge can be used as raw materials in cement production at no cost to the producer, thereby reducing the production costs. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1466–1473, 2017

Valorization of BOF Steel Slag by Reduction and Phase Modification: Metal Recovery and Slag Valorization

Basic oxygen furnace (BOF) steel slag is a main byproduct in steelmaking, and its valorization is therefore of considerable interest, from a metal-recovery perspective and from a residue-utilization perspective. In the present study, the carbothermic reduction of BOF slag was investigated systematically. The reductions of Fe- and P-containing phases (i.e., oxide and compounds) are discussed. Effects of Al2O3 and SiO2 additions on the solidification microstructure and mineralogy associated with the reduction processes were also investigated. The formation and growth of the extracted metallic phase are discussed, and the mineralogy of the residue slag is determined. We conclude that by controlling the additions under a rapid cooling condition, it is possible to extract metallic iron as high-grade metal and simultaneously to utilize the remaining slag for construction applications.

Influence of Reduction Temperatures on Reduction of FeO-Containing Slag by Agricultural Waste

Generally, the conventional carbon sources such coke/coal are used in EAF steelmaking attributed the highest growth rate in energy consumption. A substitute routes striving to improve energy efficiency by providing auxiliary sources is essential. The unique features such high carbon content, surface area, porosity and low sulphur was available in agricultural waste clearly have the potential to be used as reducing agent in steelmaking process. The present study investigated the reduction behavior of EAF slag and production of metallic iron by reduction process. The carbon materials, coke and palm char (pyrolyzed via chemical activation) were used as reducing agent composite with EAF slag respectively. The reduction reaction was conducted in horizontal tube furnace at different reduction temperatures (1250°C, 1350°C, 1450°C and 1550°C) under argon gas (flow rate 0.01L/min) within 20 minutes. The reduced sample was examined by X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) to understand the reduction behavior of both composite samples. Palm char showed more efficient due to improvement in degree of FeO reduction which was 57.72% compared to coke, 26.72%. The phase movement from iron oxide to iron was influenced by the reduction temperatures. XRD pattern revealed that the metallic iron was initiating appeared at temperature 1250°C and completely reduced at temperature of 1550°C . Predominant peak of metallic iron and the other oxides was clarified by EDS spectra. This study found that palm char has viability to be used as carbon sources in steelmaking applications.

Carbothermal reduction of copper smelter slag for recycling into pig iron and glass

Slags produced from copper smelting are siliceous and often contain valuable metals such as copper and iron as well as deleterious elements such as arsenic and lead. A copper slag was obtained from the former Anaconda smelter site, USA and characterized by SEM-EDS, XRD, TG-DTA and ICP-OES.A recovery process was developed to separate the valuables from the silicates thereby producing value-added products and simultaneously reducing environmental concerns. Results show that the major phase was an amorphous iron-calcium-aluminosilicate of variable composition with copper sulfide prills. Thermodynamic calculations and carbothermal reduction experiments indicate that most of the copper and iron can be recovered as pig iron from the initial slag using minor amounts of lime and alumina and treating at 1350°C/1623K or higher for 30–90min. The resulting secondary slag can also be recycled as a glass to the glass and ceramic industry. Statistically designed experiments were conducted on the slag to identify the most favored regime to optimize the recovery of pig iron as well as the hardness and density of the secondary slag.

Improving the processing of steelmaking waste. Part 2. Development of the basic processing system

The expediency of reducing steelmaking slags to obtain metallic and oxide phases for use in metallurgy and construction is studied experimentally. Slag from the tailings at Zlatoust Metallurgical Plant is investigated. Experiments are conducted on the reduction of slag samples by carbon. The composition of the experimental samples is determined by X-ray spectral microanalysis. Experimental and theoretical data indicate that 20% (or even more) of the initial slag mass may be converted to metal by reduction. Practically complete reduction of the iron in the slag is possible. Significant proportions of the chromium, nickel, manganese, and other valuable components may pass to the metallic phase. Reduction of the liquid slag is expedient at 1500°C or more, so as to extract the metals more completely and form a consolidated metal phase. Preliminary solid-phase reduction of the slag at 1100–1200°C is found to be expedient. This process converts much of the iron present as oxides in the slag to a form susceptible to magnetic separation. Subsequent magnetic separation allows the fraction with an elevated content of valuable metals to be extracted from the oxide phase, which has a low metal content. The oxide fraction may be used in construction materials. In the design of systems based on these principles, utilization of the large quantities of carbon monoxide and metal vapor in the gas phase is recommended. One possibility is to use the carbon monoxide for preliminary solid-phase reduction of the slag. This research permits the development of an efficient system for processing slag tailings.

Pilot Plant Melting of Steel Using Ferro-Silico-Aluminum at KSP Steel

Results are provided for pilot plant testing of steel melting using ferro-silico-aluminum (FSA) at KSP Steel (Kazakhstan). These tests show that the use of FSA during steel extra-furnace treatment has a number of technological advantages, one of which is material multifunctionality. An economic effect is achieved as a result of a reduction and exclusion of some expensive materials from standard material consumption, such as feldspar, and silicon carbide. FSA has good deoxidation capacity, and having aluminum metal within its composition makes it possible to reduce a considerable amount of alloying element oxides. Using FSA in test melts there is a reduction in Fetot content by 0.37%, MnO by 1.01%, and SiO2 by 1.24%, which provides a reduction in slag oxidizing capacity, and also leads to an increase in its basicity, as a result of which there is a reduction in slag belt lining wear and an increase in ladle life.

Numerical investigation of heat exchange in rotary furnace

Abstract Process of heat exchange in a rotary furnace during converter slag reduction was modelled.Temperature distribution in the furnace and temperature of the charge (slag) only were examined. Influence of modification of the process gas supply method by changing the number of nozzles on the course of the reduction process was analyzed. It has been found out that application of a nozzle as a submerged flame burner provides possibilities to reach higher charge temperature. Application of more nozzles in the process of converter slag reduction can increase temperature of reduced slag and provide better uniformity of charge heating.

제강 환원슬래그의 광물탄산화

제강 환원슬래그(steelmaking reduction slag)를 출발물질로 사용하여 다양한 농도의 <TEX>$H_2SO_4$</TEX>, <TEX>$NH_4NO_3$</TEX>(0.3, 0.5, 0.7, 1 M) 용액, 반응온도 <TEX>$100^{\circ}C$</TEX>와 <TEX>$150^{\circ}C$</TEX>의 조건에서 Ca 용출 및 탄산화 실험을 실시하였다. 양이온 용출과 탄산화 반응시간은 각각 2시간 및 1시간이었으며 탄산화 효율 증대를 위해 pH는 약 12로 조절하였고 <TEX>$CO_2$</TEX>의 부분압은 10 bar이었다. TG 분석결과로부터 탄산화율을 계산한 결과, <TEX>$H_2SO_4$</TEX> 0.5 M과 반응온도 <TEX>$150^{\circ}C$</TEX>의 실험 조건에서 약 86%의 고정화율이 관찰되었으나 이 이상의 농도에서는 탄산화율은 급격히 감소하였다. 그러나 <TEX>$NH_4NO_3$</TEX>용액을 사용한 결과, 산의 농도가 증가함에 따라 탄산화율도 비례적으로 증가하여 1 M 농도에서 약 93%의 탄산화율이 관찰되었다. 따라서 제강 환원슬래그를 사용한 탄산화반응은 <TEX>$H_2SO_4$</TEX>보다는 <TEX>$NH_4NO_3$</TEX>용액을 사용할 경우 유리한 것으로 분석되었다. SEM 분석결과, 합성된 아라고나이트는 나무토막 형태(wood piece shape), 둥근형태(round shape), 꽃모양(flower shape)으로 관찰되었으며, 방해석은 결정면이 잘 발달된 능면체형(rhombohedral shape)의 전형적인 형태로 확인되었다. Mineral carbonation for the storage of carbon dioxide is a CCS option that provides an alternative for the more widely advocated method of geological storage in underground formation. Carbonation of magnesium- or calcium-based minerals, especially the carbonation of waste materials and industrial by-products is expanding, even though total amounts of the industrial waste are too small to substantially reduce the <TEX>$CO_2$</TEX> emissions. The mineral carbonation was performed with steelmaking reduction slag as starting material. The steelmaking reduction slag dissolution experiments were conducted in the <TEX>$H_2SO_4$</TEX> and <TEX>$NH_4NO_3$</TEX> solution with concentration range of 0.3 to 1 M at <TEX>$100^{\circ}C$</TEX> and <TEX>$150^{\circ}C$</TEX>. The hydrothermal treatment was performed to the starting material via a modified direct aqueous carbonation process at the same leaching temperature. The initial pH of the solution was adjusted to 12 and <TEX>$CO_2$</TEX> partial pressure was 1MPa for the carbonation. The carbonation rate after extracting <TEX>$Ca^^{2+}$</TEX> under <TEX>$NH_4NO_3$</TEX> was higher than that under <TEX>$H_2SO_4$</TEX> and the carbonation rates in 1M <TEX>$NH_4NO_3$</TEX> solution at <TEX>$150^{\circ}C$</TEX> was dramatically enhanced about 93%. In this condition well-faceted rhombohedral calcite, and rod or flower-shaped aragonite were appeared together in products. As the concentration of <TEX>$H_2SO_4$</TEX> increased, the formation of gypsum was predominant and the carbonation rate decreased sharply. Therefore it is considered that the selection of the leaching solution which does not affect the starting material is important in the carbonation reaction.

Zero CO2 steelmaking in a future low carbon economy. 1. Energy conservation in smelting hematite ore directly to refined iron slab

ABSTRACTThe emphasis is on energy conservation. Efficient charge preheating by heat recovery from not only the molten reduction slag but even more important is to eliminate water cooling in the continuous casting of the molten iron, which overflows automatically from the primary melt circulation loop. It is proposed that a liquid metal coolant is used to capture the latent heat of solidification and also the sensible heat associated with cooling the near net shape cast refined iron slab from the melting point down to say 1000°C or so by counter-current radiative heat transfer to secure 800°C charge preheating. The preheated crushed hematite ore plus flux is distributed along the full length of the electrical conductively heated charge incorporation zone of the principal melt circulation loop at a multiple number of locations. The resulting wustite containing thin melt layer floating on the circulating molten iron is counter-currently reduced by hydrogen at atmospheric pressure.

Tracing the Origin of Non-ferrous Oxides in Lamination Defects on Hot-Rolled Coils: Mold Slag Entrainment vs Submerged Entry Nozzle Reaction Products

In this work, lamination defects (slivers) on hot-rolled coils of Ca-treated steel were investigated for microstructure and composition using optical and scanning electron microscopy combined with microanalysis (SEM/EDS). The goal was to identify possible origins for the observed defects which contain a complex assemblage of phases, such as different types of calcium aluminates (CA, CA2, CA6), melilite (C2AS), spinel (MA), and a newly identified phase, CNA2. Mold slag similar to that employed during the cast was absent. Analysis of the bulk composition of some of the defects indicated these to be too rich in alumina to be derived from mold slag through steel-slag redox exchange. In contrast, microstructural observation of the inner side of the submerged entry nozzles (SEN) used during casting showed deposits with compositions comparable to those of the defect material. Based on an estimation of the chemical evolution of mold slag interacting with steel, it is found that the defects are not likely to be entrained mold slag but remobilized SEN deposits, as supported by several microstructural and trace phase criteria. However, it should be noted that extensive reduction of mold slag by steel can lead to compositions rich in sodic-calcic aluminates (CNA2). Therefore, differentiation between specific locations of the defect materials within a casting system requires detailed analysis from the potential sources of origin as well as from the materials found in the defects.

Increase of chromium yield by slag reduction during production of chromium steels

The paper is focused on the evaluation of the course of Cr2O3 reduction from slag to alloyed steel under laboratory conditions. The experiments were aimed at the evaluation of increase in the chromium content in the melt together with the studying the behaviour of Cr2O3 and the mechanism of reduction by means of three reducing agents. Anthracite, ferrosilicon and mixtures of anthracite and ferrosilicon belong among the selected reducing agents. The experimental melts were focused on the proposal of a theoretical calculation of the consumption of selected reducing agents, study of reduction under laboratory conditions at application of alloyed steel with content of chromium of 12.16 wt. %, temperatures of 1600 °C and 1650 °C, together with the change of amount of reducing agents and reduction time. The results indicated in the paper constitute basic information on the possibilities of Cr2O3 reduction from slag; they will be used for verification of results in the pilot plant and operation experiments which will simulate operating conditions in the electric arc furnace.

Research and Industrial Application of a Process for Direct Reduction of Molten High-Lead Smelting Slag

A pyrometallurgical process for the direct reduction of molten high-lead smelting slag obtained by the Shuikoushan (SKS) method was reported in this article using solid anthracite as the fuel and reductant. The chemical composition, the lead phase composition, and the physical properties of the molten high-lead slag were examined. The effects of the process parameters on the recovery rate of valued metals were investigated in the laboratory. According to the experimental results, a new efficient bottom blow reduction furnace was employed in the pilot-scale test for high-lead slag reduction. The results showed the average recovery rate of lead was more than 96.0% with lower Pb and high Zn content of the reducing slag under the condition of reduction temperature 1100–1200°C, coal ratio 5.5–7.5%, reduction time 90–150 min, CaO/SiO2 ratio 0.35–0.45, and FeO/SiO2 ratio 1.4–1.55. Moreover, nearly 250 kg of standard coal per ton of crude Pb output was reduced compared with the blast furnace reduction process.