Fire conventional roasting process of the production of ammonium molybdenum concentrate, flue gas SO 2 is present serious environmental pollution, molybdenum and rhenium recovery and low defects. These defects can be avoided by thermal decomposition of molybdenum concentrate.
There are many kinds of wet processes, which are divided into molybdenum concentrate decomposition methods. The common processes are as follows (see Table 1).
Table 1 Common wet process
Process | Oxidant | Pressure (MPa) | Temperature (°C) | Dip |
Nitrogen oxide boiling | O 2 | △0.8~1.5 1 ※2.0~2.5 2 | 180~220 | 20~40g/LHNO 3 (HNO 3 : Mo = 0.2~0.3:1) |
Caustic soda | O 2 | Ibid. | 200 | |
Nitric acid decomposition | HNO 3 | 1 | 90 | 27~30% concentration nitric acid |
Decomposition of sodium hypochlorite | NaOCl | 1 | 20~40 | 30g/L NaOCl, 20~30g/L NaOH |
1 chlorine partial pressure; 2 total pressure in the kettle.
1, (nitric acid) oxygen boil
The molybdenum concentrate is hydrolyzed by nitric acid in a water medium and is an exothermic process of a three-phase (liquid-solid-gas) reaction. The reaction is:
Â
MoS 2 | 9 | O 2 +3H 2 O | → | H 2 MoO 4 +2H 2 SO 4 + △ Q |
2 |
Nitric acid acts as a catalyst and circulates in the reaction:
MoS 2 +9HNO 3 +3H 2 O→H 2 MoO 4 +9HNO 2 +2H 2 SO 4 +△Q
2HNO 2 →NO+NO 2 +H 2 O
2NO+O 2 →2NO 2 +1233kJ
3NO 2 +H 2 O→2HNO 3 +NO+484.5kJ
The equilibrium is quickly reached from the reaction of nitrous acid → NO + NO 2 → NO 2 → HNO 3 . Increasing the oxygen partial pressure and lowering the gas phase temperature all favor the reaction.
During the boiling process, a small amount of molybdenum enters the cooking liquor in a strong acid medium, and about 94% of the molybdenum remains in the solid phase in the form of molybdic acid. Most of the ruthenium associated with molybdenum concentrate is converted into soluble perrhenic acid or its salt into the cooking liquor. In the molybdenum concentrate, iron , copper , aluminum , magnesium and the like are sulfates, and some phosphorus , arsenic and silicon enter the pressurizing liquid in the form of anions.
The process of nitric acid oxygen boiling is shown in Figure 1, and the process conditions are shown in Table 2.
Table 2 Process conditions for the production of ammonium molybdate by oxygen pressure cook
Process | Process conditions | |
Boiling | Molybdenum concentrate (kg): water (L) | 1:1.5~2.5 1 |
Pressurization in the kettle (MPa) | 2 (up to 3 in the reaction) | |
Heating temperature (°C) | 14~15 (reaction rises to 20) 2 | |
Nitric acid dosage (kg HNO 3 /kg Mo) | 0.20~0.30 | |
Reaction time (h) | 2 | |
(filter cake) Ammonia dip | Filter cake (kg): water (L): ammonia (L) | 1:0.7~0.8:1.2~1.23 |
PH | 8.5~90 | |
Heating temperature (°C) | 70~75 | |
Stirring time (min) | 15~20 | |
Solution specific gravity (g/mL) | 1.16~1.18 | |
Purification | Heating temperature (°C) | 80~ |
PH | 8.5~9 | |
When sodium sulfide is added in excess | The solution is light yellow | |
concentrate | Solution specific gravity (g/mL) | 1.2~1.21 |
Cooling temperature (°C) | 40~45 | |
Acid sink | Reaction temperature (°C) | ≯60 |
PH | 2~2.5 | |
Ammonia re-crystallize | Coarse grains (kg): distilled water (L): ammonia (L) | 100: (40~50): (45~50) |
Solution specific gravity (g/mL) | 1.40~1.50 | |
Dissolution heating temperature (°C) | 70~80 | |
1 Now the cooking pressure has been reduced to 0.8~1.2Mpa;
2 During the reaction, the pressure will rise and the temperature will rise again.
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Figure 2 (acid) oxygen pressure cooking production process of ammonium molybdate
Molybdenum concentrate, nitric acid and water (or return the wash) was added titanium material autoclave, steam is fed to the kettle and heating was started bubbling of oxygen. When the temperature in the kettle rises to 140~150 °C and the pressure reaches 1.5~2.5 MPa, the steam heating is stopped. The oxygen is continuously supplied, and the heat and pressure are released as the reaction progresses, and the temperature and pressure in the kettle are increased to reach 180 to 220 ° C and 3 to 3.5 MPa. The reaction was maintained for 2 h while continuously loading. At the end of the reaction, oxygen is stopped and the temperature drops below 150 °C. The immersion liquid is cooled to lower the temperature below l00 ° C, the exhaust gas is depressurized, and then separated by liquid solid: a molybdenum acid filter cake and a press cooking liquid can be obtained. Further processing of the molybdate filter cake is similar to the molybdenum calcine ammonia leaching process.
The conversion rate of molybdenum and zinc in the oxygen cooking process can reach 98%~99%, the processing cost is not high, and the three wastes are less. But the key to whether oxygen boiling can be implemented in production is whether the equipment can withstand pressure and temperature. Acid and corrosion resistant. Titanium materials and sealing materials for high-pressure reactors can be prepared from tetrafluoroethylene materials. Attention should be paid to valves under high pressure, high temperature, high acidity and high oxidizing atmosphere.
The oxygen pressure cooking solution can be extracted by extraction or ion exchange to extract molybdenum and rhodium. See Table 3 for a comparison of several typical oxygen cooking conditions and effects.
Table 3 Oxygen boiling conditions, effect comparison
Project | Unit | Zhuzhou hard alloy plant | Former Soviet Union | US Patent 3,894,418 | US Patent 3739057 | Japanese Patent Show-37-1520 |
Oxygen partial pressure | MPa | 1.5~2.0 | 1.0 | 1.05~1.4 | 1.0~1.5 | 2.0 |
Nitric acid dosage | Kg/kg (Mo) | 0.20~0.30 | / | 0.45~0.9 | 0.34 | / |
Liquid to solid ratio | / | 1.5~2.5:1 | 10:1 | 10:1 | 5:1 | 10:1 |
temperature | °C | 180~220 | 200~225 | 120~160 | 155~160 | 200 |
Concentrate size | Head | 75%-200 | / | -325 | -200 | -200 |
Leaching time | h | 2~3 | 3~4 | 3~4 | 2 | 6 |
Molybdenum conversion rate | % | 99.13 | 93~9935 | 99.5 | >99 | 98.4 |
Pressurizing liquid molybdenum | % | ~7 | 5~7 | 20~25 | 10~15 | / |
2. Process for recovering bismuth by nitric acid oxygen cooking liquor
It is widely distributed in the earth's crust, but it has not been found in the presence of natural forms of plutonium, and it rarely appears as a major mineral component. The ruthenium present in other minerals is only traces, and molybdenite is the only important host mineral. To date, 99% of the world's produced antimony is derived from hydrothermal porphyry copper-molybdenum ore.
The method of producing bismuth from molybdenum concentrate is also dependent on the process of decomposition of molybdenum concentrate. When the molybdenum concentrate is oxidized and calcined, at a calcination temperature of 500 ° C or lower, helium is sublimed into the flue gas with Re 2 O 7 . With a high-pressure differential high scrubber, the collection rate from soot is about 65%. The hydrazine is recovered by extraction or ion exchange from a washing solution in which perrhenic acid or ammonium perrhenate is dissolved. When oxygen is boiled, 98% of the cerium in the molybdenum concentrate is converted into perrhenic acid into the cooking liquor, and the boiled liquid also contains molybdenum with a total molybdenum content of 5% to 6%.
Molybdenum and niobium can be recovered from the cooking liquor by extraction or ion exchange. The extraction process is shown in Figure 1, and the process conditions for extracting ruthenium are shown in Table 4.
Table 4 Process conditions for recovery of molybdenum and niobium in cooking liquor
Procedure | Process conditions | |||
Silicon | Polyether dosage | 50g/m 3 cooking liquor | ||
Extraction and back extraction | Condition | rhenium | molybdenum | |
Organic phase composition | N235 | 2.5 | 20 | |
Secondary octanol | 40 | 10 | ||
Coal oil | 57.5 | 70 | ||
Stripping agent (mol) | NH 4 OH | 5~6 | 9~10 | |
Detergent (mol) | NH 4 OH | 1.8 | ||
Flow ratio | extraction | Extract 1.3g/L | Molybdenum 20g/L | |
washing | 1/0.5 | |||
Back extraction | Sputum 10g/L | Molybdenum 150 g / L | ||
铼 one crystal | Potassium chloride dosage (g/L) | 50 | ||
Hydrogen peroxide dosage (ml/L) | 20 | |||
Crystallization temperature (°C) | ≤0 | |||
Secondary crystallization | Solution composition (hydrogen peroxide: water) | 1:1 | ||
Primary crystallization dissolution temperature (°C) | 95 | |||
Solid-liquid ratio | 1/10 | |||
Crystallization temperature (°C) | ≤0 | |||
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3, caustic soda oxygen boiling
At 130 ° C and an oxygen partial pressure of 0.2 MPa and a total internal pressure of 1 MPa, the molybdenum concentrate was leached with a NaOH solution. After leaching for 7~8h, 98%~99% of molybdenum and yttrium are transformed into the liquid phase. When the temperature is raised to 200 ° C, the partial pressure of oxygen can reach 1 ~ 1.5MPa, the reaction is as follows:
 Â
MoS 2 | 9 | O 2 +6OH - | → | MoO 2- 4 +2SO 2- 4 +3H 2 O |
2 |
In addition to MoO 2- 4 and ReO 4 - , the solution also contains compounds of Cu, Fe, Si, As, Sb, and P, which complicate solution processing.
Separation of molybdenum from a solution containing a high amount of sulfate ions is not suitable for the precipitation of calcium molybdate, since this will simultaneously precipitate a calcium sulfate and contaminate the calcium molybdate. Therefore, it is possible to reduce MoO 2- 4 with molybdenum powder in a weak acid solution (pH=2) of 200 ° C in an autoclave:
MoO 2- 4 +Mo+4H + →3MoO 2 ↓+2OH -
Industrial molybdenum powder can be obtained by reducing MoO 2 with H 2 . The residual residue after the reduction is used for extraction. The process extracts 96% molybdenum and 85% to 90% bismuth.
In a weakly acidic medium, it is also possible to reduce MoO 2- 4 by introducing H 2 under pressure.
MoO 2- 4 +H 2 →MoO 2 ↓+2OH -
The optimum precipitation condition of MoO 2 is 200 ° C, the partial pressure of hydrogen is 6 MPa, and the pH is 2~3. After the seed crystal is reacted for 1~4 hours, more than 98% of the phase molybdenum will precipitate as coarse MoO 3 crystal.
Another effective way to extract molybdenum from caustic cook liquor is to use a strongly basic anion exchange resin for ion exchange.
Conventional treatment of molybdenum solution extraction, activated carbon adsorption, and ion exchange processes are all applicable to acidic media. Zhuzhou Tungsten and Molybdenum Materials Research Institute uses OH - type 717 # or D296 anion resin to adsorb molybdenum from the caustic alkali oxygen boiled molybdenum solution, and the adsorption rate can reach 99.5%. And remove more than 90% of phosphorus, arsenic, silicon and more than 80% of SO 4 2- and other impurities. Test, wet resin adsorption amount is large, pH = 8 when the resin to penetrate readily # 717 (exchange column effluent and the liquid content ratio of the inflow is readily 0.01) of 25 ~ 29g / L; Saturated Capacity (when inflow, The resin content after the effluent content was equal was 38-40 g/L; the breakthrough capacity of D296-10 at pH=10 was 29.06 g/L, and the saturation capacity was 37 g/L. In the step of desorbing the resin with NH 4 Cl and desorbing the acid solution, impurities such as SO 4 2- and copper iron can be further removed to obtain a qualified high-quality ammonium paramolybdate.
4. Sodium hypochlorite oxidation method
This is often used as a wet decomposition process for low-grade molybdenum concentrates and molybdenum ore.
In an alkaline medium, the addition of oxidizing sodium hypochlorite can oxidize almost all of the sulfides:
However, at 20~40 °C, the oxidation rate of iron and copper sulfides is much lower than that of molybdenite. At this time, MoS 2 can be sufficiently converted into MoO 4 2- , and copper and iron sulfides are rarely dissolved. At the same time, iron hydroxide, especially copper hydroxide, can catalyze the decomposition of sodium hypochlorite in an alkaline medium and accelerate the oxidation of molybdenite:
NaClO→NaCl+[O]
The infusion component is usually: NaCIO 30g / L, NaOH 20 ~ 30g / L. When this method is used to leaching molybdenum ore with 5% to 23% molybdenum, the recovery of molybdenum can be as high as 96% to 98%. This method can work under normal temperature and normal pressure and is easier to control than oxygen pressure cooker. The shortcoming is that the consumption of the medicament is too large. In theory, it is necessary to consume 7 kg of sodium hypochlorite per liter of lkg molybdenum, and the actual production consumption is 1.5 to 2 times of the theoretical value.
To this end, there is a process in which chlorine gas is passed to regenerate sodium hypochlorite:
2NaOH+Cl 2 →2NaClO+H 2 ↑
Electrooxidation also occurs: leaching with an energized sodium chloride solution:
NaCl+H 2 O | electrolysis | NaClO+H 2 ↑ |
→ |
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These processes are only a branch of the sodium hypochlorite process, see Figure 2.
Figure 2 sodium hypochlorite process
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