Sintering is a thermal agglomeration process that is applied to a mixture of iron ore fines, recycled ironmaking products, fluxes, slag-forming agents, and solid fuel (coke). The purpose of the sintering process is manufacturing a product with the suitable characteristics (thermal, mechanical, physical and chemical) to be fed to the blast furnace. The process has been widely studied and researched in the iron and steelmaking industry to know the best parameters that allow one to obtain the best sinter quality. The present article reviews the sintering process that the mixture follows, once granulated, when it is loaded onto the sinter strand. There, the sinter mixture is partially melted at a temperature between 1300-1480°C and undergoes a series of reactions that forms the sinter cake to be loaded into the blast furnace to produce pig iron.

Iron Ore Sintering: Process

This paper critically reviews published research on silico-ferrite of calcium and aluminum (‘SFCA’) phases, the major bonding phases found in modern iron ore sinters. In particular, we focus on describing the different ‘SFCA’ phases formed in iron ore sinter and examining their phase chemistry, crystal structures, characteristic textures and microstructures, and formation conditions. Information for the two main bonding phases SFCA and SFCA-I are reviewed and, based on a critical analysis of the data, we suggest future research directions required to generate the information necessary to fully describe the properties of both phases.

A Review of the Chemistry, Structure and Formation Conditions of Silico-Ferrite of Calcium and Aluminum (‘SFCA’) Phases

Sinters were produced in the pilot plant using four different ore mixtures with varying proportions of iron ores, fluxes and coke. All the resulting sinters were characterised by chemical and granulometric analysis, degradation testing during reduction in the blast furnace (RDI test), cold resistance testing (Tumbler test), reducibility testing, determination of softening and melting temperatures, and determination of the sinter structure by electron microscopy. The obtained result allow for the establishment of better operation conditions to manufacture sinters.

The Influence of Different Iron Ores Mixtures Composition on the Quality of Sinter

Steel slag, a by-product generated during steel production poses a solid waste disposal challenge. The same slag contains valuables such as titanium, nickel, vanadium, iron, aluminum, silica among others. The extracted components can cause productive value addition in diverse realms like wastewater treatment to semiconductor devices. A paradigm shift is required towards waste valorization for developing profitable extraction methods for these constituent elements. In this review, an attempt was made to assimilate such technologies into one concrete and concise compendium. The pros and cons of each method were weighed comparatively with respect to applicability and innovation. An effort was attempted for assessing key design aspects and scale-up potential vis-a-vis the economic analysis for the valorization techniques. It was seen that the leaching technique was the most widely used in the resource recovery domain followed by other techniques like fusion, hydrothermal treatment. Techniques that dominate the exploration of some of the metals from their lean ores or respective mineral slags might also be explored for their recovery from steel slag. Some technologies like slag filter development for phosphate removal has already been tested in real-life conditions while others are in the nascent stages of development. Special focus can be directed towards the simultaneous extraction of multiple components or direct in-situ product formation and its subsequent separation. This paper reviews various technologies for steel slag valorization to guide researchers working in the field of slag resource recovery and sustainable waste utilization.

Waste to wealth: Recovery of value-added products from steel slag

Steel slag is a solid waste of the steel industry, produced during steel production. Three types of slag, namely electric arc furnace (EAF), basic oxygen furnace (BOF), and Linz-Donawitz processed slag (LD-slag) are the steel industry byproducts. That slag comprises precious elements including zinc (Zn), chromium (Cr), iron (Fe), nickel (Ni), silicon (Si) , aluminum (Al), and vanadium (V) and is considered a secondary source of many metals. These metal constituents can be recovered from slags by employing mineral processing techniques like crushing, grinding, magnetic separation, eddy current separation, flotation, leaching, and/or roasting. Metal extraction from steelmaking slag and slag utilization is essential not only for conserving metal supplies but also for environmental protection. This review article evaluated and summarized various extraction methods including magnetic separation, roasting, pyrometallurgical method, hydrometallurgical and bio hydrometallurgical technique to recover precious metal constituents from obtained slag. The state-of-the-art of metal recovery from slag using the aforementioned methodologies and the merits, and demerits of each procedure have been illustrated comprehensively. Suggestions have been made to overcome the shortfall and or lacuna of the technology for better performance and efficiency. The opportunities and difficulties portion of this article paints a vivid picture of turning such a beneficial technology into a more adaptable procedure with some additions that may motivate and lead future research in new directions. The essence of this survey indicates that extracted metal and treated slag might be reutilized in various fields ranging from biomedical to fertilizer applications. 

An Overview of Precious Metal Recovery from Steel Industry Slag: Recovery Strategy and Utilization

During the processing of steel in steel mills, iron oxides will form on the surface of the metal. These oxides, known as mill scale, occur during continuous casting, reheating and hot rolling operations. Mill scale is a valuable metallurgical raw material since it contains 65–70% iron. JSW Steel Ltd is a 7 Mtpa integrated steel plant and generates 270 t of mill scale per day. Most of the materials of steel plant wastes are recycled through sinter making in most of the countries. Because of its physical, chemical and mineralogical properties, it can be used as a raw material in a process like sintering. The mill scale contains high amounts of Fe and low amounts of silica and alumina. Thus, recycling it through the sintering process helps in the saving of raw materials like iron ore and limestone. This paper presents preliminary findings of a study that investigates the potential for recycling steel mill scale in the sintering process. Experiments were conducted using the mill scale in sinter making...

Recycling of steel plant mill scale via iron ore sintering plant

Dolomite and other MgO bearing materials are being increasingly used as basic flux constituents for production of fluxed sinters. Addition of flux materials in sinter influences the resultant sinter microstructure and chemical properties. The physical and metallurgical properties of sinter mainly depend on mineralogy of the sinter. Dolomite is the source of double carbonate of calcium and magnesium. Recent studies reveal that, apart from the additional fuel needed, the addition of dolomite and MgO bearing material greatly influences the magnetite content and the properties of the sinter produced. The increasing use of MgO bearing fluxes in the blast furnace burden, and the trend to incorporate a major part of fluxes in the sinter mix led to an investigation of the influence of MgO on sinter properties and productivity. In this study, the systematic investigation has been made on the influence of MgO% (1·4 to 2·6) on sinter mineralogy and sinter properties with dolomite. Microstructural examination...

Influence of magnesia on iron ore sinter properties and productivity

The heat hardening by oxidation is a process commonly used in iron ore pelletization process. The green pellets are fired in induration machine using Corex gas at JSW Steel Limited Pellet Plant. The firing temperature of induration machine strongly influences the physical and metallurgical properties of the pellet. Due to absence of exothermic reaction and poor roasting property of hematite pellet, the energy consumption of hematite pellet production is at higher side and requires higher roasting temperature. In present pelletization process, carbon burdened method is found to be more favorable technique in practice to enhance the induration of hematite pellets. Coke breeze is added in the pellet mix at JSW pellet plants to get the inherent fuel value of a hematite green ball equal to that of a magnetite pelletizing feed. The firing temperature (from corex gas) of the induration machine and carbon addition in the pellet mix is interrelated and decides physical and metallurgical properties of the pellets. At JSW Steel Pellet Plant the carbon addition varies from 0.90 to 1.50% and firing temperature varies from 1 230 to 1 320°C. Fluctuations in physical and metallurgical properties were observed due to deviation in carbon addition and firing temperature. Optimization of external firing temperature and coke breeze addition in the green pellet mix is necessary to get the desired properties of the pellet for iron making units. Basket trials were carried out at pellet plant induration machine by varying the external firing temperature from 1 220 to 1 330°C and coke breeze addition from 0.7 to 1.4%. At firing temperature of 1 220, 1 250, 1 280, 1 310 and 1 330°C the optimum carbon addition 1.30, 1.20, 1.10, 0.90 and 0.70% achieved the optimum physical and metallurgical properties of the pellet for iron making units respectively.

pdf/optimization-of-firing-temperature-for-hematite-pellets-20il7i8k0w.pdf

Optimization of Firing Temperature for Hematite Pellets

Iron ore sinter constitutes a major proportion of blast furnace burden. Hence, its quality and consistency have a significant impact on blast furnace performance. Iron ore fines are the main source for sinter, and the chemical composition of the iron ore fines, together with the thermal conditions that blends are subjected to, plays an important role in forming the primary melt during the sintering process and accordingly determines the sinter structure and quality. Therefore, considerable importance has been placed on the chemical composition and consistency of iron ore fines, particularly in terms of alumina content. Due to depletion of high grade iron ore resources, alumina content in the iron ore fines is expected to increase gradually. Ore with higher alumina content is usually expected to be detrimental in forming the sinter matrix, if sintered alone, due to the low reactivity of alumina bearing minerals and the high viscosity of primary melts. The selective granulation process is a new sintering process for high alumina iron ore fines, and can eliminate the adverse effects of ‘hard to sinter’ or ‘unsuitable – for ironmaking’ ores. In the present work laboratory sintering experiments have been carried out with iron ore fines of different alumina level (2.00 to 5.46 mass-%) to know the influence of alumina on mineralogy, productivity, physical and metallurgical properties of sinter prepared by the conventional and the selective granulation process. With increasing alumina content in sinter of both the conventional and selective granulation process, the fractions of hematite and of silico-ferrites of calcium and alumina (SFCA) as well as the pore phase increased whereas the magnetite and silicate phases decreased. With increase in alumina content sinter productivity and tumbler index (T.I.) decreased, and metallurgical properties like sinter RDI and reducibility improved. However, sinter of the selective granulation process showed better results compared to the conventional process.

Influence of Alumina on Iron Ore Sinter Properties and Productivity in the Conventional and Selective Granulation Sintering Process

Iron ore fluxed sinter is the main ferrous burden of Jindal south west steel limited (JSWSL) blast furnaces. In sinter plant fluxes including limestone and dolomite are added to improve the sinter properties of iron ore and to provide an appropriate slag composition of the blast furnace. The raw material grain size affects the sinter process considerably because the sinter productivity and quality are strongly dependent on the green permeability of the bed, which is determined by the particle size distribution of the raw materials, the granulation effectiveness and by the sintering process itself. It is well-known that in fluxed sinter, the size of limestone affects productivity and physical and metallurgical properties of the sinter. It is therefore necessary to understand the role of limestone particle size on sinter properties and productivity. In the present work laboratory sintering experiments have been carried out with different levels of limestone mean particle size (from 0.14 to 1.83mm) to understand the influence of limestone particle size on mineralogy, productivity, physical and metallurgical properties of the sinter. Sinter productivity increased with increasing limestone mean particle size due to improved sinter bed permeability. Sinter with limestone mean particle size of 1.25 to 1.52 mm yielded better sinter strength and lower RDI compared to sinter with smaller or larger limestone mean particle size. Higher sinter strength is due to better and uniform distribution of limestone particles, and better bed permeability enabled easy assimilation and effective distribution of calcium ferrite phases. The improvement in sinter RDI is due to change in mineralogy of the sinter compared to coarser and finer limestone mean particle size.

Influence of limestone particle size on iron ore sinter properties and productivity

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