The microstructure of the pig iron nuggets

The pig iron nugget process (referred to as the Iron Technology Mark 3, or ITmk3, process by Kobe Steel) was developed as an alternative to the traditional blast furnace process. Throughout this process self reducing-fluxing dried greenballs are reduced and smelted in to nuggets of metal. The objective of this research was to produce pig iron nuggets at laboratory scale, then characterize and compare them with the blast furnace pig iron. Pig iron nuggets were characterized utilizing apparent density measurements, optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, and bulk chemical analysis. It was determined that pig iron nuggets had high apparent density (6.7-7g/cm3); had a high iron content (95-97%); and exhibited microstructures similar to white cast iron, which is essentially the same as pig iron from a blast furnace. © 2007 ISIJ

Paradigm for pig iron nugget production

Economic, environmental and operational disadvantages of the traditional blast furnace process has led to the development of direct smelting reduction processes, including those that utilize self reducing/ fluxing dried greenballs as iron oxide feed materials. This is mainly due to improved carbothermic reduction, carburization and reaction kinetics. In this paper, the morphological changes of the greenballs as they transform to pig iron nuggets are examined over time at a constant temperature of 1,400° C. The products produced after each treatment were characterized using optical microscopy, scanning electron microscopy/energy dispersive spectroscopy and point counting/image analysis. The changes in the percent metallized area, wustite dendrite and slag matrix content of the structures were calculated. It was determined that the transformations were initially controlled by dissolving and containment of iron oxides in the molten slag and their consequent reduction to iron, followed by coalescence of the metallized areas. The final transformations were controlled by the carburization of the metallized areas. © Copyright 2012, Society for Mining, Metallurgy, and Exploration, Inc

Manipulation of slag separation properties from pig iron nuggets with flux additions to dried greenball mixture

© 2017 Taylor & Francis Group, LLC. Pig iron nugget process is one of the direct smelting processes developed as an alternative to the traditional blast furnace process. Throughout the process, slag-free pig iron nuggets, which have similar properties to the blast furnace pig iron and white cast iron, are produced by single-stage heat treatment of dried greenballs. During the process, slag separation from the metallized areas can be enhanced by adjustment of the slag’s chemical and physical properties. The objective of this research was to investigate the effects of flux addition rates (basic to acid ratio) to the dried greenball mixture on pig iron nugget production and slag separation. Thus, this study involved the heat treatment of six different greenball mixtures, which contained various amounts of limestone addition (basic to acid ratios, 0, 0.63, 1.02, 1.42, 1.85, and 2.29) utilizing a laboratory-scale resistance box furnace or simultaneous differential scanning calorimetry and thermalgravimetric analyzer. The samples produced by heating in the box furnace were analyzed for their morphological and chemical properties utilizing optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), macroscopic observations, iron titrations, and atomic absorption spectroscopy. It was determined that the highest percentage of iron yield in the nugget for the process and the highest distribution of iron in magnetic slag were obtained when utilizing the greenball mixture, which contained 7.5 wt% limestone as flux (basic to acid ratio of 1.42)

Can fly-ash extend bentonite binder for iron ore agglomeration?

There is great incentive to reduce bentonite use in iron ore pelletization by improving its effectiveness. In order to make bentonite more effective, it is necessary to understand the actual binding mechanisms so that they can be properly taken advantage of. Bentonite use could also be reduced by replacing bentonite with even lower-cost binders, such as high-carbon fly-ash based binder (FBB). While FBBs can be used alone as binders, it was considered possible that mixtures of FBB and bentonite could exhibit superior binding properties. In this study, it was found that bentonite bonds by a physical mechanism, while FBB bonds by a chemical mechanism. These mechanisms were determined to be incompatible. Mixtures of the two binders resulted in reduced dry magnetite concentrate pellet compressive strengths below the industrially acceptable value of 22 N (5 lbf). Activators and accelerators, which were necessary components of the FBB, deactivated the bentonite. The compatibilities and mechanisms of the two binders are explained in this paper. The classical theory of the binding mechanism of bentonite binder is challenged by the bentonite fiber mechanism that was recently identified by the authors. (C) 2000 Elsevier Science B.V. All rights reserved

Pelletization Using Humic Substance-based Binder

© 2017 Taylor & Francis. Humic substances exist widely in lignite coal as high molecular weight organic molecules. They can be used as binders in iron ore pelletization mostly in the form of salt, such as sodium humate and amine humate via extraction from lignite coal. It is worth determining if lignite can be used as a binder without extraction. As a composite binder of organic and inorganics, due to the combustion of humic substance, the strength of fired pellets made with humic substance-based binder decreases slightly. To compensate for this defect and make stronger pellets, cheap calcium bentonite was added into humic substance binder. In this study, a fluxed hematite concentrate was pelletized with various types of binders: lignite plus sodium hydroxide, calcium bentonite activated with modified humic acid (MHA), and MHA binder. Good quality pellets were obtained at optimal parameters. The results show that without extraction procedure, lignite plus sodium hydroxide can be directly used as a binder in pelletization of fluxed hematite; that calcium bentonite improves pellet strength when added to MHA; and that humic substance can partly replace calcium bentonite, reducing the dose of calcium bentonite

Simultaneous removal of CO\u3csub\u3e2\u3c/sub\u3e, NO\u3csub\u3ex\u3c/sub\u3e and SO\u3csub\u3ex\u3c/sub\u3e using single stage absorption column

Capturing flue gases often require multiple stages of scrubbing, increasing the capital and operating costs. So far, no attempt has been made to study the absorption characteristics of all the three gases (NO, SO2 and CO2) in a single stage absorption unit at alkaline pH conditions. We have attempted to capture all the three gases with a single wet scrubbing column. The absorption of all three gases with sodium carbonate solution promoted with oxidizers was investigated in a tall absorption column. The absorbance was found to be 100% for CO2, 30% for NO and 95% for SO2 respectively. The capture efficiency of sodium carbonate solution was increased by 40% for CO2 loading, with the addition of oxidizer. Absorption kinetics and reaction pathways of all the three gases were discussed individually in detail

Properties and features of direct reduced iron

The blast furnace process is still the predominant method for primary iron production. However, the disadvantages inherent to the process led to the development of alternative processes such as the mini blast furnace process, smelting reduction process, and direct reduction process. Many of these alternative processes are still under development. However, direct reduction processes have reached some level of commercial applicability and are considered to be the most developed alternative ironmaking route. It is coke-less and environmentally friendlier when compared to the blast furnace process. In addition, direct reduced iron has a well-defined chemical composition when compared with steel scrap and has efficient melting properties in the electric arc furnace. Consequently, there is a great increase in the demand for direct reduced iron in electric arc steel making. These attractive features have led to an increase in worldwide production of direct reduced iron, which is currently approaching 50 million tons. Thus, direct reduced iron is gaining more importance. Hence, this article summarizes the basic properties and features of direct reduced iron. Copyright © Taylor & Francis Group, LLC

Strategies for processing low-grade iron ore minerals

The conventional routes for making iron and steel require that the ore be upgraded through a series of physical separation processes in sequence. The unit operations involved include crushing, grinding, separation, dewatering, pelletization, blast furnace processing, and basic oxygen furnace processing. This complex sequence is not cost effective for many low-grade ores that are resistant to physical concentration. For example, many ores contain iron oxide in a nonmagnetic form and are so fine-grained that it is uneconomical to grind them to a fine enough size to separate the iron oxides from the gangue. Exploitation of these iron minerals needs to take a different approach, using fewer process steps than are required for conventional ironmaking. Results are presented showing that it is possible to produce metallic iron directly from low-grade ores. The metal is in a form that can be easily separated to produce a high-grade iron product, and the iron recovery is greater than can be achieved from difficult-to-process ores by conventional means. © Taylor & Francis Group, LLC

Effects of bentonite fiber formation in iron ore pelletization

In the production of iron ore concentrate pellets, binders are required to improve pellet green strength. The most popular binder for this purpose is bentonite clay, which is added at a rate of approximately 0.5-1.0% by weight of moist concentrate. Bentonite is a significant cost item in iron ore pelletization, and also contributes undesirable amounts of silica to the finished pellets. If the binding effectiveness of bentonite is increased, it will be possible to reduce the bentonite dosage, resulting in significant cost savings while producing higher quality, lower silica pellets. The authors have recently identified a new and important bentonite binding mechanism, which is development of bentonite fibers under compressive shear mixing. During this study, procedures were developed that took advantage of the ability of bentonite to form fibers, and resulted in a dramatic decrease in the necessary bentonite dosage. When mixing procedures were used that promoted fiber formation, the bentonite dosage needed to produce acceptable strength pellets was cut in half, from 14 (0.66%) to 7 (0.33%) lb/lt. In addition, bentonites that are currently considered poor quality can have their performance enhanced by using this fiber development method, and be used successfully as iron ore pellet binders. © 2002 Published by Elsevier Science B.V

Laboratory studies for improving green ball strength in bentonite- bonded magnetite concentrate pellets

The performance of bentonite binders in magnetite concentrate balling has been difficult to predict due to a lack of understanding of the binding mechanisms and of the effects of water chemistry. Results are presented that indicate that the most effective binding occurs when the bentonite platelets slide past one another to form sheet-like or fiber-like structures, which is produced by compressive shear mixing. It has also been determined that the effects of water chemistry on bentonite performance are much greater than had previously been believed. This is because the water retained in magnetite filter cake has been shown to have a considerably higher concentration of ions (particularly calcium and magnesium) than was present in the bulk solution, and these ions strongly impact the swelling behavior of the bentonite. Results showing the benefits of fiber development and showing the effects of the water chemistry are presented. By taking advantage of bentonite fiber development and dealing with the effects of water chemistry, the strength of bentonite-bonded magnetite concentrate pellets can be increased. These studies have brought to light a number of previously unsuspected effects, which are critically important for further improving the theories of bentonite-binding behavior. © 2003 Elsevier B.V. All rights reserved