By natural method, without destroying the means luminance molybdenum concentrate in structure and composition of molybdenum, removing only the mineral impurities mixed in the concentrate, the process to obtain natural lattice molybdenum disulfide product. Due to the different ways of removing impurities, the ore method, the leaching method, the beneficiation and leaching method can be separated.
1. Mineral processing method
The beneficiation method not only does the molybdenum ore have no phase transformation, but the impurity minerals do not need to be transformed by the phase. Common practices are:
Single flotation process: It utilizes the huge difference in natural floatability between molybdenum ore and impurity minerals, and is purified by multiple selective processes to produce high-purity molybdenum concentrate containing MoS 2 ≥97%. For example, the Beijing Tianhe Chemical Plant uses a flotation column, and the molybdenum concentrate is subjected to seven open-circuit flotation to obtain a molybdenum disulfide product containing 97% MoS 2 and 37% molybdenum recovery. For example, Salvador in Chile uses nine flotation processes to obtain molybdenum disulfide products containing about 97% MoS 2 and about 65% molybdenum recovery.
Controlled grinding-classification process: It utilizes the anisotropic mechanical properties of molybdenum ore, which is usually isotropically different from the impurity minerals. By controlling the grinding and grading, the impurity minerals are finely broken into the sieve, and the tablets are The molybdenite is difficult to pulverize and remains on the sieve for purification. For example, Canadian Molybdenum Co., Ltd. uses a four-roll mill to grade and obtain a small amount of high-purity products with a MoS 2 content of >97% and a large amount of medium ore for smelting. In another example, Kennecott uses a three-stage controlled grinding process to obtain a product with a MoS 2 content of 97% and a molybdenum recovery rate of 30.1%.
Although the above two beneficiation methods are simple in process and low in processing cost, the recovery rate of molybdenum products is too low (as mentioned above, the highest El Salvador is only 65%), resulting in high cost of molybdenum disulfide. The author has studied the new process of deactivation and strong floating, and basically solved the problem of low molybdenum recovery rate in the beneficiation method.
Deactivation-strong floatation process: In view of the poor selectivity of hydrocarbon oil non-polar collectors used in molybdenum beneficiation, the enrichment of about 3/4 of the amount of oil in the process is only 0.2%~0.8%. The surface of the molybdenum concentrate. When high-dose, poorly selective hydrocarbon oils enter the production of molybdenum disulfide with molybdenum concentrate, it is bound to cause: (1) Some impurity minerals are selected into high-purity concentrates due to the adsorption of hydrocarbon oil collectors. (2) Due to the large viscosity of the oil, some impurity minerals are mixed into the high-purity concentrate due to mechanical inclusions, which makes the purification difficult. The author developed the TL agent [T-de (To), L-Lin (Lin)], and enhanced the molybdenum concentrate by TL deactivator, and obtained MoS 2 content >97% in industrial test, molybdenum recovery High purity molybdenum concentrate with a rate of >97%. While exerting the advantages of simple process and low processing cost, the high recovery rate is achieved. The deoiling effect of TL agents is shown in the table below.
Table strong floating process deoiling effect
Test number | Oil content (%) | Deoiling rate (%) | |
Sample | Product | ||
Closed circuit test | 1.53 | 0.45 | 79.59 |
Verification test | 2.11 | 0.65 | 69.19 |
The effect on re-selection of molybdenum concentrate is shown in Figure 1.
Figure 1 Effect of TL dosage on MoS 2 grade and recovery
2, leaching method
Although this method does not change the structure of the molybdenum ore in the molybdenum concentrate (different from the synthesis method), it is necessary to change the phase of the impurity minerals and purify by phase transformation of the impurities and solid-liquid separation. Common practices are:
Single fluorination leaching process: using HF plus HCI (or H 2 SO 4 ) at 50~90 °C, the molybdenum concentrate is leached for 4~24h, so that the silicon impurities and some acid soluble minerals are transformed into Removed in liquid or gas phase, the main reaction formula is: [next]
SiO 2 +6HF=H 2 SiF 6 +4H 2 O
Fe 2 O 3 +6HCl=FeCl 2 +3H 2 O
FeS+2HCl=FeCl 2 +H 2 S↑
CaCO 4 +2HCl=CaCl 2 +CO 2 ↑+H 2 O
HF is a medium-strength monobasic acid with very low ionization. Even at a low concentration of 0.01 to 0.1 mol/L, the ionization degree is only 8.5%, and the ionization constant K a = 3.53 × 10 -4 or PK a = 3.45. H 2 SiF 6 is a strong dibasic acid with a high degree of ionization, and even in the vapor state, more than 50% of the molecules have been ionized. SiF 2- 6 is very stable, and the dissociation constant of SiF 2- 6 â†â†’SiF 4 +2F - is small, K a = 7 × 10 -7 . The reaction mechanism of HF dissolved SiO 2 is:
SiO 2 +4HF=SiF 4 ↑+2H 2 O
SiF 4 +2HF=H 2 SiF 6
SiF 4 in the gas phase escapes; SiF 4 and will wait for the escape of solution in the liquid phase F -, to form H 2 SiF 6.
The amount of HF in the immersion liquid depends on the weight of SiO 2 in the molybdenum concentrate. The results of the study on the leaching time, HF dosage and SiO 2 content are shown in Fig. 2. Obviously, the HF consumption is preferably 4 times or more the weight of SiO 2 .
Figure 2 Effect of HF dosage on leaching rate of SiO 2
In principle, the amount of HCI or (H 2 SO 4 ) in the immersion liquid only needs to ensure sufficient acidity (PH ≤ 2), but the amount of 30% HCl or (H 2 SO 4 ) added in the production often reaches the weight of the molybdenum concentrate. 1~2.5 times. For example, in a domestic leaching process, for every 1tMoS 2 powder, 50% HF 350kg and 30% HCl 2t must be added, and it is almost unnecessary to add fresh water. Whether such high acid consumption is necessary is worth considering.
After immersing the silicon and the impurities soluble in the acid, the slurry is subjected to solid-liquid separation, washing and the like to obtain a high-quality molybdenum disulfide filter cake. However, the product is often also contaminated with a filtrate containing a free acid, preferably with an alkali solution (either NaOH, KOH or NH 4 OH, preferably KOH) to neutralize the free acid. The purified filter cake is dried and finely ground to form the final molybdenum disulfide powder.
This method can maximize the removal of the silicon impurities, but not the removal of pyrite (FeS 2), yellow copper ore (CuFeS 2) ... and so poorly soluble in HCI, H 2 SO 4 impurities of vulcanization. Pyrite with a Mohs hardness of 6.5 has a great influence on the lubrication performance of the product. to this end. For molybdenum concentrates with higher FeS 2 , the following two processes are often used:
(1) Roasting-leaching process: The molybdenum concentrate is calcined at 650-800 °C for 1~2 h under the protection of nitrogen or an inert atmosphere before conventional fluorination. At this time, the pyrite will be converted into pyrrhotite (FeS x 1 < x < 2) which is low in hardness (3.5) and easily soluble in HCI (or H 2 SO 4 ). Alternatively, the molybdenum concentrate is incorporated into H 2 SO 4 , calcined in an inert atmosphere, and the pyrite is converted to soluble ferrous sulfate (FeSO 4 ). The calcined molybdenum concentrate is then leached by the above fluorination to remove both silicon and pyrite.
(2) Two-stage leaching process: The molybdenum concentrate is firstly leached by chloride (-Brunda method) to remove sulfurized impurities (see the relevant chapter of Chapter 2 for the Brenda method). The molybdenum concentrate from which the sulfurized impurities have been removed is then fed to a conventional fluorination leaching to remove desiliconized impurities.
The leaching method uses the phase transformation of impurity minerals as a means to purify the molybdenum concentrate, which has low molybdenum loss and high recovery rate. However, the drug consumption is high and the cost is high. Especially in the molybdenum concentrate, when the sulfide impurities such as pyrite are high, the roasting-leaching process is difficult to control, and the secondary leaching process is too expensive and difficult.
3. Beneficiation + leaching method
The method separately absorbs the characteristics of beneficiation and leaching, and first obtains a high-purity molybdenum concentrate containing less FeS 2 by a beneficiation method, and then obtains a high-quality natural crystal lattice of molybdenum disulfide by fluorinating and leaching desiliconized impurities. With high-purity molybdenum concentrate as the leaching raw material, the drug consumption will be greatly reduced.
Non-ferrous metal Northwest Research Institute developed a new technology, is mineral leaching +: TL deactivated reinforced using flotation, to obtain MoS 2 content of ≥97%, ≥97% molybdenum recovery of high-purity molybdenum concentrate; menses and then Solid ratio 1:1 per ton of product added 50% HF 150kg, 30% HCl 30kg, leached at 50 ~ 800 ° C for 3h, to obtain MoS 2 content ≥ 99% SiO 2 content 0.0275% high quality molybdenum disulfide powder.
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