Advances in Sintering and Pellet Technology

Topic Information

Dear Colleagues,

The pyro-metallurgical industry is in a continuous mode of innovation and advancement, attempting to tackle societal concerns about its past environmental performance, while trying to meet the ever-growing challenge of suitable materials needed for growing an ever more developed global population. Among the many aims of research in the metallurgical domain are the reduction of air emissions and carbon footprint, the improvement of energy efficiency, the processing of more complex mineral resources as the best ore grades dwindle, the search for critical and strategic metals that are essential for the green and high-tech technologies of the 21^st century, the need to improve process safety and reduce workplace risks, the adoption of alternate renewable carbonaceous energy sources, and the drive to re-think how pyro-metallurgy works and to adopt process intensification and process integration approaches for this reason.

In this context, this Topic on “Advances in Sintering and Pellet Technology” invites the submission of scientific and industrial contributions that present the latest efforts relating to the preparation and use of pellets and sinters in pyrometallurgical applications, including experimental work, characterization work, modeling work, and life cycle and exergy analyses. The following is a non-exhaustive list of potential topics:

• Studies on the reduction of greenhouse gasses, NO_x and fine particulate emissions in pyrometallurgy.
• Studies that incorporate biomass-derived materials into pyrometallurgical processes.
• Studies on the preparation of unconventional pellets and sinters that incorporate various minerals, concentrates, recycled fines, fluxes, and various additives.
• Numerical studies of particle behavior within furnaces, kinetics and phase change.
• Application of advanced characterization techniques to study pellets and sinters.
• Design and development of improved sintering and pelletizing processes.

Lumpy iron ores are extensively used in the production of steel all around the world. High-grade lumpy ores are on the verge of extinction, which necessitates the utilization of mineral processing techniques to enrich the iron values to the desired level. Due to the intricate association of iron-bearing phases with the gangue minerals at a fine particle size, comminution to liberate the iron-bearing phases is the preliminary unit operation in the mineral processing of iron ores. Subsequently, concentration processes such as gravity concentration, magnetic separation, and flotation techniques are extensively used in the concentration of low-grade iron ores. The beneficiated concentrates are fine-grained and need agglomeration before being used in the blast furnace. Amongst various processes used in agglomeration, sintering and pelletization are widely used in the iron ore industries. About 70% of the blast furnace feed is reporting from the sintering processes. The objective of iron ore agglomeration is to generate a suitable product of granules in terms of thermal, mechanical, physical, and chemical properties.

Sintering and pelletization processes are largely influenced by the source of iron ore and the way in which the beneficiation flowsheet is adopted. The beneficiation and agglomeration processes largely depend on the mineralogical characteristics of the ore. The beneficiation and agglomeration treatment selection depends on the nature of the valuable and gangue minerals present in the ore. Many methods, such as washing, jigging, advanced gravity separation, magnetic separation, and flotation are employed to improve the quality of the products.

To utilize the inexpensive fines material in a more meaningful way, agglomeration is one of the most effective measures to reduce the production cost and increase the product competitiveness. Agglomeration processes are typically of three types: pelletizing, briquetting, and sintering. Sintering is a manufacturing technology to make a wide variety of engineering materials, ceramic and metallurgical components by compacting the fine powders using thermal treatment processes. Sintering binds particles together into a designed solid structure via mass transport at the atomic level to improve the physical and chemical properties of the compacted structure. The control of sintering temperature is very crucial for grain boundary diffusion, volume diffusion among the sintering particles, particle size and its distribution, material composition and overall sintering environment to be monitored for obtaining the desired properties. Four types of sintering techniques—viz conventional pressure less sintering, hot pressing, spark plasma sintering, pulsed electric current sintering, microwave sintering and laser sintering—are used to make intricate and complicated products with minimum material loss. There has been significant progress made in understanding the processing of multi-layer composite sintering systems using multi-scale modeling in 3D printing and additive manufacturing technologies.

Pellet making is also a type of agglomeration process that converts fine powders into a solid shape material—mostly small, rounded, spherical, or cylindrical body units. A wide range of fine powder materials, like chemicals, medicines, iron ore, minerals, animal compound feed, plastic and more can be converted to pellet with strong physical and chemical properties. Pellet making processes include many methods to produce the pellets, like direct pelletizing, powder and solution layering, spheronization, spherical agglomeration, compression/balling, cryopelletization, melt spheronization, fluid bed coating and pelletization by extrusion. Developments in obtaining the desired properties of pellets by optimizing the process parameters are key areas of research. Thus, fine powder materials can be used in an effective manner for the desired purpose with ease.

Prof. Dr. Rajesh Kumar Jyothi
Dr. Rafael Santos
Dr. Shivakumar Angadi
Dr. Sanjay Agarwal
Topic Editors

Keywords

Participating Journals

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Minerals minerals	2.5	3.9	2011	18.7 Days	CHF 2400
Metals metals	2.9	4.4	2011	15 Days	CHF 2600
ChemEngineering ChemEngineering	2.5	4.7	2017	17.2 Days	CHF 1600

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Published Papers (5 papers)

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10 pages, 5453 KiB  

Open AccessCommunication

Microstructure Characteristics of Porous NiTi Shape Memory Alloy Synthesized by Powder Metallurgy during Compressive Deformation at Room Temperature

by Li Hu, Zeyi Shen, Xiaojuan Chen, Keyu Hu, Ming Tang and Li Wang

Metals 2023, 13(11), 1806; https://doi.org/10.3390/met13111806 - 26 Oct 2023

Cited by 1 | Viewed by 817

Abstract

Porous NiTi shape memory alloys (SMAs) possess compatible mechanical properties with human bones and can effectively reduce the risk of stress shielding and stress concentration; therefore, they have been termed promising candidates for orthopedic implants. However, microstructure characteristics of porous NiTi SMAs during [...] Read more.

Porous NiTi shape memory alloys (SMAs) possess compatible mechanical properties with human bones and can effectively reduce the risk of stress shielding and stress concentration; therefore, they have been termed promising candidates for orthopedic implants. However, microstructure characteristics of porous NiTi SMAs during plastic deformation have rarely been investigated. The present study aims to specifically investigate microstructure characteristics and the corresponding underlying mechanisms of fabricated porous NiTi SMAs via a conventional sintering (CS) process with NaCl space holder during compressive deformation at room temperature. To realize the aforementioned target, X-ray diffraction (XRD), scanning electron microscope (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) are applied in the present study. The results show that the fabricated porous NiTi SMA is 51.8% for porosity, 181.65 μm for the average pore size, and 0.78 μm for the average grain size. Many Ni₄Ti₃ and NiTi₂ phases are formed in the mixed matrix with dominant B2 (NiTi) and some B19′ (NiTi). Severe inhomogeneous deformation happens within compressed specimens, leading to the occurrence of tangled dislocation and shear bands. Microcracks occur within fabricated porous NiTi SMAs at a deformation degree of 9.2%; then, they extend quickly to form macrocracks, which finally results in the failure of regions between pores. The observed nanocrystallization and amorphization around microcrack tips within the 12.5%-deformed sample can be attributed to the relatively small grain size and the grain segmentation effect via statistically stored dislocation (SSD) and geometrically necessary dislocation (GND). Full article

(This article belongs to the Topic Advances in Sintering and Pellet Technology)

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13 pages, 4603 KiB  

Open AccessArticle

Influence of Basicity and Calcium-Containing Substances on the Consolidation Mechanism of Fluxed Iron Ore Pellets

by Kuo Liu, Feng Chen, Yufeng Guo, Yajing Liu, Shuai Wang and Lingzhi Yang

Metals 2022, 12(6), 1057; https://doi.org/10.3390/met12061057 - 20 Jun 2022

Cited by 3 | Viewed by 1719

Abstract

The application of fluxed pellets in iron making industry has attracted considerable attention because of the better metallurgical properties than acid pellets and environmental friendliness compared to sinters. However, fluxed pellets with different binary basicity (CaO/SiO₂) exhibited significant differences in phase [...] Read more.

The application of fluxed pellets in iron making industry has attracted considerable attention because of the better metallurgical properties than acid pellets and environmental friendliness compared to sinters. However, fluxed pellets with different binary basicity (CaO/SiO₂) exhibited significant differences in phase composition, microstructure and consolidation mechanism. These differences mainly stemmed from the influence of calcium-containing substances in fluxed pellets. Herein, the theoretical investigation discovered the calcium-containing substances from fluxed pellets, including calcium iron silicate, calcium silicate and complex calcium ferrite (SFCA), which determined the properties of fluxed pellets. Microstructure analysis revealed that the calcium-containing substances filled between hematite particles were used as a binding phase to assist in pellets’ consolidation. Furthermore, the calcium-containing binding phase formed in the low-basicity (0.4–1.0) pellets was mainly composed of the calcium iron silicate glassy phase, while the binding phase of the high-basicity (1.0–1.2) pellets was dominated by SFCA belonging to SiO₂-Fe₂O₃-CaO-Al₂O₃ multivariate system. In comparison, SFCA exhibited better crystallinity and reducibility than calcium iron silicate. Within the roasting temperature range of 1200–1250 °C, the increase of basicity contributed to the fluxed pellets obtaining better strength. To sum up, fluxed pellets with SFCA as the main calcium-containing binding phase can be obtained by increasing the basicity above 1.0–1.2, which was imperative for further improving the physical and metallurgical properties of fluxed pellets. Full article

(This article belongs to the Topic Advances in Sintering and Pellet Technology)

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14 pages, 3645 KiB  

Open AccessArticle

Spark Plasma Sintering of Copper-Niobium-Graphite Composites, and the Investigations of Their Microstructure and Properties

by Azunna Agwo Eze, Emmanuel Rotimi Sadiku, Williams Kehinde Kupolati, Julius Musyoka Ndambuki, Jacques Snyman and Idowu David Ibrahim

Metals 2022, 12(4), 574; https://doi.org/10.3390/met12040574 - 28 Mar 2022

Cited by 2 | Viewed by 1852

Abstract

The microstructures and properties of ternary copper-niobium-graphite (Cu-Nb(nano)₁₀-C₄, and Cu-Nb(micron)₁₀-C₄) composites produced via spark plasma sintering (SPS) technique have been investigated for their potential use as electrical connection materials at high-temperature application. Nowadays, there is [...] Read more.

The microstructures and properties of ternary copper-niobium-graphite (Cu-Nb(nano)₁₀-C₄, and Cu-Nb(micron)₁₀-C₄) composites produced via spark plasma sintering (SPS) technique have been investigated for their potential use as electrical connection materials at high-temperature application. Nowadays, there is much activity in the development of such material all over the world. This study was aimed to compare the effect of adding the nano and micron particles sizes of Nb powders in the microstructures and properties of Cu-Nb-C composites sintered at 700 and 650 °C temperatures. The investigated materials have been produced via the SPS method. The microstructures were observed by electron microscopy technique, the wear test was observed by Anton-Paar TRB3 tribometer, thermal diffusivity was observed by LFA427 NETzschlaser flash device within the temperature of 100–900 °C, and the corrosion test was performed by potentiodynamic polarization. The discoveries have been presented in the manuscript and were discussed with reference to the microstructure development, the composite with nanoparticles sintered at 650 °C displayed closed thermal stabilities as temperature increased, and it recorded a low coefficient of friction and suitable corrosion resistance, which correspond to requirements for electrical contacting materials. The SPS method of production of the composites caused initial microstructure refinement and improved the properties of the composites. Full article

(This article belongs to the Topic Advances in Sintering and Pellet Technology)

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16 pages, 4752 KiB  

Open AccessArticle

Preheating Behaviors of Iron Ore Pellets with Humic Substance-Based Binder

by Feiyu Meng, Yang Ou, Ke Li, Yongbin Yang, Qiang Zhong, Qian Li and Tao Jiang

Metals 2022, 12(4), 570; https://doi.org/10.3390/met12040570 - 28 Mar 2022

Cited by 1 | Viewed by 1652

Abstract

Humic substance-based binder (HB) has been found to be an effective substitution for bentonite in the production of iron ore pellets. In this study, it was found that the preheating time needed to be prolonged during the pelletization processing which is a remarkable [...] Read more.

Humic substance-based binder (HB) has been found to be an effective substitution for bentonite in the production of iron ore pellets. In this study, it was found that the preheating time needed to be prolonged during the pelletization processing which is a remarkable feature of pellets with HB instead of bentonite. As far as the oxidation behaviors were concerned, a manifest oxidation hysteresis platform was observed in the FeO content vs. preheating time curve during the second minute in the preheating process, which implied that the emission of humic substance noticeably interfered with oxidation process pellets. Consequently, in contrast to bentonite, the magnetite phase could not be completely transformed into hematite until the preheating time reached 16 min. Meanwhile, the SEM-EDS analysis showed that the crystal grains of preheated pellets with HB were well interconnected when the preheating time was 16 min. This also verified that the optimal preheating time of pellets with HB (16 min) was longer than that of pellets with bentonite (10 min). Full article

(This article belongs to the Topic Advances in Sintering and Pellet Technology)

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16 pages, 4034 KiB  

Open AccessArticle

Study on Double-Layer Ignition Sintering Process Based on Autocatalytic Denitrification of Sintering Layer

by Benjing Shi, Junying Wan, Tiejun Chen, Xianlin Zhou, Yanhong Luo, Jiawen Liu, Mengjie Hu and Zhaocai Wang

Minerals 2022, 12(1), 33; https://doi.org/10.3390/min12010033 - 25 Dec 2021

Cited by 2 | Viewed by 2393

Abstract

An efficient sintering process was proposed based on the autocatalytic denitrification of the sintered ore. The catalytic denitrification of sintered ore, the effect of double-layer ignition sintering process on the emission reduction in nitrogen oxides, and the impact on the quality of sintered [...] Read more.

An efficient sintering process was proposed based on the autocatalytic denitrification of the sintered ore. The catalytic denitrification of sintered ore, the effect of double-layer ignition sintering process on the emission reduction in nitrogen oxides, and the impact on the quality of sintered ore were studied. The results showed that the catalyzed reduction of NO with sinter ore as a catalyst has a significant effect; when the airspeed reaches 3000 h⁻¹, the temperature is 500 °C, and the conversion rate of NO can reach 99.58%. The sinter yield of double-layer ignition sintering is increased, solid fuel consumption is slightly reduced, falling strength is slightly increased, and drum strength is slightly decreased. Under the conditions of layer height proportion of 320/400 mm (lower/upper) and ignition time interval of 10 min, the yield, drum strength, shatter strength, and solid fuel consumption reached 61.60%, 54.82%, 46.75%, and 69.55%, respectively. NO_x concentration under the 16% baseline oxygen content ($c_{(N{O}_{x)}}^{’}$) in the flue gas of double-layer ignition sintering is reduced to a certain extent, and the generation time of NO_x is greatly shortened. The double-layer ignition sintering process can reduce the emission of nitrogen oxides in the sintering process under the condition of guaranteeing the quality of sinter, which has great economic and environmental benefits. Full article

(This article belongs to the Topic Advances in Sintering and Pellet Technology)

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