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3 pages, 173 KiB

Open AccessEditorial

Metallurgical Slag

by Jie Dang, Jichao Li, Xuewei Lv, Shuang Yuan and Katarzyna Leszczyńska-Sejda

Crystals 2022, 12(3), 407; https://doi.org/10.3390/cryst12030407 - 17 Mar 2022

Cited by 3 | Viewed by 1513

Abstract

The Special Issue on “Metallurgical Slag” is a collection of 23 original articles dedicated to theoretical and experimental research works providing new insights and practical findings in the field of metallurgical slag-related topics [...] Full article

(This article belongs to the Special Issue Metallurgical Slag)

Research

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19 pages, 8393 KiB

Open AccessArticle

Microwave Roasting Characteristics of Cuprous Chloride Residue from Zinc Hydrometallurgy

by Zhanyong Guo, Fachuang Li, Qian Zhang, Guang Su, Jun Chang and Huilin Zhou

Crystals 2022, 12(1), 116; https://doi.org/10.3390/cryst12010116 - 17 Jan 2022

Cited by 6 | Viewed by 1671

Abstract

High-efficiency dechlorination processes are crucial for the clean utilization of CuCl waste residue from zinc hydrometallurgical processes. A new method of oxygen-enriched microwave roasting has been proposed to improve the dechlorination process. The cavity perturbation method was used in this paper to measure [...] Read more.

High-efficiency dechlorination processes are crucial for the clean utilization of CuCl waste residue from zinc hydrometallurgical processes. A new method of oxygen-enriched microwave roasting has been proposed to improve the dechlorination process. The cavity perturbation method was used in this paper to measure the permittivity of a CuCl residue at various temperatures and apparent densities. The results show that temperature had a more significant effect on the loss tangent when it exceeded 400 °C more than that of apparent densities. The degree of dechlorination of CuCl residue exceeded 93% after 90 min of microwave roasting at 450 °C and 150 mL/min oxygen flow, which was 12% higher than that of conventional calcination. The elemental distribution in samples was studied using single-point, linear, and lateral scans at the microscale, and the microstructure and phase changes of the CuCl residue under a microwave field were characterized by XRD and SEM-EDS. This study shows that microwaves can promote the dechlorination reaction by decreasing the activation energy from 52.69 kJ/mol to 42.36 kJ/mol. Full article

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12 pages, 2209 KiB

Open AccessArticle

Carbonation of EAF Stainless Steel Slag and Its Effect on Chromium Leaching Characteristics

by Ya-Jun Wang, Meng-Jie Tao, Jun-Guo Li, Ya-Nan Zeng, Song Qin and Shao-Hua Liu

Crystals 2021, 11(12), 1498; https://doi.org/10.3390/cryst11121498 - 2 Dec 2021

Cited by 11 | Viewed by 2680

Abstract

EAF stainless steel slag (EAF slag) is one kind of chromium-bearing metallurgical solid waste, which belongs to alkaline steel slag, and contains a large number of alkaline mineral phases. The carbonation activity of these minerals gives EAF slag the capability to effectively capture [...] Read more.

EAF stainless steel slag (EAF slag) is one kind of chromium-bearing metallurgical solid waste, which belongs to alkaline steel slag, and contains a large number of alkaline mineral phases. The carbonation activity of these minerals gives EAF slag the capability to effectively capture CO₂. In this paper, EAF slag samples with different carbonation degrees were prepared by the slurry-phase accelerated carbonation route. The mineralogical identification analysis was used to qualitatively and semi-quantitatively determine the types and contents of the carbonatable mineral phases in the EAF slag. The sequential leaching test was used to study the chromium leachabilities in EAF slags with different carbonation degrees. The results showed that the main minerals with carbonation activity in EAF slag were Ca₃Mg(SiO₄)₂ and Ca₂SiO₄, with mass percentages of 56.9% and 23%, respectively. During the carbonation process, Ca₂SiO₄ was the main reactant and calcite was the main product. As the degree of carbonation increased, the pH of the EAF slags’ leachate gradually decreased while the redox potential (Eh) gradually increased. At the same time, a large amount of Ca²⁺ in the EAF slag combined with CO₂ to form slightly soluble calcium carbonate, which led to a significant decrease in the conductivity of the leachate. With the gradual increase in carbonation ratio, the leachability of chromium in the EAF slag first decreased and then increased, and reached its lowest value when the CO₂ uptake ratio was 11.49%. Full article

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14 pages, 3975 KiB

Open AccessArticle

Beading Mechanism and Performance of Porous Steel Slag Microbead Abrasive

by Jingjing Pei, Yuzhu Zhang, Hongwei Xing, Qianqian Ren, Wenqing Huo and Jinhu Wu

Crystals 2021, 11(11), 1377; https://doi.org/10.3390/cryst11111377 - 12 Nov 2021

Cited by 1 | Viewed by 1792

Abstract

The use of the gas-quenching process for preparing porous bead slag abrasive was investigated in this paper. An X-ray diffractometer, field emission scanning electron microscope, mercury intrusion porosimetry, and stereo microscope were used to analyze the microbead forming mechanism, pore structure, acid–alkali resistance, [...] Read more.

The use of the gas-quenching process for preparing porous bead slag abrasive was investigated in this paper. An X-ray diffractometer, field emission scanning electron microscope, mercury intrusion porosimetry, and stereo microscope were used to analyze the microbead forming mechanism, pore structure, acid–alkali resistance, and polishing properties of porous steel slag microbead abrasives. Results show that the porous steel slag abrasives present a mono-disperse spherical shape with a hard shell and the porosity is 42.36%. The thermodynamic fractal model indicates that the fractal dimension of the abrasive is 2.226, which shows its simple pore structure. The sample has better chemical stability in the polishing fluid than in water, acid, and alkali solution. Therefore, aluminum and copper alloys are used as substrates for polishing tests. The results indicate that the abrasives could effectively improve the quality of the workpiece surface and the polishing efficiency for aluminum alloy was higher than that for copper alloy. Full article

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10 pages, 5531 KiB

Open AccessArticle

Effect of Holding Time of Decarbonization Annealing on Recrystallization in Fe-3.2%Si-0.047Nb% Low-Temperature Oriented Silicon Steel

by Xin Tian, Shuang Kuang, Jie Li, Shuai Liu and Yunli Feng

Crystals 2021, 11(10), 1209; https://doi.org/10.3390/cryst11101209 - 7 Oct 2021

Cited by 3 | Viewed by 1577

Abstract

In this study, the effects of decarburization annealing time on the primary recrystallization microstructure, the texture and the magnetic properties of the final product of 0.047% Nb low-temperature grain-oriented silicon steel were investigated by means of OM, EBSD and XRD. The results show [...] Read more.

In this study, the effects of decarburization annealing time on the primary recrystallization microstructure, the texture and the magnetic properties of the final product of 0.047% Nb low-temperature grain-oriented silicon steel were investigated by means of OM, EBSD and XRD. The results show that when the decarburization annealing condition is 850 °C for 5 min, the uniform fine primary recrystallization microstructure can be obtained, and the content of favorable texture {111} <112> is the highest while that of unfavorable texture {110} <112> is the lowest, which is mostly distributed near the central layer. At the same time, there are the most high-energy grain boundaries with high mobility in the primary recrystallization microstructure of the sample annealed at 850 °C for 5 min, and the ∑9 boundary has the highest percentage of grain boundaries. The samples with different decarburization annealing time were annealed at high temperature. It was found that perfect secondary recrystallization occurred after high-temperature annealing when the decarburization annealing condition was 850 °C for 5 min. The texture component was characterized by a single Goss texture, and the size of the Goss grain reached 4.6 mm. Under such annealing conditions, the sample obtained shows the optimal soft magnetic properties of B₈₀₀ = 1.89 T and P_1.7/50 = 1.33 w/kg. Full article

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13 pages, 4962 KiB

Open AccessArticle

Study on the Synergistic Extraction of Lithium from Spent Lithium Cobalt Oxide Batteries by Molten Salt Electrolysis and Two-Step Precipitation Method

by Hui Li, Haotian Li, Jinglong Liang, Hongyan Yan and Zongying Cai

Crystals 2021, 11(10), 1163; https://doi.org/10.3390/cryst11101163 - 24 Sep 2021

Cited by 7 | Viewed by 3184

Abstract

With the continuous development of society, the number of spent lithium-ion batteries has also increased, and the recovery of valuable metals such as Ni, Co, and Li has become the main research direction of many scholars. In this paper, the extraction process of [...] Read more.

With the continuous development of society, the number of spent lithium-ion batteries has also increased, and the recovery of valuable metals such as Ni, Co, and Li has become the main research direction of many scholars. In this paper, the extraction process of lithium that enters the molten salt after LiCoO₂ electrolysis is studied. Oxalic acid and phosphate are added to molten salt containing lithium ions to realize the two-part precipitation method to extract lithium. The influence of pH value, temperature, reaction time, and oxalic acid (or phosphate) addition on the process of oxalic acid calcium removal and phosphate lithium precipitation is analyzed. The results show that the calcium removal rate of oxalic acid has reached 99.72% (Initial conditions: PH = 7.0, T = 70 °C, t = 1.5 h, n(H₂C₂O₄):n(Ca²⁺) = 1.2:1). The precipitation of Li₃PO₄ obtained in the phosphate extraction experiment of lithium is as high as 88.44% (Initial conditions: PH = 8.0, T = 70 °C, t = 1.5 h, n(actual dosage of Na₃PO₄):n(theoretical dosage of Na₃PO₄) = 1.2:1). The obtained lithium phosphate crystals show regular spherical particles, which can be seen by SEM. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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13 pages, 7577 KiB

Open AccessArticle

Preparation of Zinc Oxide and Zinc Ferrite from Zinc Hypoxide by Wet Process and Electrochemistry

by Hui Li, Yutian Fu, Jinglong Liang, Le Wang, Hongyan Yan and Linfei Zhao

Crystals 2021, 11(9), 1133; https://doi.org/10.3390/cryst11091133 - 18 Sep 2021

Cited by 5 | Viewed by 3252

Abstract

With the increase of zinc resource consumption, the recovery and utilization of zinc resources in zinc suboxide has become one of the current research hotspots. In this study, the electrochemical method was used to remove the impurities in the zinc leaching night and [...] Read more.

With the increase of zinc resource consumption, the recovery and utilization of zinc resources in zinc suboxide has become one of the current research hotspots. In this study, the electrochemical method was used to remove the impurities in the zinc leaching night and enrich the zinc ferrite in the ammonia leaching residue for the solution and ammonia leaching slag after the ammonia leaching of zinc hypoxide, in order to realize the comprehensive utilization of the essence of zinc immersion night and new resources. The results showed that the reduction potentials of copper, lead, cadmium, and zinc in the ammonia leaching solution were analyzed by electrochemical testing methods to be −0.76 V, −0.82 V, −0.94 V, and −1.3 V, respectively. Through constant potential electrodeposition, the removal rate of copper, lead, cadmium. The removal rate of cadmium is 98.73%, and the removal rate of lead and copper is more than 99%. The purified ammonia leaching solution is evaporated at 90 °C for 25 min to obtain basic zinc carbonate. The purity of ZnO obtained after calcination at 500 °C for 120 min is 96.31%. The ammonia leaching residue was pickled with 3 mol·L⁻¹ acetic acid for 30 min to effectively remove PbCO₃, and then magnetic separation was carried out with a current intensity of 1.4 A. The final zinc ferrite content was 83.83%. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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16 pages, 5417 KiB

Open AccessArticle

The Electrochemical Mechanism of Preparing Mn from LiMn₂O₄ in Waste Batteries in Molten Salt

by Jinglong Liang, Rui Zhang, Hui Li, Le Wang, Zongying Cai, Hongyan Yan and Weigang Cao

Crystals 2021, 11(9), 1066; https://doi.org/10.3390/cryst11091066 - 3 Sep 2021

Cited by 7 | Viewed by 2178

Abstract

The electrochemical reduction mechanism of Mn in LiMn₂O₄ in molten salt was studied. The results show that in the NaCl-CaCl₂ molten salt, the process of reducing from Mn (IV) to manganese is: Mn (IV)→Mn (III)→Mn (II)→Mn. LiMn₂O [...] Read more.

The electrochemical reduction mechanism of Mn in LiMn₂O₄ in molten salt was studied. The results show that in the NaCl-CaCl₂ molten salt, the process of reducing from Mn (IV) to manganese is: Mn (IV)→Mn (III)→Mn (II)→Mn. LiMn₂O₄ reacts with molten salt to form CaMn₂O₄ after being placed in molten salt for 1 h. The reaction of reducing CaMn₂O₄ to Mn is divided into two steps: Mn (III)→Mn (II)→Mn. The results of constant voltage deoxidation experiments under different conditions show that the intermediate products of LiMn₂O₄ reduction to Mn are CaMn₂O₄, MnO, and (MnO)_x(CaO)_(1−x). As the reaction progresses, x gradually decreases, and finally the Mn element is completely reduced under the conditions of 3 V for 9 h. The CaO in the product can be removed by washing the sample with deionized water at 0 °C. Full article

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10 pages, 4016 KiB

Open AccessArticle

Effect of Fe₂O₃ on Electro-Deoxidation in Fe₂O₃-Al₂O₃-NaCl-KCl System

by Yanke Xu, Hongyan Yan, Zhenwei Jing, Xiwei Qi, Hui Li and Jinglong Liang

Crystals 2021, 11(9), 1026; https://doi.org/10.3390/cryst11091026 - 26 Aug 2021

Cited by 2 | Viewed by 2399

Abstract

The reduction of Fe₂O₃-Al₂O₃ is one of the important reactions in the resource utilization of iron-containing oxide waste. Fe₂O₃-Al₂O₃ was electro-deoxidized in the NaCl-KCl system by molten salt electrolysis [...] Read more.

The reduction of Fe₂O₃-Al₂O₃ is one of the important reactions in the resource utilization of iron-containing oxide waste. Fe₂O₃-Al₂O₃ was electro-deoxidized in the NaCl-KCl system by molten salt electrolysis to prepare FeO/Al₂O₃. The effect of the Fe₂O₃ content on the electro-deoxidation reaction process was studied. The results show that under the conditions of 850 °C, 2.3 V, and electro-deoxidation for 4 h, FeO/Al₂O₃ could be obtained by controlling the content of Fe₂O₃. The deoxidation process was divided into three stages: electric double layer charging, Fe₂O₃ electro-deoxidation to Fe₃O₄, and Fe₃O₄ electro-deoxidation to FeO. With the increase in the Fe₂O₃ content, the deoxidation reaction rate increased, and the low-valence iron oxide particles obtained by electro-deoxidation became larger. The mechanism of the influence of Fe₂O₃ on the electro-deoxygenation process was determined by analyzing the experimental results. The increase in the Fe₂O₃ content increased the concentration of activated molecules in the system, while it reduced the resistance of electro-deoxidation. The migration of active particles in the cathode was smoother, which increased the percentage of deoxygenation of activated molecules, thereby shortening the process of the deoxidation reaction. Full article

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11 pages, 2820 KiB

Open AccessArticle

Effect of Al₂O₃–SiO₂ Addition on Gehlenite Growth and the Mechanical Performance of Steel Slag

by Ying Xu, Pan Song, Weigang Cao, Hui Li and Jinglong Liang

Crystals 2021, 11(8), 936; https://doi.org/10.3390/cryst11080936 - 12 Aug 2021

Cited by 6 | Viewed by 2258

Abstract

Steel slag, as industrial solid waste, is difficult to recycle owing to its complex components and poor mechanical properties. However, steel slag can be modified by adding Al₂O₃–SiO₂ through high temperature sintering, which would improve the mechanical properties [...] Read more.

Steel slag, as industrial solid waste, is difficult to recycle owing to its complex components and poor mechanical properties. However, steel slag can be modified by adding Al₂O₃–SiO₂ through high temperature sintering, which would improve the mechanical properties and expand the scope of its application. The phase changing, morphology evolution and the mechanical properties of the modified steel slag were investigated. The results indicate that the main phase changes to gehlenite occur with increasing temperature. The compressive strength increases to 115 MPa at 1350 °C. The relationship of the quantity of gehlenite and the compressive strength were explored. Full article

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11 pages, 4039 KiB

Open AccessArticle

The Electrochemical Reduction Mechanism of ZnFe₂O₄ in NaCl-CaCl₂ Melts

by Chang Liu, Jinglong Liang, Hui Li, Hongyan Yan, Sijia Zheng, Weigang Cao and Le Wang

Crystals 2021, 11(8), 925; https://doi.org/10.3390/cryst11080925 - 9 Aug 2021

Cited by 4 | Viewed by 2016

Abstract

The electrochemical reduction process of ZnFe₂O₄ in NaCl-CaCl₂ melts was studied. Thermodynamic analysis shows that the reduction process of ZnFe₂O₄ is carried out in multiple steps, and it is difficult to reduce Fe³⁺ to Fe [...] Read more.

The electrochemical reduction process of ZnFe₂O₄ in NaCl-CaCl₂ melts was studied. Thermodynamic analysis shows that the reduction process of ZnFe₂O₄ is carried out in multiple steps, and it is difficult to reduce Fe³⁺ to Fe in one step. Electrochemical tests revealed that the reduction process of ZnFe₂O₄ includes three steps: First, Fe³⁺ is reduced to Fe in two steps, then Zn²⁺ is reduced to Zn in one step. The reduction of Fe³⁺ on the Mo electrode is a reversible process controlled by diffusion, while the reduction of Zn²⁺ is an irreversible process controlled by diffusion. The influence of electrolysis voltage and temperature on the process of electric deoxidation has also been studied. It is indicated that properly increasing the temperature is conducive to the diffusion of oxygen ions, thereby increasing the deoxidation rate. With the gradual increase of voltage, the reduction process of ZnFe₂O₄ is ZnFe₂O₄ → FeO + ZnO → Fe + ZnO → Fe + Zn. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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15 pages, 19955 KiB

Open AccessArticle

Study on Ultrasonically-Enhanced Sulfuric Acid Leaching of Nickel from Nickel-Containing Residue

by Zhanyong Guo, Ping Guo, Guang Su and Fachuang Li

Crystals 2021, 11(7), 810; https://doi.org/10.3390/cryst11070810 - 12 Jul 2021

Cited by 7 | Viewed by 2783

Abstract

In this paper, nickel-containing residue, a typical solid waste produced in the battery production process, was used to study the cavitation characteristics of ultrasonic waves in a liquid–solid reaction. The ultrasonically-enhanced leaching technology for multicomponent and complex nickel-containing residue was studied through systematic [...] Read more.

In this paper, nickel-containing residue, a typical solid waste produced in the battery production process, was used to study the cavitation characteristics of ultrasonic waves in a liquid–solid reaction. The ultrasonically-enhanced leaching technology for multicomponent and complex nickel-containing residue was studied through systematic ultrasonic-conventional comparative experiments. An ultrasonic leaching kinetics model was established which provided reliable technological guidance and basic theory for the comprehensive utilization of nickel-containing residue. In the study, it was found that ultrasonically-enhanced leaching for 40 min obtained the same result as conventional leaching for 80 min, and the Ni extraction degree reached more than 95%. According to the kinetic fitting of the leaching process, it was found that the sulfuric acid leaching process belonged to the diffusion-controlled model of solid product layers under conventional and ultrasonic conditions, and the activation energy of the reaction was E_a1 = 17.74 kJ/mol and E_a2 = 5.04 kJ/mol, respectively. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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11 pages, 7076 KiB

Open AccessArticle

Preparation of Gradient Materials with Molten Salts Electrodeposition

by Hui Li, Jinglong Liang, Hongyan Yan, Yungang Li and Le Wang

Crystals 2021, 11(6), 590; https://doi.org/10.3390/cryst11060590 - 24 May 2021

Cited by 5 | Viewed by 2066

Abstract

A new way of preparing W–Cu functional gradient materials (FGM) with molten salts electrodeposition is studied. The results show that, with the conditions of current density 70 mA·cm⁻², electrodeposition temperature 700 °C and bidirectional pulse electrodepositing for 30 minutes (min), the [...] Read more.

A new way of preparing W–Cu functional gradient materials (FGM) with molten salts electrodeposition is studied. The results show that, with the conditions of current density 70 mA·cm⁻², electrodeposition temperature 700 °C and bidirectional pulse electrodepositing for 30 minutes (min), the Cu–Ni gradient layer prepared under this condition is widely used dense and smooth. Fundamental to the preparation of Cu–Ni functional gradient layer, Cu–Ni is used as a cathode to deposit W. Under the current density of 50 mA·cm⁻², the time of 20 min, with bidirectional pulse electrodeposition, the Cu+Ni+W gradient layer has uniform composition gradient change and larger thickness. The W–Cu gradient materials prepared in this study have good cohesiveness. The addition of Ni would promote the inter-diffusion of Cu and W, and increase the diffusion coefficient significantly. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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10 pages, 3796 KiB

Open AccessArticle

The Crystallization Behavior of TiO₂-CaO-SiO₂-Al₂O₃-MgO Pentabasic Slag with a Basicity of 1.1–1.4

by Huxu Lei, Chaowen Tan, Gangqiang Fan, Dejun Huang, Xiaoming Ding and Jie Dang

Crystals 2021, 11(6), 583; https://doi.org/10.3390/cryst11060583 - 22 May 2021

Cited by 2 | Viewed by 1953

Abstract

The utilization of titanium-containing blast furnace slag has been an unsolved problem for a long time. Failure to make effective use of the slag, which is caused by a high TiO₂ content within it, not only results in a waste of resources, [...] Read more.

The utilization of titanium-containing blast furnace slag has been an unsolved problem for a long time. Failure to make effective use of the slag, which is caused by a high TiO₂ content within it, not only results in a waste of resources, especially titanium, but also increases environmental risk. The key to address the problem is the enrichment and extraction of TiO₂ from the slag first. Therefore, in order to study the enrichment of titanium, the crystallization behavior of TiO₂-CaO-SiO₂-Al₂O₃-MgO pentabasic slag, the main compositions of titanium-containing blast furnace slag, within the basicity range of 1.1–1.4 was investigated theoretically and experimentally. Thermodynamic calculation shows that perovskite is the main titanium-containing phase and titanium can be enriched in perovskite. By decreasing the temperature, perovskite precipitates at first. Additionally, with the increase of basicity, perovskite precipitation temperature increases continuously, and its amount of precipitation almost does not change, while the amounts of other phases change obviously. The experimental results demonstrate similar results except for the amount of perovskite (with the increase of basicity, perovskite precipitation amount increases slightly), caused by kinetic reason. In addition, the morphology of the slag at different scales was observed. The surface of the cooled slag is granular, vein-like, and irregular, multilaterally shaped from outside to inside. The crystal is dendritic with a spine-like trunk, and the edge is blade-like. In terms of the structure of the crystal, the inner part of it is perovskite, and the outer part is covered with a layer of other phases with spinel inlaying it. Finally, the precipitated mechanism is proposed as well. Full article

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15 pages, 5652 KiB

Open AccessArticle

Leaching Kinetics of Secondary Zinc Oxide in a NH₃–NH₄HCO₃–H₂O System

by Hui Li, Linfei Zhao, Le Wang, Jinglong Liang, Hongyan Yan and Jinrui Liu

Crystals 2021, 11(5), 496; https://doi.org/10.3390/cryst11050496 - 30 Apr 2021

Cited by 9 | Viewed by 3323

Abstract

Secondary zinc oxide (SZO), which comes from the zinc industry, is an important secondary resource of zinc and other valuable metals. In this study, the production feasibility and rationality of a cleaner zinc recovery process using SZO and a hydrometallurgical method were described. [...] Read more.

Secondary zinc oxide (SZO), which comes from the zinc industry, is an important secondary resource of zinc and other valuable metals. In this study, the production feasibility and rationality of a cleaner zinc recovery process using SZO and a hydrometallurgical method were described. Zinc extraction is promoted by the addition of ammonium bicarbonate to a NH₃–H₂O system, and the maximum recovery of zinc could be close to 80% at the optimum leaching conditions of a stirring rate of 400 rpm, an ammonia/ammonium ratio of 7:3, a total ammonia concentration of 4 mol/L, and a liquid/solid ratio of 7 mL/g for 30 min at 35 °C. The kinetics of leaching were modeled using the shrinking core model of constant-size particles, and the rate-controlling step was determined to be the diffusion through the product layer. The apparent activation energy of the reaction was estimated to be 11.04 KJ·mol⁻¹, while the order of reaction with respect to total ammonia concentration was 1.53 and the liquid/solid ratio was 2.26. The analysis results of the initial residue and the leached residue indicated that lead was transferred from PbCl₂ to PbCO₃ and that ZnFe₂O₄ was not leached in the NH₃-NH₄HCO₃-H₂O system. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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9 pages, 3278 KiB

Open AccessArticle

Effect of Sintering Temperature on Microstructure and Mechanical Properties of Hot-Pressed Fe/FeAl₂O₄ Composite

by Kuai Zhang, Yungang Li, Hongyan Yan, Chuang Wang, Hui Li, Jinglong Liang and Jie Dang

Crystals 2021, 11(4), 422; https://doi.org/10.3390/cryst11040422 - 14 Apr 2021

Cited by 7 | Viewed by 1917

Abstract

An Fe/FeAl₂O₄ composite was prepared with Fe-Fe₂O₃-Al₂O₃ powder by a hot press sintering method. The mass ratio was 6:1:2, sintering pressure was 30 MPa, and holding time was 120 min. The raw materials [...] Read more.

An Fe/FeAl₂O₄ composite was prepared with Fe-Fe₂O₃-Al₂O₃ powder by a hot press sintering method. The mass ratio was 6:1:2, sintering pressure was 30 MPa, and holding time was 120 min. The raw materials for the powder particles were respectively 1 µm (Fe), 0.5 µm (Fe₂O₃), and 1 µm (Al₂O₃) in diameter. The effect of sintering temperature on the microstructure and mechanical properties of Fe/FeAl₂O₄ composite was studied. The results showed that Fe/FeAl₂O₄ composite was formed by in situ reaction at 1300 °C–1500 °C. With the increased sintering temperature, the microstructure and mechanical properties of the Fe/FeAl₂O₄ composite showed a change law that initially became better and then became worse. The best microstructure and optimal mechanical properties were obtained at 1400 °C. At this temperature, the grain size of Fe and FeAl₂O₄ phases in Fe/FeAl₂O₄ composite was uniform, the relative density was 96.7%, and the Vickers hardness and bending strength were 1.88 GPa and 280.0 MPa, respectively. The wettability between Fe and FeAl₂O₄ was enhanced with increased sintering temperature. And then the densification process was accelerated. Finally, the microstructure and mechanical properties of the Fe/FeAl₂O₄ composite were improved. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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9 pages, 6740 KiB

Open AccessArticle

Effect of Fe on the Microstructure and Mechanical Properties of Fe/FeAl₂O₄ Cermet Prepared by Hot Press Sintering

by Kuai Zhang, Yungang Li, Chuang Wang, Hongyan Yan, Hui Li, Jinglong Liang and Jie Dang

Crystals 2021, 11(2), 204; https://doi.org/10.3390/cryst11020204 - 19 Feb 2021

Cited by 3 | Viewed by 2408

Abstract

The Fe/FeAl₂O₄ cermet was prepared with Fe-Fe₂O₃-Al₂O₃ powder by a hot press sintering method at 1400 °C. The raw materials for the powder particles were respectively 2 µm (Fe), 0.5 µm (Fe₂ [...] Read more.

The Fe/FeAl₂O₄ cermet was prepared with Fe-Fe₂O₃-Al₂O₃ powder by a hot press sintering method at 1400 °C. The raw materials for the powder particles were respectively 2 µm (Fe), 0.5 µm (Fe₂O₃), and 0.5 µm (Al₂O₃) in diameter, the sintering pressure was 30 MPa, and the holding time was 120 min. The effects of different Fe mass ratios on the microstructure and mechanical properties of Fe/FeAl₂O₄ cermet were studied. The results showed that a new ceramic phase FeAl₂O₄ could be formed by an in situ reaction during the hot press sintering. When the Fe mass ratio was increased, the microstructure and mechanical properties of the Fe/FeAl₂O₄ cermet showed a change law that initially became better and then became worse. The best microstructure and mechanical properties were obtained in the S2 sample, where the mass ratio of Fe-Fe₂O₃-Al₂O₃ was 6:1:2. In this Fe mass ratio, the relative density was about 94%, and the Vickers hardness and bending strength were 1.21 GPa and 210.0 MPa, respectively. The reaction mechanism of Fe in the preparation process was the in situ synthesis reaction of FeAl₂O₄ and the diffusion reaction of Fe to FeAl₂O₄ grains. The increase of the Fe mass ratio improved the wettability of Fe and FeAl₂O₄, which increased the diffusion rate of Fe to FeAl₂O₄ grains, which increased the influence on the structure of FeAl₂O₄. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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11 pages, 4742 KiB

Open AccessArticle

Preparation, Sintering Behavior and Consolidation Mechanism of Vanadium-Titanium Magnetite Pellets

by Weibin Chen, Zhaoqi Dong, Yang Jiao, Lili Liu and Xidong Wang

Crystals 2021, 11(2), 188; https://doi.org/10.3390/cryst11020188 - 14 Feb 2021

Cited by 17 | Viewed by 2655

Abstract

High-quality oxidized pellets are the basis to achieve high-efficiency utilization of vanadium–titanium magnetite (VTM) ores. Bentonite was used as a binder of VTM. The main phase composition of VTM is titanomagnetite and ilmenite. When the amount of bentonite is 1%, the compressive strength [...] Read more.

High-quality oxidized pellets are the basis to achieve high-efficiency utilization of vanadium–titanium magnetite (VTM) ores. Bentonite was used as a binder of VTM. The main phase composition of VTM is titanomagnetite and ilmenite. When the amount of bentonite is 1%, the compressive strength and dropping strength of VTM pellets can meet the requirements. To improve metallurgical properties, the pellets need to be roasted. The best conditions for roasting are as follows: calcination temperature of 1523 K and a calcination time of 20 min. The consolidation mechanism, phase transformation, and crystal structure transformation of VTM in the process of oxidation roasting are also explained. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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12 pages, 3390 KiB

Open AccessArticle

Dissolution Behavior of Al₂O₃ Inclusions in CaO-Al₂O₃ Based Slag Representing Aluminothermic Reduction Slag

by Guan-Yong Shi, Ting-An Zhang, Zhi-He Dou and Li-Ping Niu

Crystals 2020, 10(11), 1061; https://doi.org/10.3390/cryst10111061 - 22 Nov 2020

Cited by 12 | Viewed by 3094

Abstract

In the preparation of CuCr alloy using the self-propagating high-temperature synthesis (SHS)-metallurgy method, the dissolution of alumina in molten slag has an important influence in two key steps: aluminum thermal reduction and slag refining. In the present work, the dissolution behavior of Al [...] Read more.

In the preparation of CuCr alloy using the self-propagating high-temperature synthesis (SHS)-metallurgy method, the dissolution of alumina in molten slag has an important influence in two key steps: aluminum thermal reduction and slag refining. In the present work, the dissolution behavior of Al₂O₃ into molten SHS-metallurgical slags was investigated by employing the rotating cylinder method and static dissolution method. It is concluded that the increase of MgO, CaF₂, CaO, and Na₃AlF₆ contents can increase the dissolution rate of alumina in SHS-metallurgical slag, and the order of influence is from strong to weak. Both temperature and rotating speed can increase the dissolution rate, and the rate-limiting step is the diffusion of alumina in the boundary layer, with the solid alumina first reacting with lime to form two intermediate phases, CaO·2Al₂O₃ and CaO·6Al₂O₃, and finally dissolving into the slag in the form of an aluminum polymer. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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13 pages, 2174 KiB

Open AccessArticle

Calcination of Calcium Sulphoaluminate Cement Using Pyrite-Rich Cyanide Tailings

by Kaiwei Dong, Feng Xie, Wei Wang, Yongfeng Chang, Chunlin Chen and Xiaowei Gu

Crystals 2020, 10(11), 971; https://doi.org/10.3390/cryst10110971 - 26 Oct 2020

Cited by 14 | Viewed by 2625

Abstract

Pyrite-rich cyanide tailings (CTs) are industrial hazardous solid wastes arising from the gold mining industry. Every year, hundreds of millions of tons of cyanide tailings are produced and discharged to tailings dams. It is of great significance to dispose of cyanide tailings harmlessly [...] Read more.

Pyrite-rich cyanide tailings (CTs) are industrial hazardous solid wastes arising from the gold mining industry. Every year, hundreds of millions of tons of cyanide tailings are produced and discharged to tailings dams. It is of great significance to dispose of cyanide tailings harmlessly and resourcefully. The feasibility of calcination of calcium sulphoaluminate (CSA) cement clinker using pyrite-rich cyanide tailings as Fe₂O₃ and SO₃ sources was investigated for this paper. The behavior of pyrite during the calcination of cyanide tailings under various calcination conditions and the properties of calcium sulphoaluminate cement clinker were examined. The results show that it is feasible to produce calcium sulphoaluminate cement clinker using pyrite-rich cyanide tailings. The optimal conditions for the calcination of calcium sulphoaluminate cement using pyrite-rich cyanide tailings are confirmed. During the calcination process, the cyanides decompose into carbonate, CO₂, and N₂. The pyrite decomposes into Fe₂O₃ and SO₂, and they react with CaO and Al₂O₃ to form the intermediates of CaSO₄, 2CaO·Fe₂O₃, and CaO·2Al₂O₃, which further react to form 3CaO·3Al₂O₃·CaSO₄, 4CaO·Al₂O₃·Fe₂O₃, and 12CaO·7Al₂O₃. The calcium sulphoaluminate cement prepared by pyrite-rich cyanide tailings exhibits excellent mechanical properties and meets the compressive strength criteria of 42.5 grade calcium sulphoaluminate cement. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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17 pages, 5083 KiB

Open AccessArticle

Cementitious Behavior of Argon Oxygen Decarburization Stainless Steel Slag and Its Stabilization on Chromium

by Ya-Jun Wang, Ya-Nan Zeng, Jun-Guo Li and Yu-Zhu Zhang

Crystals 2020, 10(10), 876; https://doi.org/10.3390/cryst10100876 - 27 Sep 2020

Cited by 8 | Viewed by 2513

Abstract

The study mainly aims at the potential of Argon Oxygen Decarburization Slag (AODS) as a supplementary cementitious material and explores the mechanisms of stabilization/solidification (S/S) of chromium in cement-based composite pastes. The basic cementitious parameters, such as water requirement, setting time, soundness, hydration [...] Read more.

The study mainly aims at the potential of Argon Oxygen Decarburization Slag (AODS) as a supplementary cementitious material and explores the mechanisms of stabilization/solidification (S/S) of chromium in cement-based composite pastes. The basic cementitious parameters, such as water requirement, setting time, soundness, hydration characteristics, and strength indexes of composite binders, were examined through standard methods. The results showed that the most beneficial mineral phase in AODS for cementitious behavior was beta dicalcium silicate (β-C₂S). The utilization of a higher AODS dosage in composite binders increased the water requirement and the setting time, while it decreased the hydration heat and the strength indexes. Although the AODS possessed limited cementitious properties, it conformed the Grade II steel slag powder qualified for concrete and cement. Sequential leaching tests were conducted targeting the leachability of chromium in the pastes with different AODS dosage and curing time. Results showed that with the lower AODS dosage and the longer curing time, the S/S efficiency for chromium leaching from the composite paste was better. Utilization of AODS as a cement substitute not only can recycle this solid waste and decrease the emission of CO₂ concerning cement production, but also helps to effectively reduce the chromium leaching risk. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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10 pages, 2102 KiB

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Ti₃O₅ and Al₂TiO₅ Crystals Flotation Characteristics from Ti-bearing Blast Furnace Slag: A Density Functional Theory and Experimental Study

by Shan Ren, Zenghui Su, Weizao Liu, Yali Sun, Xiaoming Li and Jian Yang

Crystals 2020, 10(9), 838; https://doi.org/10.3390/cryst10090838 - 19 Sep 2020

Cited by 5 | Viewed by 2993

Abstract

Anosovite crystalline is an ideal mineral for flotation from the Ti-bearing blast furnace (TBBF) slag. Ti₃O₅ crystal and Al₂TiO₅ crystal are two kinds of anosovites, and the Al element significantly affects the electronic structure and flotation performance [...] Read more.

Anosovite crystalline is an ideal mineral for flotation from the Ti-bearing blast furnace (TBBF) slag. Ti₃O₅ crystal and Al₂TiO₅ crystal are two kinds of anosovites, and the Al element significantly affects the electronic structure and flotation performance of anosovite. The floatability of Ti₃O₅ and Al₂TiO₅ crystals were studied by Mulliken populations, energy bands, and density of states (DOS). In addition, the flotation experiment of the two kinds of anosovite crystals (Ti₃O₅ and Al₂TiO₅) was conducted and proved that the density functional theory (DFT) calculation results were accurate. Compared with Ti₃O₅ crystal, the Fermi energy level of Al₂TiO₅ crystal shifts around 2 eV in a negative direction by DOS analysis, which is beneficial to flotation. And Al₂TiO₅ crystal possesses a larger value of bond population, which is 0.41, for Ti-O bonds than Ti₃O₅ crystal and the bond length of Ti-O in Al₂TiO₅ crystal is shorter, therefore Al₂TiO₅ crystal shows a stronger covalency. The changes of the Fermi energy level and the covalency bonds in Al₂TiO₅ crystal both demonstrated that doping the Al component into the Ti₃O₅ crystal was beneficial to improve the flotation effect. Moreover, the Al₂TiO₅ crystal had a higher flotation efficiency compared to the Ti₃O₅ crystal when the dosages of salicylhydroxamic acid (SHA) and sodium oleate were the same. Therefore, both DFT calculation and experiment show that the flotation effect of the Al₂TiO₅ crystal is better than that of the Ti₃O₅ crystal. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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13 pages, 6944 KiB

Open AccessArticle

The Crystallization Behaviors of SiO₂-Al₂O₃-CaO-MgO-TiO₂ Glass-Ceramic Systems

by Feifei Lai, Mei Leng, Jiangling Li and Qingcai Liu

Crystals 2020, 10(9), 794; https://doi.org/10.3390/cryst10090794 - 8 Sep 2020

Cited by 23 | Viewed by 3940

Abstract

To evaluate the crystallization behavior of Ti-bearing blast furnace slag-based glass ceramics, SiO₂-Al₂O₃-CaO-MgO-TiO₂ systems with various TiO₂ were investigated. The crystallization process and mechanical properties were analyzed. The results show that with TiO₂ increasing, [...] Read more.

To evaluate the crystallization behavior of Ti-bearing blast furnace slag-based glass ceramics, SiO₂-Al₂O₃-CaO-MgO-TiO₂ systems with various TiO₂ were investigated. The crystallization process and mechanical properties were analyzed. The results show that with TiO₂ increasing, exothermic peak temperature (T_p) decreases, and the crystallization is promoted by the introduction of TiO₂. A small amount of TiO₂ (≤4%) addition can significantly promote crystallization, and when TiO₂ continues to increase, the crystallization is decreased slightly. The Avrami parameter (n) of all samples is less than 4, indicating that in prepared glass-ceramics, it is hard to achieve three-dimensional crystal growth. The main crystalline phase is akermanite–gehlenite. The addition of TiO₂ has no obvious effect on the type of main crystalline phase. The prepared glass-ceramic with 4% TiO₂ show good mechanical properties with the hardness values of 542.67 MPa. The recommended content of TiO₂ is 4% for preparing glass-ceramics. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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Review

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16 pages, 621 KiB

Open AccessReview

Environmental and Socioeconomic Impact of Copper Slag—A Review

by Tlotlo Solomon Gabasiane, Gwiranai Danha, Tirivaviri A. Mamvura, Tebogo Mashifana and Godfrey Dzinomwa

Crystals 2021, 11(12), 1504; https://doi.org/10.3390/cryst11121504 - 3 Dec 2021

Cited by 34 | Viewed by 6883

Abstract

Copper slag is generated when copper and nickel ores are recovered from their parent ores using a pyrometallurgical process, and these ores usually contain other elements which include iron, cobalt, silica, and alumina. Slag is a major problem in the metallurgical industries as [...] Read more.

Copper slag is generated when copper and nickel ores are recovered from their parent ores using a pyrometallurgical process, and these ores usually contain other elements which include iron, cobalt, silica, and alumina. Slag is a major problem in the metallurgical industries as it is dumped into heaps which have accumulated into millions of tons over the years. Moreover, they pose a danger to the environment as they occupy vacant land (space problems). Over the past few years, studies have been conducted to investigate the copper slag-producing outlets to learn their behavior, as well as properties of slag, to have the knowledge of how to better reuse and recycle copper slag. This review article provides the environmental and socioeconomic impacts of slag, as well as a characterization of copper slag, with the aim of reusing and recycling the slag to benefit the environment and economy. Recycling methods are considered an attractive technological pathway for reducing waste and greenhouse gas emissions, as well as promoting the concept of circular economy through the utilization of waste. These metal elements have value depending on their characteristics; hence, copper slag is considered as a secondary source of valuable metals. Some of the pyrometallurgical and hydrometallurgical processes to consider are physical separation, magnetic separation, flotation, leaching, and direct reduction roasting of iron (DRI). Some of the possible metals that can be recovered from the copper slag include Cu, Fe, Ni, Co, and Ag (precious metals). Full article

(This article belongs to the Special Issue Metallurgical Slag)

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