1. Preparation method of molybdenum ore
The beneficiation method of molybdenum ore is mainly flotation, and the recovered molybdenum mineral is molybdenite. In order to improve the quality of molybdenum concentrate and remove impurities, the molybdenum concentrate is further subjected to chemical beneficiation treatment.
The molybdenite crystal has a hexagonal layered or plate-like structure and is formed by an S-Mo-S structure along the interlaminar normal bond and a polar covalent bond S-Mo in the layer. The bond between the layers is weak, and the covalent bond bonding within the layer is very strong. Therefore, Huihui molybdenum ore is easily disintegrated along the structural layer to produce flake or plate, which is the reason why the molybdenum ore is naturally floatable. Practice has proved that under suitable grinding fineness, the molybdenite crystal dissociation occurs between the S-Mo-S layers, and the hydrophilic S-Mo surface accounts for a small proportion. However, when over-grinding, the proportion of S-Mo surface increases, and the floatability decreases. Although a certain amount of polar collector such as xanthate is added at this time, it is beneficial to the recovery of molybdenum ore, but the new slime produced by over-grinding Affect the flotation effect. Therefore, the selection of molybdenite should avoid and prevent over-grinding. In the production, it is necessary to adopt segmental grinding and multi-stage sorting process to gradually achieve monomer dissociation and ensure high recovery of molybdenum concentrate.
The crushing of molybdenum ore generally adopts a three-stage and one-closed process, and the final product has a particle size of 12 to 15 mm.
Grinding is usually carried out using a ball mill or a rod mill-ball milling process. Henderson is the only semi-self-grinding process.
Flotation uses the preferred flotation method. Rough selection of molybdenum concentrates, coarse sweeping of tailings to recover associated minerals or disposal. The molybdenum coarse concentrate is re-milled in two or three stages, and the final molybdenum concentrate is obtained in four or five times.
The flotation agent of molybdenum ore uses a non-polar oil as a collector while adding a foaming agent. Surfactant Syntex is used as an oil emulsifier in the United States and Canada. The nature of the ore, as modifier with lime, sodium silicate gangue as inhibitors, sometimes add cyanide or sulfide minerals inhibit other heavy metals.
In order to ensure the quality of molybdenum concentrate, heavy metal minerals such as copper , lead and iron contained in molybdenum concentrate, calcium oxide and carbonaceous minerals need to be further separated:
Typically using sodium sulfide or sodium hydrosulfide, cyanide or ferricyanide copper and iron inhibition; inhibition by weight of lead chromate or Knox (Nokes). If an inhibitor is used, the impurity content does not reach the quality standard, and it needs to be supplemented by chemical beneficiation: secondary copper sulfide is leached with cyanide; chalcopyrite is leached with ferric chloride solution; galena with hydrochloric acid and trichlorochloride. The leaching of the iron solution can reach below the standard content.
The gangue containing calcium oxide is easily muddy, so it is not necessary to over-grind the ore containing such gangue. Production is often added sodium silicate, sodium hexametaphosphate or an organic phosphate gel as gangue inhibitor or dispersant; Activated carbon can also be added CMC (carboxymethylcellulose) inhibition carbonate gangue. Finally, it can be leached by hydrochloric acid or hydrochloric acid plus ferric chloride solution.
For the separation of carbonaceous minerals, it is first necessary to find out that the carbonaceous material is graphite , asphalt or coal . The floatability of these carbonaceous minerals is similar to that of molybdenum ore, but the density is small, and it can generally be removed by re-election; using hexapoly-sodium metaphosphate and CMC to suppress molybdenum float; or adding ferric chloride or water glass It is also effective to inhibit carbonaceous material with sodium hexametaphosphate; it is also one of the methods to remove organic carbon by roasting. It should be noted that the separation of all these carbonaceous minerals is currently unsatisfactory and is still a problem that has not yet been fully resolved.
The SiO2 (silica) content in the gangue is too high, which is often the reason for affecting the grade of molybdenum concentrate. It has been determined that the SiO2 content decreases with the increase of the grade of molybdenum concentrate, and there is a tendency for mutual consumption. As long as the molybdenum mineral reaches the monomer dissociation fineness, the SiO2 content can generally fall below the standard. Adding activated carbon to adsorb the oil on the surface of molybdenum, and adding CMC to inhibit the silicate gangue, the SiO2 content can also be reduced below the standard.
Second, molybdenum mine treatment - ammonium molybdate production
In the process of molybdenum ore beneficiation, some processes produce a low-grade molybdenum ore that is difficult to recover by flotation; some have too high levels of impurities to obtain qualified molybdenum concentrates (or low-grade molybdenum concentrates). The use of these unqualified molybdenum concentrates and molybdenum ore to produce ammonium molybdate is one way to recover this portion of molybdenum.
(1) Chemical beneficiation of molybdenum ore
The Yangjiazhangzi molybdenum mine produces a molybdenum ore containing 0.6%-0.8% molybdenum in the beneficiation process. The process for producing ammonium molybdate as raw material is as follows:
First, the molybdenum ore is concentrated to a concentration of 60% solids, and leached by adding sodium hypochlorite solution. The reaction formula is as follows:
MoS2+9NaClO+6H2O→Na2MoO4+2Na2SO4+9NaCl+3H2O
The sodium hypochlorite solution contains 130-140 g/L of NaClO and 50-60 g/L of NaOH. The leaching temperature is 45 to 55 ° C, and the fineness of the ore in the molybdenum is 0.074 mm or less.
The sodium molybdate solution formed by leaching is added to hydrochloric acid to have a pH of 5 to 6, and then calcium chloride is added and boiled with steam to form a calcium molybdate precipitate. The reaction formula is as follows:
Na2MoO4+CaCl2→CaMoO4↓+2NaCl
After the calcium molybdate precipitate is filtered, the sodium carbonate solution is decomposed by adding a sodium carbonate solution to remove the heavy metal ions contained therein, and the reaction formula is as follows:
Then, hydrochloric acid is added to make the pH of the solution = 0.5, and the reaction is carried out at 95 ° C to form a molybdic acid precipitate, and the reaction formula is as follows:
Na2MoO4+2HCl→H2MoO4↓+2NaCl
After separating the molybdic acid, it is directly dissolved in the ammonia water to form ammonium molybdate. The activated carbon was decolorized, and then hydrochloric acid was added to adjust the pH to 2.5 to obtain white crystals of ammonium tetramolybdate dihydrate [(NH 4 ) 2 O · 4 MoO 4 · 2H 2 O]. Filtration, drying and pulverization to obtain a finished ammonium molybdate. The entire production process is shown in Figure 1.
Figure 1 Process for producing ammonium molybdate in molybdenum ore
(2) Production of ammonium molybdate in low-grade molybdenum concentrate
Some of the selection plants, such as Jinkouling and Tongshan Concentrators, have a molybdenum concentrate containing only 20% to 35% of molybdenum concentrate due to the influence of carbonaceous minerals. The plant uses chemical beneficiation to make ammonium molybdate. The production process is as follows: First, the low-grade molybdenum concentrate is dried and calcined into molybdenum trioxide, and the reaction formula is as follows:
Then, the molybdenum trioxide is leached with ammonia water to form ammonium orthobewate, and the reaction formula is as follows:
Insoluble matter such as iron hydroxide is removed by filtration. The filtrate is added with sodium sulfide (or ammonium sulfide), and the copper ammonia complex in the leachate is converted into copper sulfide precipitate and separated from ammonium orthob molybdate. The solution of heavy metal ions is removed, nitric acid is added to make pH=2.5, and ammonium ortho molybdate is converted into ammonium tetramolybdate crystal, and the reaction formula is as follows:
4(NH4)2MoO4+6HNO3→(NH4)2O·4MoO3↓+6NH4NO3+3H2O
The crystals were filtered and dried at 120 ° C for 3 hours to obtain white crystals of ammonium tetramolybdate. The production process is shown in Figure 2.
Figure 2 Process for producing ammonium molybdate from low-grade molybdenum concentrate
3. Mineral processing method of associated molybdenum minerals
More than one-third of the world's molybdenum production comes from the recovery of by-products from other polymetallic ores. Molybdenum in Chile and Peru is recovered as a by-product from the copper concentrator.
Ore from the associated recovery of molybdenum, mainly from porphyry copper, from a small amount of molybdenum, tungsten, molybdenum, iron, molybdenum, bismuth and molybdenum uranium.
The porphyry copper deposit has a low copper content, generally 0.5% to 0.7% Cu, and contains about 0.01% to 0.03% of molybdenum. The porphyry copper deposits are large in reserves and the size of the plant is large, so the amount of molybdenum produced by the company is considerable.
Molybdenum minerals in porphyry copper deposits are impregnated with copper minerals with very fine particles. The molybdenum is recovered from the porphyry copper ore. The beneficiation is generally carried out by copper-molybdenum mixed coarse selection, and the mixed coarse concentrate is mixed and selected to obtain a molybdenum-containing copper concentrate containing more than 20% of copper grade. Then, the pretreatment before the separation of copper and molybdenum is carried out: concentrated de-peeling, cooking, re-grinding, etc., followed by copper-molybdenum separation and molybdenum selection. Copper-molybdenum separation usually uses copper-suppressed molybdenum; only the Bingham concentrator in the United States uses molybdenum-free float copper. Molybdenum selection uses two or three re-grindings and four to more selections. Due to the difference of copper-bearing minerals, the difference of copper ore grade of raw ore and the influence of impurities, the recovery rate of molybdenum varies greatly, about 30% to 70%.
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