Principles of Metal Refining and Recycling

An important field of study of industrial and commercial activity lies between extractive metallurgy and physical metallurgy. This book is an attempt to fill the gap. This field, which we call metal refining and recycling, has become especially important due to the use of lower grade ores, increased recycling, and higher quality requirements. Our aim is to understand the principles that guide today’s operation and to develop new solutions to tomorrow’s problems. During the Industrial Revolution, a gap developed between research with a professor and assistant in the university and practice in industry.

This became especially severe in Scandinavia for the iron and steel industry due to its strong growth. It was problematic for the universities to train a sufficient number of scientists and workers with a knowledge of extractive metallurgy, thermodynamics, physical metallurgy, economics, etc. After the Second World War an attempt was made to cover the shortage of trained workers and scientists by establishing institutes supported by both industry and government and expanding the education of PhD students trained in the needed disciplines. This book presents the scientific understanding of metal refining and recycling that resulted from this research and development activity.

To solve many industrial problems, it is necessary to draw on scientific principles from ‘non-traditional’ sources. For example, fluid mechanics and the behaviour of atoms at the solid–liquid interface are of paramount importance. These fields provide the link between physical metallurgy and process metallurgy. Measuring and controlling impurities in molten metals is necessary. For instance, Si for solar cells must be refined down to very low levels of impurities.

Changes and improvements during the past fifty years has made it possible to provide metals with low amounts of impurities. Why is it important to have a clean and properly alloyed metal? Answers to this question are presented in Chapter 1, which gives motivation
for the rest of the book. The remaining chapters can be divided into three parts:

1. Fundamentals: Thermodynamics, physical and transport properties, mixing, mass transfer, and numerical models are described in detail in Chapters 2 and 3.
2. Problems and methods: The removal of dissolved impurity elements, particles and inclusions, and refining during solidification are covered in Chapters 4, 5, and 6, respectively.
3. Applications: Remelting and the addition of alloys, refining challenges and specific processes for each metal, with a focus on steelmaking, and recycling are considered, respectively, in Chapters 7, 8, 9, and 10.
Metals are essential for the technological society in which most of us live. To ensure future availability, it is important to conserve resources and take care of our environment. Previously, it was sufficient for a worker to manage one field. Today, a broader understanding is required.
Knowledge in different scientific disciplines is often required to solve problems. Social, economic, environmental, and political (legal) factors must also be considered. To cover all of this properly is a problem. The authors have in sum more than 100 years of experience, but this was not sufficient to cover all important aspects of metal refining and recycling. Fortunately, we have been assisted and supported by a number of eminent colleagues.

We hope this book will serve two purposes. First, it should provide a detailed survey of the present state of the art. Each chapter has an extensive bibliography, so that a researcher may easily use the chapter as a starting point, or ‘launching pad’, for further activity. And second, we have paid special attention to the principles underlying the science, so the book may also be used by advanced students. Our primary intention has been to provide a comprehensive book. It was not mainly designed to serve as a textbook manual of instructions. It may be more appropriate to select portions suitable for the desired course of study. For example, parts of Chapters 2–6 should provide a course of study focusing on refining methods. In practice, the difference between the two goals is somewhat artificial. An effective worker must always be ready to learn and discover new things both theoretical and practical. One should always be a student.

As you read this, we welcome you a colleague and co-worker in the field of refining and recycling of metals. We hope you will discover topics of interest and utility. We also hope this book will ‘stand the test of time’, be useful for our world, and add to society’s knowledge of metal refining and recycling.

Extracting and recycling metals with minimal damage to the environment will become increasingly important. There will certainly be many interesting challenges to address in the future. One illustration of the challenge before us is the activity in the deep-sea mining of minerals. It would be an interesting challenge to utilize the principles in this book to process and refine metals obtained in this way.


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