ASPECTS OF FERROMANGANESE PRODUCTION IN THE SUBMERGED-ARC FURNACE. by A

328 Pages·2014·9.03 MB·English

ASPECTS OF FERROMANGANESE PRODUCTION
IN THE SUBMERGED-ARC FURNACE.
by
A. KOURSARIS
A thesis submitted to the Faculty of
Engineering in fulfilment of the
requirements for the degree of Doctor
of Philosophy
University of the Witwatersrand
Johannesburg
UNDERTAKING
I hereby certify that this is my own work,
except for the chemical analyses which were
carried out by the National Institute for
Metallurgy and the excavation and sampling
of furnace M10 which was carried out by a
team of technicians and scientists from the
National Institute for Metallurgy. This team,
of which I was a member, was assisted by
workmen at Meyerton.
This thesis has not been submitted for the
degree ot Doctor of Philosophy at any other
University.
A. Koursaris
Ill
TO
PHAEDRA, MICHAEL and ADAM
i v
ABSTRACT
A variation of the stationary charge in controlled environ­
ment (SCICE) technique was used for the first time to
investigate the influence of two reducing agents on the
rate and mechanisms of reduction of Mamatwan manganese ore ,
the resistivity of the charge and the processes that take
place in submerged-arc furnaces for the production of high-
carbon ferromanganese.
The excavation of a 5 MV A submerged-arc furnace for the
production of high-carbon ferromanganese, the taking of
samples and the examination of these samples was carried
out for the first time in an attempt to study the processes
taking place in industrial furnaces and to assess the
extent ^ o which the SC 11 E technique reproduced the conditions
in industrial units.
It was shown that the use of Delmas coal or Iscor coke did
not affect the rate or mechanisms of reduction of Mamatwan
ore to a significant extent. The physical and chemical
changes that take place in Mamatwan ore at temperatures
between 1200 and 1600 C, under oxidizing or reducing conditions,
were investigated and it was shown that reduction of manganous
oxide occurred mainly from the slag.
I he resistivity of mixtures of ore and coal was significantly
highei than that of mixtures of ore and coke for temperatures
of less than 1100°C. At higher temperatures the resistivities
of the two types of mixture were the same.
The processes that took place in the SC ICE charges were
shown to be very similar to those that take place in
industrial furnaces between stockline level and the level
of the electrode tip.
ACKNOWLEDGEMENTS
Sincere appreciation is extended to :
Drs. C W P Finn, J B See and D I Ossin for
supervising the work.
Dr. N A Bareza for supervising the excavation of
furnace M10
The management of the Meta Hoys plant of Samanco
at Meyerton who supplied the materials for this
study and for their co-operation with regard to the
excavation and sampling of furnace M10.
The National Institute for Metallurgy, Johannesburg,
for financial assistance and for permission to submit
this work for higher degree.
The Ferro Alloy Producers Association for financial
support.
PREFACE
The recent developments in the ferromanganese
industry of South Africa >~ave necessitated further
research into the reduction behaviour of Mamatwan
manganese )re when contacted with different reducing
agents. The Mamatwan orebody is of a relatively
low grade but is in plentiful supply and is therefore
of basic importance to ferromanganese producers.
The lower inherent resistance of large, modern
submerged-arc furnaces and the increasing scarcity
and cost of metallurgical coke have forced ferroalloy
producers to look at alternative reducing agents. The
suitability of a reducing agent for use in a submerged-
arc furnace is assessed mainly from the resistivity of
the reducing agent, its ability to give stable furnace
operation and its reactivity.
A limited amount of work has been carried out on the
rates and mechanisms of reduction of Mamatwan ore and on
the mineralogical changes that take place when the ore is
heated at relatively low temperatures in oxidising and
reducing atmospheres.
The aims of this work were to investigate the reactions
in, and the resistivity of, charges of Mamatwan ore
and two carbonaceous reducing agents under conditions
similar to those that obtain in the hotter regions of
a submerged-arc furnace. The applicability of the
experimental method used, to the study of the processes
taking place in an industrial furnace was assessed by
the examination ot samples taken from one such furnace.
V 1 1
The author was a bursar of the National Institute for
Metallurgy while conducting this work.
The excavation and sampling of furnace M10 was carried
out by a team of scientists and tecnnicians of which
the author was a member. This team was assisted b\
a team of workers of the Metalloys plant of Samancor
at Meyerton.
/
vi i i
CON TENTS
1.0 INTRODUCTION
2
1_i Production of Ferromanganese in South Africa
5
Reduction of Manganese Oxides
5
,2.1 Reduction oi the Higher Oxides
,2.2 Reduction of Manganous Oxide
11
.2.3 Reduction of Manganous Oxide from Slags
14
.3 The Mechanism of Reduction ot Metal Oxides
Previous Research Relating to the Metallurgical ^
Applications of Mamatwan Manganese
.5 Electrical and Thermal Aspects of Submerged- ^
arc Furnace Operat Lon
The Electrical Properties of Carbonaceous ^
.6
Reducing Agents
26
The Electrical Properties ot Ores
30
The Electrical Properties of Furnace Burdens
.8
.9 The Distribution of Zones in Submerged-arc ^
Furnaces
.10 Conclusions
2.0 EXPERIMENTAL
42
2.1 Choice of Experimental Technique
2.1.1 Critical Appraisal of the <perimental
44
Techn ique
2.2 Materials and the Preparation of SC ICE 4_
Charges
50
2.3 Apparatus and Procedure
50
2.3.1 SCICE Experiments
57
2.3.2 Additional Experiments
2.3.3 Sampling and Examination of Reacted SCICE
59
Charges
.3.4 Microanalysis by the Energy Dispersive
59
System (EDS)
IX
5.0 RESULTS
3.1 The Mineralogy of the Or~ 66
3.2 Observations During the Heating of SCICE
Charges 73
3.3 Macro-examination of the Reacted SCICE
Charges 75
3.4 Microscopic Examination of the Reacted SCICE
Charges 77
3.4.1 General Microscopic Examination of the Phases
in Particles of Partially Reduced Ore
77
3.4.2 Examination of the Metallic Component 85
3.5 The Distribution of Elements in the Phases of
Partially Reduced Ore 96
3.5.1 X-ray Microanalysis of Reacted S2ICE Charges 99
3.5.2 X-ray Diffraction Analysis 104
3.5.3 Mass Losses and Alloy and Slag Compositions 108
3.6 Results of Additional Experiments 113
3.6.1 Ore Heated in Air 113
3.6.2 Ore Heated in Carbon Monoxide 116
3.6.3 Ore Heated in Graphite Crucible 121
4.0 DISCUSSION
4.1 Some Practical Considerations on the use of
Mamatwan Ore in Submerged-Arc Furnaces 131
4.2 Reduction of Higher Oxides to Manganous Oxide 134
4.3 Reactions to Form the Slag 141
4.4 Reactions to Form the Alloy 143
4.4.1 Nucleat ion of Metal 14 5
4.4.2 Growth of Metallic Nuclei 145
4.4.3 Formation of the Alloy Layer 148
4 . 5 The Influence of Reducing Agent on the
Reduction Process 151
4.6 Conclusions 153
i
X
5.0 THE RESISTIVITY OF MIXTURES OF MAMATWAN ORE AND
--------------
5.1 Materials, Apparatus and Procedure 154
5.1.1 Determination of Resistance 154
5.1.2 Variation in Volume Fractions of Components 157
5.2 Results and Discussion 158
5.2.1 Effect of Temperature on Resistivity of
Individual Charge Components 158
5.2.2 Volume Changes During Heating of Charges 166
5.2.5 Resistivities of Charges of Ore and Reducing
Agents 167
5.5 Resistivity Measurements and Furnace
Resistance 180
5.4 Conclusions 182
6.0 EXAMINATION OF FURNACE SAMPLES
6.1 Genera 1 184
6.2 Sampling Procedure and Sample Identification 185
6.5 Appraisal of the Furnace Excavation 189
6.4 The Internal Structure of Furnace M10 191
6.5 Processing of Furnace Samples 198
6.6 Examination of Samples from Face CE^W^ 201
6.6.1 Visual Examination 201
6.6.2 Microscopic Examination 207
6.6.5 X-ray Diffraction Analysis 212
6.6.5.1 Analysis of the Non-metal lie Constituent 112
6.6.5.2 Analysis of the Alloy 212
6.7 The Chemical Composition of Alloys 219
6.8 X-ray Microanalysis of Metal , Slag and Oxide 224
6.9 Examination of Samples from Face CE 226
6.9.1 Visual Examination 226
6.9.2 Microscopic Examination 251
6.9.5 X-ray Diffraction Analysis 254
6.9.4 The Chemical Composition of Alloys 254
6.9.5 X-ray Microanalysis of Metal, Slag and Ox ide 257