Mo iron production technology and equipment

I. Introduction of Molybdenum Metal Properties
The main physical and chemical properties of molybdenum as follows:

High melting point of molybdenum, molybdenum at high temperatures the evaporation rate is very low vapor pressure is small, the most important feature is the electrical conductivity of molybdenum strong. Mo capability inorganic acid corrosion, but can quickly dissolved in nitric acid and sulfuric acid mixed solution.
Molybdenum and iron can be soluble in any ratio. In the 1453-1813K range, compounds MoFe (including Mo63.29%) solid-state stability. 1753K even in the following solid phase will crystallize Mo2Fe3. Greater than 50% of molybdenum, the alloy was significantly higher melting point, such as molybdenum alloy melting point of 60% of 2073K, a high molybdenum containing molybdenum can not flow from the furnace.
Formation of molybdenum carbide and carbon Mo2C and MoC. Mo2C the melting point of 2653K, MoC's melting point is 2843K, and may generate complex carbides Fe3Mo3C and Fe3CMo3C. Molybdenum and silicon generated Mo3Si, Mo5Si3, MoSi2. Molybdenum and aluminum generate MoAl. Generate a series of molybdenum sulfide and sulfur, MoS2, Mo2S3, MoS3, which is the main sulfide MoS2. The molybdenum containing MoS2 as molybdenite. When the temperature is higher than 673K easily oxidized when MoS2 MoO3 and MoO2.
Molybdenum oxide and oxygen to generate a series of MoO3, MoO2, Mo2O3, Mo4O11, among which is the most stable MoO3 and MoO2. MoO3 has obvious acid anhydride as molybdate, is light green powder; heating was bright yellow. Melting point of 978K, the boiling point of 1428K, the heat of formation 746kJ/mo, density 4.4g/cm3, the time when the temperature is higher than 873K for a significant sublimation of MoO3. MoO3 slightly soluble in water, soluble in caustic soda, ammonia generated molybdate solution. MoO2 is a purple-brown powder, and a metallic luster. When the temperature is significantly greater than 1273K sublimation MoO2 when its heat of formation for the 588.2kJ/mol, density 6.34g/cm3. MoO2 insoluble in water and alkaline solution, not soluble in sulfuric acid, hydrochloric acid.
Ⅱ.The oxidation of molybdenum concentrate roasting
MoS molybdenum containing about 75% because of high sulfur content can not be used to direct smelting of iron and molybdenum production of molybdenum oxide blocks, so the removal of sulfur oxidizing roasting must be used. Molybdenum concentrate roasting habits as raw material in front of molybdenum concentrate, molybdenum concentrate roasting is called after the molybdenum or molybdenum cooked baked sand. Add concentrate to the roaster before the content and impurity content of molybdenum should be the ingredients, and to be fully mixed, with a good compound error of 0.2% molybdenum content within, Mo ≥ 45%, Pb ≤ 0.8%, Cu ≤ 0.6%, SiO2 ≤ 12%, CaO ≤ 3%, H2O ≤ 4%.

The rotary kiln roasting molybdenum
With external heating in the domestic molybdenum concentrate roasting kiln, rotary kiln technical parameters: Length 28000mm; diameter 1500mm; speed 0.5-1r/min; dip 1%. each kiln Nissan molybdenum sand 6-8t.
Material in the kiln kiln rotation and tilt under the effect of movement from the kiln to kiln. Meanwhile, the oxidation of molybdenite started. MoS2 in the kiln based on thermo-chemical reaction occurs and the furnace thermal effect, the kiln can be broadly divided into three segments, with the location of feeding rate and concentrates and chemical composition of the physical properties vary:

(1)Preheating dry zone. Paragraph 6-7m in the kiln at the Department of the temperature between 773-923K, the material in this in the warm dry, remove the oil and water.
(2) Reaction zone. This paragraph in middle of 4-5m at the kiln, the temperature in the 923-1073K, MoS2 to light in this, mainly by the chemical reaction itself, the reaction of thermal oxidation of molybdenum oxides. When the material of the residual sulfur to 3.5% or less, can not rely on thermal desulfurization reaction, this time by the supply of high-temperature furnace, the residual sulfur to take off.
(3) Cooling zone. 7-8m in the kiln at the temperature between 923-1023K, well cooked roasted molybdenum ore in the cooling during this period of cooling baked.
Molybdenum concentrate roasting kiln, the material in the furnace to stay for about 4h. Of gravity and the cyclone dust collection. Rotary kiln calcination rate was 97% -98.5% molybdenum, molybdenum cooked to less than 0.07% sulfur content below 90% pass rate. Internal heating type rotary kiln heating mode, a change to the outside of the heating shortcomings. The rotary kiln use fixed number of year 1-10 years.

Ⅲ. The production of molybdenum-iron furnace process Introduction

1. Raw materials

Molybdenum is cooked main raw material for production of molybdenum is molybdenum in the molybdenum source of iron, in addition to other requirements of high grade, the impurities have strict requirements. General components: Mo48％－52％，S≤0.065％，P≤0.023％，Cu≤0.30％，SiO28％－14％，Pb0.2％－0.5％。Size no larger than 20mm ,10-20mm size not greater than 20% of the total.
75% ferrosilicon ferrosilicon powder by crushing, milling the powder raw material used to restore the mature molybdenum, iron scale and other oxides. Ferrosilicon powder before use must be accurate silicon, aluminum content analysis, silicon content of 75% -77% requirements, size requirements are :1.0-1 .8 mm less than 1% ,0.5-1 .0 mm particle size of not more than 10%, the rest is 0.5mm or less. Too much size increase caused by molybdenum silicon, the use of high silicon content results of ferrosilicon powder silicon content lower than the good.
Aluminum aluminum particles have the exact amount of ingredients as the basis for calculation, the size requirements in the 3mm or less. Particle size is too small, the production of unsafe; too large, the adverse reaction of smelting. The amount of aluminum particles with addition of molybdenum according to the temperature of cooked, containing molybdenum content, the production scale, the temperature conditions, and generally with each batch of material into the X kg.
Iron scale is rolling, forging the iron oxide skin, and the smelting of the oxidant flux. Smelting reaction in about 30% into the alloy, is one of the sources of iron alloys; about 70% of the iron scale in the form of FeO into the slag, slag from the dilution effect. The requirements of the iron scale: Fe ≥ 68%, S ≤ 0.05%, P ≤ 0.035%, C ≤ 0.30%, Cu ≤ 0.1%.Iron scale heat and dry before use to remove moisture and oil, can also be used in the production of iron ore, but the high sulfur iron ore, now China has been rarely used.
Steel scrap is the main source of iron alloy, requiring more than 98% iron, steel scrap carbon steel for general use. Fluorite particle size should be 20mm below the heat and dry before use, remove the water, fluorite CaF ≥ 90%, S ≤ 0.05%, P ≤ 0.05%, before use. With addition of fluorspar in the charge depends on the actual situation and the maturity of slag in the SiO2 content of molybdenum.
Saltpeter is sodium nitrate, when cooked with a low molybdenum molybdenum, often because lack of oxygen, reducing agent can not pay more, which leads to charge low heat, heat can make saltpeter for the agent .
The total heat release in each batch of charge to:
102195.6＋266662＋17170＋8716.9＋25288.3＝420032.8（kJ）

2.The melting operation

Charge to
Be processed into a suitable size, and then to be dried, by ingredients than the ingredients. Charge is to ensure the accuracy of weighing a prerequisite for normal smelting. Weighing the order is cooked molybdenum, nitrate, aluminum particles, iron scales, ferrosilicon, steel scrap, fluorite. Weighed into the mixer in charge of mixing and mixing time of about 8min, mixed together into the hopper of Charge.Charge for
Ingredients is a very careful work, does not allow the slightest mistake the work of staff to focus on ingredients, strong sense of responsibility. As much as possible electronically controlled devices.
Ingredients should be strictly fire, due to charge characteristics of flammable and explosive dust, requiring strict fire safety measures. Mixing process must be tightly closed to smoke dust removal facilities.

3.Furnace

Molybdenum iron smelting furnace is the main equipment. Furnace shell is welded with 10mm round steel tube, lined with refractory brick, the lower edge away from the furnace shell at the opening of a diameter of 100mm 120mm to put on the furnace slag prepared based on the sand, made in the sand base in the hemisphere shaped pits to accommodate the molten alloy. Said the sand pit to accommodate the alloy nest.
Dried river sand with a nest made of sand, put right after the furnace tube nest tamping sand, particularly the lower edge of the furnace tube and the junction between sand nests, to which trace 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, or splashing phenomenon will cause serious, even splashing wounding.

4.The melting process

Mixed good charge into the furnace. After the first hopper plus returns should be added finishing materials, debris, paved circle ring hollow, not near the furnace wall to prevent the adhesive does not melt in the furnace wall, can not leave no response pathway in the center, cut off response . Ring paved, and then add a second fight charge, installed after the material surface charge from the edge of the stove should not be less than 500mm, to prevent splash spill response.
Centre in charge to make a pit surface, add the mixture and then firing into the ignition material in the rock drill rod, so that material with the lower part of the ignition charge connected. Fire after ignition mall agent magnesium shavings , put right after the exhaust hood with a fire lit, the reaction automatically.
Change reaction is started by the Centre down and spread to the surrounding. Normal response time of less than 10 minutes. The first 1 / 4 time, moderate reaction; strong response in the middle of a period of time, emit large amounts of brown smoke, there is a slight boil and splash phenomenon; in the post 1 / 4 time reaction is slowed down, bright flame, smoke slowed, the reaction at the end of there was light.
Smelting process is the normal signs:
(1) reacted strongly to a strong gas discharge, the reaction in the non-stop, no splash, the end of reaction was, no prolonged phenomenon, the reaction after the gas light up refreshed;
(2) put scum slag flow is better, a little bonding phenomenon. After cooling, residue tank scum surface projections, shiny, dark green slag.
(3) pulled up tube furnace slag when pulling wire phenomenon, molybdenum iron ingots to the concave top Java Micro cap.
(4) response time within 2-10 minutes.
Smelting process is not normal, causes, consequences and treatment methods are:

1. Other phenomena normally, but a lot of splashing. This is due to charge excessive humidity or heat units, or wet sand caused by litter. This phenomenon is likely to cause leakage of furnace or splash assault charge, so that the high silicon alloys. If the heat is too high, we must reduce the aluminum particles to increase the amount of ferrosilicon powder blended with; charge or sand nest if it is wet, it is necessary to solve the dry charge and sand litter problem.

2. reaction is too intense, a lot of splash, the reaction time is very short end of the fast; the end of bright smoke, slag viscosity, color blue and green, remove the kind of small molybdenum easily broken after cooling, was the section of bright stars silver. This is a reducing agent over the performance of high silicon molybdenum alloy often leads to the end, then blended with the need to reduce the amount of reducing agent, usually each batch of material to reduce .

3. reaction smoothly, the reaction stopped, and dark brown smoke rose slowly. Long reaction time and prolong the obvious conclusion. After pulling furnace, molybdenum iron ingot surface slag surface bubbles, and a flaming phenomenon. Molybdenum is not cold in the remove small pieces of iron ingots molybdenum sample is cooled, then hung dark brown surface scum, hard like a small molybdenum, section irregular, grayish black. This is a reducing agent enough. This will lead to higher molybdenum alloys, silicon is low .molybdenum iron ingots layered, cooling easily rust, finishing problems, high molybdenum slag, metal particles and more time must be increased reducing agent, usually each batch of material to increase .

4. the slow reaction, no obvious normal gas, the reaction time is long. This is the charge of insufficient heat. This often leads to high molybdenum alloys, silicon is high, iron ingots, or segregation of reaction layer 30 minutes after sedation metal taken. Alloy surface is smooth, the microstructure green residue, the fracture was dense silver, crystal fine, no bright stars, marking the molybdenum iron of good quality. Normal alloy, slag composition range is as follows. , Then to check the charge particle size, composition and oxygen content, and then adjust the ingredients according to specific ratio.

Reaction for 30 minutes after the end of the metal particles calm settling time to ensure that the slag at 0.35% molybdenum. Mouth open slag, slag into the slag pot, sampling and analysis of molybdenum content. 0.35% higher than the rich to return smelting slag. Residue can be discarded or poor utilization. After discharge residue, pull tube furnace, with iron scoop from the sand on the base metal ingot iron samples taken. Alloy surface is smooth, the microstructure green residue, the fracture was dense silver, crystal fine, no bright stars, marking the molybdenum iron of good quality. Normal alloy, slag composition range is as follows.

5.the alloy and slag composition

Alloy ingots nest in the sand to cool 7-8h, with a special fixture from iron. Sintering in the sand to scrape the bottom of the ingot, ingots to use a rake turned down the upper residue cover, residue cover the upper part of ingots to use a rake turned down, and then compressed air to slag Chuijin. Cooling water in the tank 30min, water-cooled alloy easy natural burst finish. To prevent rust alloy water-cooled, water-cooled hard time too long, the center has to be terminated when the red hot water, natural cooling, the alloy by its own heat drying the residual moisture.
Finishing before the alloy samples taken for analysis, because the alloy ingots with segregation, so the method of sampling should be the following: the metal ingots were divided into three equal portions, taken in three equal portions of metal line column, and then in the metal column , since the center column to the edge of the column in the order 4,3,2, respectively, even taking a sample, a total of nine samples, and then mixing, each sample weight of approximately 200g, iron ingots containing molybdenum segregation may not exceed ± 3%. Segregation of alloy composition, carbon and sulfur segregation is not only the center of a little high. Greater segregation of molybdenum with silicon and molybdenum content in the ingot bottom 2% higher than the upper, while the center of a slightly higher silicon content in the upper and middle parts of the maximum difference of about 0.7%. These instructions segregation is extremely serious. In addition to finishing when the residue on the fight to the alloy and slag inside, the alloy ingots but also to the 40-50mm broken only after packaging.
Improve the recovery of molybdenum is to improve the economic efficiency of the fundamental measures of iron molybdenum. Molybdenum production losses caused by smoke is the main way away loss and slag losses. Molybdenum in the flue gas mainly in the form of molybdenum oxide dust; slag mainly of molybdenum in the form of metal particles. At present, some manufacturers use a large bag filter to recover the molybdenum metallurgical dust, with good results. Molybdenum slag can be used in the method of re-election or magnetic separation to recover. To maximize the production of the molybdenum metal particles settling down from the slag, which requires a low melting point slag, not sticky. Therefore, if the FeO content of slag remain at 16% or more, and to a slight excess of reducing agent in charge, with enough heatparticles settling time to ensure that the residue at 0.35% molybdenum. Mouth open slag, slag into the slag pot, sampling and analysis of molybdenum content. 0.35% higher than the rich to return smelting slag. Residue can be discarded or poor utilization. After discharge residue, pull tube furnace, with iron scoop from the sand on the base metal ingot iron samples