Method for preparing high-purity molybdenum disulfide by removing impurities from low-grade molybdenum concentrate

Abstract

The invention discloses a method for preparing high-purity molybdenum disulfide through impurity removal of low-grade molybdenum concentrate, and belongs to the technical field of mineral purification and comprehensive utilization of resources. The method comprises two key steps of chloridizing roasting of a microwave reinforced composite chloridizing agent and double-frequency ultrasonic reinforced acid leaching. Firstly, a low-temperature co-melting system is constructed through a composite chlorinating agent, the chlorination reaction temperature is remarkably reduced, selective chlorination conversion of impurities is achieved under the action of a microwave field, and the impurities such as chalcopyrite and pyrite which are difficult to effectively remove through a conventional method are converted into chlorides easy to remove; and therefore, the impurity removal difficulty of the subsequent leaching procedure is greatly reduced. And then, double-frequency ultrasonic synergistic enhancement is introduced in the acid leaching process, and deep purification of the minerals is achieved through the surface purification effect of high-frequency ultrasonic and structural dissociation and mass transfer enhancement of low-frequency ultrasonic. According to the method, the removal efficiency of impurities such as iron, copper and silicon in the low-grade molybdenum concentrate can be remarkably improved, the removal rates of the iron, the copper and the silicon all reach 98% or above, and particularly the technical problem that the impurities of the chalcopyrite are difficult to remove efficiently is solved.

Description

Technical Field

[0001] This invention belongs to the field of low-grade molybdenum concentrate impurity removal technology, and relates to a method for preparing high-purity molybdenum disulfide from low-grade molybdenum concentrate. Background Technology

[0002] Molybdenum is an important strategic non-renewable resource, mainly found in molybdenite (MoS2), accounting for approximately 90% of global molybdenum mining. According to the latest data, global molybdenum reserves are approximately 15 million tons, with my country ranking first with 5.9 million tons. However, the overall grade of these resources is low, and the industry structure is dominated by primary products such as molybdenum oxide and ferromolybdenum, with deep-processed products accounting for only about 5%. High-end molybdenum products still rely on imports. High-purity molybdenum disulfide, as a high-performance solid lubricant, is widely used in key fields such as aerospace and defense. Although its traditional purification processes are mature, they are mainly for high-grade ore sources.

[0003] With the dwindling resources of high-grade molybdenum ore, low-grade ore is gradually becoming the primary raw material. Currently, this type of ore is mostly used to produce intermediate products such as ferromolybdenum and ammonium molybdate. If traditional multiple flotation processes are used for purification, it easily leads to molybdenum dispersion loss and decreased recovery rate. Therefore, developing a new, efficient, and environmentally friendly molybdenum disulfide purification process that can directly process low-grade ore is of great significance for ensuring resource security and promoting the green upgrading of the industry.

[0004] Common impurities in low-grade molybdenum concentrate include pyrite (FeS2), chalcopyrite (CuFeS2), and quartz (SiO2). Pyrite can be removed by roasting and acid leaching, while quartz can be removed by hydrofluoric acid. However, chalcopyrite, due to its close embedding with molybdenite and its stable structure at high temperatures, is not easily decomposed and does not react with acids, making it difficult to remove effectively by conventional acid leaching. This has become a key bottleneck restricting the preparation of high-purity molybdenum disulfide. Current research on the removal of chalcopyrite impurities from molybdenum concentrate is relatively limited. Most related processes currently focus on wet extraction and conversion to obtain products such as ammonium molybdate. For example, the oxygen-pressure water leaching-co-extraction process described in patent application number CN202410641167.X, although highly efficient in removing copper, does not produce molybdenum disulfide as its final product, which is inconsistent with the goal of directly obtaining solid lubricating materials.

[0005] Against this backdrop, chlorination roasting technology, through high-temperature chlorination reactions, transforms metallic impurities into volatile chlorides, providing a new approach for deep impurity removal. Currently, research on this technology for removing impurities from molybdenum concentrate is still limited: Patent application CN202110612383.8 uses vacuum chlorination roasting to remove iron, achieving good results but requiring vacuum treatment and demanding high-level equipment and processes; patent application CN202411914292.X achieves chlorination roasting for iron removal under an inert atmosphere, with significant iron removal effects, but neither of these patents addresses chalcopyrite removal and only uses calcium chloride as the chlorinating agent, requiring high reaction temperatures. In contrast, composite chlorinating agent systems, due to their low eutectic point and high chlorination activity, can promote the volatilization of impurities under milder conditions, thereby optimizing the process, reducing energy consumption, and providing a new technical path for deepening research on molybdenum concentrate impurity removal. Overall, systematic research on chlorination roasting for removing chalcopyrite impurities from low-grade molybdenum concentrate is still lacking and requires further exploration.

[0006] Therefore, conducting research on chlorination roasting purification of low-grade molybdenum concentrate and developing efficient, direct, and low-energy-consumption green preparation technology for molybdenum disulfide is of great scientific significance and engineering value. Summary of the Invention

[0007] To address the bottleneck of existing technologies in effectively removing chalcopyrite (CuFeS2) impurities from low-grade molybdenum concentrate, this invention proposes a microwave-enhanced composite chlorinating agent roasting synergistic with calcium hydroxide chlorination. This method utilizes the microwave heating effect to induce thermal dissociation of tightly coexisting quartz, MoS2, FeS2, and CuFeS2 in the molybdenum concentrate, effectively disrupting the mineral encapsulation structure and enhancing the reaction contact between each phase and the composite chlorinating agent. This strengthens the chlorination conversion process and significantly improves the impurity removal rate in subsequent leaching processes. Under the synergistic effect of the microwave field and the composite chlorinating agent, this system can achieve selective chlorination decomposition of impurity minerals at relatively low temperatures. Pyrite (FeS2) is chlorinated into FeCl2; while chalcopyrite (CuFeS2) is efficiently converted through a dual reaction pathway of "direct chlorination" and "decomposition-chlorination," forming a porous structure on its surface, significantly enhancing the mass transfer process, thereby promoting the conversion and removal of copper and iron impurities into gaseous chlorides. This process reduces the activation energy required for the reaction and improves the conversion efficiency, while ensuring that it does not react with the target component molybdenum disulfide, thereby guaranteeing the purity and performance of the final product and laying a solid foundation for subsequent acid leaching to remove iron, copper, and silicon impurities.

[0008] Meanwhile, the calcium hydroxide added to the system decomposes into calcium oxide above 600℃. On the one hand, it captures Cl2 and HCl in the gas phase, fixing them as CaCl2, reducing chlorine loss and enhancing chlorine source circulation; on the other hand, it reacts with Al2O3 and SiO2 in the minerals to form acid-soluble aluminosilicates, avoiding ineffective consumption of chlorinating agents and improving chlorine utilization efficiency and fixation effect. This method, through the synergistic mechanism of microwave-induced dissociation, chlorination-induced conversion, and calcium-based chlorination, systematically improves the removal efficiency of Fe and Cu impurities, providing an effective route for the preparation of high-purity molybdenum disulfide.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0010] The method includes the following steps:

[0011] (1) Microwave-enhanced composite chlorination roasting: At least two of calcium chloride, sodium chloride and calcium hydroxide are mixed evenly in a certain proportion and then thoroughly mixed with molybdenum concentrate. The mixture is then microwave-heated and roasted in an inert atmosphere. The roasting tail gas is treated in a tail gas treatment device to obtain the roasting product. The inert atmosphere can be nitrogen, argon, helium or other gases.

[0012] (2) Dual-frequency ultrasonic enhanced acid leaching: The roasted material obtained in step (1) is added to hydrochloric acid or hydrofluoric acid solution for segmented leaching or mixed acid leaching. First, enhanced leaching is carried out under high-frequency ultrasonic conditions, and then switched to low-frequency ultrasonic for enhanced leaching. After that, filtration, washing and drying are carried out in sequence to complete the removal of iron, copper and silicon from molybdenum concentrate.

[0013] Preferably, in step (1), the amount of calcium chloride added is 10%-40% of the mass of molybdenum concentrate, the amount of sodium chloride added is 0%-20% of the mass of molybdenum concentrate, and the amount of calcium hydroxide added is 10%-30% of the mass of molybdenum concentrate. For example, the mass ratio of CaCl2-NaCl-Ca(OH)2 can be 10%:0%:10%, 10%:20%:30%, 20%:0%:10%, 20%:20%:30%, 30%:0%:10%, 30%:20%:30%, 40%:0%:10%, or 40%:20%:30%. Of course, besides the above schemes, the present invention preferably uses a mass ratio of CaCl2-NaCl-Ca(OH)2 of 10-40:10-20:10-30.

[0014] Preferably, in step (1), the calcination temperature is 600-900℃ and the holding time is 30-150min. With the synergistic effect of other parameters of the present invention, for the first time, a relatively low calcination temperature, such as 600-620℃, can be used to achieve efficient removal of impurities such as iron, copper, and silicon.

[0015] Preferably, in step (2), the solid-liquid ratio of the calcined product to hydrochloric acid is 1g:2-7ml, the total duration of ultrasonic-enhanced acid leaching is 16-90min, the acid leaching temperature is 65-95℃, and the microwave power range is 1800-2600W.

[0016] Preferably, in step (2), the concentration of the hydrochloric acid solution is 5-25%.

[0017] Preferably, in step (2), the solid-liquid ratio of the acid-leaching material to the hydrofluoric acid solution is 1g:2-7ml, the total duration of ultrasonic-enhanced acid leaching is 16-90min, and the leaching temperature is 50-80℃.

[0018] Preferably, in step (2), the concentration of the hydrofluoric acid solution is 5-25%, more preferably 5-20%.

[0019] As a preferred option, in step (2), the solid-liquid ratio of the calcined product to the mixed acid solution is 1g:2-7ml, the total time for ultrasonic-enhanced acid leaching is 30-180min, and the leaching temperature is 50-95℃.

[0020] Preferably, in step (2), the concentration of hydrochloric acid in the mixed acid solution is 5% to 20%; the concentration of hydrofluoric acid is 5% to 20%.

[0021] Preferably, in step (2), the high-frequency ultrasound frequency range is 34-40kHz, the low-frequency ultrasound frequency range is 16-20kHz, and the power density is 50-400W / L.

[0022] Preferably, the low-grade molybdenum concentrate is a low-grade molybdenite concentrate obtained from primary molybdenum ore after preliminary mining and beneficiation, with a molybdenum disulfide content of 60%-75% and a particle size distribution of the ore satisfying: D90≤74μm.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] 1. This invention employs a calcium chloride-sodium chloride composite chlorinating agent to construct a low-temperature eutectic system, with its eutectic temperature reduced to approximately 504°C, significantly lower than that of single calcium chloride (melting point approximately 772°C) or sodium chloride (melting point approximately 801°C). During roasting, this system forms a highly fluid molten salt medium that can fully encapsulate mineral particles, transforming traditional solid-solid reactions or high-viscosity solid-liquid contacts into highly efficient molten salt reactions, significantly enhancing the mass transfer process. In this molten salt environment, the diffusion of chloride ions into the mineral interior is accelerated, and the activation energy of chlorination decomposition of pyrite (FeS2) and chalcopyrite (CuFeS2) is significantly reduced, thus enabling efficient conversion into easily soluble or volatile chlorides at lower temperatures. This reaction process also forms a porous structure on the chalcopyrite surface, further optimizing the generation and separation interface of volatile metal chlorides. Simultaneously, the molten salt layer effectively inhibits secondary oxidation of the products, and sodium chloride can also react with gangue components or intermediate products, synergistically releasing HCl gas with calcium chloride, broadening the chlorination reaction pathway. This system achieves efficient conversion of impurities while reducing roasting temperature and energy consumption. The byproducts are acid-soluble and leave no solid residue, combining the advantages of economy, energy saving and consumption reduction, and process cleanliness.

[0025] 2. This invention utilizes microwave-enhanced chlorination roasting of molybdenum concentrate with a composite chlorinating agent. This process induces thermal stress dissociation of tightly embedded and interlocking quartz, MoS2, FeS2, and CuFeS2 within the molybdenum concentrate, effectively breaking down the intermineral structures and enhancing the reaction contact between impurity phases and the composite chlorinating agent. This significantly reduces or eliminates mass transfer barriers between reactants during subsequent leaching, thereby further improving the overall impurity removal rate. The introduction of a chlorinating agent, Ca(OH)2, into the roasting system directly captures small amounts of unreacted HCl in the gas phase, converting it into CaCl2, thus enabling chlorine recycling and replenishment of the effective chlorinating agent. Furthermore, calcium oxide preferentially reacts with Al2O3 and SiO2 in the minerals to generate a stable silicate phase, CaAl2Si2O8. This phase not only inhibits the ineffective decomposition of calcium chloride, improving the directional fixation and utilization efficiency of chlorine, but also absorbs elemental sulfur released from gangue minerals during roasting, thereby reducing chlorine source loss and lowering sulfur-containing tail gas emissions. In addition, this silicate phase is soluble during subsequent leaching, preventing the introduction of secondary impurities.

[0026] 3. This invention employs a staged dual-frequency ultrasonic enhanced leaching process, systematically improving the removal efficiency of impurity elements from molybdenum concentrate by sequentially applying high-frequency and low-frequency ultrasound. First, the high directivity and strong jet effect of high-frequency ultrasound effectively removes impurities and residual reagents adhering to the mineral surface, fully exposing the fresh reaction interface. Subsequently, the strong stirring and cavitation effects of low-frequency ultrasound further disrupt the macroscopic structure of the molybdenum concentrate, promoting internal mass transfer and reaction processes. With increasing ultrasonic power, energy density increases, significantly enhancing leaching kinetics. The microjets and impact forces generated by cavitation further intensify, thereby strengthening the activation effect on mineral leaching. This sequential treatment strategy, through staged and directional energy input, significantly improves the leaching efficiency of iron, copper, silicon, and related byproducts, achieving systematic optimization of impurity removal.

[0027] 4. Under the same power conditions, the effect of ultrasonic frequency on leaching efficiency exhibits a regular difference: low frequency (16kHz) results in intense cavitation and strong penetration, effectively breaking down hard structures, but its effect is concentrated and prone to thermal damage; 20kHz is more uniform and gentle, which is beneficial for the preservation of active ingredients. Mid-frequency (34kHz) offers a relatively balanced approach between cavitation intensity and range of action, suitable for routine extraction; while 40kHz produces fine and dense cavitation, excelling in surface and microscopic treatment, but with weaker mixing and deep mass transfer capabilities.

[0028] 5. This invention significantly reduces the roasting temperature while shortening the roasting cycle, enabling efficient removal of chalcopyrite-type copper impurities from molybdenum concentrate that are complex in form and difficult to remove using conventional methods. This achieves a simultaneous improvement in impurity removal rate and chlorinating agent utilization efficiency. Furthermore, this method can significantly suppress the emission of sulfur-containing tail gas, achieving deep cleaning and impurity removal while also demonstrating outstanding environmental friendliness. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0030] In the embodiments and comparative examples of this invention, unless otherwise specified, all chemical reagents used in the experiments were commercially available analytical grade.

[0031] Example 1:

[0032] This embodiment removes impurities from molybdenum concentrate using the following method:

[0033] (1) Microwave-enhanced composite chlorination roasting: Calcium chloride, sodium chloride, and calcium hydroxide were thoroughly mixed in a mass ratio of 1:2:1. This mixture was then thoroughly mixed with molybdenum concentrate containing 41.68% Mo, 5.05% Fe, 3.32% Cu, and 6.03% Si. The mixture was then placed in a microwave heating device and charged with nitrogen. The roasting was carried out at 600℃ for 30 minutes. The microwave power was 1800W, the frequency was 2.45GHz, and the wavelength was 12.2cm. After cooling, the roasted material was obtained. The material was then ground to a particle size range that met the requirement of D90≤74μm. The amount of calcium chloride added was 10% of the mass of molybdenum concentrate, the amount of sodium chloride added was 20% of the mass of molybdenum concentrate, and the amount of calcium hydroxide added was 10% of the mass of molybdenum concentrate.

[0034] (2) Dual-frequency ultrasonic enhanced acid leaching: The calcined material obtained in step (1) was added to a 5% hydrochloric acid solution at a solid-liquid ratio of 1g:2ml. The solution was leached for 8 minutes at a temperature of 65℃, an ultrasonic frequency of 34kHz, and a power density of 50W / L. The leaching was then repeated at an ultrasonic frequency of 16kHz and a power density of 50W / L for another 8 minutes. After leaching, the material was washed, filtered, and dried to obtain the acid-leached material. The acid-leached material was then added to a 5% hydrofluoric acid solution at a solid-liquid ratio of 1g:2ml. The solution was leached for 8 minutes at a temperature of 50℃, an ultrasonic frequency of 34kHz, and a power density of 50W / L. The leaching was then repeated at an ultrasonic frequency of 16kHz and a power density of 50W / L for another 8 minutes. During the leaching process, the liquid was continuously stirred at a stirring speed of 300rpm. After leaching, the liquid was washed, filtered, and dried to complete the removal of impurities.

[0035] The final product of this embodiment was tested and found to contain 0.265% iron by mass, with an iron removal rate of approximately 95.93%; 0.236% copper by mass, with a copper removal rate of approximately 95.10%; 0.252% silicon by mass, with a silicon removal rate of approximately 96.95%; and 57.93% molybdenum by mass, with a molybdenum recovery rate of 98.30%.

[0036] Example 2:

[0037] This embodiment removes impurities from molybdenum concentrate using the following method:

[0038] (1) Microwave-enhanced composite chlorination roasting: Calcium chloride, sodium chloride, and calcium hydroxide were thoroughly mixed in a mass ratio of 2:2:1.5. This mixture was then thoroughly mixed with molybdenum concentrate containing 41.68% Mo, 5.05% Fe, 3.32% Cu, and 6.03% Si. The mixture was placed in a microwave heating device and filled with nitrogen. The mixture was roasted at 700℃ for 60 minutes with a microwave power of 2000W, a frequency of 2.45GHz, and a wavelength of 12.2cm. After cooling, the roasted material was obtained and ground to a particle size range that met the requirement of D90≤74μm. The amount of calcium chloride added was 20% of the mass of molybdenum concentrate, the amount of sodium chloride added was 20% of the mass of molybdenum concentrate, and the amount of calcium hydroxide added was 15% of the mass of molybdenum concentrate.

[0039] (2) Dual-frequency ultrasonic enhanced acid leaching: The calcined material obtained in step (1) was added to a 10% hydrochloric acid solution at a solid-liquid ratio of 1g:3ml. The solution was leached for 15 minutes at a temperature of 75℃, an ultrasonic frequency of 34kHz, and a power density of 100W / L. The solution was then switched to an ultrasonic frequency of 16kHz and a power density of 100W / L for another 15 minutes. After leaching, the material was washed, filtered, and dried to obtain the acid-leached material. The acid-leached material was then added to a 10% hydrofluoric acid solution at a solid-liquid ratio of 1g:3ml. The solution was leached for 15 minutes at a temperature of 60℃, an ultrasonic frequency of 34kHz, and a power density of 100W / L. The solution was then switched to an ultrasonic frequency of 16kHz and a power density of 100W / L for another 15 minutes. During the leaching process, the liquid was continuously stirred at a stirring speed of 300rpm. After leaching, the liquid was washed, filtered, and dried to complete the removal of impurities.

[0040] The final product of this embodiment was tested and found to contain 0.188% iron by mass, with an iron removal rate of approximately 97.10%; 0.176% copper by mass, with a copper removal rate of approximately 96.36%; 0.170% silicon by mass, with a silicon removal rate of approximately 97.85%; and 58.37% molybdenum by mass, with a molybdenum recovery rate of 98.63%.

[0041] Example 3:

[0042] This embodiment removes impurities from molybdenum concentrate using the following method:

[0043] (1) Microwave-enhanced composite chlorination roasting: Calcium chloride, sodium chloride, and calcium hydroxide were thoroughly mixed in a mass ratio of 3:2:2. This mixture was then thoroughly mixed with molybdenum concentrate containing 41.68% Mo, 5.05% Fe, 3.32% Cu, and 6.03% Si. The mixture was placed in a microwave heating device and filled with nitrogen. The mixture was roasted at 750℃ for 60 minutes. The microwave power was 2200W, the frequency was 2.45GHz, and the wavelength was 12.2cm. After cooling, the roasted material was obtained. The material was then ground to a particle size range that met the requirement of D90≤74μm. The amount of calcium chloride added was 30% of the mass of molybdenum concentrate, the amount of sodium chloride added was 20% of the mass of molybdenum concentrate, and the amount of calcium hydroxide added was 20% of the mass of molybdenum concentrate.

[0044] (2) Dual-frequency ultrasonic enhanced acid leaching: The calcined material obtained in step (1) was added to a 15% hydrochloric acid solution at a solid-liquid ratio of 1g:4ml. The solution was leached for 30 minutes at a temperature of 75℃, an ultrasonic frequency of 40kHz, and a power density of 200W / L. The solution was then switched to an ultrasonic frequency of 20kHz and a power density of 200W / L for another 30 minutes. After leaching, the solution was washed, filtered, and dried to obtain the acid-leached material. The acid-leached material was then added to a 10% hydrofluoric acid solution at a solid-liquid ratio of 1g:4ml. The solution was leached for 30 minutes at a temperature of 60℃, an ultrasonic frequency of 40kHz, and a power density of 200W / L. The solution was then switched to an ultrasonic frequency of 20kHz and a power density of 200W / L for another 30 minutes. During the leaching process, the liquid was continuously stirred at a stirring speed of 300rpm. After leaching, the solution was washed, filtered, and dried to complete the removal of impurities.

[0045] The final product of this embodiment was tested and found to contain 0.134% iron by mass, with an iron removal rate of approximately 97.98%; 0.129% copper by mass, with a copper removal rate of approximately 97.38%; 0.121% silicon by mass, with a silicon removal rate of approximately 98.39%; and 58.72% molybdenum by mass, with a molybdenum recovery rate of 98.88%.

[0046] Example 4:

[0047] This embodiment removes impurities from molybdenum concentrate using the following method:

[0048] (1) Microwave-enhanced composite chlorination roasting: Calcium chloride, sodium chloride, and calcium hydroxide were thoroughly mixed in a mass ratio of 4:2:3. This mixture was then thoroughly mixed with molybdenum concentrate containing 41.68% Mo, 5.05% Fe, 3.32% Cu, and 6.03% Si. The mixture was placed in a microwave heating device and filled with nitrogen. The mixture was roasted at 800℃ for 120 min with a microwave power of 2400W, a frequency of 2.45GHz, and a wavelength of 12.2cm. After cooling, the roasted material was obtained and ground until the particle size range met the requirement of D90≤74μm. The amount of calcium chloride added was 40% of the mass of molybdenum concentrate, the amount of sodium chloride added was 20% of the mass of molybdenum concentrate, and the amount of calcium hydroxide added was 30% of the mass of molybdenum concentrate.

[0049] (2) Dual-frequency ultrasonic enhanced acid leaching: The calcined material obtained in step (1) was added to a 20% hydrochloric acid solution at a solid-liquid ratio of 1g:6ml. The solution was leached for 45 minutes at a temperature of 85℃, an ultrasonic frequency of 40kHz, and a power density of 300W / L. The leaching was then repeated at an ultrasonic frequency of 20kHz and a power density of 300W / L for another 45 minutes. After leaching, the material was washed, filtered, and dried to obtain the acid-leached material. The acid-leached material was then added to a 15% hydrofluoric acid solution at a solid-liquid ratio of 1g:6ml. The solution was leached for 45 minutes at a temperature of 70℃, an ultrasonic frequency of 40kHz, and a power density of 300W / L. The leaching was then repeated at an ultrasonic frequency of 20kHz and a power density of 300W / L for another 45 minutes. During the leaching process, the liquid was continuously stirred at a stirring speed of 300rpm. After leaching, the liquid was washed, filtered, and dried to remove impurities.

[0050] The final product of this embodiment was tested and found to contain 0.103% iron by mass, with an iron removal rate of approximately 98.52%; 0.095% copper by mass, with a copper removal rate of approximately 98.10%; 0.088% silicon by mass, with a silicon removal rate of approximately 98.77%; and 59.08% molybdenum by mass, with a molybdenum recovery rate of 99.10%.

[0051] Example 5:

[0052] This embodiment removes impurities from molybdenum concentrate using the following method:

[0053] (1) Microwave-enhanced composite chlorination roasting: Calcium chloride, sodium chloride, and calcium hydroxide were thoroughly mixed in a mass ratio of 4:2:3. This mixture was then mixed evenly with molybdenum concentrate containing 41.68% Mo, 5.05% Fe, 3.32% Cu, and 6.03% Si. The mixture was placed in a microwave heating device and filled with nitrogen. The mixture was roasted at 900℃ for 150 min with a microwave power of 2600W, a frequency of 2.45GHz, and a wavelength of 12.2cm. After cooling, the roasted material was obtained and ground until the particle size range met the requirement of D90≤74μm. The amount of calcium chloride added was 40% of the mass of molybdenum concentrate, the amount of sodium chloride added was 20% of the mass of molybdenum concentrate, and the amount of calcium hydroxide added was 30% of the mass of molybdenum concentrate.

[0054] (2) Dual-frequency ultrasonic enhanced acid leaching: The calcined material obtained in step (1) was added to a mixed acid solution (20% hydrochloric acid solution concentration + 20% hydrofluoric acid solution concentration) at a solid-liquid ratio of 1g:7ml. The leaching was carried out for 90min at a temperature of 95℃, an ultrasonic frequency of 40kHz, and a power density of 400W / L. The ultrasonic frequency was then switched to 20kHz and the power density was 400W / L, and the leaching was carried out for another 90min. During the leaching process, the liquid was continuously stirred at a stirring speed of 300rpm. After the leaching was completed, the liquid was washed, filtered, and dried to remove impurities.

[0055] The final product of this embodiment was tested and found to contain 0.066% iron by mass, with an iron removal rate of approximately 99.05%; 0.058% copper by mass, with a copper removal rate of approximately 98.88%; 0.053% silicon by mass, with a silicon removal rate of approximately 99.16%; and 59.30% molybdenum by mass, with a molybdenum recovery rate of 99.27%.

[0056] Comparative Example 1:

[0057] Comparative Example 1 removes impurities from molybdenum concentrate using the following method:

[0058] This comparative example uses the same method as Example 1 to remove impurities from molybdenum concentrate. The difference is that in this comparative example, only CaCl2 is added as a chlorinating agent during the microwave roasting stage to perform microwave chlorination roasting of molybdenum concentrate.

[0059] The final product of this comparative example was tested and found to contain 0.495% iron by mass, with an iron removal rate of approximately 92.28%; 0.455% copper by mass, with a copper removal rate of approximately 90.46%; 0.418% silicon by mass, with a silicon removal rate of approximately 95.13%; and 57.06% molybdenum by mass, with a molybdenum recovery rate of 97.52%.

[0060] Comparative Example 2:

[0061] Comparative Example 2 removes impurities from molybdenum concentrate using the following method:

[0062] This comparative example uses the same method as Example 1 to remove impurities from molybdenum concentrate. The difference is that no chlorinating agent is added during the microwave roasting stage in this comparative example.

[0063] The final product of this comparative example was tested and found to contain 1.463% iron by mass, with an iron removal rate of approximately 77.15%; 1.463% copper by mass, with a copper removal rate of approximately 69.10%; 1.037% silicon by mass, with a silicon removal rate of approximately 88.43%; and 54.23% molybdenum by mass, with a molybdenum recovery rate of 97.02%.

[0064] Comparative Example 3:

[0065] Comparative Example 3 removes impurities from molybdenum concentrate using the following method:

[0066] This comparative example uses the same method as Example 1 to remove impurities from molybdenum concentrate. The difference is that in this comparative example, calcium hydroxide, a chlorinating agent, is not added during the microwave roasting stage, and the molybdenum concentrate is subjected to microwave chlorination roasting.

[0067] The final product of this comparative example was tested and found to contain 0.412% iron by mass, with an iron removal rate of approximately 93.57%; 0.383% copper by mass, with a copper removal rate of approximately 92.11%; 0.300% silicon by mass, with a silicon removal rate of approximately 96.40%; and 57.53% molybdenum by mass, with a molybdenum recovery rate of 97.72%.

[0068] Comparative Example 4:

[0069] Comparative Example 4 removes impurities from molybdenum concentrate using the following method:

[0070] This comparative example uses the same method as Example 1 to remove impurities from molybdenum concentrate, the difference being that in this comparative example, only high-frequency ultrasonic treatment is applied during the acid leaching process.

[0071] The final product of this comparative example was tested and found to contain 0.469% iron by mass, with an iron removal rate of approximately 92.55%; 0.427% copper by mass, with a copper removal rate of approximately 90.92%; 0.383% silicon by mass, with a silicon removal rate of approximately 95.55%; and 57.21% molybdenum by mass, with a molybdenum recovery rate of 98.12%.

[0072] Comparative Example 5:

[0073] Comparative Example 5 removes impurities from molybdenum concentrate using the following method:

[0074] This comparative example uses the same method as Example 1 to remove impurities from molybdenum concentrate, the difference being that in this comparative example, only low-frequency ultrasonic treatment is applied during the acid leaching process.

[0075] The final product of this comparative example was tested and found to contain 0.423% iron by mass, with an iron removal rate of approximately 93.30%; 0.391% copper by mass, with a copper removal rate of approximately 92.04%; 0.328% silicon by mass, with a silicon removal rate of approximately 96.13%; and 57.42% molybdenum by mass, with a molybdenum recovery rate of 98.04%.

[0076] Comparative Example 6:

[0077] Comparative Example 6 removes impurities from molybdenum concentrate using the following method:

[0078] This comparative example uses the same method as Example 1 to remove impurities from molybdenum concentrate, the difference being that ultrasonic treatment is not applied during the acid leaching process in this comparative example.

[0079] The final product of this comparative example was tested and found to contain 0.673% iron by mass, with an iron removal rate of approximately 89.33%; 0.621% copper by mass, with a copper removal rate of approximately 86.88%; 0.523% silicon by mass, with a silicon removal rate of approximately 94.04%; and 56.38% molybdenum by mass, with a molybdenum recovery rate of 98.27%.

[0080] Comparative Example 7:

[0081] Comparative Example 7 removes impurities from molybdenum concentrate using the following method:

[0082] This comparative example uses the same method as Example 5 to remove impurities from molybdenum concentrate. The difference is that in this comparative example, the acid leaching process first involves adding a 20% hydrochloric acid solution at a solid-liquid ratio of 1g:7ml, leaching for 45 minutes at a temperature of 95℃, an ultrasonic frequency of 40kHz, and a power density of 400W / L, then switching to an ultrasonic frequency of 20kHz and a power density of 400W / L for another 45 minutes. After leaching, the material is washed, filtered, and dried to obtain the acid-leached material. This acid-leached material is then added to a 20% hydrofluoric acid solution at a solid-liquid ratio of 1g:7ml, leaching for 45 minutes at a temperature of 95℃, an ultrasonic frequency of 40kHz, and a power density of 400W / L, then switching to an ultrasonic frequency of 20kHz and a power density of 400W / L for another 45 minutes. During the leaching process, the liquid is continuously stirred at a stirring speed of 300rpm. After leaching, the material is washed, filtered, and dried to complete the impurity removal.

[0083] The final product of this embodiment was tested and found to contain 0.082% iron by mass, with an iron removal rate of approximately 98.87%; 0.069% copper by mass, with a copper removal rate of approximately 98.66%; 0.065% silicon by mass, with a silicon removal rate of approximately 99.02%; and 59.12% molybdenum by mass, with a molybdenum recovery rate of 99.28%.

[0084] A comparison of Example 1 and Comparative Example 1 shows that the impurity removal effect of Comparative Example 1 is significantly reduced. This is because calcium chloride alone has a high melting point, low reactivity at the roasting temperature, and difficulty in forming a highly fluid molten salt phase. The reaction system is mostly in solid-solid contact or high-viscosity solid-liquid mixture state, resulting in low mass transfer efficiency and insufficient wetting and encapsulation of mineral particles, leading to slow chloride ion diffusion and hindered reaction interface renewal. Simultaneously, the lack of synergistic effect from sodium chloride prevents the continuous in-situ release of HCl gas through its reaction with gangue components. The chlorination reaction pathway is singular, providing insufficient impurity conversion for minerals such as pyrite and chalcopyrite. Furthermore, it fails to promote the dissociation of tightly embedded and mutually encapsulated quartz, MoS2, FeS2, and CuFeS2 in the molybdenum concentrate. These factors collectively lead to incomplete impurity chlorination and low subsequent leaching removal efficiency, ultimately affecting the purity and recovery rate of the molybdenum disulfide product.

[0085] A comparison of the experimental results of Example 1 and Comparative Example 2 shows that the impurity removal efficiency of Comparative Example 2 is significantly reduced. The main reasons are: the pyrite in the molybdenum concentrate failed to undergo complete decomposition and transformation, and the remaining unreacted pyrite was difficult to dissolve effectively in subsequent leaching processes; simultaneously, the products generated from the decomposition of chalcopyrite had low chemical activity and insufficient reactivity with acidic and alkaline media, resulting in the incomplete removal of impurities such as copper and iron; furthermore, the process failed to effectively disrupt the tightly intergrowth symbiotic structure between the molybdenum concentrate and gangue minerals, limiting the penetration and mass transfer of the reaction medium. In contrast, the composite chlorinating agent used in Example 2 significantly promoted the decomposition and chlorination transformation of pyrite and chalcopyrite, generating volatile and acid-soluble metal chlorides, while simultaneously disrupting the symbiotic structure between minerals, thereby achieving highly efficient impurity removal in subsequent leaching stages.

[0086] The comparison between Example 1 and Comparative Example 3 shows that the impurity removal effect in Comparative Example 3 is significantly reduced. This fully demonstrates that the addition of calcium hydroxide, a chlorinating agent, can increase the content of effective chlorinating agent in the actual chlorination process through high-temperature decomposition reaction, as well as suppress ineffective side reactions between chlorinating agent and gangue minerals, thereby reducing non-target consumption of chlorinating agent.

[0087] A comparison between Example 1 and Comparative Example 4 shows that the impurity removal effect in Comparative Example 4 is significantly reduced. The main reason for its poor impurity removal effect is that the effect of high-frequency ultrasound alone is mainly focused on surface cleaning and shallow activation. Although it can remove some surface-attached impurities, it has limited ability to destroy tightly embedded impurities and deep encapsulated structures inside the mineral. In contrast, the staged treatment, which exposes a fresh interface with high-frequency ultrasound and then utilizes the strong cavitation and stirring effect of low-frequency ultrasound, can achieve deep dissociation and enhanced mass transfer from the surface to the interior, thereby significantly improving the impurity removal efficiency.

[0088] A comparison of Example 1 and Comparative Example 5 shows that the impurity removal effect in Comparative Example 5 is significantly reduced. Although low-frequency ultrasound alone can destroy the overall structure of the mineral through its mechanical and cavitation effects, it cannot effectively remove the impurity layer attached to the mineral surface, resulting in insufficient exposure of the internal reaction interface. In contrast, the staged process first removes surface impurities and opens the reaction channels using high-frequency ultrasound, and then uses the mechanical and cavitation effects of low-frequency ultrasound to penetrate and destroy the internal structure and enhance mass transfer, achieving a step-by-step deep impurity removal from the surface to the interior. Therefore, the impurity removal efficiency and thoroughness of using low-frequency ultrasound alone are insufficient due to the lack of an effective preliminary surface cleaning step.

[0089] A comparison of Example 1 and Comparative Example 6 shows that the impurity removal effect of Comparative Example 6 is significantly reduced, mainly because ultrasonic enhancement leaching was not used. Ultrasonic action, through its unique mechanical and cavitation effects, can effectively enhance the mass transfer process and improve the leaching process kinetics, thereby significantly improving leaching efficiency.

[0090] A comparison of Example 5 and Comparative Example 7 shows that Comparative Example 7 has a lower impurity removal efficiency. This is mainly because the mixed acid leaching process utilizes the low pH environment maintained by hydrochloric acid and the strong dissociation effect of hydrofluoric acid on the silicon impurity coating layer to form a synergistic etching mechanism, effectively increasing the exposure degree of Fe, Cu, and Si impurities and accelerating their dissolution kinetics. This process follows a diffusion-controlled model and has a low activation energy. While ensuring efficient impurity removal, it significantly simplifies the operation process, thus achieving better purification efficiency and economy overall.

[0091] The comparison between Comparative Example 4 and Comparative Example 5 shows that Comparative Example 5 has a better impurity removal effect. The main reason is that low-frequency ultrasound can effectively destroy the macroscopic agglomeration structure of molybdenum concentrate and the encapsulation state between minerals through its strong mechanical stirring and cavitation effect, significantly enhancing the renewal and mass transfer process of the reaction interface, thereby promoting the release and dissolution of internal impurities. While high-frequency ultrasound alone can remove surface-attached impurities, its depth of action is limited, and it is difficult to effectively destroy and remove tightly bound impurities inside the mineral.

[0092] In summary, the method of this invention for processing low-grade molybdenum concentrate can not only efficiently remove chalcopyrite-type copper impurities that are difficult to handle by conventional processes, but also significantly improve the overall impurity removal efficiency, thereby eliminating the need for traditional flotation processes and directly producing molybdenum disulfide products with higher purity and better quality.

[0093] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for preparing high-purity molybdenum disulfide from low-grade molybdenum concentrate by removing impurities, characterized in that: The method includes the following steps: (1) Microwave-enhanced composite chlorination roasting: At least two of calcium chloride, sodium chloride and calcium hydroxide are mixed evenly in a certain proportion and then fully mixed with molybdenum concentrate. Microwave heating roasting is carried out in an inert atmosphere. The roasting tail gas is treated in a tail gas treatment device to obtain the roasting product. (2) Dual-frequency ultrasonic enhanced acid leaching: The roasted material obtained in step (1) is added to hydrochloric acid or hydrofluoric acid solution for segmented leaching or mixed acid leaching. First, enhanced leaching is carried out under high-frequency ultrasonic conditions, and then switched to low-frequency ultrasonic for enhanced leaching. After that, filtration, washing and drying are carried out in sequence to complete the removal of iron, copper and silicon from molybdenum concentrate.

2. The method according to claim 1, characterized in that: In step (1), the amount of calcium chloride added is 10%-40% of the mass of molybdenum concentrate, the amount of sodium chloride added is 0%-20% of the mass of molybdenum concentrate, and the amount of calcium hydroxide added is 10%-30% of the mass of molybdenum concentrate.

3. The method according to claim 1, characterized in that: In step (1), the temperature is 600-900℃, the heat preservation time is 30-150min, and the microwave power range is 1800-2600W.

4. The method according to claim 1, characterized in that: In step (2), the solid-liquid ratio of the calcined product to hydrochloric acid is 1g:2-7ml, the total time for ultrasonic-enhanced acid leaching is 16-90min, and the acid leaching temperature is 65-95℃.

5. The method according to claim 1 or 4, characterized in that: In step (2), when hydrochloric acid is used for leaching, the concentration of the hydrochloric acid solution is 5-25%, and when hydrofluoric acid is used for leaching, the concentration of the hydrofluoric acid solution is 5-25%.

6. The method according to claim 1, characterized in that: In step (2), the solid-liquid ratio of the material to the hydrofluoric acid solution is 1g:2-7ml, the total time for ultrasonic-enhanced acid leaching is 16-90min, and the leaching temperature is 50-90℃.

7. The method according to claim 1, characterized in that: In step (2), the solid-liquid ratio of the calcined product to the mixed acid solution is 1g:2-7ml, the total time for ultrasonic-enhanced acid leaching is 30-180min, and the leaching temperature is 50-95℃.

8. The method according to any one of claims 1 or 7, characterized in that: In step (2), the concentration of hydrochloric acid in the mixed acid solution is 5%~20%; the concentration of hydrofluoric acid is 5%~20%.

9. The method according to claim 1, characterized in that: In step (2), the high-frequency ultrasonic frequency range is 34-40kHz, the low-frequency ultrasonic frequency range is 16-20kHz, and the power density is 50-400W / L.

10. The method according to any one of claims 1, 2, 3, 4, 6, 7, and 9, characterized in that: The low-grade molybdenum concentrate is a low-grade molybdenite concentrate obtained from primary molybdenum ore after preliminary mining and beneficiation. The molybdenum disulfide content in the molybdenum concentrate is 60%-75%, and the particle size distribution of the ore meets the following condition: D90≤74μm.