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As the oxidation time and temperature increase, the contact angle of molybdenite decreases. The oxide formed by low-temperature calcination can be removed by washing with water, and the oxide formed by high-temperature calcination cannot be removed by washing with water, and it can be removed by KOH alkali solution. Obviously, the low temperature oxide is about MoO 2 or MoO 2.5 which can fall on water, and the high temperature oxide is the acid anhydride MoO 3 which is insoluble in water and soluble in the KOH alkali solution.
Fig.1 Relationship between ξ-potential and pH of different molybdenum oxides
Figure 2 Molybdenum floatability and ξ-potential versus PH
When the molybdenite sample is leached with a 0.1 mol/L KOH alkali solution, after removing the oxide coating layer, the absolute value of the ξ-potential is small in an acidic medium having a lower pH value, indicating that the isoelectric point pH is <3.0. . RM Hoover and D. Malhotra divide the ξ-pH curve into three segments: the acidic region, the ξ-potential is negative, and the absolute value is small; the neutral region ξ-potential is also negative, and The pH does not change much; the alkaline zone ξ-potential position is still negative, and the absolute value is large. According to S. Chand (Fig. 3, 2) and others, the ξ-potential of the alkaline region does not change with pH. However, as a result of the RM Hoover measurement, the bismuth-potential of the molybdenite in the alkaline zone plummeted with an increase in pH (Fig. 3, 1). This may be related to the conditions of the assay (see Figure 3).
Fig. 3 Relationship between bismuth-potential and pH of molybdenite in water
Figure 4 ξ-potential and molybdenum recovery in different media
Fig. 5 Effect of PH on the recovery rate of yttrium-potential molybdenum in different media
Figure 6 Effect of molybdenum oxide oxidation rate on flotation recovery
After studying different Jinduicheng molybdenum ore, the Shenyang Institute of Mining and Metallurgy found that for molybdenum ore with an oxidation rate of only 1.47%, the recovery rate of molybdenum from flotation can reach 99.3%; the oxidation rate is 20.96%, and the molybdenum ore in the crush zone is crushed. The recovery rate of molybdenum flotation is only 68.65%. The molybdenum recovery rates differ by more than 30%, as shown in Table 2 (flotation conditions are the same).
Obviously, the effect of molybdenite oxidation is consistent with the effect of adding MoO 4 2- ions in the flotation medium, further confirming that Chand et al. speculated that there is HMoO 4 - or MoO 4 2 on the "edge" of the molybdenite in the slurry. - Ions are present. [next]
Fig. 7 Effect of electrolyte on bismuth-potential of molybdenite
Figure 8 Effect of calcium ion on recovery of molybdenite
Molybdenum oxide oxidation and floatability-molybdenite oxidation and contact angle, ξ-potential, floatability
Among MoO 2 , MoO 3 and transition oxides (MoO 2.5~3 ) formed by molybdenite oxidation, MoO 3 is an acid anhydride. It is soluble in the KOH alkaline solution, and the remaining various oxides are alkaline oxides.
The effect of oxidation on the contact angle of molybdenite is shown in Table 1, which is the average value after multiple measurements.
Table 1 Effect of oxidation on the contact angle of molybdenite
Oxidation condition
Contact angle (degrees)
Time (h)
Temperature (°C)
After oxidation
After washing
After KOH washing
1
300
63
75
1
350
67
68
2
350
65
66
68
3
350
74
75
75
1
400
62
80
80
2
400
57
70
70
1
450
66
71
2
450
54
65
76
3
450
49
63
67
1
500
53
59
78
2
500
46
66
81
3
500
30
60
73
1
500
35
49
71
Not oxidized
80
80
80
The oxidation products are different, and the ξ-potential changes with pH. The relationship between MoO 2 and MoO 3 ξ-potential is shown in Fig. 1.
It can be seen from the figure that the ξ-potential of MoO 2 does not change due to the change of pH; while the ξ-potential of MoO 3 increases with the increase of pH, the absolute value of ξ-potential decreases sharply. They differ from the MoS 2 in the aqueous medium in the ξ-potential and pH changes.
S. Chand and DW Fuerstinau studied the effect of oxidation on the zeta potential and recovery of molybdenite. Due to the oxide coating, molybdenum ore in the acidic medium (especially pH<4) has a high absolute value of ξ-potential and low flotation recovery, which may be related to the presence of molybdenum oxide on the mineral surface. The pH value increases, the absolute value of the ξ-potential decreases, and the molybdenum recovery rate increases. In alkaline media, the absolute value of the bismuth-potential of molybdenite is also large, and the recovery rate of molybdenum flotation is also low (see Figure 2), which may be caused by adsorption of MoO 4 2 - or OH - ions.
(1×10 -3 mol/L KCl solution)
It can also be seen from the above figure that the absolute value of the ξ-potential decreases with the increase of the "face ratio" of the molybdenum ore. [next]
Their research proves that the recovery rate of molybdenum ore varies with ξ-potential, and its recovery is highest when the absolute value of ξ-potential is the smallest (see Figure 4).
It can be seen from the figure that as long as the zeta potential is the same, the recovery rate of molybdenite will not vary from medium to medium. However, the bismuth-potentials of molybdenite in different media are different.
S. Chand et al. determined the change of ξ-potential with pH and the effect on molybdenum recovery in molybdenite in KCl or KCl + Na 2 MoO 4 medium (see Figure 5).
Obviously, when NaMo 2 O 4 was added to the flotation medium, the absolute value of the bismuth-potential of the molybdenum ore was significantly increased, and the recovery rate of the molybdenite was significantly reduced, which was consistent with the surface oxidation of the molybdenite. This is related to the increase of MoO 4 2- ion adsorption on the surface of molybdenite.
The production practice of molybdenum beneficiation found that oxidation has a great influence on the recovery rate of molybdenum ore. When Eanxaщ treated the East Cohenrad molybdenum mine, 60% of the molybdenum in the tailings was present as an oxidized molybdenum-calcium deposit. Yang Jiazhang also found the same result. There are reports on the production of the gold heap molybdenum plant and the Yangjiazhangzi molybdenum plant. With the increase of the oxidation rate of molybdenum ore, the recovery rate of molybdenum flotation is significantly reduced (see Figure 6).
1—Yang Jiazhangzi; 2—Jinducheng
Table 2 Effect of oxidation rate on molybdenum recovery rate (Jinducheng ore)
Ore type
Molybdenum oxidation rate (%)
Molybdenum recovery rate (%)
Granite porphyry
Black mica
Green mud and petrochemical Anshan shale (crushing belt)
1.47
4.8
20.96
99.3
90.04
68.65
Other ions have an effect on the ξ-potential and molybdenum recovery of molybdenite. More important is calcium ion (Ca 2+ ).
Calcium ions have a great influence on the molybdenum surface charge and flotation yield, but they are opposite to Na 2 MoO 4 . Ca 2+ ions can reduce the absolute value of the ξ-potential or even reverse (see Figures 7 and 8).
It can be seen from the figure that when the concentration of CaCl 2 in the solution is greater than 10 -3 mol/L, the absolute value of the ξ-potential of the molybdenum ore is significantly reduced, which is larger and faster than the surface of the molybdenum ore washed with the KOH solution. The concentration of CaCl 2 increases to a certain extent, and the potential also has a zero point (PH<3), or even a reverse, and the ξ-potential is positively charged. At this time, the molybdenum flotation recovery rate also changes with the ξ-potential change, and a maximum value occurs at zero.
JM Wei (Wie) and DW Fuerstinau also found that the absolute value of the bismuth-potential of the molybdenite after the addition of dextrin in the medium also decreased (zero point pH<3.0), but the molybdenum floatability is not only Without rising, it also dropped sharply and the molybdenite was suppressed. This may be because the non-ionic dextrin is not only adsorbed on the molybdenum ore, but the MoO 4 2- or HMoO 4 - is reduced; it can also be adsorbed on the surface, masking the hydrophobicity of the surface and inhibiting it.
In the flotation of polymetallic sulphide ore, in order to achieve good sorting effect, in many cases, depending on the degree of oxidation of the mineral surface, their separation is strictly controlled by the pulp redox potential (Eh). In order to separate the molybdenum ore and non-molybdenum sulfide impurities, the pulp oxidation-reduction potential (Eh) must be kept within the appropriate range (see Table 3).
Table 3 Sulfide mineral separation and oxidation reduction potential
Sulfide mineral
Oxidation reduction potential (Eh) (V)
Floating up
inhibition
Anaerobic
Aerobic
Yellow copper ore
Molybdenite
+0.15~+0.41
Sphalerite
Molybdenite
+0.13
Pyrite
Molybdenite
+0.15~+0.41
Molybdenite
Chalcopyrite
+0.15~+0.41
Molybdenite
Galena
+0.15
Molybdenite
Sphalerite
+0.13
Molybdenite
Pyrite
+0.15~+0.41