Structure and properties of floating phase solid phase

1. The crystal structure of minerals

The mineral surface properties are the main factors determining the ease of mineral attachment to bubbles (also known as floatability), and the main factors affecting the mineral surface properties are the chemical composition and structure of minerals. All minerals are linked by a certain bond (force) of ions, atoms, molecules and other particles. These particles can be arranged regularly or irregularly within the mineral. When the rules are arranged, they are called crystals, and when they are irregularly arranged, they are called amorphous. It is precisely because different minerals have different crystal structures that they have different surface properties and floatability.

Figure 4-6-3 Saturated health of the surface of the crystal

The surface of the mineral after fragmentation and dissociation has a certain "surface energy" due to the destruction of the crystal, and the surface has the remaining unsaturated bond energy. As shown in Figure 4-6-3, a cubic particle, the internal force of the lattice, and the force of the surrounding particle (the bond force) are in a state of saturation equilibrium. Therefore, the bond between the particle and the surrounding particle is called a saturated bond. The three particles B, C, and D of the layer respectively have one, two, and three unsaturated bonds pointing to the space. These unsaturated bonds pointing to the space have the property of attracting surrounding materials to satisfy or compensate for the surface unsaturated energy. The difference in nature and strength plays a decisive role in the adsorption of mineral surfaces with water, with flotation agents, with bubbles, with ions and molecules in water, and the ion, atom or molecule of the mineral surface is not saturated. The surface bond energy characteristics and size are determined by the nature of the particle inside the bond, the bond energy characteristics and the fracture surface characteristics.

In the crystal structure, the mass points are arranged in the most symmetrical form in the most compact manner. The interaction force between the particles (key force) makes the particles close to each other. When a certain distance is reached, the repulsive force is generated due to the insertion of the electron cloud. The particle distance does not change generally. The particle size of the crystal lattice is different, the bond strength is different, and the crystal structure type is different, which determines the surface floatability of the fracture surface after fracture. From the perspective of flotation, How to understand the relationship between the internal structure of a crystal and its surface properties from complex and diverse crystal structures, the key is to understand the nature and strength of the particles inside the crystal, and secondly to understand which part of the mineral is broken, and then what kind of properties of the surface are generally clear It is.

In crystal chemistry, mineral crystals are classified into four types according to the nature of the internal particles and bonds of the crystal: ionic crystals, atomic crystals (covalent crystals), molecular crystals, and metal crystals. Figure 4-6-4 lists six typical mineral crystals. Lattice structure and possible fracture surface (dashed line).

(1) Ionic crystal

The ionic crystal is composed of an anion and a cation. The anions and cations are alternately arranged on the lattice node, and they are combined by electrostatic attraction. The bond formed by this bonding force is called an ionic bond. When the mineral breaks, it breaks along the ion interface, and the surface exposed after the fracture is an unsaturated ionic bond. Since the electron clouds of anion and cation can be approximated as spherical symmetry, the ionic bond has no directionality, and generally has a high coordination number, a large hardness, and a strong polarity. Mineral crystal having ionic bonds are typical rock salt NaCl, fluorite CaF2, sphalerite ZnS, TiO 2 rutile and calcite.

(2) Atomic crystal

Atomic crystals are composed of atoms. Arranged on the lattice nodes are neutral atoms that are joined together by a common pair of electrons. This bond is called an atomic bond or a covalent bond. The covalent bond has directionality and saturation, and the general coordination number is small. Therefore, the crystal structure is much tighter than the ion lattice. There is no free electron in the atomic lattice, so the crystal is a poor conductor; when the lattice breaks, the covalent bond must be destroyed, so the polarity is strong. The covalent bond bonding strength is higher than the ion bond, so the hardness of the crystal is higher than that of the ionic crystal. Crystals that are simply covalently bonded in nature are rare in minerals. The most typical ones are diamonds . Most crystals are mixed bonds of ionic bonds and covalent bonds, such as quartz SiO2 and cassiterite SnO2.

(3) Molecular crystals

The molecules in the crystal lattice of a molecular crystal are the basic unit of structure. The molecules are connected by extremely weak van der Waals forces (ie, intermolecular forces) or molecular bonds. When the lattice breaks, the weak molecular bonds are exposed, and the intermolecular gravitation and molecules The inverse of the distance between the 7th power. The characteristics of the molecular crystal: there is no free electron movement between the molecules, so it is a poor conductor. The molecular bonds that make up the crystal are weak, so the hardness is small, and the affinity for water is weak. Most layered structural minerals The layers are often connected by weak molecular bonds, such as graphite and molybdenite .

The above are three typical crystal structures, in addition to metal crystals. The metal crystal is a metal cation at the junction, surrounded by free-moving electrons, and the cation interacts with the public electron to form a metal bond. Metal bonds are non-directional and saturated, with the largest coordination number and the tightest packing. After the lattice breaks, the fracture surface is a strong unsaturated bond. Natural gold and natural copper belong to this category. In fact, natural minerals are rarely composed of a single bond, and common minerals are mostly mixed bonds or transitional bond crystals. For example, sulfide minerals and oxidized minerals are mostly ion-covalent bonds or ions-covalently-metal bonds; hydroxides and oxygen-containing salts are mostly ion-molecular chains and ions-covalent bonds. For example, the rutile Ti--O is a bond type which is mainly a transition from a ionic bond to a covalent bond, but the ionic bond is dominant, so it is classified as an ionic crystal. Crystals composed of multiple elements often have several bonds of different nature. In the crystal composed of the same element, sometimes there are different bonds. Therefore, the internal bonding properties of specific minerals should be studied in detail.

From the fracture surface, if the force between fluorite Ca2+ and F- is weak, it is easy to break along this interface. Heavy gold stone and calcite each contain groups SO42-, CO32-, the inside of the group are covalent bonds, the metal ions and the group are ionic bonds, and the lattice often breaks along the ion interface. Graphite and molybdenite have a typical layered structure. The carbon atoms in the graphite are 1.32 X10-10 m apart from each other in the same layer. The distance between the layers is 3.39 X10-10 m, so it is easy to break along the layers.

2. The relationship between the surface bond energy, polarity and natural floatability of minerals

When the mineral lattice is broken, the surface properties of the mineral are different due to the different bond types exposed to the surface. The laws are as follows:

1 When the fracture surface is dominated by ionic bonds, the surface unsaturated bond has a strong electrostatic attraction and is a strong unsaturated bond.

2 When the fracture surface is dominated by covalent bonds, the surface unsaturated bonds are mostly atomic bonds. These types of surfaces have strong electrostatic or dipolar effects and are also strongly unsaturated.

3 When the fracture surface is dominated by molecular bonds, the surface unsaturated bonds are mostly weak bonds. For example, the mineral surface is mainly oriented and induced, and this weak bond is stronger than the weak bond mainly composed of dispersive force.

The difference in mineral surface bond energy has a great influence on the floatability of minerals. This is the "key energy factor" that determines the floatability of minerals. When the mineral surface has strong ionic bonds and covalent bonds, its degree of unsaturation is high, and the mineral surface has strong polarity and chemical activity, which has great attraction to polar water molecules, and the mineral surface shows Hydrophilic, called a hydrophilic surface, where the mineral is poorly floatable. When the surface of the mineral is a weak molecular bond, its degree of unsaturation is low, the polarity and chemical activity of the mineral surface are weak, and the attraction to polar water molecules is small. The surface of the mineral is hydrophobic, called hydrophobic. Sexual surface, the mineral at this time is good floatability.

There are fewer natural floatable minerals in nature. Generally, crystals with molecular bonds, such as paraffin and sulfur, have good natural floatability; crystals with flake or layer structure, such as graphite and talc , have moderate natural floatability; most other minerals have strong hydrophilicity. Sexuality, its natural floatability is poor. Most sulfide minerals, oxidized minerals, silicate minerals, etc. are strongly hydrophilic. To achieve the flotation of various minerals is mainly to artificially change the floatability of minerals. To artificially change the floatability, the most effective method is to adjust the adsorption of different flotation agents on different mineral surfaces. If the collector is adsorbed on the surface of the mineral, it has a polarity at one end, facing the mineral surface, which can satisfy the unsaturated bond energy of the mineral surface, and the other end is non-polar outward, which causes the artificial surface of the mineral to be "floating". It is as hydrophobic as paraffin or hydrocarbon oil.

3. Mineral surface unevenness and floatability

Flotation often finds that the floatability of the same mineral is quite different. The reason is that the actual minerals are rarely ideal for pure minerals. They have many physical inhomogeneities, chemical inhomogeneities, and physical-chemical heterogeneities (semiconductors), which cause surface non-uniformity and make floatability. Various changes have taken place. Mineral surface heterogeneity is the result of a variety of causes, but mainly physical and chemical.

[1) Physical inhomogeneity of minerals

Typical intact mineral crystals are rare and have a variety of structural disadvantages. During the formation and experience of mineral deposits, the macroscopic heterogeneity of the mineral surface and the crystals produce various defects, vacancies, inclusions, misalignment and even mosaic phenomena, collectively referred to as physical inhomogeneity.

Defects in actual minerals are common: there are anion vacancies, or interstitial cations; there are cation vacancies, or interstitial anions. In the first two cases, the metal cations of the mineral are excessive; in the latter two cases, the non-metal anions are excessive. The dislocation of the crystal is an unconformity of the crystal, which is a phenomenon in which the crystal is deformed by an external force or slips along a crystal plane or the crystal lattice is disordered. The actual crystal is often inlaid with many different orientations of crystallites, forming a so-called "mosaic phenomenon". The "microdefects" of actual crystals cause mineral inhomogeneities and have a direct impact on the floatability of minerals.

Natural minerals, such as sulphide galena, chalcopyrite, pyrite, have semiconductor properties. The N-type semiconductor is electrically conductive, and the P-type semiconductor is electrically conductive by holes. The semiconducting properties of minerals are mainly affected by impurities contained in the crystal. When an anion vacancy or entrained interstitial cation is present in the crystal, an N-type semiconductor is formed; when a cation vacancy or an entrained interstitial anion is present in the crystal, a P-type semiconductor is formed due to the presence of a "positive hole". Generally, sulfide minerals belong to N-type semiconductors before they interact with oxygen, and are electrically conductive. After the action with oxygen, the concentration of free holes on the surface of the mineral increases, and it can be converted into a P-type semiconductor. After the sulfide mineral adsorbs oxygen into a P-type semiconductor, the energy level of the adsorbent xanthogen anion is increased, and the sulfide mineral is easy to realize flotation.

There are often fine voids and cracks in the actual mineral surface. Different minerals differ greatly in the specific surface area of ​​minerals due to the difference in internal voids and cracks. For example, the specific surface area of ​​quartz with a particle size of 147 ~ 208μm is 3000 cm2 / g; the specific surface area of ​​soft coal is 155000 cm2 / g, and the specific surface area of ​​bituminous coal with the same particle size is as high as 1500000 cm2 / g.

(2) Surface chemical heterogeneity of minerals

In actual minerals, the bonding of various elements is not as simple as the mineral chemical formula, and often contains many non-metering compositions of non-chemical molecular formula. Cu, Pb, Zn, Hg, and Ag have strong bonding strength to S and have conditions for forming sulfides, and thus sulfide minerals of such metals are often formed. However, As, Sb and Bi form a sulfur-containing mineral in the form of a complex sulfur anion with Cu+, Pb+, Ag+, etc., and may also be in the form of AsS, As2S3, Bi2S3 or the like. The properties of Se and Te are similar to those of S, so they are often mixed into various sulfide minerals (such as pyrite and pyrrhotite) in a similar manner.

Among the sulfide minerals, some non-metering inclusions are often of great importance. Such as nickel in pyrrhotite, gold in pyrite and chalcopyrite, silver in galena, and the like. Mastering the law of metal symbiosis and understanding the relationship between chemical heterogeneity and floatability of minerals has great practical significance for comprehensive recovery of useful components and improvement of beneficiation effect.

(3) Mineral surface unevenness and floatability

The unevenness of the mineral surface directly affects the mineral surface and the action of water and chemicals. In modern times, the use of tracer atoms to study the effects of chemicals and minerals has shown that the distribution of agents on mineral surfaces is uneven and often spotted. There is no adsorbent at one site, and several or even dozens of molecular thicknesses are adsorbed at another site. The active part that interacts with the agent is called the activation center. It is generally believed that the action of the agent and mineral begins with the activation center and then extends outward. In summary, due to the non-uniformity of the mineral surface, the difference in flotation properties of various regions of the mineral surface is caused.

Figure 4-6-5 Schematic diagram of the defects of galena (PbS) and the reaction of xanthate ions

Figure 4-6-5 is a schematic diagram of the reaction of a physical inhomogeneity of minerals (lattice defects, cationic vacancies) with a flotation collector, xanthate. Due to the cation vacancy, the valence and charge state are out of balance. The state of charge near the vacancy makes the sulfide ion have a strong attraction to electrons, while the cation forms a higher charge state and more free outer orbits. The defect causes the crystal to become P-type, thus forming a strong adsorption center for xanthogen (anion) ions. Conversely, if the defect causes the crystal to be N-type (anion vacancy or cation gap), it is not conducive to the adsorption of xanthogen (anion) ions.

In the ideal galena crystal, most of Pb-S is a covalent bond, and only a small amount is an ionic bond, and its internal valence charge is balanced, so the adsorption force to external ions is not strong. Defects cause the internal valence charge to be unbalanced. Thus, surface activity is formed, which is one of the reasons why the type and concentration of defects (number of defects) directly affect the floatability and make different galenas have different floatability. For sulfide ore, the defects affect the redox state and the interface electrochemical reaction in addition to the adsorption of the collector.

FIG 4-6-6 chemical relationship of the floating unevenness may apatite. As mentioned earlier, the floatability anomalies of many sulfide minerals such as galena, sphalerite, chalcopyrite, and pyrite are related to the irregularity of chemical composition. For example, sphalerite (ZnS) of different deposits have different colors and are associated with impurities contained therein. Green, gray, and yellow-green are caused by divalent iron ions; dark brown, tan, and yellowish brown are caused by the coloration properties of zinc ions themselves and the substitution of isomorphous copper ions. As the iron ions in the zinc blende crystal lattice increase, the color changes from shallow to deep. When the iron ion content reaches about 20%, or even reaches 26%, the sphalerite becomes black and is called high-iron sphalerite. The floatation anomalies of various colors of sphalerite are extremely obvious. Generally, impurities such as Ag, Cu and Pb can improve the floatability of sphalerite, while other impurities, especially iron, reduce the floatability of sphalerite and affect the quality of zinc concentrate. The substitution of impurities alternates, causing changes in ion bond distribution, lattice parameters, crystal surface energy, and semiconductor electrical properties in sphalerite, resulting in extensive chemical inhomogeneity of sphalerite.

The influence of mineral chemical composition irregularities on non-sulfurized ore is also obvious. For example, there are two kinds of apatite: 0H apatite and F apatite. Their components are Ca5(PO4)3OH and Ca5(PO4)3F, respectively, of which Ca2+ can be replaced by the following components: Mn, Sr, Mg, Na, K, Cu, Sn, Pb and rare earth elements; PO43- It is substituted by SO42-, SiO44-, CO32-, AsO43-, VO42- and CrO42-, etc., and F- can be substituted by 0H-.C1-. These substitutions give the apatite a wide range of chemical inhomogeneities and thus different floatability. As shown in Figure 4-6-7, the apatite of different components and origins has great differences in floatability.

　

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