Advances in Sintering and Pellet Technology

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
Prof. Dr. Rafael Santos
Dr. Shivakumar Angadi
Dr. Sanjay Agarwal
Topic Editors