1. Molybdenum features introduction
Molybdenum main physical and chemical properties are as follows:
|Relative atomic mass||95.95||Density/（g/cm3）||10.2|
|Melting point / degree||2883||Boiling Point/K||5833|
|Heat of fusion / (kJ / mol)||7.37||Evaporation heat / (kJ / mol)||536.3|
|Entropy (298K temperature) / (ten / (mol.K)||28.61|
High melting point of molybdenum, molybdenum at high temperatures the vapor pressure is low evaporation rate is small, the most important feature of molybdenum strong conductivity. Molybdenum inorganic acid corrosion resistant, but can quickly dissolved in nitric acid and sulfuric acid mixed solution.
Molybdenum and iron may be miscible in any proportion. In the 1453-1813K range, compound MoFe (including Mo63.29%) solid stability. 1753K less even in the solid phase will crystallize MO 2 sub> Fe3. Molybdenum greater than 50%, significantly higher melting point, such as 60% molybdenum alloy melting point of 2073K, the high molybdenum molybdenum can flow from the furnace.
Molybdenum carbide and carbon generation MO2C and MoC. MO2C melting point of 2653K, MoC melting point of 2843K, may also generate composite carbide Fe3MO3C and Fe3CMO3C. Molybdenum and silicon generate MO 3 sub> Si, Mo5Si3, MoSi2. Molybdenum and aluminum generated MoAl. Generate a series of molybdenum sulfide and sulfur, MoS2, MO2S3, MoS3, which is the main sulfide MoS2. MoS2 containing molybdenum mine called molybdenite. When the temperature is higher than 673K is easily oxidized into MoO MoS23And MoO2。
Molybdenum oxide and oxygen to generate a series of MoO3、MoO2、MO2O3, Mo4O11, among which the most stable MoO3And MoO2。 MoO3Has obvious acidity, called molybdic anhydride, is light green powder; heating was bright yellow. Melting 978K, boiling 1428K, generate heat 746kJ/mo, density 4.4g/cm3When the temperature is higher than 873K when MoO3On significant sublimation. MoO3Slightly soluble in water, soluble in caustic soda, ammonia solution generated molybdate. MoO2Is a purple-brown powder, and a metallic luster. When the temperature is greater than 1273K MoO2Significant sublimation, which generates heat as 588.2kJ/mol, density 6.34g/cm3。MoO2Insoluble in water and alkaline solution, not soluble in sulfuric acid and hydrochloric acid.
2. Molybdenum concentrate roasting
MoS molybdenum containing about 75% because of high sulfur content can not be used directly to produce molybdenum smelting of iron and molybdenum block, it must go through roasting removal of sulfur can be used. Customary before roasting molybdenum molybdenum called raw, cooked roasted molybdenum concentrate molybdenum or molybdenum called calcine。
Add to concentrate roaster before the molybdenum content and impurity content should be ingredients, and to fully mixed, with a good compound error of 0.2% molybdenum content within, Mo ≥ 45%, Pb ≤ 0.8%, Cu ≤ 0.6%, SiO 2 sub> ≤ 12%, CaO ≤ 3%, H2O ≤ 4%.
1.Single oven roasted molybdenum concentrate
Only one layer reverberatory hearth furnace, said intermediate layer. Usually single furnace parameters: hearth high 850mm, hearth length 6000mm, hearth width 1500mm, high furnace 500mm, door 4.
Refractory clay brick masonry stove. The stove has a coal-fired combustion chamber and ash pit below the middle height of about 850mm, width 1500mm, length 6000mm hearth, stove and a roof to prevent falling into the combustion chamber and the level of concentrate blocked flue wall, retaining wall furnace tail slightly higher. Generally have four door, it is customary to close the rear door as the first door, near the combustion chamber door called the fourth door, the first door into molybdenum, fourth door is the material used, the door can be used as mixing all the materials used and allocated. End of a wall in the furnace pit, where a large collection of molybdenum dust particles, then the flue gas into the upright section, and then to the main flue horizontal section, the way to the main flue dust collection chamber, the general level of single furnace smoke long road to recovery of dust, and finally into the chimney flue.
Concentrate installed furnace through 2mm sieve prior to, to increase the contact area with the gas concentrates to increase the reaction rate.
A charge of about 300kg, tile in the entrance area of the first furnace hearth, a thickness of 65mm, about 120 minutes continuous firing forward appropriated second furnace door area. About 120 minutes and then forward appropriated third furnace door area. Loading from each door, the fourth door baked, to be roughly 8 hours to move the first door area when dialing material, the prepared concentrate to a first furnace door area, continuously calcined .
First furnace door gas temperature 503-573K, concentrate temperature of 453-503K. Removal of the first door area is mainly oil and water, stirring once every 30 minutes or so. The second furnace door of the gas temperature is 673-723K, concentrate temperature of 683-733K. The second major area is heated door concentrates, and desulfurization reaction, stirring once every 20 minutes. Third furnace gas temperature in front of 813-853K, concentrate temperature of 823-873K. The third furnace door area total sulfur removal of about 75%, stirring once every 10 minutes. The fourth furnace door of the gas temperature is 873-953K, concentrate temperature of 883-973K. The fourth furnace door area close to the combustion chamber, the furnace temperature is high, there has been to concentrate in order to burn than 0.07% sulfur released every 7-8 minutes, stirring once. Curing occurs when you open a large door stirring constantly, until the dispersion concentrate has desulfurization qualified, should be immediately released.
The door can be controlled by adjusting the temperature of the furnace and the combustion chamber of the flapper tail for the heat to achieve. Try to control the temperature of 923K less concentrate to reduce evaporation. Single oven roasting molybdenum recovery was about 94%.
2. Kiln roasted molybdenum concentrate
In the country with external heating molybdenum roasting kiln, rotary kiln technical parameters: Length 18000mm; diameter of 1100mm; Speed 0.5-1r/min; inclination of 1%. Hourly feeding 190-200kg, each kiln Nissan molybdenum sand 3.8-4.5t.
The material in the kiln kiln rotation and tilt action, by the kiln to kiln movement. Meanwhile, molybdenite oxidation reaction begins. According MoS2 occurred in the kiln furnace thermal chemical reactions and thermal effect, the kiln can be broadly divided into three segments, with the feed rate and the location of the physical properties of concentrates and chemical composition varies:
(1) preheating dry belt. Paragraph in section 6-7m kiln at a temperature of between 773-923K, in preheating the material during drying to remove oil and water.
(2) reaction zone. This section of the kiln at the intermediate 4-5m, the temperature at 923-1073K, MoS2 during achieve ignition, mainly by chemical reaction heat of their own oxidation reaction of molybdenum oxide. When the material of the residual sulfur to 3.5%, the desulfurization can not rely on the heat of reaction, this time supplied by the furnace temperature, the residual sulfur continue off.
(3) cooling belt. 7-8m in the kiln at a temperature of between 923-1023K, roasting molybdenite good cooked inside during cooling down after baked.
Molybdenum roasting kiln, the material in the furnace to stay for about 4h. Using gravity and cyclone dust collector. Kiln roasting molybdenum recoveries of 96.6% -97.5%, cooked molybdenum sulfur content of less than 0.08% or less, a pass rate of 90%. Rotary kiln heated parts of the body to be burned easily, usually changed every three months.
3. Multilayer oven roasted molybdenum concentrate
Multilayer furnace more commonly used at home and abroad, is a good roasting equipment. Furnace is lined with refractory brick consisting of a cylindrical steel shell, the furnace is equipped with a central gear rotated by the motor through the central axis of the fixed arm is fixed rake rake teeth in the center axis, the rake teeth on the hearth make a circular motion around the central axis. Rake arm is fed from the central axis of air cooling.
Eight furnace diameter 6034mm, an inner diameter of 5034mm, total height of 12970mm, central speed 0.75,0.98 r / min.
With a good charge, with the screw feeder hopper joined the furnace, according to the need to adjust the feed rate of the concentrate to the first layer of the outer edge of the hearth, with fixed arm with a rake angle of rake teeth dial material agitation, charge from the outer edge of the hearth furnace center movement, and finally the furnace near the center axis blanking aperture, the second layer hearth furnace fell within the edge region. Since rake stirring pull material, charge movement to the outer edge of the hearth, the third layer blanking Kong fell the outer edge of the hearth area, so concentrate through all of the hearth, cooked roasted molybdenum concentrate by qualified eighth fall below the hearth layer material storage tank.
Molybdenum sulfide oxidation heat released when larger, so fuel consumption is not. Roaster with gas via underground pipes and nozzle configuration around the stove into the furnace sixth, seventh and eighth. 1-7 layers respectively, outlet pipe, the exhaust gas is discharged through the duct. Each floor has a door, furnace conditions for observation and adjust the temperature used.
Seen by the production practice, two, three bottom oven temperature slightly, charge dark red, furnace gas flow helps pellets was loose state, the maintenance of normal operation the stove will play a good role. Allow the temperature is slightly different, but the furnace temperature is too low, will slow down and not sweet roasting calcine; oven temperature is too high due to volatilization of molybdenum trioxide, molybdenum losses increase, and the charge will be sintered into blocks, roasting impervious would lead sinter ore hearth layer long since accelerated wear of tooth harrow, so special attention should be layers of molybdenum roasting temperature control.
Layers into the furnace temperature can increase or decrease the amount of gas, increase or decrease Choudao, opening and closing the layers and layers of gas pipeline valve door approach to regulation. To increase the temperature of the layers 3-7 layers, you need to open the eighth floor of a small door and increase the supply of gas or off cored, seven of the exhaust valve; to raise six, seven temperature, the need to increase gas consumption . If these methods fail to achieve the effect, want to increase the temperature of each layer must be reduced Choudao. To lower the temperature must be increased Choudao. 2-5 layers in order to reduce the high temperature, returned goods should be added, if necessary, a small door opens 3,4 layer.
The oven is preheating zone 1-2, 3-5 layer is the main desulfurization zone 6-8 removal of residual sulfur layer region. The sixth layer cured layer control to favor the oxidation of sulfur, so that when moved to the fifth layer or the cured layer seventh layer, should reduce or increase the suction of the suction means adjusted.
As for roasting the concentrate characteristics of appearance also changed, molybdenum roasting good cooked in hot yellow and shiny. When the multilayer molybdenite roasting oven, about 10% -15% escaping dust, dust collection system generally composed of cyclone and electrostatic precipitator, dust removal efficiency of 99% and collected dust to return furnace for roasting . Each eight-furnace stove circadian output of about 14t.
4. Molybdenum roaster roasting
This method is widely used for roasting sulphide concentrates. Roasting process flow of air from the bottom up, upwardly flowing gas stream so that the charge particles in a boiling state, this state is characterized by a stream of particles moving violently, which looks like a boiling liquid, so called roasting.
Roasting has obvious advantages, such as:
(1) improve production efficiency 15-20 times than the multilayer furnace;
(2) roasting process can be carried out automatically;
(3) is not easy to generate firing molybdate and molybdenum oxide calcine not contain two;
(4) roasting rhenium escape rate of 92%.
Production of molybdenum furnace Process Description
Cooked molybdenum mine is the main raw material production of molybdenum, molybdenum molybdenum iron sources, in addition to requirements of high grade outside of the impurities also have strict requirements. General composition of: Mo48% -52%, S ≤ 0.065%, P ≤ 0.023%, Cu ≤ 0.30%, SiO 2 sub> 8% -14%, Pb0.2% -0.5%. Particle size not greater than 20mm ,10-20mm size shall not exceed 20% of total.
75% ferrosilicon ferrosilicon powder by crushing, milling the powder raw material used to restore the cooked molybdenum, iron scale and other oxides. Ferrosilicon powder must have accurate before use of silicon, of aluminum content, the silicon content of 75% -77% required particle size requirement is :1.0-1 .8 mm not more than 1% ,0.5-1 .0 mm particle size of not more than 10% , the rest is 0.5mm or less. Particle size is too general cause elevated molybdenum silicon, using high silicon content of ferrosilicon powder is better than a good low silicon content.
Aluminum particles have accurate ingredient aluminum content as a basis for calculation, the size requirements of 3mm or less. Particle size is too small, the production of safe; too large, then the smelting reaction negative. Increase the amount of aluminum particles with cooked according to the temperature of molybdenum, molybdenum content, production scale, temperature conditions, and generally with each batch into 5-8kg.
Ironscale is rolling, forging the iron skin, is smelting oxidants and flux. In about 30% of the smelting reaction into the alloy, a source of iron in the alloy; about 70% of the iron scale in the form of FeO into the slag, the slag from the dilution effect. Requirements of iron scale: Fe ≥ 68%, S ≤ 0.05%, P ≤ 0.035%, C ≤ 0.30%, Cu ≤ 0.1%. Ironscale be heated and dried before use to remove moisture and oil, can also be used in the production of iron ore, but high sulfur iron ore, is now the country has rarely used.
Alloy steel scrap is the main source of iron, requiring greater than 98% iron, steel scrap carbon steel for general use. Fluorite size should be less than 20mm, heated and dried prior to use to remove moisture, fluorite CaF ≥ 90%, S ≤ 0.05%, P ≤ 0.05%, can be used. Charge distribution in fluorite slag dosage depends on the actual situation and cooked molybdenum ore SiO 2 sub> content, generally with the amount of each batch into 2-3kg.
Saltpeter is sodium nitrate, when cooked using a low molybdenum molybdenum, often because lack of oxygen, reducing agents can not pay more, resulting in low heat charge, available as a supplement saltpeter thermal agents, each batch with addition of 1-3kg .
Charge ratio of: cooked molybdenum 100kg; saltpeter 3kg; aluminum particles 6kg; Ironscale 20kg; ferrosilicon powder 28.28kg; steel scrap 23.06kg; fluorite 2kg; Total 182.34kg.
Total heat of each batch of charge:
Charge to be processed into a suitable size, and then to be dried, according to ingredients than the ingredients. The charge is to ensure accurate weighing smelting normal prerequisites. Weighing order is cooked molybdenum, saltpeter, aluminum particles, iron scale, ferrosilicon, steel scrap, fluorite. Weighed charge into the mixing machine mixing, mixing time of about 8min, mix together the charge into the hopper.
Ingredients job is a very carefully, do not allow the slightest mistake job batching staff to focus, strong sense of responsibility. Maximize the use of electronic-controlled device.
Ingredients should be strictly fire, because the charge characteristics of flammable and explosive dusts, require strict fire safety measures. Mixing process should be tightly closed smoke dust removal facilities.
Molybdenum iron smelting furnace is the main equipment. Furnace shell is welded with 10mm round steel tube lined with refractory bricks, furnace shell at a distance of 100mm at the lower edge of the discharge opening with a diameter of 120mm ready furnace slag on the sand base, in the hemisphere in sand foundation made shaped recess for receiving the molten alloy. Accommodate alloy sand pit called nest.
Made with a dried river sand sand pit, put sand pit furnace tube after tamping, especially with the lower edge of the furnace tube junction between the sand pit, to pound inside high 150-200mm, 400mm high to pound out smelting slag to prevent leakage from the seam binding. Sand nest by natural drying, non-nest with wet sand, otherwise it will cause serious splash phenomenon, and even splash wounding.
The melting process
Good mix charge into the furnace. Plus a good first hopper after finishing return goods should be added, debris, paved ring hollow circle, not near the furnace wall, to prevent the adhesive does not melt in the furnace wall, nor can not stay in the center of the reaction pathway, partition the reaction . Ring paved, and then add a second bucket charge, installed after the material surface charge from the upper edge of the stove should not be less than 500mm, to prevent splashing when the spill response.
In the center of the surface charge to do a pit, and then joined the ignition mixture was shaken things drill rod inserted into the ignition, the ignition material connected with the lower charge. After ignition mall plus pyrophoric agent magnesium shavings 100g, straighten the exhaust hood with a fire ignited after the reaction automatically.
Reaction process change is downward from the center and spread to the surrounding. Normal reaction time is less than 10 minutes. Previous 1/4 time to react smoothly; intense reaction in the middle of a period of time, emit large amounts of brown smoke, there is a slight boil and splash phenomenon; in the rear 1/4 hours reaction is slowed down, bright flame, smoke slowed reaction at the end significant light.
Smelting process normal signs are:
(1) reacted strongly, exhaust gas rich, the reaction continuously, without splashing significant end of the reaction, no prolonged phenomenon, after completion of the reaction, gas lights refreshed.
(2) put the slag slag better mobility, a little bonding phenomenon. After cooling, the slag tank scum surface protrusions, shiny, dark green residue samples.
(3) uprooted slag furnace tube when pulling wire phenomenon, molybdenum iron ingot upper slag cover slightly concave downward.
(4) The reaction time in the range of 2-10 minutes.
Smelting process is not a normal phenomenon, causes, consequences and treatment methods are:
(1) Other phenomena normal, but a lot of splashing. This is due to charge excessive moisture or heat units or sand pit caused by moisture. This phenomenon is likely to cause leakage stove or splashing wounding charge, so that the high silicon alloy. If the heat is too high, it is necessary to reduce aluminum particles, ferrosilicon powder with increasing intake; charge or sand nest if it is wet, it is necessary to solve the charge and dry sand nest problems.
(2) the reaction is too intense, a lot of splash, the reaction time is very short, the end of the fast; bright after the flue gas, slag viscosity, color, blue, green, remove a small sample cooled molybdenum easily broken, the section was a bright star silver white. This is reducing excessive performance, often leading to high molybdenum alloy silicon substrate, then the need to reduce the amount of reducing agent is blended with the general decrease each batch 0.3-0.7kg.
(3) smooth reaction, the reaction stopped, and dark brown smoke rising slowly. Reaction time is long, the end of the obvious and prolonged. After pulling furnace, molybdenum iron ingot surface slag surface bubbles, and a flaming phenomenon. Molybdenum is not cold to remove small pieces of iron ingot ferro molybdenum sample is cooled, after hanging dark brown surface scum, a small sample of molybdenum iron hard, irregular cross-section, grayish black. It is a reducing agent less than the performance. This causes higher molybdenum alloys, silicon is low (less than 0.05%), molybdenum iron ingots layered, easy cooling rust, finishing difficult, molybdenum slag is high, the metal particles are mostly, then must be increased reducing agent, usually each batch increase 0.2-0.5kg.
(4) the reaction is slow, no normal gas, and the reaction time is long. This is the burden of insufficient heat. This often leads to a high molybdenum alloys, silicon is high, delamination or segregation of iron ingot 30 minutes after the reaction of the metal particles sedation settling time to ensure that the residue containing molybdenum 0.35% or less. Open the Java port, slag flows slag pot, the sampling and analysis of molybdenum content. Higher than 0.35% of the rich to return smelting slag. Depleted residue can be discarded or utilization. Discharge residue, uprooted furnace tube with Tieshao from the sand on the base metal ingot iron sample is taken. Alloy surface is smooth, green slag microstructure, fracture dense silver gray, crystalline tiny, no bright stars, marking the molybdenum iron of good quality. Normal alloys, slag composition range is as follows. , This time to check the charge particle size, composition and oxygen, and then adjust the ratio of ingredients according to specific circumstances.
30 minutes after completion of the reaction of the metal particles sedation settling time to ensure that the residue containing molybdenum 0.35% or less. Open the Java port, slag flows slag pot, the sampling and analysis of molybdenum content. Higher than 0.35% of the rich to return smelting slag. Depleted residue can be discarded or utilization. Discharge residue, uprooted furnace tube with Tieshao from the sand on the base metal ingot iron sample is taken. Alloy surface is smooth, green slag microstructure, fracture dense silver gray, crystalline tiny, no bright stars, marking the molybdenum iron of good quality. Normal alloys, slag composition range is as follows.
Alloy and slag composition
- Alloy ingots nest in the sand cooled 7-8h, with a special jig from iron. In sintered sand to scrape bottom of the ingot, ingot upper lid to use a rake turned down slag, slag cover the upper part of ingot to use a rake turned down, and then compressed air to slag Chuijin. Cooling water in the water tank 30min, cooled alloy naturally burst easy finishing. To prevent rusting alloy water-cooled, water-cooled time not too long, to the center also terminates when the red hot water, natural cooling, the alloy waste heat by itself residual moisture drying.
- After finishing alloy samples were taken prior to analysis because there is segregation of alloy ingots, so the sampling method shall be as follows: the metal ingots were divided into three equal portions, the bisector take three metal column, and then the metal column , from the center to the edge of the column in the order column 4,3,2 samples were evenly distributed between a total of nine samples and mix each sample mass of about 200g, iron ingot segregation of molybdenum shall not exceed ± 3%. Alloy composition of segregation, segregation of carbon and sulfur is not only the center of the slightly higher. Greater segregation of molybdenum and silicon and molybdenum content in the ingot lower than 2% higher than the upper, while the center of the slightly higher silicon content in the upper and middle parts of the maximum difference of about 0.7%. These instructions segregation is extremely serious. Except when finishing the fight go alloy slag residues and internal, the alloy ingot also broken into 40-50mm only after packaging.
- 1t55% Mo standard smelting iron unit consumption of molybdenum: molybdenum (discounted at 45% Mo, molybdenum recovery was 98.33%) 1213kg; 75% ferrosilicon 339-350kg; iron scale 250kg; steel scrap 260-270kg; Aluminum grain 45-60kg; fluorite 30kg; saltpeter 40kg.
- Increase is to improve the recovery of molybdenum molybdenum economic fundamental measures. Molybdenum production losses caused by the main way is to take away the loss of gas and slag losses. Mo in the flue gas mainly in the form of molybdenum oxide dust; molybdenum slag mainly in the form of metal particles. At present, some manufacturers use a large bag filter to recover molybdenum smelting flue gas dust, has received good results. Molybdenum slag can be re-elected or magnetic separation methods to recycle. To maximize the production of the molybdenum metal particles settling down from the slag, which requires low melting point slag, not sticky. Therefore, if the slag FeO content maintained at 16% or more, and to charge a slight excess of the reducing agent, with sufficient heat.
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