Molybdenum concentrate oxygen-enriched roasting method and roasting product

Abstract

The invention relates to the technical field of non-ferrous metallurgy, in particular to a molybdenum concentrate oxygen-enriched roasting method and a roasted product, and in the method, corresponding oxygen-enriched air is input by adopting a segmented oxygen control strategy in each stage. According to the method, a segmented oxygen control strategy is designed, in the original multi-hearth furnace molybdenum concentrate oxidizing roasting process, rich oxygen is increased in roasting furnace layers, the dynamic oxygen content in the furnace layers is increased, the total amount of oxygen participating in an oxidizing reaction in roasting atmospheres in all the furnace layers is overall increased, the oxygen-rich atmospheres are manufactured in all the roasting furnace layers, and the oxidizing desulfurization rate of materials is overall increased; therefore, accurate distribution of oxygen is achieved, the oxygen utilization rate is increased, and the thermal load and energy consumption of equipment are reduced.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal metallurgy technology, specifically to a method for oxygen-enriched roasting of molybdenum concentrate and the roasting product. Background Technology

[0002] Molybdenum is an important strategic metal, widely used in metallurgy, petrochemicals, electronics and other industries. Oxidative roasting of molybdenum concentrate (mainly molybdenite MoS2) is a key process step in the production of industrial molybdenum trioxide, the purpose of which is to oxidize molybdenum disulfide to molybdenum trioxide while achieving complete desulfurization.

[0003] The oxidative roasting of molybdenum concentrate is a complex multiphase reaction process, mainly involving the oxidation of molybdenum disulfide. The process is as follows: First stage (preheating and deoiling): At 300℃, flotation oil volatilizes and precipitates, creating a clean surface for subsequent oxidation. Second stage (exothermic oxidation): At 580℃, molybdenum disulfide reacts with oxygen in a strongly exothermic reaction: 2MoS2 + 7O2 → 2MoO3 + 4SO2 (ΔH = -235 kcal / mol), with the reaction exothermic to maintain the furnace temperature. Third stage (reheating oxidation): At 650℃, molybdenum dioxide is further oxidized: 2MoO2 + O2 → 2MoO3 (ΔH = -68 kcal / mol), requiring reheating from the natural gas burner inside the furnace. Fourth stage (enhanced desulfurization): Under oxygen-rich conditions at 700℃, residual sulfides are completely oxidized.

[0004] Multi-hearth furnaces are one of the main pieces of equipment for the oxidative roasting of molybdenum concentrate. A typical multi-hearth furnace consists of 10-16 hearth layers, with a diameter usually of 2-6 meters. The molybdenum concentrate is added from the top layer, and the material falls layer by layer between the hearth layers through the rake arms and teeth driven by the central shaft. During the fall, it comes into countercurrent contact with the rising hot airflow, achieving the oxidation reaction. US4523948A discloses a method for roasting molybdenum concentrate containing flotation oil in a multi-hearth furnace. This method achieves the staged deoiling and oxidation reactions through zoned temperature control. The molybdenum concentrate is heated to a temperature sufficient to initiate an autothermal roasting reaction (not exceeding about 667°C) in the first roasting zone, and then continues to pass through subsequent roasting zones to complete desulfurization and form molybdenum trioxide. In traditional multi-hearth furnace processes, air is introduced from the bottom layer or in stages, with an oxygen concentration of about 21%. The roasting process usually takes 10-12 hours. To ensure the furnace temperature, each layer is equipped with 2-4 natural gas burners for supplemental heating. To improve the efficiency of oxidation reaction, oxygen-enriched roasting technology has gradually attracted attention. CN202717823U discloses an oxygen-enriched roasting device for molybdenum sulfide concentrate, which uses an overall oxygen-enriched roasting method, but it still cannot solve the problems of low oxygen utilization and long roasting time. Summary of the Invention

[0005] In view of the problems of long roasting time and high energy consumption caused by low oxygen utilization in the oxygen-enriched roasting of molybdenum concentrate in the prior art, the present invention discloses an oxygen-enriched roasting method for molybdenum concentrate and roasting products.

[0006] This invention is achieved through the following technical solution: An oxygen-enriched roasting method for molybdenum concentrate employs a segmented oxygen control strategy to roast the molybdenum concentrate in multiple stages to obtain roasting products.

[0007] Preferably, the composition of the molybdenum concentrate includes: 45%≤Mo≤54%, moisture≤5%, Cu≤0.4%, and others.

[0008] Preferably, oxygen-enriched air includes oxygen and nitrogen.

[0009] Preferably, the multi-stage roasting includes a preheating stage, an oxidation stage, a supplementary heating oxidation stage, and an enhanced desulfurization stage. The segmented oxygen control strategy refers to inputting oxygen-enriched air with different oxygen concentrations in each stage.

[0010] Preferably, the segmented oxygen control strategy is designed based on the reaction kinetic equation, which is: v=k[O2] n In the formula, v represents the reaction rate, which is the amount by which the concentration of reactants decreases or the concentration of products increases per unit time, i.e. the rate at which MoS2 is oxidized to MoO3, in mol / (L·s). n is the reaction order; for MoS2, the oxidation order is n≈0.8. k represents the rate constant, which is closely related to temperature and usually follows the Arrhenius equation: k = Ae Ea / (RT) A is the pre-exponential factor, Ea is the activation energy of the reaction, R is the gas constant, and T is the thermodynamic temperature.

[0011] Preferably, during the preheating stage, the oxygen concentration in the oxygen-enriched air is 25%~30%, and the temperature is 200~300℃; During the exothermic oxidation stage, the oxygen concentration in the oxygen-enriched air is 30%~38%, and the temperature is 550~650℃. During the reheating and oxidation stage, the oxygen concentration in the oxygen-enriched air is 30%~38%, and the temperature is 600~700℃; During the enhanced desulfurization stage, the oxygen concentration in the oxygen-enriched air is 35%~40%, and the temperature is 650~750℃.

[0012] Preferably, the entire roasting process time is set based on a kinetic model of material oxidation conversion rate and desulfurization rate. This kinetic model is as follows: η = 1 - exp(-kt) In the formula, η is the conversion rate, k is the reaction rate constant, and t is the residence time.

[0013] Preferably, the entire roasting process takes 8 to 10 hours.

[0014] A roasting product obtained by oxygen-enriched roasting of molybdenum concentrate.

[0015] Preferably, the calcined product is molybdenum trioxide with a sulfur content ≤0.1%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a segmented oxygen control strategy for oxygen-enriched roasting of molybdenum concentrate. In the traditional multi-hearth furnace oxidative roasting process, oxygen enrichment is added to the roasting furnace layers to increase the dynamic oxygen content within each layer. This overall increases the total amount of oxygen participating in the oxidation reaction in each roasting layer, creating an oxygen-enriched atmosphere that comprehensively enhances the oxidation and desulfurization rate of the material. This achieves precise oxygen distribution, improves oxygen utilization, and reduces equipment heat load and energy consumption. Verification shows that this increases the oxidation reaction rate by 20%–25%, reduces natural gas consumption by 15%–20%, shortens the roasting cycle to 8–9 hours, and maintains a stable product sulfur content of <0.1%. Specific quantitative indicators include: oxygen utilization rate increased from the traditional 21% to 35%, energy consumption decreased from 12.5 GJ / t to 10.2 GJ / t, and production capacity increased from 3.2 t / m²·d to 3.8 t / m²·d. This invention significantly reduces molybdenum smelting production costs, improves equipment utilization, and meets environmental emission requirements. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a segmented oxygen control strategy for an oxygen-enriched roasting method for molybdenum concentrate according to the present invention. Figure 2 This is a schematic diagram of the segmented oxygen control strategy for the oxygen-enriched roasting method of molybdenum concentrate shown in Example 1. Figure 3 This is a schematic diagram of the segmented oxygen control strategy for the oxygen-enriched roasting method of molybdenum concentrate shown in Example 2. Detailed Implementation

[0018] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0019] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0020] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0021] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0022] This invention discloses an oxygen-enriched roasting method for molybdenum concentrate, which employs a segmented oxygen control strategy to roast the molybdenum concentrate in multiple stages to obtain roasting products.

[0023] The composition of molybdenum concentrate includes: 45%≤Mo≤54%, moisture≤5%, Cu≤0.4% and others.

[0024] The segmented oxygen control strategy is designed based on the reaction kinetic equation, which is: v=k[O2] n In the formula, v represents the reaction rate, which is the amount by which the concentration of reactants decreases or the concentration of products increases per unit time, i.e. the rate at which MoS2 is oxidized to MoO3, in mol / (L·s). n is the reaction order; for MoS2, the oxidation order is n≈0.8. k represents the rate constant, which is closely related to temperature and usually follows the Arrhenius equation: k = Ae Ea / (RT) A is the pre-exponential factor, Ea is the activation energy of the reaction, R is the gas constant, and T is the thermodynamic temperature.

[0025] Multi-stage roasting includes a preheating stage, an oxidation stage, a supplementary heating and oxidation stage, and an enhanced desulfurization stage. The segmented oxygen control strategy involves introducing oxygen-enriched air with different oxygen concentrations at each stage. For details, please refer to... Figure 1 During the preheating stage, the oxygen concentration in the oxygen-enriched air is 25%~30%, and the temperature is 200~300℃; During the exothermic oxidation stage, the oxygen concentration in the oxygen-enriched air is 30%~38%, and the temperature is 550~650℃. During the reheating and oxidation stage, the oxygen concentration in the oxygen-enriched air is 30%~38%, and the temperature is 600~700℃; During the enhanced desulfurization stage, the oxygen concentration in the oxygen-enriched air is 35%~40%, and the temperature is 650~750℃.

[0026] The entire roasting process time was set based on a kinetic model of material oxidation conversion rate and desulfurization rate. This kinetic model is as follows: η = 1 - exp(-kt) In the formula, η is the conversion rate, k is the reaction rate constant, and t is the residence time. The entire calcination process takes 8-10 hours.

[0027] The present invention also discloses a product obtained by oxygen-enriched roasting of molybdenum concentrate, wherein the roasting product is molybdenum trioxide with a sulfur content ≤0.1%.

[0028] This invention discloses an oxygen-enriched roasting method for molybdenum concentrate. By employing a segmented oxygen control strategy designed based on reaction kinetics, different oxygen-enriched environments are precisely introduced into different layers of the roasting furnace. This method specifically increases the total amount of oxygen participating in the oxidation reaction in the roasting atmosphere, creating an oxygen-enriched atmosphere in each roasting furnace layer. This accelerates the oxidation and desulfurization process of the material, achieving precise distribution and efficient utilization of oxygen. It not only improves oxygen utilization but also reduces the heat load of the equipment and overall energy consumption.

[0029] This invention also discloses a multi-hearth furnace for oxygen-enriched roasting of molybdenum concentrate. Each hearth layer of the furnace is equipped with a central shaft, rake arms, rake teeth, a feeding port, an operating door, an air inlet, and a flue gas outlet. The feeding ports of odd-numbered hearth layers are located at the edges, while those of even-numbered hearth layers are located in the middle. The central shaft drives the rake arms and rake teeth to achieve continuous stirring and tumbling of the material. Oxygen is produced using a molecular sieve oxygen generator through pressure swing adsorption (PSA). The core principle is to utilize the characteristic that zeolite molecular sieves have a much stronger adsorption capacity for nitrogen than for oxygen. Oxygen is produced from air through a cyclic process of pressure adsorption and depressurization desorption. Nitrogen is dynamically separated to obtain high-purity oxygen. The produced oxygen is mixed with air in an oxygen-enriched air mixing system to obtain oxygen-enriched air with an oxygen concentration of 30-40%. The oxygen-enriched air is delivered in stages to each layer of the hearth of the multi-hearth furnace through combustion air ducts via a combustion air blower. The segmented oxygen supply control system realizes gradient control of oxygen concentration. The oxygen concentration of the oxygen-enriched air in the upper hearth (layers 1-2) is 25%-30%, the oxygen concentration of the oxygen-enriched air in the middle hearth (intermediate layer) is 30%-38%, and the oxygen concentration of the oxygen-enriched air in the lower hearth (last two layers) is 35%-40%.

[0030] Each furnace bed is equipped with 2 to 4 natural gas burners. Precise temperature control of each section is achieved by adjusting the combustion power of the burners and the amount of waste heat compensation from the flue gas.

[0031] The flue gas waste heat recovery system includes an indirect cooler and a heat exchanger. It recovers heat from the flue gas exiting the multi-hearth furnace. The flue gas temperature is approximately 400℃, which is cooled to approximately 300℃ by the indirect cooler. The recovered waste heat, at 300-400℃, is dynamically distributed to the sixth to third-to-last hearths requiring supplemental heating based on their temperature requirements via the heat exchanger. This achieves heat compensation and reduces natural gas consumption in the multi-hearth furnace. The burner is connected to the heat exchanger, enabling coordinated control of burner heating and waste heat compensation.

[0032] The cooling fan is used to deliver cooling air to the bottom of the central shaft of the multi-hearth furnace, forcibly cooling the central shaft and rake arms to prevent them from bending, deforming and being damaged due to excessive heat. The temperature of the cooling air when it is discharged from the top of the central shaft is 170-200℃.

[0033] The residence time of molybdenum concentrate in the multi-hearth furnace is 8-10 hours, which shortens the roasting cycle compared to the 10-12 hours of the traditional process.

[0034] The flue gas waste heat recovery system also includes a cyclone dust collector and an electrostatic precipitator to purify the flue gas after passing through the indirect cooler, recover molybdenum-containing dust from the flue gas and return it to the feeding system, and send the purified flue gas to the sulfuric acid plant for acid production.

[0035] The molybdenum product obtained from the bottom of the multi-hearth furnace after oxidation roasting is molybdenum trioxide with a sulfur content of less than 0.1%, which meets the requirements of subsequent molybdenum smelting processes.

[0036] The operating principle of this multi-hearth furnace is as follows: molybdenum concentrate is added from the top layer of the multi-hearth furnace, and oxygen-enriched air with an oxygen concentration of 30% to 40% obtained by mixing with a molecular sieve oxygen generator is sent in stages to each layer of the furnace bed through a combustion fan, so that the molybdenum concentrate undergoes preheating and deoiling, exothermic oxidation, supplementary heating oxidation reaction and oxidative desulfurization in each layer of the furnace bed in sequence; the waste heat of flue gas with a temperature of 300-400℃ in the indirect cooler is recovered and sent to the furnace bed layer of the multi-hearth furnace that needs to be supplemented for heat compensation; the oxidized roasted molybdenum product is obtained from the bottom layer of the multi-hearth furnace.

[0037] In summary, this multi-hearth furnace combines molecular sieve pressure swing adsorption oxygen generation technology with multi-hearth furnace segmented oxygen-enriched roasting process, and is equipped with a flue gas waste heat recovery and compensation system to achieve efficient and energy-saving oxidative roasting of molybdenum concentrate.

[0038] Example 1: The roasting method proposed in this invention was used to roast molybdenum concentrate in a 14-layer multi-hearth furnace.

[0039] The 14-layer multi-hearth furnace has a furnace diameter of 4m and is equipped with a molecular sieve oxygen generator with an oxygen production capacity of 500 Nm³ / h (oxygen purity 93%). It is used for oxygen-enriched roasting of molybdenum concentrate with a molybdenum grade of 45%. Each hearth has an area of ​​approximately 12.56 m². The first and second layers each have 3 natural gas burners (150 kW / burner), the third to twelfth layers each have 2 natural gas burners (100 kW / burner), and the last two layers each have 4 natural gas burners (120 kW / burner). The molecular sieve oxygen generator adopts a dual-tower pressure swing adsorption process, with an adsorption pressure of 0.6 MPa, a desorption pressure of 0.02 MPa, and a cycle time of 60 seconds. The molecular sieve is a 13X type zeolite molecular sieve with a loading of 3000 kg. The oxygen-enriched air mixing system uses a Venturi mixer to ensure uniform mixing of oxygen and air. The combustion fan has an air volume of 5000 Nm³ / h and an air pressure of 50 kPa. The flue gas waste heat recovery system includes an indirect cooler (heat exchange area of ​​80 m²) and a plate heat exchanger (heat exchange efficiency of 85%). The cyclone dust collector has a dust removal efficiency of 90%, and the electrostatic precipitator has a dust removal efficiency of 99.5%. The cooling fan has an air volume of 2000 Nm³ / h.

[0040] Implementation steps: Molybdenum concentrate feeding: Molybdenum concentrate with a particle size of -100 mesh accounting for 80% (moisture content of 8%) is fed from the top of the first layer of the multi-hearth furnace through a screw feeder at a feeding speed of 2.5 t / h.

[0041] Molecular sieve oxygen generation: When the molecular sieve oxygen generation device is started, compressed air is filtered and dried before entering the adsorption tower, where nitrogen is adsorbed at a pressure of 0.6 MPa. The desorption tower releases nitrogen at a pressure of 0.02 MPa, continuously producing 500 Nm³ / h of oxygen with a purity of 93%.

[0042] Oxygen-enriched air preparation: The produced oxygen is mixed with air in a Venturi mixer. The first two layers are supplied with oxygen-enriched air with an oxygen concentration of 28% (oxygen flow rate 200 Nm³ / h, air flow rate 2300 Nm³ / h), the third to eighth layers are supplied with oxygen-enriched air with an oxygen concentration of 34% (oxygen flow rate 250 Nm³ / h, air flow rate 1800 Nm³ / h), the ninth to twelfth layers are supplied with oxygen-enriched air with an oxygen concentration of 36% (oxygen flow rate 280 Nm³ / h, air flow rate 1600 Nm³ / h), and the last two layers are supplied with oxygen-enriched air with an oxygen concentration of 38% (oxygen flow rate 300 Nm³ / h, air flow rate 1400 Nm³ / h).

[0043] The roasting process is as follows: Figure 2Preheating stage: The molybdenum concentrate stays in the first and second layers of the furnace bed for 1.5 hours. Under the atmosphere of 28% oxygen-enriched air, the natural gas burner heats the furnace bed and controls the temperature at 250℃. The material temperature rises evenly under the stirring of the rake arms and rake teeth. The flotation oil (mainly kerosene, boiling point 180~250℃) volatilizes and is discharged with the flue gas, with an oil removal rate of 98%.

[0044] Exothermic oxidation stage: The material falls into the 3rd to 8th layers of the furnace bed in sequence. Under the atmosphere of 34% oxygen-enriched air, molybdenum disulfide undergoes a strong exothermic oxidation reaction. The furnace bed temperature automatically rises to 600℃. The residence time is 2 hours, and the oxidation rate reaches 70%, producing molybdenum trioxide and molybdenum dioxide (molar ratio of about 3:1). Sulfur dioxide is also generated at the same time.

[0045] Reheating and oxidation stage: The material enters the 9th to 12th layers of the furnace bed. Under the reheating effect of 36% oxygen-enriched air and natural gas burners, the furnace bed temperature is maintained at 680℃. Molybdenum dioxide is gradually oxidized to molybdenum trioxide. The residence time is 4 hours, and the oxidation conversion rate reaches 95%. The flue gas waste heat recovery system draws flue gas at a temperature of 380℃ from the 7th layer flue, which is then cooled to 320℃ by an indirect cooler. The recovered heat is dynamically distributed to each furnace bed from the 6th to the 12th layers through a heat exchanger. The waste heat distribution ratio is adjusted in real time according to the temperature of each layer (40% for the 6th to 8th layers and 60% for the 9th to 12th layers). Natural gas consumption is reduced by 30% compared to when there is no waste heat recovery.

[0046] Enhanced desulfurization stage: The material falls into the last two layers of the furnace bed (layers 13-14). Under the action of 38% oxygen-enriched air and enhanced burners, the furnace bed temperature is raised to 720℃ and the residence time is 1.5 hours. The residual molybdenum dioxide and trace amounts of molybdenum disulfide are completely oxidized, and the sulfur content is reduced from 12% of the feed to 0.06% of the product, with a desulfurization rate of 99.5%.

[0047] Product discharge and flue gas treatment: Molybdenum oxide products are discharged from the bottom outlet of the 14th layer, cooled to 80°C by a cooler, and then packaged; flue gas is collected from the outlets of each layer, treated by a cyclone dust collector and an electrostatic precipitator, recovering approximately 20 kg / h of molybdenum-containing dust (containing 40% molybdenum) and returning it to the feeding system. The purified flue gas (containing 8-10% SO2) has a temperature of approximately 150°C and is sent to a sulfuric acid plant for acid production; Central shaft cooling: The cooling fan continuously supplies cooling air at ambient temperature (25℃) to the bottom of the central shaft at a volume of 2000 Nm³ / h. The cooling air circulates inside the central shaft to cool the rake arm and the central shaft body. When it is discharged from the top of the central shaft, the temperature is 185℃, ensuring that the temperature of the central shaft is below 300℃ to prevent deformation.

[0048] The oxygen concentration of 28-38% is based on reaction kinetics calculations. Too low a concentration will result in insufficient oxidation, while too high a concentration will lead to excessively high local temperatures and agglomeration. The furnace bed temperature range is based on the oxidation reaction temperature window of molybdenum disulfide and molybdenum dioxide and product quality requirements. The residence time of 8-10 hours is based on the kinetic model of material oxidation conversion rate and desulfurization rate: η = 1 - exp(-kt), where η is the conversion rate, k is the reaction rate constant (related to temperature and oxygen concentration), and t is the residence time. In this embodiment, the total residence time is 9 hours, which meets the requirements of conversion rate ≥95% and desulfurization rate ≥99%.

[0049] This embodiment produces molybdenum trioxide with a sulfur content of 0.06% ± 0.01% (n = 10, standard deviation 0.01%), and a molybdenum metal recovery rate of ≥99% (including dust recovery); the material residence time is shortened from 10-12 hours in the traditional process to 9 hours, increasing production capacity by 20%; oxygen-enriched roasting increases the oxidation reaction rate by 35% (according to the reaction kinetic equation v = k[O2]). n Calculations show that increasing the oxygen concentration from 21% to 34% increases the rate constant k by approximately 35%. Waste heat recovery from flue gas reduces natural gas consumption from 480 Nm³ / h to 336 Nm³ / h, saving 30% in energy and reducing the natural gas cost per ton of molybdenum product by approximately 600 yuan. The desulfurization rate reaches 99.5%, ensuring stable product quality and meeting the requirements for subsequent production of products such as ferromolybdenum and ammonium molybdate. The molybdenum dust recovery rate is ≥95%. The SO2 concentration in the flue gas is ≥3%, suitable for sulfuric acid preparation, achieving sulfur resource recovery and utilization.

[0050] Example 2: The roasting method proposed in this invention was used to roast molybdenum concentrate in a 16-layer multi-hearth furnace with a low oxygen concentration endpoint value. In this embodiment, the 16-layer multi-hearth furnace has a furnace diameter of 5m and is equipped with a molecular sieve oxygen generator with an oxygen production capacity of 400 Nm³ / h (oxygen purity of 90%), which is used to roast molybdenum concentrate with a molybdenum grade of 48% in an oxygen-enriched manner.

[0051] The main difference from Example 1 is: The lower limit of the oxygen concentration selection endpoint is as follows: 25% oxygen-enriched air for the first and second layers (lower limit of oxygen concentration range in the preheating stage), 30% oxygen-enriched air for the third to tenth layers (lower limit of oxygen concentration range in the exothermic oxidation stage), 32% oxygen-enriched air for the eleventh to fourteenth layers, and 35% oxygen-enriched air for the last two layers (lower limit of oxygen concentration range in the enhanced desulfurization stage). The furnace bed temperature is adjusted accordingly: 200℃ for the first and second layers (lower limit of the temperature range in the preheating stage), 550℃ for the third and fifth layers (lower limit of the temperature range in the exothermic oxidation stage), 600℃ for the sixth and fourteenth layers (lower limit of the temperature range in the reheat oxidation stage), and 650℃ for the last two layers (lower limit of the temperature range in the enhanced desulfurization stage). The residence time is extended to 10 hours (upper limit) to compensate for the reaction rate under lower oxygen concentrations.

[0052] The waste heat recovery temperature of the flue gas adopts the lower limit of the range. Flue gas with a temperature of 300℃ is drawn out from the 9th layer flue and kept at 300℃ (lower limit of the range) by the indirect cooler before being directly sent into the heat exchanger.

[0053] Implementation steps: The molybdenum concentrate feed rate is 3.0 t / h, the molecular sieve oxygen production rate is 400 Nm³ / h, and the oxygen-enriched air is supplied in stages as per reference. Figure 3 The oxygen concentration is 25% for layers 1-2, 30% for layers 3-10, 32% for layers 11-14, and 35% for the last two layers. The preheating and deoiling stage is held at 200℃ for 2 hours, the exothermic oxidation stage is held at 550℃ for 2.5 hours, the supplementary heating oxidation stage is held at 600℃ for 4.5 hours (waste heat recovery reduces natural gas consumption by 25%), and the enhanced desulfurization stage is held at 650℃ for 1.5 hours.

[0054] In this embodiment, a lower oxygen concentration (25%~35%) reduces the oxidation reaction rate, according to the reaction kinetic equation v=k[O2]. n (n is the reaction order, n≈0.8 for MoS2 oxidation). When the oxygen concentration is reduced from 34% to 30%, the reaction rate decreases by about 12%. Therefore, it is necessary to extend the residence time and appropriately reduce the temperature to avoid local overheating and agglomeration. The equilibrium constant Kp of the molybdenum dioxide oxidation reaction (2MoO2+O2→2MoO3) is slightly lower at lower temperatures, but it can still ensure a conversion rate of more than 95% at 620℃, while reducing the heat load and energy consumption of the equipment.

[0055] This embodiment produces molybdenum trioxide with a sulfur content of 0.08% ± 0.015%, and a molybdenum metal recovery rate of ≥99% (including dust recovery). The material residence time is 10 hours (comparable to the traditional process), but oxygen-enriched roasting still achieves a 20% increase in oxidation efficiency and improved product quality. The lower oxygen concentration and temperature reduce the equipment corrosion rate by 15% and extend the service life of refractory materials by about 20%. Waste heat recovery from flue gas achieves 25% energy savings from natural gas, which is lower than the 30% in Example 1, but still has significant economic benefits under lower temperature conditions. The desulfurization rate reaches 99.2%, and the product quality meets most application requirements. This embodiment is suitable for molybdenum concentrate with a molybdenum grade of 53%-54% or production scenarios with high requirements for equipment life.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements also fall within the scope of protection covered by the claims.

Claims

1. A method for oxygen-enriched roasting of molybdenum concentrate, characterized in that, A segmented oxygen control strategy was adopted to roast molybdenum concentrate in multiple stages to obtain roasting products.

2. The oxygen-enriched roasting method for molybdenum concentrate according to claim 1, characterized in that, The composition of molybdenum concentrate includes: 45%≤Mo≤54%, moisture≤5%, Cu≤0.4%, and others.

3. The oxygen-enriched roasting method for molybdenum concentrate according to claim 1, characterized in that, Oxygen-rich air includes oxygen and nitrogen.

4. The oxygen-enriched roasting method for molybdenum concentrate according to claim 3, characterized in that, Multi-stage roasting includes a preheating stage, an oxidation stage, a supplementary heating oxidation stage, and an enhanced desulfurization stage. The segmented oxygen control strategy refers to inputting oxygen-enriched air with different oxygen concentrations in each stage.

5. The oxygen-enriched roasting method for molybdenum concentrate according to claim 4, characterized in that, The segmented oxygen control strategy is designed based on the reaction kinetic equation, which is: v=k[O2] n In the formula, v represents the reaction rate, which is the amount by which the concentration of reactants decreases or the concentration of products increases per unit time, i.e. the rate at which MoS2 is oxidized to MoO3, in mol / (L·s). n is the reaction order; for MoS2, the oxidation order is n≈0.

8. k represents the rate constant, which is closely related to temperature and usually follows the Arrhenius equation: k = Ae Ea / (RT) A is the pre-exponential factor, Ea is the activation energy of the reaction, R is the gas constant, and T is the thermodynamic temperature.

6. The oxygen-enriched roasting method for molybdenum concentrate according to claim 4, characterized in that, During the preheating stage, the oxygen concentration in the oxygen-enriched air is 25%~30%, and the temperature is 200~300℃; During the exothermic oxidation stage, the oxygen concentration in the oxygen-enriched air is 30%~38%, and the temperature is 550~650℃. During the reheating and oxidation stage, the oxygen concentration in the oxygen-enriched air is 30%~38%, and the temperature is 600~700℃; During the enhanced desulfurization stage, the oxygen concentration in the oxygen-enriched air is 35%~40%, and the temperature is 650~750℃.

7. The oxygen-enriched roasting method for molybdenum concentrate according to claim 1, characterized in that, The entire roasting process time was set based on a kinetic model of material oxidation conversion rate and desulfurization rate. This kinetic model is as follows: η = 1 - exp(-kt) In the formula, η is the conversion rate, k is the reaction rate constant, and t is the residence time.

8. The oxygen-enriched roasting method for molybdenum concentrate according to claim 7, characterized in that, The entire roasting process takes 8 to 10 hours.

9. A roasting product obtained by the oxygen-enriched roasting method of molybdenum concentrate according to any one of claims 1 to 8.

10. The calcined product according to claim 9, wherein the calcined product is molybdenum trioxide and has a sulfur content ≤0.1%.

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