Molybdenum ore is oxidized and calcined to form molybdenum trioxide (MoO 3 ). The oxidation process is a strong exothermic reaction, and the gas-solid heterogeneous reaction process involved is complicated. In the past, it was generally believed that MoS 2 was directly oxidized to MoO 3 ; while MoO 2 was only a product of secondary reaction of MoS 3 with MoO 3 , and MoO 2 was further oxidized to MoO 3 :
MoS 2 + 3 | 1 | O 2 → | MoO 3 + 2SO 2 ↑ |
2 |
MoO 2 + 6MoO 3 → 7MoO 2 + 2SO 2
MoS 2 + | 1 | O 2 → | MoO 3 |
2 |
PR Amman and TAost studied the oxidation kinetics of molybdenite powder at 525-635 °C. They believed that the oxidation of molybdenite to molybdenum trioxide was carried out in two stages: the first stage, Molybdenum ore is first oxidized to a low-oxide oxide of molybdenum - MoO 2 :
MoO 2 + 3O 2 → MoO 2 + 2SO 2 ↑ △S=—905kJ/mol
The SO 2 generated at this stage accounts for 75 to 80% of the total production. In the second stage, MoO 2 is reoxidized, and after undergoing a series of intermediate oxidation processes, it finally produces MoO 3 :
MoS 2 + | 1 | O 2 → | MoO 3 |
2 |
A. r. Robarlev's thermal analysis showed that the synthesis of the MoS 2 oxidation process was also confirmed.
Chu Shaobin et al. analyzed the oxidation process of molybdenite by thermal analysis combined with X-ray diffraction. It also confirmed that MoS 2 →MoO 3 is a series of low-oxides (MoO 3 , MO 4 O 11 ...) that have undergone molybdenum. The process of reacting to high valence oxides.
Chu Shaobin also measured the phase and its change of molybdenum at different oxidation temperatures. The oxidation of pure minerals (MoS 2 lubricant) and impure molybdenum concentrates is shown in Table 1.
Table 1 X-ray analysis of molybdenum oxide products 1
Sample and temperature (°C) Phase | MoS 2 lubricant | Containing MoS 2 98% | Molybdenum concentrate (including MoS 2 78.1%) |
360 430 | 540 670 | 460 560 670 | |
MoS 2 MoO 2 Mo 4 O 11 MoO 3 | Strong Very weak | in in in Medium strong | Very strong and weak Weak Medium Weak |
1 oxidizing atmosphere Air: oxygen = 1:7; heating rate: 7.4 ° C / min.
Obviously, the molybdenite oxidation has undergone a phase from low to high, and molybdenum trioxide is the high temperature final oxidation product of molybdenite. The table also shows that in the calcined material, the purity of the molybdenite is different, the oxidation rate is different, and the purity decreases and the oxidation rate decreases.
VC Vineall and A. Taylor also studied the effects of molybdenum fineness, ambient temperature, and calcination time on oxidation rate (see Table 2 and Table 3).
Obviously, the finer the molybdenum ore, the higher the calcination temperature and the longer the roasting time, the more the molybdenum oxide is oxidized.
There are many factors affecting molybdenum ore oxidation. In the mixed product after oxidation, the reaction of MoO 2 to MoO 3 is accelerated after the MoS 2 content is lowered to 15% or less. The oxidation is sufficient, the oxidizing atmosphere and the oxygen content are to be trained, and the residual oxygen concentration is reduced to 50%, and the amount of MoO 3 is reduced. When the oxygen concentration reaches 400%, MoO 3 is formed rapidly. [next]
Molybdenite lattice isomorphous entrainment rhenium, generally in the late luminance molybdenite oxidation before the oxidation. The newly formed Re 2 O 7 is extremely vaporizable and volatilized. Generally, when the residual sulfur is 4 to 6%, when the residual amount of MoS 2 is 0.2%, more than 90% of the antimony is oxidized and vaporized.
Table 2 Effect of temperature on oxidation of molybdenite (1.7μm)
time (h) temperature (°C) | 1 | 3 | 6 | 18 | twenty four | 48 | 72 | 76 |
250 | <0.1 | <0.1 | 0.1< | <0.1 | 0.2 | 0.4 | 0.5 | 0.6 |
300 | 1.0 | 3.2 | 5.0 | 15.0 | 19.5 | 24.3 | 26.0 | 27.3 |
400 | 2.9 | 12.1 | 16.0 | 22.0 | 24.5 | 27.9 | 37.0 | 46.0 |
500 | 57.2 | 74.5 | 79.3 | 80.2 | 84.7 | 94.7 | 96.0 | 96.5 |
Table 3 Effect of particle size on oxidation of molybdenite (400 ° C)
time (h) temperature (°C) | 1 | 3 | 6 | 18 | twenty four | 48 | 72 | 76 |
4.2 | <0.1 | 4.0 | 5.8 | 10.4 | 17.4 | 22.0 | 30.1 | 38.2 |
1.7 | 2.9 | 12.1 | 16.0 | 20.5 | 24.5 | 27.9 | 37.0 | 46.0 |
0.66 | 48.0 | 55.0 | 62.3 | 69.8 | 84.4 | 85.6 | 86.9 | 89.0 |
What are the similarities and differences between the “face†and “edge†oxidation of molybdenum ore during roasting? Xing Yongqing used X-ray diffraction to determine the difference in oxidation rate of each molybdenum fracture surface during oxygenation roasting. The [001] surface oxidation rate is less than 20% at 250 ° C, and [100] has exceeded 60%. The other five facet oxidation rates are somewhere in between (see Figure 1).
If it is not oxidized by oxygen, it is heated to 100~300 °C, and [001] still has no obvious oxidation.
Xing Yongqing also used X-ray diffraction to determine the difference between the "face" and "edge" oxidation rates of molybdenum in sodium hypochlorite (see Table 4).
Fig.1 Comparison of oxidation rates of different fracture surfaces of molybdenite
Table 4 hui leach rate comparison of different crystal faces molybdenum â‘
Face type | Planes | Leaching speed (mg·cm - 2 ·min -1 ) | proportion |
surface edge | [001] [100] | 0.56×10 -3 2.43×10 -3 | 1 4.34 |
1 Test conditions: 25 ° C, 0.6 mol NaClO; 5 test average
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