Sustainable and Economic Waste Management

Resource Recovery Techniques

Hossain Md Anawar, Vladimir Strezov, Abhilash, Hossain Md Anawar, Vladimir Strezov, Abhilash

• Publisher: CRC Press
• Year: 2019
• ISBN:
  9781000761979
• Edition: 1
• Topic: Scienze biologiche
• Subtopic: Conservazione e Tutela dell'Ambiente

This book compiles research findings directly related to sustainable and economic waste management and resource recovery. Mining wastes and municipal, urban, domestic, industrial and agricultural wastes and effluents—which contain persistent organic contaminants, nanoparticle organic chemicals, nutrients, energy, organic materials, heavy metal, rare earth elements, iron, steel, bauxite, coal and other valuable materials—are significantly responsible for environmental contamination. These low-tenor raw materials, if recycled, can significantly address the demand–supply chain mismatch and process sustainability as a whole while simultaneously decreasing their impacts on human life and biodiversity. This book summarises the large volume of current research in the realm of waste management and resource recovery, which has led to innovation and commercialisation of sustainable and economic waste management for improved environmental safety and improved economics.

Key Features:

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• Reviews the key research findings related to sustainable and economic resource recovery and waste management techniques

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• Discusses minimizing waste materials and environmental contaminants with a focus on recovering valuable resources from wastes

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• Examines the potential uses of mining waste in the re-extraction of metals, provision of fuel for power plants, and as a supply of other valuable materials for utilisation/processing

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• Presents research on recycling of municipal, urban, domestic, industrial and agricultural wastes and wastewater in the production and recovery of energy, biogas, fertilizers, organic materials and nutrients

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• Outlines topical research interests resulting in patents and inventions for sustainable and economic waste management techniques and environmental safety

1

Pyrometallurgical Process for Recycling of Valuable Materials and Waste Management: Valorisation Applications of Blast Furnace Slags

Sara Yasipourtehrani, Vladimir Strezov^*, Tim Evans, and Hossain Md Anawar

Department of Environmental Sciences, Faculty of Science and Engineering, Macquarie University, Sydney, New South Wales, Australia

CONTENTS

1.1 Introduction

1.2 Pyrometallurgical Process

1.3 The Iron Making Process

1.4 Blast Furnace Slag Properties

1.4.1 Liquid Properties of BFS

1.4.1.1 Basicity

1.4.1.2 Viscosity

1.4.1.3 Melting Point

1.4.1.4 The Cooling Process

1.4.1.5 Eutectic Point

1.4.1.6 Energy Efficiency

1.4.2 Microstructure of Solid BFS

1.4.3 Slag Composition and End Use

1.4.3.1 Concrete and Cementitious Products

1.4.3.2 Phosphate Removal

1.4.3.3 Dye Removal

1.5 Conclusion and Recommendations

References

1.1 Introduction

Metal extraction technologies have impacts on the environment and generate waste materials during processing (Dippenaar, 2005), causing challenges with their storage, transportation and environmental pollution (Ozturk and Gultekin, 2015). In recent decades, industrialisation and urbanisation have increased rapidly leading to large amounts of waste materials being generated at significant rates. As such, existing landfill sites have filled rapidly, increasing the importance for exploration of new disposal sites (Francis, 2005). A critical issue of environment protection is the treatment of increased and diverse waste materials that threaten public health (Kuo et al., 2008). To mitigate landfill and environmental issues associated with waste disposal, increasing recycling or the development of new by-products has become a principal incentive for industry (Francis, 2005). Iron and steel making are some of the major industrial activities where recycling and reusing of process wastes is required.

1.2 Pyrometallurgical Process

Pyrometallurgical and hydrometallurgical processes are the two main metal extraction and recovery technologies generally used to produce refined metals. The pyrometallurgy is a process that utilises high temperatures to alter the mineral chemically, separate desired metals from other materials and ultimately reduce the metal oxides to free metals. This process applies high temperature reactions, roasting, smelting and conversion of metal oxide to metal (Ramachandra Rao, 2006). The differences between oxidation potentials, melting points, vapour pressures, densities and/or miscibility of the ore components are used in these processes (Roto, 1998). Pyrometallurgical processes are also used to recycle iron, copper, lead, steel and other scrap metals (Espinosa et al., 2015). After beneficiation (crushing, grinding, floating and drying), an ore is sintered or roasted (calcined) with other materials, such as baghouse dust and flux, during pyrometallurgical processing and then smelted, or melted, in a blast furnace in order to fuse the desired metals into an impure molten bullion. The various metals, such as gold and silver, may also be produced as by-products depending on the origin of the ore and its residual metal contents. Cobalt and zinc are produced by roasting, which is an important pyrometallurgical process, and then undergo further hydrometallurgical processing.

The sulphidic ores are smelted or roasted (another pyrometallurgical process) to produce a partially oxidized metal concentrate that is subsequently processed to separate metals by hydrometallurgical processing.

2ZnSs+3O2g→2ZnOs+2SO2g

(1.1)

Calcination process is used to heat an ore, decompose and eliminate a volatile product as follows.

PbCO3s→ΔPbOs+CO2g

(1.2)

Valuable metals can be recovered from the metal oxides existing in many metallurgical residues by direct reduction of the oxides at elevated temperatures exceeding 1000°C using pyrometallurgical processes, carbon, flux, etc. (Ramachandra Rao, 2006). The most important sources of iron are the iron oxide minerals: hematite, Fe₂O₃, and magnetite, Fe₃O₄, and the reduction of iron is the most important pyrometallurgical operation. Therefore, the aim of this chapter is to describe the different steps of the pyrometallurgical process used in iron and steel production from iron ore and waste, as depicted in the following sections. In this chapter, the iron making process is described and blast furnace slag (BFS) properties are reviewed. The potential for reusing BFS in other industries is further discussed. Specifically, this chapter discusses the use of BFS as a cementitious material and in wastewater treatment for phosphate and dye removal.

1.3 The Iron Making Process

Iron ore contains iron oxides and other mineral impurities named as gangue, which can comprise of oxides of aluminum and silicon as the main gangue constituents, and nickel, zinc, copper and other metals as part of the trace element fraction. According to the mineralogy, there are different types of iron ores, such as hematite, magnetite, goethite, limonite or siderite (Mou and Morrison, 2016). Pure hematite or other pure forms of iron ore are rare but mixtures of these forms are common in nature. The grade of iron ore is an important factor for the iron making industry and high-grade iron ore means high iron and low impurities. Magnetite and hematite have higher concentrations of iron in their ores (Mou and Morrison, 2016).

In the blast furnace (BF) based iron making process, iron oxides are reduced to metallic iron while the gangue materials are removed in the form of slag that is a waste product. The BF needs solid fuel to provide the energy and act as a reductant, and coke is the material that fulfills this process. Coke is a carbonaceous mass product from the destructive distillation of coal. The coal also contains a fraction of gangue material. Another step before the BF is sintering of iron ore fines generated during mining. Sintering is the process that agglomerates fine ores and allows the recycling of dusts and other ferrous materials. In the iron making industry, lump iron ore and iron ore sinter are placed in the BF and, with the assistance of coke as a reductant and fuel, are reduced to molten pig iron, with the impurities melting to form molten slag. The pig iron is separated from the slag in the molten state, with the molten pig iron being further processed into molten steel and the slag cooled to form a solid by-product (Brodnax and Rochelle, 2000). The steel making furnace is used to convert pig iron into the final steel product (Dippenaar, 2005).

Both iron and steel making processes produce environmental impacts and generate greenhouse gas emissions (Kan et al., 2015). The target of industry is to save natural resources by using waste materials and, where possible, conserve energy where material properties and characteristics are suitable (Motz and Geiseler, 2001). Iron making also produces waste material that can potentially be recycled in different industrial processes (Motz and Geiseler, 2001).

During the iron making process, large amounts of blast furnace slag (BFS) are produced, which are estimated at 175–225 million tonnes per year worldwide (Savastano et al., 2001). The properties of different slags vary and are determined primarily by the ore type and ash of the coke. BFS largely consists of Al₂O₃, SiO₂, CaO, and MgO as the main components with other compounds like TiO₂, FeO, and MnO₂ present in small amounts (Ozturk and Gultekin, 2015). Slag can be considered a renewable material that has not been used before, and the properties of this waste make its use possible in different industrial processes (Dimitrova, 1995), helping to reduce environmental contamination, energy use and production costs (Ozturk and Gultekin, 2015). The possible reuses of the BFS depend on the slag properties, heat treatment, cooling process of the molten slag and its separation in the BF.

In the BF, the pig iron and molten slag accumulate at the hearth of the BF, and the slag is positioned above the pig iron, as its density is lower than molten iron (Ito et al., 2014). BFS segregates from the pig iron during the production proc...