Physical chemistry of metallurgical processes m shamsuddin (wiley TMS, 2016)

The principal objective of the bookis to enlighten graduate students of metallurgy and metallurgical engineering lizing in chemical-extractive metallurgy and chemical engineering with th

METALLURGICAL PROCESSES

PHYSICAL CHEMISTRY

OF METALLURGICAL PROCESSES

M SHAMSUDDINB.Sc (Met Engg.), M.Sc (Met Engg.), Ph.D (Met Engg.)

Ex Professor and Head, Department of Metallurgical Engineering,

Banaras Hindu University, Varanasi, India

Published by John Wiley & Sons, Inc., Hoboken, New Jersey.

Published simultaneously in Canada.

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or

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Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose No warranty may be created or extended by sales representatives or written sales materials The advice and strategies contained herein may not be suitable for your situation You should consult with a professional where appropriate Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited

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Library of Congress Cataloging-in-Publication Data:

Shamsuddin, M (Mohammad), 1945 –

Physical chemistry of metallurgical processes / M Shamsuddin.

pages cm

Includes bibliographical references and index.

ISBN 978-1-119-07833-3 (cloth) – ISBN 978-1-119-07832-6 (oBook) – ISBN 978-1-119-07831-9 (ePDF) – ISBN 978-1-119-07827-2 (ePUB)

1 Metallurgy 2 Chemistry, Physical and theoretical I Title.

TN665.S4825 2016

669 9 –dc23

2015024793 Cover image courtesy of M Shamsuddin.

Set in 10/12pt Times by SPi Global, Pondicherry, India

Printed in the United States of America.

10 9 8 7 6 5 4 3 2 1

3.1.3 Matte Converting, 76

3.1.4 Ausmelt/Isasmelt: Top Submerged Lancing (TSL) Technology, 803.2 Matte Smelting of Galena, 83

3.3 Matte Smelting of Nickel Sulfide, 85

3.3.1 Theory of Direct Conversion of Molten Nickel Sulfide

into Nickel, 873.4 Continuous Converting, 89

3.4.1 Noranda Continuous Converting Process, 90

3.4.2 Outokumpu Flash Converting Process, 90

3.4.3 Mitsubishi Continuous Converting Process, 91

3.5 Direct Metal Extraction from Concentrates, 92

3.5.1 Outokumpu Flash Smelting Process, 93

4.1.1 Role of Ion Dimension, 104

4.1.2 Metal–Oxygen Bonds, 106

4.2 Structure of Slag, 108

4.3 Properties of Slag, 110

4.3.1 Basicity of Slag, 110

4.3.2 Oxidizing Power of Slag, 112

4.3.3 Sulfide Capacity of Slag, 112

4.3.4 Electrical and Thermal Conductivity, 113

4.3.5 Viscosity, 113

4.3.6 Surface Tension, 117

4.3.7 Diffusivity, 117

4.4 Constitution of Metallurgical Slag, 118

4.4.1 State of Oxidation of Slag, 120

5.2.3 Reduction with Carbon Monoxide, 155

5.2.4 Reduction with Hydrogen, 159

5.3 Kinetics of Reduction of Oxides, 161

5.3.1 Chemical Reaction with Porous and Nonporous Product Film, 1625.4 Commercial Processes, 170

6.2 Nucleation of Gas Bubbles in a Liquid Metal, 205

6.2.1 Role of Interfaces in Slag–Metal Reactions, 208

6.3 Emulsion and Foam, 209

7.1.2 Open Hearth Process, 235

7.1.3 Electric Arc Furnace (EAF) Process, 236

7.1.4 Top-Blown Basic Oxygen Converter Process, 236

7.1.5 Rotating Oxygen-Blown Converter Process, 238

7.1.6 Bottom-Blown Oxygen Converter Process, 239

7.1.7 Hybrid/Bath Agitated/Combined-Blown Process, 240

7.2.6 Kinetics of Slag–Metal Reactions, 256

7.3 Pre-treatment of Hot Metal, 261

7.4 Chemistry of Refining, 264

7.4.1 Bessemer Process, 264

7.4.2 Open Hearth Process, 266

7.4.3 Electric Arc Furnace (EAF) Process, 266

7.4.4 Top-Blown Basic Oxygen Converter Process, 267

7.4.5 Rotating Oxygen-Blown Converter Process, 272

7.4.6 Bottom-Blown Oxygen Converter Process, 274

7.4.7 Hybrid/Bath Agitated/Combined-Blown Process, 276

8.4.2 Stainless Steelmaking Processes, 305

8.5 Injection Metallurgy (IM), 307

8.6 Refining with Synthetic Slag, 309

8.7 Vacuum Degassing, 311

8.7.1 Nitrogen in Iron and Steel, 312

8.7.2 Hydrogen in Iron and Steel, 315

8.7.3 Vacuum Treatment of Steel, 319

9.2.1 Purification of Titanium Tetrachloride, 363

9.2.2 Purification of Columbium Pentachloride, 363

9.2.3 Purification of Vanadium Tetrachloride, 363

10.2.2 Metal–Metal Refining, 391

10.2.3 Metal–Gas Refining, 394

11.2 Breakdown of Refractory Minerals, 431

11.2.1 Concentrated Sulfuric Acid Breakdown, 432

11.2.2 Concentrated Alkali Breakdown, 432

11.3 Physicochemical Aspects of Leaching, 433

11.3.1 Thermodynamics of Aqueous Solutions, 433

11.3.2 Stability Limit of Water, 435

11.5 Recovery of Metals from Leach Liquor, 492

11.5.1 Precipitation of Metal Sulfides, 492

11.5.2 Cementation, 495

I had been planning to write a book on Physical Chemistry of Metallurgical Processes

based on my experiences of teaching a graduate course with the same title at theDepartment of Materials Science and Engineering, Massachusetts Institute of Tech-nology and association/interaction with the faculty members of the Department ofMetallurgy and Metallurgical Engineering, University of Utah, Salt Lake City, during

my 3 years (1978–1981) of visit to the United States But while taking account of rapiddevelopment of the theoretical knowledge in recent years in gas–solid (roasting andreduction) and liquid–solid (leaching and precipitation) reactions, I was in a dilemmaregarding the extent to which mathematical expressions should be incorporated in thebook After spending a lot of time on the mathematical contents while teaching thesame course at the Department of Metallurgical Engineering, Banaras Hindu Univer-sity, I concluded that it should be possible to discuss the new developments in a sat-isfactory manner without going into the use of advanced mathematics by giving moreemphasis on thermodynamics that brings out more convincing evidence as compared

to kinetics involving complex expressions This decision has helped me in the aration of a book of reasonable size covering various process steps in production ofdifferent types of metals, namely common, reactive, rare, and refractory

prep-In the past, during 1950–1970, most textbooks on extractive metallurgy describedprocesses for production of different metals emphasizing the technology rather than thebasic principles involved The physical chemistry of the processes has been restricted

to mere listing of chemical reactions expected to be taking place However, the book

entitled Physical Chemistry of Iron and Steel Making by Professor R G Ward

pub-lished in 1962 has been an exception With rapid increase in the number of extractionprocesses on the industrial scale, it became difficult to bring out the comprehensiveidea of all metallurgical fundamentals for the development of future technology

During 1970–1995, Professors C Bodsworth, W G Davenport, J F Elliott, F Habashi,

E Jackson, J J Moore, R H Parker, R D Pehlke, T Rosenqvist, H Y Sohn, M E.Wadsworth and Dr E T Turkdogan paid due attention to the physicochemical aspects

of metallurgical fundamentals in their books I have benefited from their texts whilepreparing this manuscript and owe them most sincerely In addition, I have tried to collectinformation on this subject from different journals and proceeding volumes For thebenefit of readers, important references have been listed in each chapter This may also

be considered as a tribute to various academicians, researchers, and investigators ated with the publication of various books and research articles in different journals

associ-By giving more emphasis on the physical chemistry of different metallurgical cesses, I aim to solve some of the problems Attention has not been paid to how dif-ferent processes are carried out; instead, the emphasis has been on why the step hasbeen adapted in a particular manner These queries, with a clear understanding of thephysical chemistry, may open ways and means for future developments Lecturing onphysical chemistry of metallurgical processes is associated with a number of challeng-ing exercises and difficulties It requires not only a thorough understanding of chem-ical reactions taking place in a process, but also a sound knowledge of chemicalthermodynamics and reaction kinetics In addition, technical principles of heatand mass transfer are also needed in designing a metallurgical reactor Lastly, thechemical-extractive metallurgist must know about the existing processes and should

pro-be capable of employing his imagination in encouraging students/investigators inimproving the existing techniques

Currently, university courses provide inadequate background in lurgical thermodynamics At the majority of institutions, thermodynamics coursesare formal Often teachers feel satisfied by solving a few problems by plugging data

chemical/metal-in the thermodynamic expressions derived chemical/metal-in the class In this book, the namic interrelationships concerning the problems have been summarized inChapter 1, and for clarity the thermodynamics quantities have been defined togetherwith an explanation of their physical significance It has been presumed that readersare familiar with the undergraduate course in chemical/metallurgical thermodynam-ics For details, readers are advised to consult the textbooks and necessary compila-tions listed in this book Reaction kinetics of different processes has not been covered

thermody-in detail, and topics on heat and mass transfer have not been thermody-included with the primaryobjective of publishing a book of reasonable volume Depending upon the responsefrom readers, it may be taken up in the second volume or edition

The book deals with various metallurgical topics, namely, roasting of sulfideminerals, sulfide smelting, slag, reduction of oxides and reduction smelting, interfa-cial phenomena, steelmaking, secondary steelmaking, role of halides in extraction ofmetals, refining, hydrometallurgy, and electrometallurgy in different chapters Eachchapter is illustrated with appropriate examples of application of the technique

in extraction of some common, reactive, rare, or refractory metal together withworked-out problems explaining the principle of the operation The problems requireimagination and critical analysis At the same time, they also encourage readers forcreative application of thermodynamic data Exercises have not been given because

I am confident that the worked-out examples provide ample platform for the

framework of additional problems In selecting these problems, I am grateful to thelate Professor John F Elliott of MIT and late Dr Megury Nagamori of theNoranda Research Center, Canada I am not consistent in using the SI unitthroughout the book Based on my long teaching experience of about fourdecades, I strongly feel that the use of different units will make students mature withregard to the conversion from one unit to another The principal objective of the book

is to enlighten graduate students of metallurgy and metallurgical engineering lizing in chemical-extractive metallurgy and chemical engineering with the basicprinciples of various unit operations involved in the extraction of different types ofmetals It will also be useful to senior undergraduate students of metallurgy andchemical technology

specia-However, the success of the process is dictated by economic evaluation The use ofthermodynamic principles and reactor design becomes insignificant if the process isuneconomical and/or the product has poor demand This aspect has not been consid-ered in this book I advise the industrial metallurgists and researchers to be carefulabout the economic consequences of their work

I am grateful to a number of friends and colleagues for necessary help in the aration of the manuscript It is not possible to mention all, but I shall be failing in myduty if I do not thank Professor H Y Sohn of the University of Utah, Salt Lake City,USA, Professor Fathi Habashi of the Laval University, Canada, and Professor T R.Mankhand of the Banaras Hindu University for their advice and constructive criticismand also Dr C K Behera and Dr S Jha of the Banaras Hindu University for theirassistance in the preparation of diagrams and the manuscript I am also thankful tolibrary staffs of the Department of Metallurgical Engineering for their active cooper-ation in locating the reference materials Although due acknowledgments have beengiven to authors at appropriate places in the texts for adapting their tables and figurespublished in various books and journals, I take this opportunity to thank the publishers(authors as well) listed below for giving permission to reproduce certain figures andtables:

prep-I ASSOCIATION FOR IRON & STEEL TECHNOLOGY (AIST)

1 Pehlke, R D., Porter, W F., Urban, P F and Gaines, J M (Eds.) (1975)BOF Steelmaking, Vol 2, Theory, Iron & Steel Society, AIME, New Yorkfor Table 6.2 and Figs 4.12, 4.14, 7.7, 8.1, 8.3, and 8.4

2 Taylor, C R (Ed.) (1985) Electric Furnace Steelmaking, Iron & Steel Society,AIME, New York

i Elliott, J F (1985) Physical chemistry of liquid steel, In Electric FurnaceSteelmaking, Taylor, C R (Ed.), Iron & Steel Society, AIME, New York(Chapter 21, pp 291–319) for Figs 8.1, 8.2, 8.3, 8.4, 8.7, 8.8, 8.9, 8.10,and 8.11

ii Hilty, D C and Kaveney, T F (1985) Stainless steel making, In ElectricFurnace Steelmaking, Taylor, C R (Ed.), Iron & Steel Society, AIME,New York (Chapter 13, pp 143–160) for Figs 8.5 and 8.6

3 Chipman, J (1964) Physical chemistry of liquid steel, In Basic Open HearthSteel Making, Derge, G (Ed.), AIME, New York (Chapter 16, pp 640–724)for Figs 7.4 and 8.7.

II ADDISON-WESLEY PUBLISHING COMPANY, INC.

Muan, A and Osborn, E F (1965) Phase Equilibria among Oxides in Steelmaking,Addison-Wesley Publishing Company, Inc., Reading, MA for Fig 4.14

III AMERICAN CERAMIC SOCIETY

Osborn, E F and Muan, A (1960) Phase Equilibrium Diagrams of Oxide Systems,American Ceramic Society, Columbus for Figs 4.10 and 4.11

IV ASM INTERNATIONAL

Marshall, S and Chipman, J (1942) The carbon-oxygen equilibrium in liquid iron,Trans Am Soc Met.30, pp 695–741 for Fig 7.6.

VII DISCUSSION FARADAY SOCIETY

Peretti, E A (1948) Analysis of the converting of copper matte, Discuss FaradaySoc.4, pp 179–184 for Fig 3.1(b).

VIII EDWARD ARNOLD

Ward, R G (1962) An Introduction to Physical Chemistry of Iron and SteelMaking, Edward Arnold, London for Figs 7.2, 7.3, and 7.5

IX ELLIS HARWOOD LIMITED

Jackson, E (1986) Hydrometallurgical Extraction and Reclamation, EllisHarwood Ltd (a division of John Wiley), New York for Figs 11.3, 11.4, 11.5,11.6, 11.7, 11.8, 11.10, and 11.13 and Resin structures and chemical equationsrelated to solvent extraction equilibria

X ELSEVIER

Davenport, W G., King, M., Schlesinger, M and Biswas, A K (2002) ExtractiveMetallurgy of Copper, 4th Edition, Elsevier Science Ltd., Oxford for Figs 3.1(a),3.1(b), and 11.12 and data concerning smelting, converting and leach liquors

XI GORDON & BREACH

1 Habashi, F (1970) Principles of Extractive Metallurgy, Vol 1 General ciples, Gordon & Breach Science Publishing Co., New York for Table 5.1

Prin-2 Habashi, F (1970) Principles of Extractive Metallurgy, Vol 2 tallurgy, Gordon & Breach Science Publishing Co., New York forTable 11.1 and Figs 11.11 and 11.14

Hydrome-XII JOURNAL OF IRON & STEEL INSTITUTE

1 Turkdogan, E T and Pearson, J (1953) Activity of constituents of ironand steelmaking slags, Part I, iron oxide, J Iron Steel Inst 173,

XIV MESHAP SCIENCE PUBLISHERS, MUMBAI, INDIA

Shamsuddin, M., Ngoc, N V and Prasad, P M (1990) Sulphation roasting of anoff-grade copper concentrate, Met Mater Process.1(4), pp 275–292 for Table 2.1

and Figs 2.3, 2.4, 2.5, and 2.6

XV PERGAMON

1 Parker, R H (1978) An Introduction to Chemical Metallurgy, 2nd tion, Pergamon, Oxford, Figs 7.8

Edi-2 Coudurier, L., Hopkins, D W and Wilkomirski, I (1978) Fundamentals

of Metallurgical Processes, Pergamon, Oxford for Tables 4.1, 4.2, 4.3 and4.4 and Figs 4.2, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 4.10, and 4.11

XVI PRENTICE HALL INTERNATIONAL

Deo, B and Boom, R (1993) Fundamentals of Steelmaking Metallurgy, PrenticeHall International, London for Figs 7.11 and 7.12

XVII THE INSTITUTE OF MATERIALS, MINERALS & MINING, LONDON

Turkdogan, E T (1974) Reflections on research in pyrometallurgy and gical chemical engineering, Trans Inst Min Metall., Sect C, 83, pp 67–23 forFigs 7.9 and 7.10

metallur-XVIII THE MINERALS, METALS & MATERIALS SOCIETY (TMS)

1 Rocca, R N., Grant, J and Chipman, J (1951) Distribution of sulfurbetween liquid iron and slags of low iron concentrations, Trans Am.Inst Min Metall Eng.191, 319, for Fig 7.1.

2 Elliott, J F (1955) Activities in the iron oxide-silica-lime system,Trans Am Inst Min Metall Eng.203, 485, for Fig 4.13.

3 Queneau, P E., O’Neill, C E., Illis, A and Warner, J S (1969) Somenovel aspects of the pyrometallurgy and vapometallurgy of nickel, PartI: Rotary top-blown converter, JOM21(7), 35, for Table 3.1.

4 Pehlke, R D and Elliott, J F (1960) Solubility of nitrogen in liquidiron alloys, I Thermodynamics, Trans Met Soc., AIME 218, 1088,

for Figs 8.8 and 8.9

5 Weinstein, M and Elliott, J F (1963) Solubility of hydrogen at oneatmosphere in binary iron alloys, Trans Met Soc., AIME.227, 382,

for Figs 8.10 and 8.11

XIX THE INDIAN INSTITUTE OF METALS

Sundaram, C V., Garg, S P and Sehra, J C (1979) Refining of reactive metals, InProceedings of International Conference on Metal Sciences– Emerging Frontiers,Varanasi, India, November, 23–26, 1977, Indian Institute of Metals, Calcutta,

pp 361, for Table 10.2

Last but not the least, I am extremely grateful to Mrs Abida Khatoon for takingcare of the family, and for offering moral support and patience for my long hoursspent working on the book

M SHAMSUDDIN

The limited availability of textbooks in chemical and extractive metallurgy is evidentfrom their paucity in different library websites Hence, there is a need to enrich theextractive metallurgy library In this field, hardly one or two books are publishedwithin a span of 5–10 years Considering the requirement and circumstances, thisbook by Professor M Shamsuddin, which discusses the physical chemistry of varioussteps involved in the extraction of different types of metals, is an important contribu-tion in the field of chemical metallurgy It is well known that the exploitation of manylow-grade and complex ores/minerals has been possible in recent years by a thoroughunderstanding of slag–metal reactions with the aid of thermodynamics and reactionkinetics The fundamental principles of chemical metallurgy are based on physicalchemistry that includes thermodynamics and kinetics In general, textbooks on phys-ical chemistry deal mainly with contents that are appreciated by the students of chem-istry but are of less interest to metallurgists and chemical engineers In this book,physical chemistry is presented for aspects concerning chemical metallurgy withappropriate examples drawn, as much as possible, from extractive metallurgicalprocesses

The physical chemistry principles that are key to extraction technologies play adecisive role in the development and improvement of processing methods As a con-sequence, metallurgists and chemical engineers often face the problem in selecting theappropriate technique for treatment of the concentrate In order to overcome such achallenging task, a sound knowledge of physical chemistry of different extractionmethods is extremely useful Since the chemistry of the extraction process variesaccording to the nature of the metal, which may fall under the categories of common,rare, reactive or refractory, a comprehensive and collective treatment in one book isvery much desired at the present time Depending on the interest, one may further

study the details in a book/monograph dealing with the particular metal This is themain objective of this book.

This is a very special book for three reasons: Firstly, it includes discussions onphysicochemical principles involved in different steps, namely, roasting of sulfideminerals, matte smelting/converting, reduction smelting, iron- and steelmaking, deox-idation, refining, degassing, leaching, purification of leach liquor, precipitation,cementation, etc., during extraction/production of not only common metals but alsorare, reactive, and refractive metals by pyro- and hydrometallurgical methods Sec-ondly, it provides a number of worked-out examples in each chapter, which makeunderstanding of the process easier Thirdly, the author has systematically summar-ized and presented scattered information on physicochemical aspects of metal extrac-tion from previously published books and journal articles

The book will undoubtedly fulfil the need of students and teachers by providinginformation on the principles and methods of extraction of different metals: common,rare, reactive, and refractory in one place I am confident that the book will be indemand throughout the world by universities and institutes offering courses in Met-allurgy, Chemical Engineering and Technology, and also by various metallurgical andchemical research laboratories It will be more useful to students of metallurgical engi-neering specializing in chemical/extractive metallurgy, but the basic principles of var-ious unit operations involved in extraction will also be appreciated by chemicalengineering students

In addition to his long tenure at Banaras Hindu University, Professor Shamsuddinhas had diversified interactions with faculty members of two premier institutions,namely the Department of Metallurgical Engineering, University of Utah, Salt LakeCity, and the Department of Materials Science and Engineering, Massachusetts Insti-tute of Technology, Cambridge, on various aspects of metal extraction, thermody-namics, and kinetics I have no reservation in stating most strongly that this book

on Physical Chemistry of Metallurgical Processes will achieve a high standard in

the field of chemical/extractive metallurgy and be appreciated by metallurgists andchemical engineers

H Y SOHNFellow, The Minerals, Metals & Materials SocietyProfessor, Departments of Metallurgical Engineering and Chemical Engineering

135 S 1460 E Rm 412University of Utah, Salt Lake City, UT 84112-0114, USA

Tel: (801) 581-5491; Fax: (801) 581-4937

http://myprofile.cos.com/sohnh18http://www.metallurgy.utah.edu

C Heat capacity, component, constant

Cp Heat capacity at constant pressure

Cv Heat capacity at constant volume

D Diffusion coefficient

DP Dephosphorization index

DS Desulfurization index

e Electron charge, interaction coefficient

E Energy, electrode potential, emf, electron field mobility

EA Activation energy

E η Activation energy for viscous flow

f Henrian activity coefficient, fraction reacted

F Degree of freedom, Faraday constant

f(θ) Shape factor

(g) Gaseous phase

g Acceleration due to gravity

G Free energy

G‡ Free energy of activation

h Planck constant, height (metal head)

J Flux, (mass transferred per unit area per unit time), Joule

k Rate constant, partition/segregation/distribution coefficient, Sievert’s stant, Boltzmann constant, kilo

con-km Mass transfer coefficient

K Equilibrium constant, distribution coefficient

K Equilibrium quotient of cations

L Latent heat of transformation, liter

Le Latent heat of evaporation

Lf Latent heat of fusion

(l) Liquid state, liter

ln Napierian logarithm (loge)

pi Partial pressure of the component i

p Partial pressure of the pure component

q Quantity of heat

Q Total extensive thermodynamic quantity

Q Molar extensive thermodynamic quantity

r Radius, rate of evaporation

R Gas constant, rate of reaction

ω Weight, work done

x Atom/mole fraction, ionic fraction, distance in the direction of x

z Valence, a factor in reduction of an oxide, electrochemical equivalent

GREEK SYMBOLS

α Stoichiometry factor, separation factor

γ Raoultian activity coefficient

γ Raoultian activity coefficient at infinite dilution

δ Thickness of the stagnant boundary layer

ε Interaction parameter

η Viscosity, overvoltage due to polarization

θ Contact angle made by nucleus with the substrate

μ Chemical potential (partial molar free energy), mobility

l Liquid, e.g., H2O(l)

s Solid, e.g., SiO2(s)

SUBSCRIPTS

a Anode potential Ea, anode polarizationηa

c Cathode potential Ec, cathode polarizationηc

cell Ecell,ΔGcell

f Formation, e.g.,ΔGf

M Metal, e.g., EM

sol Solution, e.g.,ΔGsol

vol Volume, e.g.,ΔGvol, ΔHvol

SUPERSCRIPTS

‡ Transition of activated state

_ Partial molar functions, e.g., Gi

Thermodynamic standard state, e.g.,ΔG

id Ideal thermodynamic functions, e.g.,ΔGM,id

M Mixing, e.g.,ΔGM

, ΔHM

xs Excess thermodynamic functions, e.g., Gxs

ADDITIONAL SYMBOLS

( ) Solute in slag phase

[ ] Solute in metallic phase, e.g., [S], concentration of a species in solution,e.g., CN−

{ } Gaseous phase

cmi Concentration of the metal at the interface

cm

b Concentration of the metal in the bulk of the metal phase

csi Concentration of the slag at the interface

dt Rate of mass transfer

km Mass transfer coefficient in the metal phase

ks

m Mass transfer coefficient in the slag phase

INTRODUCTION

Metals generally occur in combined states in the form of ores and minerals as oxides,for example, cassiterite (SnO2), cuprite (Cu2O), chromite (Feo Cr2O3), hematite(Fe2O3), pyrolusite (MnO2), rutile (TiO2), wolframite [Fe(Mn)WO4]; sulfides, forexample, chalcopyrite (CuFeS2), cinnabar (HgS), galena (PbS), molybdenite(MoS2), pentlandite [(NiFe)9S8], sphalerite (ZnS), stibnite (Sb2S3); silicates, forexample, beryl (3BeO Al2O36SiO2), zircon [Zr(Hf )SiO4]; titanate, for example,ilmenite (FeO TiO2); carbonates, for example, azurite [2CuCO3Cu(OH)2], dolomite(MgCO3CaCO3), malachite [CuCO3Cu(OH)2], magnesite (MgCO3); phosphate, forexample, monazite [Th3(PO4)4]; vanadate, for example, carnotite (K2O 2UO3V2O5)and so on A few precious metals like gold, silver, and platinum are found in the native

or uncombined form because they are least reactive As naturally occurring ores andminerals are associated with gangue such as silica, alumina etc., the first step in theextraction of metals is the removal of gangue from the ore containing the metal value

by mineral beneficiation methods incorporating comminution, preliminary thermaltreatment and concentration by magnetic separation, heavy media separation, jigging,tabling, and flotation The choice of the method depends upon the nature of the gangueand its distribution in the ore and the degree of concentration of the metal valuerequired, which depends on the extraction technology to be adopted The extractionmethods incorporate various steps to obtain the metal from the concentrate, ore orsome mixture, or from chemically purified minerals; occasionally, the mineral may

be first converted to a more amenable form The mineral beneficiation step lies

Physical Chemistry of Metallurgical Processes, First Edition M Shamsuddin.

© 2016 The Minerals, Metals & Materials Society Published 2016 by John Wiley & Sons, Inc.

between mining and extraction The extraction processes are classified into three maingroups, namely:

1 Pyrometallurgical methods including smelting, converting, and fire refining

are carried out at elevated or high temperatures A step called roasting or cination may also be incorporated in the flow sheet in the treatment of sulfide orcarbonate minerals

cal-2 Hydrometallurgical methods incorporate leaching of metal values from the

ores/minerals into aqueous solution The resultant solution is purified before

precipitation of the metal by pH and pO 2control, gaseous reduction, or tation Roasting or calcination also forms an important step in the treatment ofsulfide and carbonate ores In the production of rare metals like uranium, tho-rium, zirconium and so on, the leach liquor may be purified by fractional crys-tallization, ion exchange, and/or solvent extraction techniques

cemen-3 Electrometallurgical methods use electrical energy to decompose the pure

mineral that is present in aqueous solutions or in a mixture of fused salts Ifthe metal is extracted from the electrolyte using an insoluble anode the method

is called electrowinning On the other hand if the impure metal (in the form ofthe anode) is refined using a suitable electrolyte, the method is known aselectrorefining

The choice of the technique mainly depends on the cost of the metal produced, which

is related to the type of ore, its availability, cost of fuel, rate of production, and thedesired purity of the metal The fuel or energy input in the process flow sheet may

be in the form of coal, oil, natural gas, or electricity Being an electrically based ess electrothermic smelting is an expensive method This process can only be adopted

proc-if cheap hydroelectric power is available Highly reactive metals like aluminum andmagnesium can be produced in relatively pure states by fused salt electrolysis Elec-trowinning is often employed as a final refining technique in hydrometallurgicalextraction Hydrometallurgy seems to be a better technique for the extraction of metalsfrom lean and complex ore although it is slower than pyrometallurgical methods.Major quantities of metals are obtained by the pyrometallurgical route as compared

to the hydrometallurgical route because kinetics of the process is much faster at vated temperatures This is evident from the discussion in the following chapters onmatte smelting, slag, reduction smelting, steelmaking, refining, and halides, whichdeal with the pyrometallurgical methods of extraction Separate chapters have beenincluded on hydrometallurgy and electrometallurgy

ele-In addition to the well-established tonnage scale production of the ferrous and sixcommon nonferrous metals (aluminum, copper, lead, nickel, tin, zinc), in recent yearsmany other metals, namely, beryllium, uranium, thorium, plutonium, titanium, zirco-nium, hafnium, vanadium, columbium, tantalum, chromium, tungsten, molybdenumand rare earths have gained prominence in nuclear power generation, electronics, aer-ospace engineering, and aeronautics due to their special combination of nuclear,chemical, and physicochemical properties Many of these metals are categorized asrare despite their more abundant occurrence in nature compared to copper, zinc, or

nickel This is due to the diversified problems associated with their extraction and version to usable form Production of some of these metals in highly pure form ontonnage scale has been possible recently by efficient improvement of the conventionalextraction methods as well as through the development of novel unit processes.

con-On account of the refractory nature of the minerals and stability of the oxides andcarbides of many rare metals direct smelting of the ores with carbon is not feasible forrare metal extraction The refining methods like fire refining, liquation, distillation and

so on are also not applicable Hence, the flow sheets for rare metal extraction andrefining involve many steps, each with the specific objective of successfully removing

a particular impurity On account of the co-occurrence of chemically similar elements,for example, uranium/thorium, columbium/tantalum, zirconium/hafnium and rareearths there are often problems in rare metal extraction For the separation of suchelements, unconventional techniques like ion exchange and solvent extraction have

to be incorporated in the process flow sheet for production of high-purity metals.Finally, during the reduction and consolidation stages one has to be extremely carefulbecause rare metals in general, and titanium, zirconium and hafnium in particular, arevery sensitive to atmospheric gases that affect their physical, chemical, and mechan-ical properties

It would be appropriate to outline here the general steps in the extraction of raremetals:

1 Physical mineral beneficiation: Beach sand, a source of many rare metals

like titanium, zirconium, hafnium, and thorium, is processed by exploitingthe characteristic differences in the size, shape, density, and electromagneticand electrostatic behavior of mineral constituents, that is, rutile, ilmenite,zircon, monazite and so on

2 Selective chemical ore breakdown: In order to bring the metal values to an

extractable state, hydrometallurgical unit processes like acid or alkali leaching

or pyrometallurgical techniques like fusion with alkalis and alkali double ides are employed

fluor-3 Ion exchange: The technique developed long back for purification and

deion-ization of water is currently used extensively for concentration and purification

of lean leach liquor and for separation of chemically similar elements

4 Solvent extraction: An analytical technique once developed for selective

trans-fer of specific metal ions from aqueous solution to an organic phase, has ently come up to the stage of large-scale unit process for purification andseparation of a number of rare and nuclear metals

pres-5 Halogenation: For the production of oxygen-free reactive metals like titanium,

uranium, zirconium and so on it has become essential to adopt intermediateroutes by converting oxides into chlorides or fluorides prior to reduction

6 Metallothermic reduction: The traditional “thermit process” has been very

successfully employed in rare metal extraction For example, uranium fluoride is reduced with calcium for tonnage production of uranium metalrequired in atomic reactors Similarly, magnesium is used for the production

tetra-of titanium and zirconium from their respective tetrachlorides

7 Consolidation and vacuum refining: As most of the metals mentioned above

are high melting and very corrosive in the molten state they pose problems ing melting and consolidation Special consumable electrode arc melting withsuper-cooled copper hearths have been developed for the production of titaniumand zirconium alloys Electron beam melting technique has been practiced formelting and refining of columbium and tantalum The high superheat at tem-peratures around 3000 C under vacuum helps in removing all impurities includ-ing oxygen, nitrogen, and carbon

dur-8 Ultra-purification: The performance of rare and reactive metals during usage

depends on purity For proper assessment it is important that metals are freefrom impurities Similarly, high order of purity is specified for semiconductingelements like silicon and germanium, required in electronic industry In recentyears a number of ultra-purification methods, for example, thermal decompo-sition, zone refining, and solid-state electrolysis have been developed forlarge-scale purification of these metals

A number of textbooks dealing with ironmaking, steelmaking, extraction of rous metals and principles of extractive metallurgy are available Each book has someedge over the other in certain aspects of presentation in terms of theory and practice.Some emphasize on technology and some on principles Thermodynamics and kinet-ics have been discussed In this book an attempt has been made to discuss the phys-ical chemistry of different steps, for example, roasting, sulfide smelting/converting,reduction smelting, steelmaking, deoxidation, degassing, refining, leaching, precip-itation, cementation involved in the extraction of metals A chapter on slag whichplays an important role in the extraction of metals from sulfide as well as oxideminerals, has been included Similarly, another chapter highlights the significance

nonfer-of interfacial phenomena in metallurgical operations The physicochemical aspects

of desulfurization, dephosphorization, decarburization, and silicon and manganesereactions in steelmaking have been discussed along with brief accounts on varioussteelmaking processes highlighting the differences in their chemistry of refiningand pretreatment of hot metal Role of halides, ion exchange, and solvent extraction

in metal production and refining have been discussed in different chapters Methods

of construction of predominance area diagrams applicable in selective roasting andleaching have been explained with suitable and appropriate examples in Chapters 2and 11 At the of end the book, flow sheets demonstrating various steps in theextraction of copper, lead, nickel, zinc, tungsten, beryllium, uranium, thorium, tita-nium, zirconium, aluminum, and magnesium from their respective ores have beenpresented

Relevant worked out examples have been included in each chapter to illustrateprinciples While reading the topics on continuous smelting and submerged lancetechnology in different books and journals one may feel that the chapter on roasting

is outdated but one must realize that these developments have been possible only after

a sound understanding of the physical chemistry and thermodynamics of all the stepsinvolved in the extraction of metals Although, currently, almost the entire production

of steel comes from top-blown (LD), bottom-blown (OBM) and combined-blown

(Hybrid) converters and electric arc furnaces a discussion on the obsolete Bessemerprocess has been included to highlight the contributions of Henry Bessemer whoseinvention laid the foundation for the modern steelmaking processes Readers may alsoraise questions on SI units not being used uniformly throughout the book I want tostress here that based on my 40 years of teaching experience I strongly feel that sol-ving problems in different units will make students mature with respect to conversionfrom one system to another As some basic knowledge of under-graduate level chem-ical/metallurgical thermodynamics is necessary to understand the worked out pro-blems in different chapters, a brief account on thermodynamic quantities and theirinterrelationships has been included in this chapter.

1.1 THERMODYNAMIC QUANTITIES AND THEIR

INTERRELATIONSHIPS

1.1.1 General Thermodynamics

First law of thermodynamics: Energy can neither be produced nor destroyed in a

system of constant mass, although it can be converted from one form to another.According to the first law of thermodynamics, the total heat content of the system,

called enthalpy (H) is expressed as:

that is, heat content (enthalpy) = internal energy (U) + energy term, dependent on the state of the system (pv), where p and v are, respectively, the pressure and volume of the

system

Heat capacity at constant volume and constant pressure: Heat capacity, C may be

defined as the ratio of the heat, Q absorbed by a system to the resulting increase in temperature (T2− T1), that is, ΔT Since the heat capacity usually varies with

where q = quantity of heat, dT = small rise in temperature.

At constant volume, qv=ΔUv

∴ Cv=dUv

∂T v

1 3

Hence, the heat capacity of a system at constant volume is equal to the rate of increase

of internal energy content with temperature at constant volume

Similarly, at constant pressure,

Cp= qp

Thus, the heat capacity of a system at constant pressure is consequently equal to therate of the increase of heat content with temperature at constant pressure The well

known expression Cp−Cv= R can be established from the knowledge of differential

calculus

Effect of temperature on heat of reaction: The variation of the heat of reaction with

temperature can be expressed as:

ature In case reactant(s) and/or product(s) undergo any transformation at Ttthe aboveequation is modified as:

sur-states that the overall heat change of a chemical reaction is the same whether it takesplace in one or several stages, provided the temperature and either the pressure or thevolume remains constant

Second law of thermodynamics: The first law of thermodynamics is concerned with

the quantitative aspects of inter-conversion of energies This law neither allows us topredict the direction of conversion nor the efficiency of conversion when heat energy

is converted into mechanical energy In the last half of the nineteenth century manyscientists put their concentrated efforts to apply the first law of thermodynamics to thecalculation of maximum work obtained from a perfect engine and prediction of fea-sibility of a reaction in the desired direction These considerations led to the develop-ment of the second law of thermodynamics, which has had a far-reaching influence onthe subsequent development of science and technology The Carnot cycle made it pos-sible to assess the efficiency of engines and it also showed that under normal condi-tions all the heat supplied to the system cannot be converted into work even by perfectengines A perfect engine would convert all the heat supplied into work if the lowertemperature of the process could be made equal to zero This proof of practical impos-sibility of complete conversion of heat energy into mechanical work/energy was thestarting point of the second law of thermodynamics Based on this law, the concept ofentropy was introduced by Clausius

Entropy: In Carnot cycle, the calculated heat absorbed or evolved during isothermal

steps depends on the temperature at which these steps occur However, the numericalvalues of the ratiosqrev

T were the same, so that for example:q1

T = 0, for a number of steps forming

a cyclic process In 1850, Clausius recognized the fact that dqrev

T was characteristic

(state property) of the system and not the value dqrev, since this varies from ature to temperature The name entropy change was finally given to the ratioδq/T by

temper-Clausius who denoted the entropy change by the symbolΔS and considered it to be a

state function Entropy depends on the state of a substance or system and not on itsprevious history, irrespective of whether the path is thermodynamically reversible ornot and it is also irrespective of the substance involved Entropy is a state property It is

an extensive property of the system as it depends on the mass of the system, and is athermodynamic variable Since entropy = energy/temperature, its unit would be: caldeg−1mol−1(e.u.) or J deg−1mol−1 As the system absorbs heat, its entropy increases,for example, during melting and boiling

Calculation of entropy change from heat capacities: From Clausius’ mathematical

definition, entropy change,ΔS = qrev

T , since heat capacity Cphas exactly the same units

as entropy, that is, cal deg−1mol−1, for a limiting case of an infinitesimal change in theprocess, the entropy change can be expressed by the equation:

Equation 1.9 is a general differential equation for change in entropy and if we assume

that entropy is zero at absolute zero, then the entropy of a substance at temperature T

can be calculated from the equation:

Equation 1.11 is applicable in cases where there is no transformation from 0 to T K.

In case of solid-solid, solid-liquid, and liquid-gas transformations (between 0 and

T K), at Tt, Tf, and Te, respectively, with the corresponding latent heat of

trans-formation (Lt), heat of fusion (Lf), and heat of evaporation (Le) Equation 1.11 ismodified as:

Driving force of a chemical reaction: The driving force of a reaction can be

calculated as (ΔH − TΔS); the more negative this factor, the greater the driving force

and if the factor is +ve, the reaction will not proceed spontaneously

Free energy: The factor (ΔH − TΔS) has dimensions of energy because ΔH is an

energy term and ΔS is the heat absorbed divided by the absolute temperature It

has been called the change in the“free energy” of the system Free energy is a modynamic function of great importance Consider a system undergoing a thermody-namically reversible change at constant temperature and constant volume From thefirst law of thermodynamics:ΔU = qr−w, where qris the heat absorbed reversibly by

ther-the system at temperature T and w is ther-the maximum work done by ther-the system.

A is a thermodynamic variable, depending only on the state of the system, not on its history, because U, T, and S are all thermodynamic variables At constant temperature

and constant pressure, work may be done by the system as a result of a volume change

This work (= P ΔV) will not be a “useful” work The useful work will then be the

maximum work,−w, less the energy lost due to volume change (−PΔV).

We can then define the“useful work” as ΔG, the Gibbs free energy change of the

system:

From Equations 1.15 and 1.16, we get:

In Equation 1.17:ΔG = ΔH − TΔS, G is the Gibbs free energy of the system (after

J Willard Gibbs), which depends only on the thermodynamic variables, H, T, and

S It is the maximum work available from a system at constant pressure other than

that due to a volume change Most metallurgical processes work at constant pressure

rather than constant volume so we are more concerned with G than with A We had

already seen the fundamental importance of the factor (ΔH − TΔS), which is equal to

ΔG Hence, ΔG is a measure of the “driving force” behind a chemical reaction For a

spontaneous change in the system,ΔG must be negative; the more negative the ΔG,

the greater will be the driving force

Some more thermodynamic relationships: By definition G = H − TS = U +

PV − TS On differentiation, we get:

Assuming a reversible process involving work due only to expansion at constant

pressure, and according to the first law: dU = dq − PdV, and from the second law:

This corresponds to the maximum work done by a gaseous system at constant

temperature when pressure alters from PAto PB, w = RT ln PA

but ΔG = GB− GA and ΔS = SB− SA∴ d ΔG = −ΔS dT and δΔG δT

Equation 1.24 is known as the Gibbs–Helmholtz equation

Since free energy is an extensive thermodynamic quantity it can be added and tracted in the same way as enthalpy changes Values ofΔS are usually tabulated at

sub-298 K and thus,ΔG298can be calculated.ΔH and ΔS vary with temperature and this

variation can be calculated from the following equations Combining Equations 1.5,1.10, and 1.17 we get:

However, experimental errors involved in the determination of the data do not oftenjustify such complex formulae and normally two or three term formulae of the follow-ing types suffice:

ΔG T = a + bT

ΔG T = a + bTlog T + cT

van’t Hoff isotherm: The van’t Hoff isotherm relates free energy change of a reaction

with the equilibrium constant and activities of the reactants and products(concentrations/partial pressures) of the reaction:

The above relation, known as van’t Hoff’s equation shows the effect of temperature on

the equilibrium constant of a reaction If K1and K2are equilibrium constants at

tem-peratures T1and T2respectively, assuming enthalpy to be independent of temperature

in the close temperature interval (T1− T2), Equation 1.26 can be integrated:

T2

This is known as the Gibbs–Helmholtz equation, useful in determining ΔH at a

par-ticular temperature ifΔG vs T equation is known.

Phase Rule: Thermodynamics has been found to be useful in predicting the maximum

number of possible phases in a given system and in establishing simple equilibriumphase diagrams from very limited thermodynamic data The phase rule mathemati-cally relates phase, component, and degree of freedom by the following relation:

F = C + P−2 1 29where P, C, and F refer to the phase, component and degree of freedom, respectively,which are defined as:Any homogeneous and physically distinct part of a system, sepa-rated from other part(s) of the system by a bounding surface is known asPhase For

example, ice, water, and water vapor co-existing in equilibrium at 273.15 K, constitute

a three phase system When ice exists in more than one crystalline form, each formwill represent a separate phase because it is clearly distinguishable from each other

By and large, every solid in a system constitutes a separate phase But, a homogeneoussolid or liquid solution forms a single phase irrespective of the number of chemicalcomponents present in it However, two immiscible liquids constitute two phasessince they are separated by a boundary Gases on the other hand, pure or as a mixture,always give rise to one phase due to intimate mixing of their molecules

The number ofComponents at equilibrium is the smallest number of independently

variable constituents by means of which the composition of each phase present in a systemcan be expressed directly or in the form of a chemical equation As an example, let usconsider the decomposition of calcium carbonate: CaCO3(s) = CaO(s) + CO2(g) Accord-ing to the above definition, at equilibrium this system will consist of two components sincethe third one is fixed by the equilibrium conditions Thus, we have three phases: two solids(CaCO3and CaO) and a gas (CO2) and the system has only two components

The number ofDegrees of freedom is the number of variables, such as

tempera-ture, pressure, and concentration that need to be fixed so that the condition of a system

at equilibrium is completely stated

Clausius–Clapeyron equation: The Clausius–Clapeyron equation is extremely

use-ful in calculating the effects of temperature and pressure changes on the melting point

of solids, boiling point of liquids, and any solid-solid phase transformations It alsoenables us to quantify the effect of the changes in the concentration of solutions ontheir freezing points, boiling temperatures and is therefore very useful for calculation

of phase boundaries of systems, which are either immiscible or partially miscible inthe solid state The equation is expressed in its simplest form as:

where qrevis the quantity of heat absorbed during fusion of 1 g mol of the substance

and Lfrefers to the corresponding latent heat of fusion, and vsand vlare the volumes insolid and liquid states, respectively

The above equation is known as the Clausius–Clapeyron equation and has beenderived for a single chemical substance undergoing a change from one phase to

another This equation will also be applicable to liquid-vapor, solid-vapor tions and for transformations between two crystalline substances In each case theappropriate latent heat and the volume change have to be substituted into this equa-

transforma-tion In every case, L is the heat absorbed during the process and Δv is the

accompa-nying volume change

The Clausius–Clapeyron equation in the above form enables us to calculate thechanges in either pressure with temperature or latent heat of solid-solid, solid-liquid,solid-gas, and liquid-gas transformation The above Equation 1.31 does not allow us

to calculate the absolute value of pressure and temperature for a given system Theequation will be of much wider application when transformed into a form suitableforintegration by making the following assumptions:

a In the liquid-gas transformation, the volume of 1 g atom of the gaseous phase is

much larger compared to the volume of 1 g atom of the liquid phase, that is,the volume of the liquid is negligible This assumption is reasonable because

in case of Fe(s) = Fe(l), v (liquid iron) = 10 cc g atom−1and v (iron vapor) =

22,400 cc g atom−1

b Since metallic vapors behave ideally, PV = RT.

c The latent heat of transformation is constant over the range of pressure and

tem-perature under consideration

Thus, for liquid-gas transformation we have:

This equation allows us to calculate:

1 The latent of transformation provided p1, p2 and corresponding T1, T2are known

2 The variation in boiling point with change in vapor pressure, provided p1, p2,

and T1are known

3 The value of p, provided T1, T2, and L are known.

Integration of Equation 1.32 may also be written as:

ln P =− L

This form of equation is very useful because plot of ln P vs1

T gives a straight line, theslope of which is −L

R

1.1.2 Solution Thermodynamics

Solutions: A solution may be defined as a homogeneous phase composed of different

chemical substances, whose concentration may be varied without the precipitation of anew phase It differs from a mixture by its homogeneity and from a compound bybeing able to possess variable composition The composition may be expressed interms of either weight percent (wt% or simply%) or atom percent (at%) or mole per-

cent (mol%) The atom/mole fraction (x), most widely used in thermodynamic

equa-tions, is defined as the number of atoms/moles of a substance divided by the total

number of atoms/moles of all the substances present in the solution If nAnumber

of moles of A and nBnumber of moles of B form a solution: A–B, atom fractions

of A and B are given as:

rel-to the mole fraction of the solute in the solution Suppose xAatom/mole fraction of

A and xBatom/mole fraction B form a solution in which pAand pBare the partial

pres-sures exerted by vapors of A and B, respectively, and P is the total pressure of the solution If po

Aand po

B are the partial pressure of pure A and pure B, respectively,

at the same temperature at which solution exists, then according to the Raoult’slaw we have:

1− pA

po A

= xB and 1− pB

po B

= xA

or

pA

po A

= 1−xB= xA and pB

po B

Ideal solutions: An ideal solution obeys Raoult’s law, which may be represented by

plotting vapor pressure against the mole fraction This gives straight lines with

poAand pBo being the intersection of the line with the vapor pressure axes as shown

in Figures 1.1 and 1.2 In ideal solutions, gas pressures pA and pB obey the ideal

gas equation: PV = RT and their physical properties will be additive, that is, total sure, P = pA+ pB

pres-Nonideal or real solutions: Deviations from Raoult’s law occur when the attractive

forces between the molecules of components A and B of the solution are weaker orstronger than those existing between A and A or B and B in their pure states Forexample, if there were an attractive force between components A and B in the solu-tion, which is weaker than the mutual attraction between molecules of A in pure A andmolecules of B in pure B, there would be a higher tendency for these components toleave the solution In this case the vapor pressure would be more than that predictedfrom Raoult’s law This is known as the positive deviation from Raoult’s law(Fig 1.1) In case of a stronger attraction between A and B as compared to A and