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2022 | Buch

Coordination Principle of Minerals Flotation


Über dieses Buch

The advent of flotation, with selective interaction of reagents with minerals at its core, has greatly advanced the development of modern mining. Ever since, there has been continuous researched into the mechanism of mineral-reagent interactions, in an effort to design and develop more effective reagents. A unique perspective from coordination is presented to illustrate the principles of reagent molecules interacting with metal ions on mineral surface. For the first time, the influence is unveiled of mineral crystal structures and surrounding atoms on metal ion properties and further on mineral-reagent interactions. The introduction of classical theories for modern chemistry, including orbital structure, electron spin and orbital symmetry matching, into flotation is realized. Researchers, engineers and graduate students among others in the field of mineral processing may gain new insight into flotation and the development of novel reagents.


Chapter 1. Theory of Coordination Chemistry
Since ancient alchemy, mankind has continued to explore the composition and principles of matter. By the early nineteenth century, many inorganic compounds and a few organic compounds were known to exist. Through the continuous exploration of the existed chemical substances, the chemical valence theory was gradually developed. In 1803, Dalton suggested that there was a simple integer ratio relationship when simple atoms combined to form complex atoms. For example, one atom A and one atom B will form an AB complex atom, and one atom A and two atoms B will form an AB2 complex atom; the total of atoms remains unchanged before and after the reaction. In 1839, after replacing three hydrogens in acetic acid with chlorines to produce a compound with similar properties, Dumas proposed a “theory of type”, dividing organic compounds into hydrogen-like, hydrogen-chloride-like and ammonia-like. In 1852, while studying metal–organic compounds, Frankland discovered that the affinity of atoms was always satisfied by the same number of bonding atoms, and thus introduced the concept of combining power. In 1857, Kekule put forward the concept of atomic affinity, arguing that when atoms of an element combined with atoms of another element the total number of atoms was determined by basicity numbers or affinity numbers of the constituent atoms. The following year, Kekule wrote in a renowned work On the Constitution and Metamorphoses of Chemical Compounds and on the Chemical Nature of Carbon that one carbon atom could at most bond to four hydrogen atoms in a compound, which has laid a foundation for valence theory. In 1865, Hofmann presented the most initial concept of chemical valence: “quantivalence” in Introduction to Modern Chemistry, the idea that elements had different quantitative values of 1, 2, 3, etc. In 1867, Kekule adopted the word “valenz”, which was widely recognized and applied in European countries. It is called valence in modern academic literature.
Jianhua Chen
Chapter 2. Coordination Characteristics of Mineral Flotation System
Mineral flotation is a complicated multiphase system, including the interactions among mineral surfaces, reagents, and various ions in flotation pulp. These interactions are attributed to chemical reactions with metal ions in traditional flotation theories. In fact, simple chemical reactions are a small part of flotation interactions, most of which is coordination. Firstly, the ions on the mineral surface are different from the free ions. The surface atom is in a semi-constrained state, of which properties are related to the property and the coordination structure of surrounding atoms. For example, the iron in hematite is highly ionic whereas the iron in pyrite is strongly covalent. Secondly, thionocarbamate collectors represented by Z-200 (O-isopropyl-N-ethyl thionocarbamate) do not have ionizable functional groups in the molecular structure. Thus, the interactions between Z-200 and metal ions are typical coordination. In addition, water molecules, as a flotation medium, are electrically neutral. Thus, the interaction between water molecules and metal ions is also coordination. This chapter will discuss the coordination characteristics of mineral crystals, reagent molecules and the interaction between them.
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Chapter 3. Geometry Principles of Coordination on Mineral Surface
Metal ions on mineral surfaces are in a semi-constrained state. This indicates semi-constrained metal ions are confined by surrounding atoms, in terms of spatial structure, as well as properties. The constraint affects the interaction between metal ions and reagent molecules, also known as steric hindrance. The spatial geometry of mineral surfaces is the physical basis of the interaction between flotation reagents and metal ions. In this chapter, valence bond theory and the close-packing principle are employed to investigate the geometry of the interaction between mineral surfaces and reagent molecules.
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Chapter 4. Coordination of Flotation Reagents with Metal Ions on Mineral Surfaces
According to the coordination model of mineral flotation, the interaction between the flotation reagent and the mineral surface can be divided into two categories: one is typical coordination, that is, the reagent molecule provides electron pairs to the unoccupied orbital of metal ions on mineral surface; the other is π-backbonding, that is, the surface metal ion donates π electron pairs to the reagent π orbitals. In essence, the reaction of flotation reagents with minerals is an interaction between orbitals and electrons. For typical coordination, the electron pair provided by the reagent can be either a σ electron pair or a π electron pair; for π-backbonding, the electron pair donated by the metal ion can only be a π electron pair, as the σ electron is relatively localized and cannot extend to the ligand orbital. Therefore, π-backbonding exhibits selectivity.
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Chapter 5. Influence of Crystal Field Stabilization Energy on Interaction of Flotation Reagents
In coordination chemistry, the field of ligands leads to the splitting of metal d orbitals, with electrons redistributed into the split d orbitals. The energy drop generated by electron rearrangement is called crystal field stabilization energy (CFSE), which plays a crucial role in the stability of complexes. In addition, the value of CFSE generally ranges from tens to hundreds of kJ/mol, which is in the scope of the adsorption energy of flotation reagents on mineral surfaces. Hence, CFSE will greatly influence the adsorption and desorption of flotation reagents. This chapter discusses the effect of CFSE on the adsorption of reagents on mineral surfaces.
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Chapter 6. Symmetry Matching Between Reagent Molecules and Mineral Surface Orbitals
The wave function |ψ|2 in the Schrodinger equation represents the probability density of electrons appearing somewhere outside the nucleus. The electron cloud is associated with the likelihood of electrons present somewhere outside the nucleus, namely, probability density. Extranuclear electrons exhibit different motions, with corresponding wave functions and probability density, such as ψ1s, ψ2s, ψ2p and
1s|2, |ψ2s|2, |ψ2p|2, respectively. Since those wave functions as well as probability density vary, electrons in different states have various electron cloud distributions, denoted by s, p, d, and f among others.
Jianhua Chen
Coordination Principle of Minerals Flotation
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Jianhua Chen
Springer Nature Singapore
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