Coordination Principle of Minerals Flotation

234 Pages·2022·8.882 MB·English

by  Jianhua Chen

Jianhua Chen
Coordination
Principle
of Minerals
Flotation
Coordination Principle of Minerals Flotation
Jianhua Chen
Coordination Principle
of Minerals Flotation
Jianhua Chen
School of Resources, Environment
and Materials
Guangxi University
Nanning, China
ISBN 978-981-19-2710-2 ISBN 978-981-19-2711-9 (eBook)
https://doi.org/10.1007/978-981-19-2711-9
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Preface
Mineral flotation is a remarkable invention in human history, employing
hydrophilicity/hydrophobicity on mineral surfaces to achieve the separation of
various minerals. Flotation makes it possible for mankind to develop and utilize
mineral resources on a large scale, improving the situation of insufficient resources
in social development. Currently, a modern mining industry system has been formed,
with mining and beneficiation as the core.
As Bulatovic stated in the Preface to the Handbook of Flotation Reagents: Chem-
istry, Theory and Practice, “Without reagents there would be no flotation, and without
flotation the mining industry, as we know it today, would not exist”. Flotation has
become one of the most common and most efficient technologies for separating
mineral resources today. The understanding of flotation has been evolving. In 1930,
Ostwald suggested that the collector existed only at the solid–liquid–gas interface.
Christmann believed that xanthate exhibited collecting power merely in the pres-
ence of frother. Kellerman and Bender considered that the collecting capability of
xanthate was derived from its decomposition products. In 1933, Ravitz and Porter
proposed that the role of xanthate was to remove oxides from mineral surfaces.
These initial hypotheses might not be accurate, but they promoted the understanding
of flotation to varying degrees. Subsequently, the electrostatic hypothesis was put
forward to explain the interaction between cationic collectors and negatively charged
mineral surfaces, which, however, was not applicable to systems involving chem-
ical interactions. For instance, under alkaline conditions, the complete ionization of
xanthate into anions and the negative-charged sulfide mineral surface do not affect
the collecting power of xanthate on sulfide minerals. In 1934, Targart introduced
the solubility product hypothesis, suggesting that the interactions of collectors with
mineral surfaces were essentially chemical reactions. Yet, this hypothesis cannot
explain why the same metal ion exhibits differences in various minerals.
The solubility product hypothesis attracted attention to the oxidation of mineral
surfaces. According to the solubility data of sulfide minerals, only oxidized mineral
surfaces could provide a sufficient amount of metal ions. In 1953, Salamy and Nixon
proposed the electrochemical theory of sulfide ore flotation, which explained the role
v
vi Preface
of oxygen in flotation. Since then, researchers worldwide have conducted a consid-
erable number of investigations on the electrochemistry of sulfide ore flotation for
nearly 70 years. Since nonferrous minerals possess the property of semiconductors,
the occurrence of electrochemical phenomena in sulfide ore flotation is unavoid-
able. Still, collectors and depressants are required to modify the hydrophilicity and
hydrophobicity of mineral surfaces. The reagent–surface interaction remains the core
problem in flotation.
As of today, the theoretical study of flotation lags far behind industrial practice
given the large-scale and mature applications in flotation industries. This is due to the
fact that flotation is a complex interfacial process involving minerals, reagents, and
their interactions, spanning the disciplines of chemistry (reagents) and solid-state
physics (minerals). Chemical theory focuses on describing the properties of indi-
vidual particles, such as molecules and ions, while solid-state physics primarily deals
with the properties of systems comprising a large number of particles, such as the
structure and properties of mineral crystals. Chemical theory is the most widely used
theory in flotation studies. However, classical chemical theories applied to flotation,
such as solubility product hypothesis, do not take into account the influence of mineral
crystals and their properties on metal ions and therefore cannot explain a range of
phenomena including xanthate floating pyrite but not hematite. On the other hand,
the author has made attempts to introduce solid-state physics into flotation studies
but encountered difficulties in accuracy of describing the interaction between metal
ions and reagents, although solid-state physics provides a satisfactory explanation for
floatability differences from the perspective of mineral crystal structure and its prop-
erties. The interaction of flotation reagents with mineral surfaces involves charged
reagent ions and charged surface metal ions, while solid-state physics describes a
many-body theoretical problem that does not address the case of charged particles. A
sound and self-consistent theoretical system of flotation requires an accurate repre-
sentation of both the polyatomic structure of mineral crystals and the molecular
properties of individual reagents so as to obtain results in line with the flotation
practice.
The work aims to provide a coordination model for the interaction between flota-
tion reagents and mineral surfaces and a theoretical guide for targeting design of
flotation reagent molecules. Analyzing the crystal structure and coordination, this
book presents the surface coordination theory for reagent–mineral interactions, which
refers to the case that the surface metal ions have already been coordinated with
surrounding atoms before interacting with the reagent molecules. Systematic inves-
tigation has been carried out on the interaction between flotation reagent molecules
and surface metal ions, and a flotation theory based on coordination chemistry has
been established, from the perspectives of geometry matching, electron–orbital inter-
actions, orbital symmetry matching, and crystal field stabilization energy. Given the
fact that ligand field theory mainly discusses the complexes with d orbitals, this book
primarily focuses on the nonferrous minerals containing d orbitals.
At last, the author would like to extend gratitude to Prof. Sun Chuanyao, academi-
cian of the Chinese Academy of Engineering, for providing immense encouragement
Preface vii
and support. From discussions with him, the author benefited a lot. Without his inspi-
ration, this book would not have been successful. The author’s appreciation also goes
to Li Yue for language services and Tang Xiaoqin for her contributions to language
editing.
Nanning, China Jianhua Chen
Prologue
Minerals flotation is a complex interfacial process in which mineral crystals, reagents,
and water as the flotation medium all exhibit coordination characteristics. The interac-
tion of flotation reagents with the metal ions that are semi-constrained on the mineral
surface can be regarded as typical surface coordination. Based on coordination
chemistry, this book represents the reagent–mineral (surface) interactions from the
perspective of geometry principles, surface coordination, crystal field stabilization
energy, and orbital symmetry matching.
This book mainly discusses minerals containing d orbitals employing ligand field
theory (LFT).
ix
Contents
1 Theory of Coordination Chemistry .............................. 1
1.1 Introduction ............................................... 1
1.2 Valence Bond Theory ....................................... 5
1.2.1 Hybridization Types and Spatial Structures of Orbitals .... 6
1.2.2 Outer-Orbital Complexes and Inner-Orbital
Complexes .......................................... 10
1.2.3 Defects of Valence Bond Theory ....................... 11
1.3 Crystal Field Theory ........................................ 13
1.3.1 Ideas of Crystal Field Theory .......................... 13
1.3.2 d Orbital Splitting .................................... 14
1.3.3 Electronic Distribution in High Spin and Low Spin
States .............................................. 18
1.3.4 The Jahn–Teller Effect and Configurational Distortion ..... 20
1.3.5 Crystal Field Stabilization Energy ...................... 22
1.3.6 Applications of Crystal Field Theory .................... 23
1.3.7 Improvements of Crystal Field Theory .................. 26
1.4 Molecular Orbital Theory .................................... 28
1.4.1 Key Ideas of Molecular Orbital Theory .................. 28
1.4.2 Molecular Orbitals for Regular Octahedral Complexes .... 29
1.4.3 Molecular Orbitals for Tetrahedral Complexes ........... 33
1.4.4 Molecular Orbital Theory and Ligand Field Theory ....... 36
2 Coordination Characteristics of Mineral Flotation System ......... 39
2.1 Coordination Characteristics of Mineral Crystals ................ 39
2.1.1 Coordination Structure of Minerals ..................... 39
2.1.2 Splitting of D Orbitals in Mineral Crystals ............... 41
2.1.3 Relationship Between the Lattice Energy of Crystals
and Crystal Field Stabilization Energy .................. 44
2.1.4 The Relationship Between the Bond Length
of Mineral Crystals and d-Electron Configuration ......... 48
xi
xii Contents
2.1.5 Effect of CFSE on the Distribution of Metal Ions
in Mineral Crystals ................................... 52
2.1.6 Jahn–Teller Effect in Mineral Crystals .................. 57
2.2 Coordination of Water Molecules as a Flotation Medium ......... 58
2.3 Coordination Properties of Flotation Reagents .................. 60
2.3.1 Coordination Power of the Collector .................... 60
2.3.2 Coordination Power of the Depressant .................. 65
2.4 Coordination of Reagents with Metal Ions ..................... 65
2.5 π-Backbonding ............................................ 69
2.6 HSAB Theory ............................................. 70
2.7 Ligand Field Model of the Interaction of Reagents
with Minerals .............................................. 73
References ..................................................... 75
3 Geometry Principles of Coordination on Mineral Surface .......... 77
3.1 Spatial Geometry Foundation for Coordination ................. 77
3.1.1 Configuration of Orbital Hybridization .................. 77
3.1.2 Close Packing of Crystal Atoms ........................ 79
3.2 Geometric Principle of the Maximum Coordination Number ...... 83
3.2.1 The 3-Coordinated Close-Packing Structure .............. 83
3.2.2 The 4-Coordinated Close-Packing Structure .............. 84
3.2.3 The 6-Coordinated Close-Packing Structure .............. 85
3.2.4 The 8-Coordinated Close-Packing Structure .............. 86
3.3 Relationship Between the Coordination Number
and the Spatial Structure of Metal Ions ........................ 88
3.4 Spatial Structure of 4-Coordinated Compounds ................. 94
3.5 Steric Hindrance of Sulfurization on Oxide Surfaces ............. 98
3.5.1 The 5-Coordinated Iron on Hematite Surface ............. 98
3.5.2 The 5-Coordinated Zinc on Smithsonite Surface .......... 100
3.5.3 The 4-Coordinated Copper on Malachite Surface ......... 102
3.5.4 The 5-Coordinated Lead on Cerussite Surface ............ 104
3.6 Influence of Space Structure on Metal Ion Valence and Orbital
Hybridization .............................................. 105
3.7 Steric Hindrance of Interaction of Collectors
with 3-Coordinated Metal Ion ................................ 108
3.7.1 Interaction Between Sphalerite Surface and Xanthate ...... 108
3.7.2 Interaction Between Chalcopyrite Surface and Z-200
Molecule ........................................... 112
3.8 Spatial Structure Matching of Reagent Molecules
with Mineral Surfaces ....................................... 114
References ..................................................... 116