Production of Hematite in Acidic Zinc Sulphate Media

299 Pages·2003·10 MB·French

Production of Hematite in Acidic
Zinc Sulphate Media
by
Terry Chi-Ming Cheng
Department of Mining, Metals, and Materials Engineering
McGill University
Montreal, Quebec, Canada
March 2002
A Thesis submitted to the Faculty of Graduate
Studies and Research in partial fulfilment
of the requirements of the degree of
Doctor of Philosophy
@Terry Chi-Ming Cheng, 2002
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Abstract
In this work, the kinetic and equilibrium profiles of each individual reaction step
involved in the production ofhematite at 200°C via oxydrolysis offerrous sulphate in
concentrated zinc sulphate media were established. Crystallizationofferrous sulphate
was found to play a crucial role in the overallprocess due to its relatively low solubility
and fast crystallization kinetics at elevated temperatures. In fact, the overall kinetics
of the oxydrolysis process were found to be limited by the re-dissolution of ferrous
sulphate. Pre-crystallization offerrous sulphate prior to oxidation was found to result
in enhanced overall kinetics, cutting down the required retention time from 3 to
2 hours. Enhanced kinetics were also achieved by performing oxydrolysis in two
temperature stages: a low temperature (T = 180°C) first stage with retention time
2: 20 min and an elevated temperature (T = 200°C) second stage with retention time
2: 100 min.
The typical composition of the hematite material produced in this work was
64.3% Fe, 1.3% 8 (as 804), 0.6% Zn, and 4.6% H20. The sulphur content was
found to be predominantly (0.6-0.8%) due to formation of sodium jarosite with the
remaining (0.3-0.5%) attributed to 80 chemisorption, and (to less extent) basic fer
4
rie sulphate formation. In the absence of zinc sulphate, the majority of sulphate
contamination was due to basic ferric sulphate formation. Hematite was found to
form via a predominantly homogeneous nucleation mechanism with sub-micron crys
tallites clustered together as aggregates of 5-10 /-Lm size and around 7 m2/ g specifie
surface area. In contrast, hematite produced by direct hydrolysis of ferric sulphate
possessed one order of magnitude higher specifie surface area. As for the industrial
hematite product, its composition was found to be 52.6% Fe, 4.6% 8, 1.0% Zn, and
ii
8.8% H 0. The sulphur contamination in the industrial product was mainly due to
2
co-precipitation ofjarosite and basic ferric sulphate compounds. Hydrothermal trans
formation ofthe industrial hematite product at elevated temperatures (2 200°C) and
retention time of 2 60 min with solids loading as high as 16 wt.% proved to be
effective in reducing the sulphur content to less than 1%.
Résumé
Dans cette thèse, la cinétique et les courbes d'équilibres de chaque réaction individu
elle impliquée dans la production de l'hématite à 200°C par oxydrolyse du sulfate
ferreux contenu dans du sulfate de zinc concentré furent établies. La cristallisation
du sulfate ferreux s'est révélée jouer un rôle déterminant dans l'ensemble du procédé
du fait de sa solubilité relativement faible et de ses cinétiques de cristallisation rapides
à hautes températures. En fait, la cinétique générale du procédé d'oxydrolyse s'est
révélée limité par la redissolution du sulfate ferreux. La précristallisation du sulfate
ferreux avant l'oxydation se montrant améliorer la cinétique générale, réduisant le
temps de séjour de 3 à 2 heures. L'amélioration de la cinétique fût aussi réalisée en
faisant l'oxydrolyse en 2étapes de températures différentes: un temps de séjour court
(2: 20 min) à la première étape (T = lSO°C) et un temps de séjour long (2: 100 min)
à la deuxième étape (T = 200°C).
La composition typique de l'hématite produite au cours de ce travail était de
64.3% Fe, 1.3% 8 (sous forme 80 0.6% Zn et 4.6% H 0. La présence de sulfure
4), 2
s'est révélée être principalement (0.6-0.8%) du à la formation de jarosite de sodium
avec le sulfure restant (0.3-0.5%) attribué à la chimisorption du 80 et (en moindre
4
part) par la formation de sulfateferreux basique. En absence de sulfate de zinc, lacon
tamination principale en sulfate était due à la formation de sulfate ferrique basique.
L' hématite s'est révélée être formé principalement par un mécanisme de nucléation
homogène avec des cristaux sub-microniques groupés ensemble en agrégats de taille
de 5-10 pm et de surface spécifique d'environ 7 m2jg. Pour sa part, l'hématite
produite par hydrolyse directe du sulfate ferrique possède une surface spécifique d'un
ordre de magnitude supérieur. Comme pour l'hématite produite industriellement, sa
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IV
composition était de 52.6% Fe, 4.6% S, 1.0% Zn et 8.8% H 0. La contamination
2
en sulfure dans le produit industriel était principalement due à la coprécipitation des
composants de lajarosite et du sulfate ferrique basique. Latransformation hydrother
mique de l'hématite produite industriellement à hautes températures (~ 200°C) et
un temps de séjour 2:: 60 min avec un pourcentage de solide massique de plus de 16%
s'est révélée faisable en réduisant la présence de sulfure à moins de 1%.
Acknowledgements
First ofall, 1would like to express my sincere gratitude to Professor G.P. Demopoulos,
my supervisor (and teacher), for his endless inspiration and unconditional support
throughout all these years of my study at McGill University. His optimistic view
and tireless patience have provided me the courage and will to complete this lengthy
journey that 1 alone would have never finished. 1 am also grateful to his wonderful
family for the great hospitality 1received so often that 1was even welcome there to
spend hours discussing work on the Day of Christmas Eve - to me, the authentic
Greek cookies 1 had that day were not just delicious but indeed full of love - the
best love a student can ever wish for.
During the course ofthis work, 1was very fortunate to have many people who were
always ready to give me a hand. 1am grateful to Dr. Qiankun Wang, a great friend
and mentor, whom 1had spent so many evenings with in the laboratory exchanging
ideas and thoughts that in many occasions led to fruitful results. My thanks extend
to Frank Principe and Georgiana Moldoveneau, great partners and friends for years,
for their advice and help in many fronts, especially in the area ofsolution analysis and
solids characterization. 1would like to thank Vincent Ménard, a new member of the
Group, who spent his first day at McGill translating my abstract in French. Thanks
are due to Prof. D. Ryan for performing the Mossbauer spectroscopic analysis, and
spending so rnuch of his precious time with me on discussing the results. l would
also like to thank Drs. Mark Naklieki, and Zhen Fang for their help on the FT-IR
spectroscopie studies, Dr. Carols A. Leon-Patina on specifie surface area measure
ment, Dr. D.H. Rubisov on particle size analysis, Helen Campbell on SEM analysis,
Glenna Keating on XRF and sulphur combustion analyses, and Glenn Poirier on mi-
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VI
croprobe analysis. l am also grateful to the excellent technical support l received
from Monique Riendeau, Raymond Langlois, Alain Gagnon, and Harold Ward. My
thanks also go to the great administrative staff of the Department, Carol Rousseau
Purnima Mujumdar, Barbara Hanley, Norma Procyshyn, and Genny Snider for their
friendship and care. It has been a great pleasure to be one of the members of the
McGill Hydrometallurgy Research Group, and l am always thankful to everyone in
the Group - now and then - for being there and helping me to shape my future
Thank you!
Natural Sciences and Engineering Research Council of Canada (NSERC) and
Akita Zinc Co. Ltd. in Japan are acknowledged for providing financial support for
this work. l am particularly grateful to Mr. H. Masuda for initially setting up this
collaboration project. l would like to express my sincere thanks to ML T. Yamada,
ML K. Sato, ML Y. Shibachi and all the staff at the Iijima Refinery of Akita Zinc
Co. for their great professionalism and hospitality.
For pursuing higher education overseas, l have been away from home for more than
fifteen years. During all these years, thanks to my Family in Hong Kong, l have been
provided with a very stable environment to focus on my study. This would not come
easily without anyone sacrificing for other's cause. l am extremely fortunate to have
a wonderful family, my Mom and Dad, my four sisters (Lai-Kuen, Lai-Han, Lai-Ping,
Lai-Man) and my brother (Chak-Ming), who have supported me unconditionally since
Day One - to this, l would like to express my sincere gratitude to them. Another
person l am particularly indebted to is Joanne, for she has supported me relentlessly
during all these years and never abandoned me even when l fell down blue. Finally,
l would like to dedicate this work to my Family and Joanne for their love.
Contents
Abstract i
Résumé iii
Acknowledgements v
List of Symbols xxviii
1 Introduction 1
References 4
2 Literature Survey 6
2.1 Introduction................... 6
2.2 Iron control and disposaI in the zinc industry . 6
2.2.1 The iron problem . . 6
2.2.2 Iron removal options 8
2.2.3 Iron removal processes in hydrometallurgy 8
2.3 Industrial production of hematite . 16
2.3.1 General process description 16
2.3.2 The Akita Zinc Hematite Process 18
2.4 A review of the hematite process chemistry . 24
2.4.1 The stability region and solubility of hematite in sulphate media 24
2.4.2 Precipitation of hematite through hydrolysis of ferric sulphate 34
2.4.3 Precipitation of hematite through oxydrolysis of ferrous sulphate 46
vu