Resource recycling method for molybdenum slag

Abstract

The invention relates to the technical field of molybdenum slag resource recycling, in particular to a molybdenum slag resource recycling method which comprises the following steps: performing crushing, washing and drying pretreatment on molybdenum slag; naCl, KCl and NaF serve as fused salt, the fused salt, the cathode and the anode form a fused salt electrochemical system, the pretreated molybdenum slag is added into the fused salt for an electrochemical reduction reaction, and molybdenum in the molybdenum slag is reduced and separated out at the cathode; washing the precipitated metal molybdenum, and drying to obtain Mo powder. Resourceful treatment of the molybdenum-containing solid waste residues is achieved by adopting a molten salt electrochemical reduction recovery mode, and molybdenum elements are efficiently recovered into a metal state from complex molybdenum residues through electrochemical selective reduction in a molten salt system.

Description

Technical Field

[0001] This application relates to the technical field of resource recovery of molybdenum slag, and particularly relates to a method for resource recovery and utilization of molybdenum slag. Background Art

[0002] As an important critical metal, molybdenum is widely used in many high-end manufacturing fields such as special steel, alloys, petrochemical catalysts, electronic devices, and spacecraft components. During the metallurgical extraction process of molybdenum, especially in processes such as oxidation roasting, high-temperature reduction, chemical precipitation, and molybdenum compound production, a large amount of molybdenum slag is usually generated. These molybdenum slags generally contain unreacted or incompletely converted molybdenum oxides (such as MoO3, MoO2), iron oxides, silicates, aluminum-silicon impurities, and certain proportions of non-metallic components such as calcium and magnesium. Depending on the source, the molybdenum content in molybdenum slag ranges from 0.5% to 20%, having a high secondary resource value.

[0003] Currently, the recycling technologies for molybdenum slag mainly include the following categories: The acid leaching-extraction method uses hydrochloric acid or sulfuric acid to leach molybdenum slag, and then enriches molybdenum through means such as solvent extraction; the roasting oxidation-water leaching method converts the reduced state of Mo to MoO3 by air roasting, and then recovers Mo by water leaching. The direct reduction-enrichment method directly reduces Mo in molybdenum slag to metallic molybdenum at high temperature using carbon materials (such as coke), and then enriches molybdenum metal through magnetic separation or flotation.

[0004] The acid leaching-extraction method has a relatively high recovery rate of molybdenum (60% - 90%), but has defects such as a large consumption of acid solution, strong corrosiveness, a complex process flow, high requirements for equipment, a large amount of acidic waste liquid generated, causing environmental pollution, and high costs of extractants. The roasting oxidation-water leaching method is technically mature, but has problems such as high energy consumption (roasting temperature ≥ 500 °C), a large amount of SO2 gas released during the process, and large fluctuations in Mo recovery rate. The direct reduction-enrichment method has poor reduction selectivity and easily reduces impurities (such as Fe, V) at the same time, resulting in low product purity and being difficult to apply to high-end materials. In addition, a small amount of research has tried to use molybdenum slag as a raw material for cement or brick and tile materials, but due to the certain toxicity risk of molybdenum itself, high-Mo content slag has been listed as "hazardous waste" in some regions, resulting in strict restrictions on its application in the building materials industry. In addition, the dissolution behavior of molybdenum and heavy metal ions in the slag is unstable, which may cause long-term environmental risks.

[0005] In summary, the existing molybdenum slag treatment methods have the following key problems: the molybdenum recovery methods are highly polluting, costly, or have unstable recovery rates; the molybdenum forms in the slag are complex, with some being difficult to leach and reduce; the utilization rate of the remaining residue is low, and it is even classified as industrial solid waste or hazardous waste, with high disposal costs; there is a lack of an integrated green technology that takes into account the efficient recovery of molybdenum, environmental friendliness, and the coordinated utilization of residue resources. Therefore, there is an urgent need to develop a green metallurgical technology path that is simple to operate, has low energy consumption, low pollution, and can achieve the full-value conversion of molybdenum slag resources, promoting the efficient recycling of molybdenum resources. Summary of the Invention

[0006] The purpose of this application is to overcome the deficiencies in the prior art and provide a method for the resource recovery and utilization of molybdenum slag. By adopting the method of "molten salt electrochemical reduction recovery", the resource treatment of molybdenum-containing solid waste residue is realized. Through the electrochemical selective reduction in the molten salt system, molybdenum elements are efficiently recovered as metallic state from complex molybdenum slag.

[0007] This application is realized through the following technical solutions: A method for the resource recovery and utilization of molybdenum slag includes the following steps: Crush, wash, and dry the molybdenum slag for pretreatment; Use NaCl, KCl, and NaF as molten salts, which together with the cathode and anode form a molten salt electrochemical system. Add the pretreated molybdenum slag to the molten salt for an electrochemical reduction reaction, so that molybdenum in the molybdenum slag is reduced and precipitated at the cathode; Pickle the precipitated metallic molybdenum and then dry it to obtain Mo powder.

[0008] This application realizes good solubility and ion migration characteristics of Mo oxides through the selection of the molten salt system, which is significantly different from traditional high-temperature or acidic systems.

[0009] According to the embodiments of this application, the molar ratio of NaCl, KCl, and NaF is 5:5:1. The specific molten salt components and ratios are conducive to the selective electrochemical reduction of molybdenum.

[0010] According to the embodiments of this application, the operating temperature of the electrochemical reduction reaction is controlled at 650 - 800 °C. That is to say, for example, 650 °C, 700 °C, 750 °C, or 800 °C can be selected. In this application, the preferred temperature is 750 °C, which can ensure the full melting of the molten salt and guarantee the progress of the Mo oxide reduction reaction.

[0011] According to the embodiments of this application, the electrolytic cell of the molten salt electrochemical system is a graphite or alumina crucible, and the protective gas is one of argon or nitrogen; the cathode material is one of molybdenum sheet or titanium sheet; the anode material is graphite. The setting of the electrolysis conditions is conducive to achieving the selective reduction of Mo.

[0012] According to an embodiment of the present application, the electrochemically reduction reaction voltage is -2.0 to -2.4 V, the current density is 0.05 to 0.2 A / cm², and the reaction time is 2 - 6 h. By setting the reaction conditions, Mo preferentially deposits on the cathode during electrolysis, avoiding the co-deposition of impurity metals.

[0013] According to an embodiment of the present application, the electrolytic residue of the electrochemically reduction reaction is used for building materials after treatment, which can realize the recycling of the remaining residue, avoid pollution and improve economic benefits at the same time.

[0014] According to an embodiment of the present application, the specific process of treating the electrolytic residue is as follows: the electrolytic residue is screened and then mixed with an auxiliary agent in a certain proportion, and then calcined at a high temperature to promote the phase stabilization of the residue and endow it with gelling activity.

[0015] According to an embodiment of the present application, the auxiliary agent is lime powder, and 5% - 15% by mass of lime powder is added to the residue to adjust the Ca / Si ratio in the residue.

[0016] According to an embodiment of the present application, the calcination temperature is 900 - 1200 °C and the calcination time is 12 h, which can promote the phase stabilization of the residue and endow it with gelling activity.

[0017] According to an embodiment of the present application, the tail gas generated by the electrochemically reduction reaction electrolysis is neutralized by a NaOH spray absorption device to achieve the up-to-standard discharge of gaseous pollutants and no acid liquid discharge.

[0018] Beneficial effects: By using an optimized NaCl-KCl-NaF molten salt system and a specific electrolysis potential range, molybdenum oxide can be stably dissolved and preferentially reduced and deposited on the cathode. The recovery rate of molybdenum can stably reach more than 85%, and the purity of the deposited product is high (>98%), which is much higher than traditional methods such as wet acid leaching extraction or high-temperature roasting reduction. It effectively inhibits the co-reduction of impurity elements such as Fe, Al, and Si, improves the product quality, realizes the harmless and building material resource recycling of electrolytic residues, does not require the use of strong acids or organic solvents throughout the process, has no liquid wastewater discharge, and the electrolytic tail gas is absorbed by a NaOH solution to meet the requirements of environmental protection up-to-standard discharge. Description of the drawings

[0019] The above and / or additional aspects and advantages of the present application will become obvious and easy to understand from the following description of the embodiments in conjunction with the drawings, in which: Figure 1 It is a flow chart of the method for resource recycling of molybdenum slag in the present application. Detailed implementation manners

[0020] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0021] According to one aspect of the present application, the present application provides a method for resource recovery and utilization of molybdenum slag, as Figure 1 shown, including the following steps: S100: Pretreatment of molybdenum slag The molybdenum slag is subjected to crushing, washing and drying pretreatment. Specifically, the specific pretreatment process has the following aspects: First, perform crushing and grinding: crush the massive molybdenum slag to a particle size of less than 100 μm to increase the contact area of the reaction interface. Then, perform drying and dehumidification: dry at 100-150 °C for 3-6 hours to remove free water and part of the crystal water in the material. Then, acid washing can be selected according to the specific composition of the molybdenum slag. Specifically, for slag with relatively high Fe and Ca contents, weak acid (such as 0.5 mol / L HCl) can be selectively used for cleaning to reduce the interference with the subsequent molten salt system. In addition, mixed pretreatment can be selected according to the morphology and composition of the molybdenum slag. The specific situation is as follows: if the molybdenum slag has a relatively coarse particle size or contains too much silicon, 5-15 wt% of a flux (such as NaF or CaCl2) can be admixed to promote uniform reaction.

[0022] S200: Construct a molten salt electrochemical system to reduce and prepare metallic molybdenum from molybdenum slag Using NaCl, KCl, and NaF as molten salts, they form a molten salt electrochemical system with the cathode and anode groups. Add the pretreated molybdenum slag to the molten salt for electrochemical reduction reaction, so that molybdenum in the molybdenum slag is reduced and precipitated at the cathode. The precipitated metallic molybdenum is pickled and dried to obtain Mo powder. The present application adopts an optimized design of the NaCl-KCl-NaF molten salt system and a specific electrolysis potential range, enabling molybdenum oxide to be stably dissolved and preferentially reduced and deposited at the cathode. The recovery rate of molybdenum can stably reach over 85%, and the purity of the deposited product is high (>98%), far higher than traditional wet acid leaching extraction or high-temperature roasting reduction methods, effectively suppressing the co-reduction of impurity elements such as Fe, Al, and Si, and improving the product quality. The present application realizes good dissolution performance and ion migration characteristics of Mo oxide through the selection of the molten salt system, which is significantly different from traditional high-temperature or acidic systems.

[0023] In some embodiments of the present application, the molar ratio of NaCl, KCl, and NaF is 5:5:1. The specific molten salt components and ratio are beneficial to the selective electrochemical reduction of molybdenum. This ternary system molten salt has excellent eutectic behavior and can provide a stable liquid-phase environment in the temperature range of 650 - 800 °C, ensuring the stable dissolution of the Mo source and ion migration. The ratio balances the requirements of melting point, conductivity, and compositional stability, avoiding the problems of increased system corrosivity or viscosity caused by excessive NaF.

[0024] In some embodiments of the present application, the operating temperature of the electrochemical reduction reaction is controlled within 650 - 800 °C. That is to say, for example, 650 °C, 700 °C, 750 °C, or 800 °C can be selected. The preferred temperature in the present application is 750 °C. According to the phase diagram of the NaCl - KCl - NaF ternary molten salt system, the eutectic temperature is 550 - 580 °C. In this temperature range (650 - 800 °C), the molten salt is completely liquefied, and the ion diffusion efficiency is high, which can ensure the full melting of the molten salt and the progress of the Mo oxide reduction reaction, ensuring the effective migration of Mo ions during electrolysis.

[0025] In some embodiments of the present application, the electrolytic cell of the molten salt electrochemical system is a graphite or alumina crucible, and the protective gas is one of argon or nitrogen; the cathode material is one of molybdenum sheet or titanium sheet; the anode material is graphite. The setting of the electrolysis conditions is conducive to achieving the selective reduction of Mo.

[0026] In addition, the voltage of the electrochemical reduction reaction is -2.0 ~ -2.4 V, the current density is 0.05 - 0.2 A / cm², and the reaction time is 2 - 6 h. By setting the reaction conditions, Mo preferentially reduces and precipitates at the cathode during electrolysis, avoiding the co-precipitation of impurity metals. Within the set voltage range, Mo 6 ⁺ ions can complete the selective reduction in two steps (Mo 6 ⁺ → Mo³⁺ → Mo), effectively avoiding the problems of coarse deposition or encapsulation effect caused by too fast one-time reduction. The current density is controlled within 0.05 - 0.2 A / cm², which is beneficial to forming a relatively uniform deposition field, avoiding local overheating of the electrode or the formation of metal agglomeration, and at the same time providing a sufficient electron reduction environment for carbon ions on the cathode surface; the 2 - 6 h reaction time combined with the above current density can achieve the target reduction depth and the completeness of the carbonization reaction, and effectively reduce the risk of by-product formation and co-deposition of metal impurities.

[0027] Specifically, the molten salt used in this molten salt system is a ternary system of NaCl-KCl-NaF. The structure of the electrolysis device: The material of the electrolytic cell is graphite or alumina crucible; the anode is a graphite rod with a diameter of 5-10 mm; the cathode is a molybdenum sheet or a titanium sheet with a size of 20×40 mm, which is hung on the electrode rack; the power supply is a DC constant voltage / constant current power supply, and the voltage is controlled at -2.0 V to -2.4 V (relative to the Cl2 / Cl⁻ electrode), or the current density is controlled at 0.05-0.2 A / cm²; the atmosphere protection is to introduce argon or nitrogen with a flow rate of 100-300 mL / min to avoid the influence of the oxidation atmosphere on the reduction reaction. The reaction time is 2-6 h, and the specific time is determined according to the Mo content in the slag; the method for collecting the electrolysis product is that molybdenum metal is deposited on the cathode, taken out regularly, desalted with dilute acid after cooling, and dried to obtain Mo powder with a purity of over 98%.

[0028] This application realizes the selective reduction of Mo through the collaborative design of the electrolysis voltage and the cathode material.

[0029] In some embodiments of this application, the electrolysis residue of the electrochemistry reduction reaction is processed and used in building materials, which can realize the recycling of the remaining residue, avoid pollution and improve economic benefits at the same time. It can be understood that after the electrolysis residue is formulated, roasted and ball milled, it has good gelling activity and thermal stability, and can be used as a admixture for functional building materials such as high-performance refractory concrete, special ceramics, and spraying aggregates. The Mo content in the residue is less than 0.2 wt%, and the heavy metal leaching rate is low, meeting the harmless utilization standard and realizing the transformation from "hazardous waste to resources".

[0030] Furthermore, the specific process of processing the electrolysis residue is as follows: After screening the electrolysis residue, it is mixed with an auxiliary agent in a certain proportion, and then roasted at a high temperature to promote the stabilization of the residue phase and endow it with gelling activity. Specifically in this application, the auxiliary agent is lime powder, and 5%-15% of lime powder by mass is added to the residue to adjust the Ca / Si ratio in the residue. The roasting temperature is 900-1200 °C, and the roasting time is 12 h, which can promote the stabilization of the residue phase and endow it with gelling activity. In addition, after roasting, the product is ground, that is, the sintered product is ball milled to a specific surface area greater than 300 m² / kg to prepare a functional filler suitable for concrete or ceramics. That is to say, the powder obtained after grinding can be used as: an admixture for high-strength cement or refractory concrete (replacing part of silica fume); a functional filler for high-temperature ceramic matrix materials; an aggregate matrix for wear-resistant spraying materials.

[0031] In some embodiments of this application, the tail gas generated by the electrochemistry reduction reaction electrolysis is neutralized by a NaOH spray absorption device to achieve the up-to-standard discharge of gas pollutants, without acid liquid discharge. The tail gas treatment and the system closed-loop design ensure environmental protection and compliance.

[0032] In addition, the electrolyzed molten salt can be recycled in multiple rounds. After sedimentation or centrifugation of the electrolyzed molten salt, it can be continuously used for 10 to 20 rounds. The activity and fluidity of the molten salt system can be maintained by regularly adding NaF, and the accumulation rate of impurities can be controlled to ensure the stable operation of the system. Therefore, the molten salt system can be recycled more than 10 to 20 times. The system constructs a complete resource closed-loop path, reflecting the typical characteristics of green metallurgy technology.

[0033] The economy and industrialization level of this application are high. The process flow is compact, the operating temperature is relatively low (650 - 800 °C), and the energy consumption is significantly lower than that of the traditional roasting reduction method; the electrode materials and molten salt can be reused, the equipment structure is simple, suitable for pilot-scale and large-scale promotion; the comprehensive treatment cost is more than 30% lower than the traditional molybdenum slag treatment method, with prominent economic benefits.

[0034] In addition, this application has a wide application prospect and strong promotion value. This application is applicable to molybdenum slag from various sources (such as molybdenum concentrate roasting slag, chemical molybdenum waste slag, etc.), with wide adaptability. It can be extended to the combined recovery of multi-metal slag containing Mo, W, V, etc., and can provide a win-win resource collaborative utilization plan for the molybdenum metallurgy industry, waste slag treatment enterprises, cement or building materials industries, with good industrialization prospects and social and environmental benefits.

[0035] Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by this application. The experimental methods without specific conditions noted in the following embodiments are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions or parts are by weight.

[0036] The reagents and raw materials used in the examples and comparative examples of this application can be obtained through commercial channels without special instructions.

[0037] The following will illustrate this application with reference to specific examples and comparative examples. It should be noted that these examples are merely illustrative and should not be construed as limiting this application.

[0038] Example: A method for the resource recovery and utilization of molybdenum slag includes the following steps: Step 1: Pretreat the molybdenum slag: Crush the massive molybdenum slag to a particle size less than 100 μm, and then dry the crushed molybdenum slag at 120 °C for 4 hours to remove the free water and part of the crystal water in the material. For the slag with high Fe and Ca contents, wash it with 0.5 mol / L HCl. For the molybdenum slag with coarser particle size or excessive silicon content, admix 10 wt% of the flux NaF in the washed molybdenum slag to promote uniform reaction.

[0039] Step 2: Construct a molten salt electrochemical reaction system: Use NaCl, KCl, and NaF with a molar ratio of 5:5:1 as the molten salt. Add the pretreated molybdenum slag to the molten salt. The electrolytic cell material is a graphite or alumina crucible. The anode is a graphite rod with a diameter of 10 mm, and the cathode is a molybdenum sheet or titanium sheet with dimensions of 20×40 mm, which is hung on the electrode rack. The power supply is a DC constant voltage / constant current power supply, with the voltage controlled at -2.0 V to -2.4 V (relative to the Cl2 / Cl⁻ electrode), or the current density controlled at 0.05 - 0.2 A / cm². Argon gas is introduced at a flow rate of 200 mL / min, and the reaction time is 4 h. The reaction temperature is 750°C to construct a molten salt electrochemical system for the electrochemical reduction of molybdenum in the molybdenum slag. After the reaction, metallic molybdenum is deposited on the cathode, taken out regularly, desalted with dilute acid after cooling, and dried to obtain Mo powder. The recovery rate of Mo reaches over 85%, and the purity can reach over 98%.

[0040] Step 3: Treat the electrolyzed molybdenum slag and reuse it in building materials: The Mo content in the electrolyzed molybdenum slag is usually less than 0.2 wt%. The main components are SiO2, Al3O2, Fe2O3, CaO, etc. Add 10% limestone powder according to the residue mass to adjust the Ca / Si ratio. Then, roast the mixture at 1200°C for 2 hours to promote the phase stabilization of the residue and endow it with cementitious activity. Grind the sintered product into a powder with a specific surface area greater than 300 m² / kg. This powder can be used as a admixture for high-strength cement or refractory concrete (replacing part of the silica fume), a functional filler for high-temperature ceramic matrix materials, and an aggregate matrix for wear-resistant spraying materials.

[0041] Step 4: Recovery and reuse of the molten salt: After the reduced molten salt is deslagged by natural sedimentation and centrifugation, it can be recycled 10 - 20 times. If the concentration of NaF decreases, it can be replenished to maintain the activity of the system.

[0042] Step 5: Neutralize the tail gases such as Cl2 and HF generated by electrolysis through a NaOH spray absorption device.

[0043] Comparative example: A method for resource recovery and utilization of molybdenum slag is basically the same as that in Example 1. The main difference is that no NaF flux is used when constructing the molten salt electrochemical system in Step 2, that is, the molten salt composition is NaCl:KCl = 1:1 (molar ratio), and no NaF is added. Other process parameters such as voltage, current density, temperature, time, electrode settings, etc. remain the same. The recovery rate of molybdenum in this method is less than 85%. It can be seen that the ternary system molten salt composition of this application can ensure the stable dissolution of the Mo source and ion migration. The ratio of the three components balances the requirements of melting point, conductivity, and composition stability, ensuring the reduction depth and completeness of the molybdenum slag during the electrochemical reduction process.

[0044] Finally, it should be noted that the above are only preferred embodiments of the present application and are not used to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for resource recovery and utilization of molybdenum slag, characterized in that, It includes the following steps: Perform pretreatment of crushing, washing and drying on molybdenum slag; Use NaCl, KCl, and NaF as molten salts, which together with the cathode and anode groups form a molten salt electrochemical system. Add the pretreated molybdenum slag to the molten salt for an electrochemical reduction reaction, so that molybdenum in the molybdenum slag is reduced and precipitated at the cathode; Pickle the precipitated metallic molybdenum and then dry it to obtain Mo powder.

2. The method according to claim 1, wherein The molar ratio of the NaCl, KCl, and NaF is 5:5:

1.

3. The method according to claim 1, wherein The operating temperature of the electrochemical reduction reaction is controlled at 650 - 800 °C.

4. The method according to claim 1, wherein The electrolytic cell of the molten salt electrochemical system is a graphite or alumina crucible, and the protective gas is one of argon or nitrogen; The cathode material is one of molybdenum sheet or titanium sheet; and / or The anode material is graphite.

5. The method according to claim 1, characterized in that, The voltage of the electrochemical reduction reaction is -2.0 ~ -2.4 V, the current density is 0.05 ~ 0.2 A / cm², and the reaction time is 2 - 6 h.

6. The method according to claim 1, characterized in that, The electrolytic residue of the electrochemical reduction reaction is used for building materials after treatment.

7. The method according to claim 6, characterized in that, The specific process of treating the electrolytic residue is: screen the electrolytic residue and mix it with an auxiliary agent in a certain proportion, and then calcine it at a high temperature.

8. The method according to claim 7, wherein The auxiliary agent is lime powder, and 5% - 15% by mass of lime powder is added to the residue to adjust the Ca / Si ratio in the residue.

9. The method according to claim 7, characterized in that, The calcination temperature is 900 - 1200 °C, and the calcination time is 12 h.

10. The method according to claim 1, characterized in that The tail gas generated by the electrolysis of the electrochemical reduction reaction is neutralized by a NaOH spray absorption device.

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