Carbonaceous gangue is another gangue mineral that is difficult to remove in molybdenum beneficiation .
Carbonaceous minerals in nature can be classified into inorganic carbon (crystalline graphite , amorphous graphite, etc.) and organic carbon ( coal , asphalt, etc.).
Graphite has a typical layered structure. Within the layer, carbon atoms are covalently bonded; between the layers, carbon atoms are linked by molecular bonds, as shown in Figure 1.
Graphite-like molybdenum ore also has a well-defined [001] cleavage surface, which is also a molecular bond fracture surface of van der Waals force, is hydrophobic, and has good natural floatability. The ξ-potential versus pH curve of graphite is very similar to that of molybdenite, as shown in Figure 2.
Coal is a complex organic sedimentary mineral that varies with the composition of organic matter. Anthracite ξ - the relationship between potential and pH is shown in Figure 3. Bituminous coal and vermiculite are similar (the figure is no longer marked). They all have obvious zero points.
Coal also has good natural floatability. F. Aplan determines the floatability of Pittsburgh coal as shown in Figure 4.
Figure 1 Crystal structure of graphite
Figure 2 Graphite and molybdenite ξ-potential system comparison chart
Figure 3 Anthracite ξ-potential and PH relationship [I Campbell)
(Campbell, Bliss)]
Figure 4 Zone Zbo coal floatability (Ilfelstenau)
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Asphalt is a residue of natural volatile oil , which is very hydrophobic and is a good natural floatable mineral.
Copper -molybdenum ore sometimes contains carbon-bearing shale , carbon-bearing quartzite , and carbon-containing siliceous hornite composed of these carbonaceous minerals and silicates. Molybdenite and most carbonaceous minerals have strong hydrophobic surfaces and good natural floatability. In molybdenum beneficiation, the molybdenite collector, hydrocarbon oil, is also effective in allowing carbonaceous minerals to be harvested and floated; and molybdenite inhibitors (dextrin, starch, lignosulfonate, Aniline black, tannic acid, anionic polymers, etc. can also inhibit carbonaceous minerals (according to the study of Alan copper-molybdenum ore, the inhibition of molybdenum ore by hardening of lignosulfonate is shown in Fig. 5.
Figure 5 Effect of inhibitors on molybdenum-carbon separation
Carbonaceous minerals have low density, low hardness and easy muddy. Particulate carbonaceous minerals are easily adsorbed on other mineral surfaces. In view of the above reasons, in the copper-molybdenum mine molybdenum beneficiation operation, it is extremely difficult to obtain high-quality molybdenum concentrate by effectively separating molybdenum carbon.
The mineral deposits containing carbonaceous gangue in the Aylan copper mine in the United States account for 1/4 of the total ore. The carbonaceous mineral was identified by infrared spectroscopy. In China's copper-molybdenum mines, gangues containing carbonaceous minerals are also common, and graphite is common and coal is also found. The carbonaceous minerals contained in Xuanhua copper-molybdenum ore are identified as Yangquan coal by infrared spectroscopy (see Figure 6), and also oil shale . Jurong Copper Mountain copper - molybdenum, gold Tongling port Ridge copper - molybdenum, BAINAIMIAO Cu - Mo deposit, the carbon content shown in Table 1.
Figure 6 Infrared spectrum of an organic carbon
Table 1 Statistics on carbon content of several mine molybdenum ores (%)
species | Jinkouling | Tongshan | Bai Nai Temple | |
C total C graphite | 2.94 1.97 | 1.16 | 0.005 |
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The influence of carbonaceous minerals on molybdenum beneficiation: (1) The carbonaceous minerals themselves float up, causing the carbon content of molybdenum concentrates to soar; (2) the carbonaceous minerals are extremely fine and easily adsorbed on the surface of other gangue minerals, making them Pollution rises. If only carbonaceous minerals enter the molybdenum concentrate, when the molybdenum calcination is produced by oxidative roasting, the carbonaceous minerals will be burned to form CO 2 and removed, which is not harmful to the quality of the molybdenum calcine. While carbonaceous minerals contaminate silicates and impurity sulfide minerals to float above, the hazards are much greater (see Table 2).
Table 2 Effect of milling on the quality (%) of concentrate in molybdenum ore
Concentrate | Raw ore without carbon | Raw ore C (graphite) 0.4~0.5% |
Molybdenite Carbonaceous mineral Other impurities | 90~95 0 5~10 | 25~35 25~35 30~50 |
In the practice of mineral processing, these two effects are combined, making it difficult to select molybdenum and produce qualified molybdenum concentrate. The Ailan copper mine found that in the molybdenum coarse concentrate, the carbon to molybdenum ratio has a great influence on the grade and recovery rate of the molybdenum concentrate. The higher the carbon content (the higher the carbon to molybdenum ratio), the lower the grade and recovery of the molybdenum concentrate is shown in Figure 7.
Fig. 7 Effect of carbon on molybdenum flotation in Ailan copper mine
Due to the interference of carbonaceous gangue, molybdenum selection has become quite difficult. The main component of the qualified or unqualified molybdenum concentrate produced in Jinkouling is shown in Table 3.
Table 3 Multi-element analysis of Jinkouling molybdenum concentrate (%)
materials | Mo | Ca | C graphite | Cu | Fe | Zn | S | SiO 2 | CaO | MgO | |
Qualified molybdenum concentrate Unqualified molybdenum concentrate | 49.17 24.29 | 2.45 4.59 | 1.30 3.20 | 0.19 2.47 | 3.66 5.13 | 0.019 0.133 | 32.50 19.50 | 2.42 19.14 | 1.08 5.08 | 0.563 1.37 |
Obviously, in the molybdenum concentrate, with the increase of C content, the content of gangue minerals composed of SiO 2 , CaO, MgO, etc. is also greatly increased, and the content of sulfide impurities composed of Cu, Fe, Zn and the like is also greatly increased, so that the molybdenum content of the product is increased. Hard to improve. At the beginning of the production of the Jinkouling plant in 1973, the molybdenum concentrate contained 35% molybdenum and the molybdenum recovery rate was 53%. Later, with the increase of carbon content in the ore, the silver content of the silver concentrate in 1974 decreased to 20%, and the recovery rate of molybdenum fluctuated between 46% and 63%. The Inner Mongolia Bai Nai Temple ore contains only 0.005% of graphite. In the molybdenum concentrate containing 44% of molybdenum, the carbon content is as high as 4.48% and the enrichment rate is 896 times. Before the Dexing molybdenum selection, the material contained only 0.27% carbon. After the selection, the carbon in the molybdenum concentrate was as high as 11.88%. It is also difficult to select a molybdenum concentrate containing 40% molybdenum when the Ailan copper mine processes ore containing hard asphalt.
In order to eliminate the interference of carbonaceous gangue on the quality of molybdenum concentrate, it is often necessary to increase the process of molybdenum-carbon separation. Molybdenum-carbon separation can be sandwiched in a molybdenum sorting process to produce low-carbon qualified molybdenum concentrates; it can also be decarburized after carbon molybdenum selection, yielding qualified deep processing product. [next]
Decarburization of molybdenum concentrate is a process for separating in the decomposition process of unqualified molybdenum concentrate containing carbon, using the difference in molybdenum and carbon phase transformation. Different from the decomposition method of molybdenum concentrate, it can be divided into two types: oxidative roasting and leaching:
When the molybdenum concentrate is oxidized and roasted, the carbonaceous material is converted into CO 2 gas by oxidation and combustion into the exhaust gas to escape:
C + O 2 | â–³ | CO 2 |
→ | ||
Molybdenite is oxidized to form MoO 2 :
MoS 6 | + | 2 | O 2 | → | MoO 3 | + | 2SO 2 |
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It is left in the molybdenum baking sand to achieve separation of molybdenum and carbon. As long as the impurities in the molybdenum concentrate are mainly carbonaceous, even if the content is high, the oxidative roasting can be removed without affecting the quality of the molybdenum baking.
The molybdenum concentrate leaching process is numerous (see the ammonium molybdate wet process) but the same is true. During the leaching process, the molybdenite is converted into soluble molybdate into the liquid phase; the carbon and gangue do not change and remain in the solid phase, and are discarded with the filter residue. The leaching method can also remove metal ions such as Cu, Pb, Fe, etc. in the solution through the (NH 4 ) 2 S purification process, and obtain a chemical product with high purity. Therefore, the leaching method is particularly suitable for the removal of carbon (and other impurities) that cannot be removed by other carbon removal processes.
The products decomposed by molybdenum concentrate are no longer mineral products, and the processing has been applied to the deep processing of molybdenum concentrates, which is not within the scope of this chapter. For a detailed description of the oxidative roasting and leaching process of molybdenum concentrate, refer to the relevant chapter in Chapter 4.
There are three main decarburization processes in the molybdenum selection process: reselection decarburization-flotation; flotation: roasting-flotation.
Re-selection of decarburization is based on the small density of carbonaceous minerals and the difference in density between molybdenum minerals, see Table 4.
Table 4 Density of various carbonaceous gangues
materials | Molybdenite | graphite | Alan (hard asphalt) | Tongshan (graphite) | Jinkouling (Graphite-based) | Dexing |
Density (g/cm 3 ) | 4.7 | 2.21~2.26 | 1.3 | 2.8 | 2.73 | 1.5~1.7 |
Ailan uses organic heavy liquid analysis to obtain fast and effective results of molybdenum recovery and decarburization rate of more than 90%. The re-selected decarburization feedstock may be a molybdenum selected intermediate or a raw ore.
For the 20~0mm powder ore block, Jinkouling uses a jig to re-select the carbonaceous surrounding rock, and then floats the molybdenum ore to obtain a molybdenum concentrate containing 44.8% of molybdenum and 80.3% of molybdenum recovery.
Most of the re-election methods are used for decarburization of molybdenum beneficiation intermediate products. At this time, the particle size of the material is often small and can only be selected by equipment such as a shaker or a cyclone.
When using a shaker for molybdenum-carbon separation, the Alan copper mine found that when the feedstock contains more than 30% molybdenum and 10% to 25% carbon, the content of molybdenum is more than 40% and the recovery rate of molybdenum is 60. %~90% of molybdenum concentrate. The average result of 12 samples of molybdenum containing 27.1% and containing 18.3% of carbon. The molybdenum concentrate contains 34.9% molybdenum, 3.2% carbon, 75.4% molybdenum recovery rate and 90.9% decarburization rate. The ore sample containing 28.1% molybdenum and 20.7% carbon, the average result of 34 tests by the Laka field research institute in Canada, the molybdenum concentrate contains 38% molybdenum, the molybdenum recovery rate is 90%~92%, and the decarburization rate is 60. %~80%.
Dexing Copper Mine has a decarburization test of materials containing 32%~37% molybdenum and 20%~22% carbon. The molybdenum concentrate has a molybdenum content of 45% and a decarburization rate of over 82%. Jinkouling passed the re-selection decarburization test on unqualified molybdenum concentrate, and obtained qualified molybdenum concentrate containing 48.44% molybdenum and 46.3% molybdenum recovery rate. The float-heavy-floating molybdenum process was tested by Jinkouling. The molybdenum concentrate contained 45% molybdenum and 40% molybdenum recovery.
In the production of Ailan copper mine, a cyclone group with ¢25.4mm and large cone angle (60°C) was used for decarburization, and good production index was obtained. When C:Mo>2, qualified molybdenum concentrate was obtained. They use a two-stage cyclone. If the second stage is used for selection, the molybdenum recovery rate is 78%~80%, and the decarburization rate is 90%~93%. If the second stage is used for sweeping, the molybdenum recovery rate is 87%~90%, the decarburization rate is 78%~80%. In the industrial production of Ailan, decarburization has been carried out by cyclones since 1976. Jinkouling also tested the decarburization of the spiral concentrator and achieved a good indicator of 75% molybdenum recovery.
When de-carbonization is carried out by re-election, other metal minerals, especially sulfide minerals of copper and iron , also enter the molybdenum concentrate due to the high density. Therefore, in the re-election decarburization and flotation molybdenum ore, the re-election should be preceded by molybdenum selection, usually forming a float-heavy-floating molybdenum removal process.
Flotation decarburization is simple and easy in copper-molybdenum flotation plants, but the separation effect is not ideal. The grade or recovery rate of molybdenum concentrate is difficult to increase at the same time. [next]
In the Jinkouling test, the preferred molybdenum molybdenum was selected for the carbon-bearing copper-molybdenum ore, instead of the copper-molybdenum mixed flotation. In molybdenum selection, aluminum sulfate is used in combination with water glass to suppress carbonaceous gangue, and a better decarburization effect is obtained. The process used is shown in Fig. 8, and the obtained indexes are shown in "4" of Table 5.
Figure 8 Jinkouling flotation decarbonization process diagram
Table 5 Comparison of decarbonization process in Jinkouling
Process number | Molybdenum concentrate (%) | Copper concentrate (%) | Remarks | ||
grade | Recovery rate | grade | Recovery rate | ||
1 2 3 4 | 45.7 44.8 48.44 55.4 | 48.5 80.3 46.3 66.1 | 10.01 11.69 10 18.9 | 77.36 71 71 80.5 | Flotation method Raw ore block jigging decarbonization Floating-heavy-floating Flotation decarbonization |
In the study of Xuanhua carbon-bearing copper-molybdenum ore, the results of various inhibitors are shown in Figure 9. When the selected operations to add a small amount of phosphorus and sodium hexametaphosphate cellulose inhibition organic carbon (similar YANGQUAN coal), can be from 0.089% molybdenum, 0.96% carbon (C molybdenum ratio was 1: 10.79) ore by flotation Obtained 45.22% of molybdenum, 4.66% of organic carbon, and 85.12% of molybdenum recovery. The molybdenum concentrate and the famous Tongshan copper-molybdenum mine with basic output of molybdenum-carbon separation are treated by segmental open-circuit flotation process and acidic medium to treat molybdenum concentrate. A better molybdenum carbon separation effect is obtained.
Figure 9 Different inhibitors inhibit molybdenum selection results
Calcination-flotation decarburization is a process in which the surface properties of molybdenite and carbonaceous gangue are changed by roasting to remove surface agents.
Unlike oxidative calcination, roasting flotation should avoid oxidation of molybdenite. It is usually calcined at a lower temperature (250 ° C or 350 ° C) or at 450 to 650 ° C under anoxic conditions. In foreign countries, Ailan has studied roasting at 250 °C, and also studied roasting at 450-650 °C in an oxygen-deficient atmosphere in a boiling furnace.
Rotary kiln roasting-flotation process is shown in Figure 10, and test results are shown in Table 6.
Figure 10 Schematic diagram of the roasting process of Ailan rotary kiln
Table 6 Roasting-flotation results
product | grade(%) | Molybdenum recovery rate (%) | |
Mo | C | ||
Carbonaceous concentrate Calcination Molybdenum concentrate | 34.1 37.9 51.5 | 27.6 15~17 | 100 98~100 95.5 |
Note: Calcination temperature: 250 ° C, roasting time: 150 min.
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The calcination-flotation of the fluidized furnace, the influence of the calcination temperature on the molybdenum grade of the product is shown in Fig. 11. For the ore sample containing 35% molybdenum, 22% carbon and 1% copper, it is calcined by anoxic acid at 450^~650 °C, molybdenum is added with hydrocarbon oil and foaming agent, and the flotation concentrate is magnetically separated. After copper and iron, the final molybdenum concentrate contains 45% to 53% molybdenum, 80% to 95% molybdenum recovery, and 0.2% to 0.6% copper.
Figure 11 Fluidized roasting temperature and product molybdenum grade
CM Buren and GR Pent Gate compare the decarburization rate with the molybdenum recovery rate for various decarbonization studies, as shown in Figure 12. However, the choice of process in production must be determined through trial and economic analysis.
Figure 12 Comparison of decarburization rate and molybdenum recovery rate of various processes
Whether it is easy to float gangue, muddy gangue or carbonaceous gangue. Their appearance has caused trouble for molybdenum beneficiation and should be treated with caution.
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