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1. Types of fracture surface In the grinding operation, molybdenite decreases with particle size and the specific surface area increases (see Table 1). The mechanical characteristics of the anisotropy of molybdenite crystals make it produce seven kinds of fracture surfaces with different properties during grinding: [001], [100], [101], [103], [104], [105] [112]. Table 1 Specific surface changes of molybdenite with different particle sizes

Screen order

Size (μm)

Specific surface area (m 2 /g)

—60 +100 —100 +150 —150 +200 —200 +400 —400

—246 +147 —147 +107 —107 +74 —74 +38 —38

0.60 0.66 0.70 0.74 1.59

{001} is the rupture surface of the molybdenum crystal along the interlayer cleavage. At this time, the lower sulphur surface mesh of the upper interlayer is separated from the upper sulphur surface mesh of the next interlayer to maintain molecular bond breakage therebetween. The face consists of sulfur atoms on the same sulphur surface network, which are tightly bound together by non-polar covalent bonds. RM Hoover et al. refer to the {001} fracture surface as the "surface" or "face". Obviously, the "face" shows typical non-polar features. According to the Fowkeg interfacial tension concept, the "face" is hydrophobic. {100} is the rupture surface of the molybdenum crystal along the [001] plane. The substance on the surface has not only a sulfur atom but also a molybdenum atom, forming a composition of -S-Mo-SS-Mo-S-, and the ratio of molybdenum to sulfur atom is 0.5:1 (while {001} is 0:1). On {100}, molybdenum and sulfur are ionically bonded, and sulfur and sulfur are linked by molecular bonds. Grinding and breaking chemical bonds is the same as the net surface covalent bond between the sulfur and sulfur, or a metallic bond between molybdenum and molybdenum. These cleavage bonds are much stronger than the molecular bonds that break on {001}. Therefore, cleavage along {100} is much more difficult than cleavage along {001}. The five rupture planes {101}, {103}, {104}, {105}, {112} are rupture planes that intersect the {001}. The surface composition of the material is sulfur and molybdenum, and the molybdenum/sulfur is between {001} and {100} (between 0:1 and 0.5:1). The chemical bonds between the atoms on the fracture surface and the chemical bonds that have been broken include the four bonds present in the molybdenum crystal. These five fracture surfaces are similar to {100}, and all reflect the characteristics of the polar fracture surface. The non-polar surface characteristics of {001} are quite different. To this end, RM Hoover referred to these six polar fracture surfaces as “facets” or “edges”. The molecular bonds of both van der Waals bonds are broken, forming a non-polar, hydrophobic “surface”. "; There are also ionic or covalent bond cleavage, forming a polar, hydrophilic "facet". D. w. Fuerstenau refers to such combinations as "heteropolar surfaces". 2, "face" and "edge" properties (1) Strength anisotropy: To form "edges", it is necessary to break the bond ionic valence, covalent bond and metal bond, which is obviously difficult. The generation of "face", as long as a small shear force is applied, can break the molecular bond between them to form a good slip surface. Kennecott Copper Company uses the anisotropy of molybdenum strength to control the grinding through three stages. The molybdenum ore can only form large and thin sheets; while other impurity mineral anisotropies are not obvious. The fine mud is formed in the grinding, and then the molybdenite is enriched to a high purity (MoS2 ≥ 97%) by sieving. The solid lubrication field also utilizes molybdenum strength anisotropy, which is widely used as a solid lubricating material. (2) Surface energy anisotropy: According to Japan’s Nishimura, the surface energy on the “face” of the ZH-type molybdenite is 2.4×10-2J/M2. The surface energy on the "rib" is 0.7 J/m2. The microhardness on the "face" was 3.136 × 108 Pa, and the "edge" was 8.82 × l09 Pa. It can be seen that the surface energy of the "face" is less than 5% of the surface energy of the "edge". It constitutes a high-energy "edge" and a low-energy "face". According to the energy similarity principle of bonding, it is difficult to adsorb polar and high-energy water on the "face", and the surface is hydrophobic. "Ring" is easy to adsorb water and is hydrophilic. When it is combined with a non-polar, low-energy hydrocarbon oil (3×10-2J/m2), the “face” is more hydrophobic and more hydrophobic, while the “rib” is less likely to adsorb hydrocarbon oil. The state of water droplets captured by Chender on the “face” or “edge” of molybdenite shows the characteristics of “hydrophobic surface” and “hydrophilic edge”. (3) Oxidation rate anisotropy: The "face" and "rib" oxidation rates are different. After the molybdenum ore is heated at 250 ° C for one hour, the oxidation rate on the surface is less than 20%, and the oxidation of the "edge" has reached 60%. If oxygen is not applied, at 100~300 °C, the "edge" is obviously oxidized, while the "face" is not oxidized. When the molybdenum ore is soaked in 0.6 mol of sodium hypochlorite solution, the "face" leaching rate is less than one quarter of the "edge" leaching rate. At normal temperature and pressure, the molybdenum ore is in the space (4) ξ-potential, flotation yield and contact angle anisotropy: the molybdenite ξ-potential determined by Chandler, DW Furstenau and RM Hoover Relationship with PH, see Figure 1 and Figure 2, respectively.
Figure 1 Molybdenum ore - relationship with PH 1 - Hoover; 2 - Chand

Fig. 2 Relationship between molybdenum ore (KOH treated) ξ-potential molybdenum yield and pH

The upper curve is the result of RM Hoover's Claymax B grade molybdenum concentrate with lower grinding degree and higher surface roughness. The middle curve is the crushing of Chandler and DW Fuerstenau by roller machine. Out of -250 mesh, the surface is relatively large molybdenum ore. The lower curve is the molybdenum ore which is pulverized by jet mill and DW Fuerstinau with a small aspect ratio. Obviously, from the top three curves, the aspect ratio is gradually reduced, and the absolute value of the ξ-potential increases correspondingly, that is, the larger the rib ratio, the smaller the absolute value of the molybdenite ξ-potential. The generation of helium-potential negative value of molybdenum ore and the change of pH value, Chandler and DW Furstenau use ion exchange to explain the molybdenum ore deposit in the gas-water medium. The electric surface exists: MoO42- + H+←→HMoO4-equilibrium coefficient pK=5.95. Since the molybdenite surface has a negatively charged surface ion, its ξ-potential is negative. And balanced with H+ ions. It can be seen that there is a dependence between ξ-potential and pH; acidity increases, H+ ion concentration increases, equilibrium shifts to the right, charged ion HMoO4- increases, ξ-potential absolute value decreases; alkalinity enhances, H+ ion concentration decreases, balance Moving left, the charged ions are dominated by HMoO42-, and the absolute value of ξ-potential increases. This analysis is consistent with the measured results. In gas and water media, oxidation sometimes occurs on the ribs to form MoO42-, HMoO4-, MoO2+ ions; on the surface, almost no oxidation occurs. The molybdenite ξ-potential has some relationship with the flotation recovery rate, as shown in Figure 2-6: the higher the absolute value of ξ-potential, the lower the flotation recovery rate. JLG, Randolph, Forve, and Overbeck jointly lead to the "DL VO" theory based on the repulsion and attraction of colloidal particles. From this theory, unless the zeta potential is about -0.01 V (assuming a certain bubble potential is -0.055 V), flotation will not occur. This is inconsistent with the measured results of molybdenite. According to Figure 2, the measured ξ-potential molybdenum ore is theoretically calculated and should not rise. In fact, the recovery rate of molybdenite is not low. In contrast to this contradiction, Chandler and DW Fuerstenau believe that this is because the "face" and "edge" are not the same as the potential, and the "face" has a very small absolute value of -0.01V. It can meet the theoretical calculation of DLVO. On the "edge", the absolute value of the potential is very large. They believe that "edge" controls the ξ-potential of the test, so the absolute value of the ξ-potential is high; the "face" determines the flotation effect (of course, "edge" also has an effect); and the contact angle is mainly It is a measured value on the "face". Therefore, in the range of pH = 3 to 9, the molybdenite contact angle hardly changes due to pH. 3. Factors affecting the aspect ratio The surface ratio has a great influence on the molybdenum ore flotation. There are many factors affecting the aspect ratio in the molybdenite crushing process, including grinding grain size, grinding method, molybdenite ore, etc. Xing Yongqing uses X-ray diffraction analysis to different grades of molybdenite in Jinduicheng. The fracture surface was measured, see Figure 3. The results of Xing Yongqing's fracture surface measurement of molybdenum ore from different places are shown in Figure 4 and Table 2 and Table 3. From the above test results, Xing Yongqing proposed that the smaller the molybdenite grain size, the larger the “face ratio”. Obviously this conclusion and the traditional view: after the pulverization, the smaller the molybdenite grain size, the smaller the "face ratio". The molybdenum selection operation is to obtain high-quality molybdenum concentrate. The need for dissociation from the monomer is often high. The fineness of the US Claymax molybdenum concentrate is 80%-20μm; Canada Nidaco re-grinding The fineness is 50%~70%-71μm; the re-grinding degree of Jindengcheng First Selection Plant is 83%-25μm. Both are finer than the test sample. Obviously, for the micron-scale or fine-grained molybdenum ore, whether the "face-to-edge ratio" varies with the particle size is consistent with the above test law, and further research is needed.

Figure 3 Molybdenite grain size and fracture surface distribution (Golden heap city sample)

Fig.4 Distribution of molybdenum fracture surface of different origins and fineness Table 2 Grain size distribution of molybdenum concentrates from different regions

Granular grade Suichuan (production sample) Persimmon bamboo garden (production sample) Xinhua (small sample) Yang Jiazhangzi (production sample)
Yield(%) Grade (%Mo) Yield(%) Grade (%Mo) Yield(%) Grade (%Mo) Yield(%) Grade (%Mo)
+250 57.08 44.61 24.71 48.75 4.28 49.96 35.86 43.82
-250+320 5.28 5.59 4.42
-203+400 4.55 6.07 5.82
400- 33.13 50.91 63.63 52.82 95.72 52.49 53.90 42.34

Figure 3 Distribution of various fracture surfaces of molybdenite

Rupture surface Suichuan Persimmon garden Xinhua Yang Jiazhangzi
{001} 54.12 61.88 75.88 63.27
{100} 4.75 47.05 2.15 38.03 1.58 24.12 2.94 36.82
{101} 3.05 1.94 1.32 2.00
{103} 12.97 7.77 2.29 7.11
{104} 8.39 10.93 8.92 9.92
{105} 9.09 6.24 2.01 5.59
{112} 8.80 8.97 7.91 9.26
total 100.96 99.91 100 100.09
Degree of crystallization 1 (%) 100 80~90 40~70
Face ratio 1.2:1 1.6:1 3.2:1 1.7:1
1 When the production method, measurement conditions, and sample properties are basically the same, the best crystallization grade is the standard (100%), and the results are measured and estimated. Grinding methods also affect the size of the molybdenite "face ratio". After using scanning electron microscopy to observe the molybdenum ore crushed by the roller machine and the jet mill, Chaudeu pointed out that the shearing force-based roll machine crushed the molybdenite, the surface of the product was smooth and the level was clear; Molybdenum ore with a rough surface. The former product is larger than the "face ratio" of the latter product. There are still many factors that affect the aspect ratio, but they are less affected than the above.

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