Method for removing molybdenum from tungstate based on stepwise sulfurization process and tungstate

Abstract

To provide a method for removing molybdenum in tungstate based on step-wise sulfidation by overcoming issues such as the difficulty of removing extremely low concentrations of molybdenum in the producing process of ultra-high purity tungstate, the low recovery rate of tungstic acid, high energy consumption, and harsh conditions; by employing molybdenum removal technology based on staged sulfidation to enable deeply sulfurization of the extremely low concentrations of molybdenum in the solution, thereby enhancing the molybdenum removal rate and completeness, resulting in good removal efficiency for extremely low concentrations of molybdenum.SOLUTION: The method includes a process of sulfidation of a tungstate solution based on soluble sulfides, a process of molybdenum removal from the sulfated tungstate solution based on soluble copper salts, and performing the sulfidation process and molybdenum removal process sequentially multiple times to obtain high-purity tungstate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of separation and purification technology, and in particular to a method for removing molybdenum from tungstate based on a stepwise sulfurization process, and to tungstate. [Background technology]

[0002] Tungsten metal is expected to be widely used in the fields of special steel and semiconductors, etc. For example, high-purity tungsten has advantages such as high electromigration resistance, good high-temperature stability, and high electron emissivity, and will replace copper as a key material for the diffusion barrier layer and bonding layer of new-generation semiconductor chips.

[0003] Molybdenum and tungsten are group VIB elements, and because they have more similar chemical properties than their neighboring homologous elements in the periodic table, they are called "similar elements." Molybdenum is the most difficult impurity to remove during the manufacturing process of high-purity tungsten. The presence of molybdenum affects the electrical conductivity of tungsten, adversely affecting its applications, so the molybdenum content of ultra-high-purity tungsten used in the semiconductor industry must be less than 0.1 ppm.

[0004] Current technology, traditional tungsten refining processes utilize the differences in the properties of tungsten's oxygen affinity and molybdenum's sulfophilicity to prepare molybdenum sulfide from elemental molybdenum and tungsten oxide from which the molybdenum is further separated to achieve tungsten purification through selective precipitation. However, this method falls far short of the requirement of a molybdenum content of less than 0.1 ppm in ultra-high purity tungsten, so further purification is usually performed through multiple crystallization. The multiple crystallization method requires multiple "dissolution and crystallization" of soluble paratungstate (e.g., ammonium paratungstate APT) to achieve the desired molybdenum concentration. However, paratungstates that are difficult to dissolve in ammonia (ammonium paratungstate APT) require an extreme high-pressure environment and large amounts of energy consumption, and the single crystallization rate must be kept relatively low to ensure the molybdenum removal rate of the product, resulting in a recovery rate of less than 60% for qualified ultra-high purity ammonium paratungstate. Therefore, the industry is seeking a method that can remove molybdenum from tungstate solutions with high recovery rate and energy saving. Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above analysis, the present invention aims to propose a method for removing molybdenum from tungstate based on a stepwise sulfurization process in order to solve at least one of the problems in the production process of ultra-high purity tungstate, such as the difficulty in completely removing extremely low concentrations of molybdenum as much as possible, the low recovery rate of tungstate, high energy consumption, and harsh conditions. [Means for solving the problem]

[0006] The object of the present invention is mainly achieved by means of the following technical solutions.

[0007] The molybdenum removal method in tungstate based on stepwise sulfurization process is as follows: sulfurizing the tungstate solution based on soluble sulfides; performing molybdenum removal on the sulfided tungstate solution based on a soluble copper salt; and a step of obtaining high-purity tungstate by sequentially performing the sulfurization step and the molybdenum removal step multiple times.

[0008] Preferably, the step of sulfurizing the tungstate solution is carried out by adding an excess of sulfurizing agent and increasing the amount of MoS4 in the sulfurized product. 2- The molar ratio of

[0009] Preferably, the step of subjecting the sulfurized tungstate solution to molybdenum removal comprises adding an excess of soluble copper salt to achieve a molybdenum removal rate of 80% or more in the tungstate solution.

[0010] Preferably, the method for removing molybdenum from tungstate based on a stepwise sulfurization process comprises: S1: adding a sulfurizing agent to a tungstate solution to perform sulfurization treatment; S2: Adding a soluble copper salt to the sulfurized tungstate solution to remove molybdenum, thereby obtaining a molybdenum-removed tungstate solution; S3: The molybdenum-removed tungstate solution of S2 is treated as a pre-treatment raw material of S1 in accordance with S1-S2 in succession.

[0011] Preferably, the sulfiding agent is any one of sodium sulfide and ammonium sulfide.

[0012] Preferably, the amount of sulfurizing agent used is such that the molar concentration of the sulfurizing agent is 1×10 of the molar concentration of molybdenum in the tungstate solution. 2 times ~4×10 5 The condition of doubling is met.

[0013] Preferably, the soluble copper salt is one or more of copper sulfate, copper nitrate, and copper chloride.

[0014] Preferably, the amount of soluble copper salt used satisfies the condition that the molar concentration of the soluble copper salt is 4 to 14 times the molar concentration of molybdenum in the tungstate solution.

[0015] Preferably, in the sulfurization treatment, the sulfurization time is set to 24 hours to 32 hours and the sulfurization temperature is set to 30°C to 70°C, and / or in the first molybdenum removal, the molybdenum removal time is set to 8 hours to 12 hours and the molybdenum removal temperature is set to 35°C to 65°C.

[0016] The tungstate produced by the method for removing molybdenum from tungstate based on the stepwise sulfurization process has a molybdenum impurity content of less than 0.1 ppm. [Effects of the Invention]

[0017] The present invention may achieve at least one of the following beneficial effects over the current art:

[0018] (1) The present invention employs a molybdenum removal technology based on stepwise sulfurization, allowing the sulfurization reaction of molybdenum and the coprecipitation reaction with copper salts to slowly reach a reversible equilibrium, thereby obtaining deeply sulfurized molybdenum sulfides, which increases the molybdenum removal rate and achieves good removal effect for extremely low concentrations of molybdenum.

[0019] (2) The present invention uses a soluble copper salt as a molybdenum removal agent, and by carrying out a coprecipitation reaction with molybdenum sulfide and removing impurities such as sulfurizing agents introduced into the system, the reaction conditions are made milder, thereby increasing the molybdenum removal rate.

[0020] (3) The present invention employs a molybdenum removal technique based on stepwise sulfurization of "sulfurization-addition of soluble copper salt" to selectively remove molybdenum and refine soluble tungstate with a molybdenum impurity content of 0.05 ppm to 15 ppm. Furthermore, the present invention not only achieves good separation effect but also guarantees a much higher yield than the 60% of the current technology (recrystallization method) by sequentially performing multiple sulfurization processes, resulting in a total yield of ≥ 80% from the tungstate from which molybdenum has been removed.

[0021] (4) The present invention employs a molybdenum removal technique based on stepwise sulfurization of "sulfurization-addition of soluble copper salt" to selectively remove molybdenum and produce high-purity soluble tungstate with a molybdenum impurity content of <0.1 ppm. Furthermore, the total yield of the molybdenum-removed tungstate reaches ≥ 80% through multiple successive sulfurization processes, thereby achieving a good separation effect and ensuring a high yield.

[0022] Other features and advantages of the present invention will be set forth in the following specification, and some of the advantages will be apparent from the specification or may be learned by practice of the invention. The objectives and other advantages of the present invention will be met and attained by what is set forth in the examples and drawings of the specification. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a process flow diagram of a method for removing molybdenum from tungstate based on a stepwise sulfurization process. DETAILED DESCRIPTION OF THE INVENTION

[0024] We will now describe preferred embodiments of the present invention in combination with the drawings, which constitute a part of the present invention and, together with the embodiments of the present invention, explain the principles of the present invention and are not used to limit the scope of the present invention.

[0025] The findings we have obtained through our research are as follows:

[0026] On the one hand, the sulfurization reaction of molybdenum is a reversible reaction with multiple reaction steps, producing various molybdenum sulfides. When the molybdenum concentration is extremely low, the reaction will proceed in the reverse direction, but the tendency to proceed in the forward direction is very weak. This results in a poor sulfurization effect, a low content of complete sulfurization products in the molybdenum sulfide product, and poor subsequent impurity removal and tungstate separation effects. This makes it difficult for traditional selective precipitation methods to further improve the separation effect of molybdenum and tungstate (e.g., the molybdenum impurity content is less than 0.1 ppm).

[0027] On the other hand, the current technology (recrystallization method) requires multiple "dissolution and crystallization" of paratungstates (such as ammonium paratungstate), which are difficult to dissolve at low temperatures, and requires an extreme high-pressure environment and large amounts of energy consumption. In addition, there is a contradiction in that it does not simultaneously achieve a high recovery rate and a high impurity removal rate.

[0028] In view of the deficiencies in the current technology, the present invention proposes a method for removing molybdenum from tungstate based on a stepwise sulfurization process.

[0029] The method includes the steps of sulfurizing a tungstate solution based on a soluble sulfide, removing molybdenum from the sulfurized tungstate solution based on a soluble copper salt, and sequentially performing the sulfurization step and the molybdenum removal step multiple times to obtain a high-purity tungstate.

[0030] In carrying out this method, the soluble sulfide and the molybdenum impurities in the tungstate solution undergo a molybdenum sulfidation reaction to produce a molybdenum sulfide product; the soluble copper salt reacts with sulfur to produce a copper sulfide precipitate, and the copper sulfide reacts with the molybdenum sulfide product to form a precipitate, thereby achieving the steps of separating molybdenum from the tungstate solution system and purifying the tungstate solution; and the sulfidation process and the molybdenum removal process are carried out multiple times to further remove the molybdenum impurities in the tungstate solution.

[0031] Specifically, the sulfurization reaction of molybdenum using a soluble sulfide as a sulfurization agent is as follows. [ka]

[0032] Here, set X to 1 to 3 and MoO x S 4-x 2- can be a molybdenum sulfide product of any one of reaction formulas (1) to (3).

[0033] Soluble copper salts and MoS4 2- The coprecipitation reaction is carried out according to the following reaction formula: MoS4 2- + CuS →Mo x Cu y S z ↓+S 2- (6)

[0034] Our research has shown that due to the existence of reversible reactions in the sulfurization process, there are always unsulfurized molybdate ions in the solution, and the sulfurization product is MoO3S. 2- The number of incompletely sulfurized molybdenum ions directly affects the subsequent impurity removal effect, so complete molybdenum removal cannot be achieved in a single sulfurization.

[0035] Preferably, the step of sulfurizing the tungstate solution is carried out by adding an excess of sulfurizing agent and forming MoS4 in the sulfurization product. 2- The molar ratio of

[0036] Specifically, the amount of sulfurizing agent used is determined by adjusting the molar concentration of the sulfurizing agent to 1×10 of the molar concentration of molybdenum in the tungstate solution. 2 times ~4×10 5 The condition of doubling is met.

[0037] Preferably, with the dynamic change of the molybdenum concentration, the lower the molybdenum concentration, the greater the amount of sulfurizing agent used.

[0038] Specifically, in the sulfurization treatment, the sulfurization time is set to 24 hours to 32 hours, and the sulfurization temperature is set to 30°C to 70°C.

[0039] Therefore, the stepwise sulfurization process corresponds to removing molybdenum after each sulfurization. With the dynamic change of molybdenum concentration, the lower the molybdenum concentration, the more soluble copper salt is used.

[0040] Preferably, the step of removing molybdenum from the tungstate solution using a soluble copper salt comprises adding an excess of the soluble copper salt to achieve a molybdenum removal rate of 80% or more in the tungstate solution.

[0041] Specifically, the amount of the soluble copper salt used satisfies the condition that the molar concentration of the soluble copper salt is 4 to 14 times the molar concentration of molybdenum in the tungstate solution.

[0042] Preferably, with the dynamic change in molybdenum concentration, the lower the molybdenum concentration, the more soluble copper salt is used.

[0043] Specifically, in the molybdenum removal step, the molybdenum removal time is set to 8 hours to 12 hours, and the molybdenum removal temperature is set to 35°C to 65°C.

[0044] Excess sulfurizing agent converts most of the molybdenum ions into MoS4 2- It is understood that the relatively complete degree of sulfidation promotes the formation of sulfomolybdate precipitates.

[0045] The sulfurization process of molybdenum itself is a slow reversible process, and it is understandable that a longer reaction time is required because the reaction rate slows down when the molybdenum ion concentration is low, causing the sulfurization reaction to proceed slowly. A sufficient sulfurization time is required to convert molybdenum more completely into MoS4 2- sulfurization to ensure subsequent molybdenum removal

[0046] The excess soluble copper salt ensures complete precipitation of molybdenum ions, and Cu 2+ The excess amount of Cu becomes smaller, but the appropriate excess 2+ S added during the sulfurization process 2- and form CuS precipitates, and in addition, CuS forms MoS4 2- It is understandable that this promotes the precipitation of copper ions and reduces the amount of copper ions remaining in the solution. Copper ions combine with sulfur ions or sulfomolybdic acid groups in the solution to form precipitates, and the sulfur element in the solution is in great excess compared to the copper element, which helps to reduce the amount of copper residue in the solution.

[0047] It is understandable that in the molybdenum removal process, the molybdenum removal time is set to 8 to 12 hours to save time and ensure that as much molybdenum as possible is precipitated to achieve the purpose of molybdenum removal.

[0048] In one feasible embodiment, the molybdenum content in the raw tungstate is set to 100 ppm to 330.0 ppm, and the initial molybdenum concentration in the tungstate solution after dissolution preparation is set to 10 mg / L≦Mo≦100 mg / L. The amount of sulfurizing agent used satisfies the condition that the molar concentration of the sulfurizing agent is 100 to 1000 times the molar concentration of molybdenum in the tungstate solution.

[0049] In practice, excess sulfurization reagent within this range results in MoS4 in the sulfurization product. 2- The molar ratio of exceeds 90%.

[0050] Specifically, the amount of the soluble copper salt used satisfies the condition that the molar concentration of the soluble copper salt is three to four times the molar concentration of molybdenum in the tungstate solution.

[0051] In practice, the excess soluble copper salt within this range can ensure that the molybdenum removal rate exceeds 90%, the molybdenum impurity content in the tungstate solution reaches 1 mg / L to 10 mg / L, and the molybdenum impurity content in the tungstate after crystallization and concentration reaches 10 ppm to 33.33 ppm.

[0052] In one feasible embodiment, the molybdenum content in the raw tungstate is set to 10 ppm to 33.33 ppm, and the initial molybdenum concentration in the tungstate solution after preparation for dissolution is set to 1 mg / L≦Mo≦10 mg / L. The amount of sulfurizing agent used satisfies the condition that the molar concentration of the sulfurizing agent is 1,000 to 5,000 times the molar concentration of molybdenum in the tungstate solution.

[0053] In practice, excess sulfurization reagent within this range results in MoS4 in the sulfurization product. 2- The molar ratio of exceeds 90%.

[0054] Specifically, the amount of the soluble copper salt used satisfies the condition that the molar concentration of the soluble copper salt is 4 to 6 times the molar concentration of molybdenum in the tungstate solution.

[0055] In practice, the excess soluble copper salt within this range can ensure that the molybdenum removal rate exceeds 90%, the molybdenum impurity content in the tungstate solution reaches 0.1 mg / L to 1 mg / L, and the molybdenum impurity content in the tungstate after crystallization and concentration reaches 1.00 ppm to 3.33 ppm.

[0056] In one possible embodiment, the molybdenum content in the raw tungstate is set to 1.00 ppm to 3.33 ppm, and the initial molybdenum concentration in the tungstate solution after dissolution preparation is set to 0.1 mg / L≦Mo≦1 mg / L. The amount of sulfurizing agent used is determined by setting the molar concentration of the sulfurizing agent to 5×10 of the molar concentration of molybdenum in the tungstate solution. 3 times ~6×10 4 The condition of doubling is met.

[0057] In practice, excess sulfurization reagent within this range results in MoS4 in the sulfurization product. 2- The molar ratio of exceeds 90%.

[0058] Specifically, the amount of the soluble copper salt used satisfies the condition that the molar concentration of the soluble copper salt is 6 to 8 times the molar concentration of molybdenum in the tungstate solution.

[0059] In practice, the excess soluble copper salt within this range ensures that the molybdenum removal rate exceeds 85%, the molybdenum impurity content in the tungstate solution reaches 0.01 mg / L to 0.1 mg / L, and the molybdenum impurity content in the tungstate after crystallization and concentration reaches 0.1 ppm to 0.5 ppm.

[0060] In one possible embodiment, the molybdenum content in the raw tungstate is set to 0.1 ppm to 0.5 ppm, and the initial molybdenum concentration in the tungstate solution after preparation for dissolution is set to 0.01 mg / L≦Mo≦0.1 mg / L. The amount of sulfurizing agent used is determined by setting the molar concentration of the sulfurizing agent to 6×10 of the molar concentration of molybdenum in the tungstate solution. 4 times ~4×10 5 The condition of doubling is met.

[0061] In practice, excess sulfurization reagent within this range results in MoS4 in the sulfurization product. 2- The molar ratio of exceeds 85%.

[0062] Specifically, the amount of the soluble copper salt used satisfies the condition that the molar concentration of the soluble copper salt is 8 to 14 times the molar concentration of molybdenum in the tungstate solution.

[0063] In practice, the excess soluble copper salt within this range ensures that the molybdenum removal rate exceeds 80%, the molybdenum impurity content in the tungstate solution reaches 0.002 mg / L to 0.02 mg / L, and the molybdenum impurity content in the tungstate after crystallization and concentration reaches 0.02 ppm to 0.1 ppm.

[0064] Compared with the current technology, the present invention employs a molybdenum removal technology based on stepwise sulfurization, which allows the molybdenum sulfurization reaction and the coprecipitation reaction with copper salt to slowly reach a reversible equilibrium, thereby obtaining deeply sulfurized molybdenum sulfides, thereby increasing the molybdenum removal rate and achieving good removal effect for extremely low concentrations of molybdenum.

[0065] Compared to the current technology, the present invention uses a soluble copper salt as a molybdenum removal agent and adjusts the amount of copper salt used to simultaneously and deeply remove extremely low concentrations of molybdenum and excess copper, making the reaction conditions milder and increasing the molybdenum removal rate.

[0066] Specifically, as shown in FIG. 1, the present invention proposes a method for removing molybdenum from tungstate based on a stepwise sulfurization process.

[0067] The method comprises: S1: adding a sulfurizing agent to a tungstate solution to perform sulfurization treatment; S2: Adding a soluble copper salt to the sulfurized tungstate solution to remove molybdenum, thereby obtaining a molybdenum-removed tungstate solution; S3: The molybdenum-removed tungstate solution of S2 is treated as a pre-treatment raw material of S1 in accordance with S1-S2 in succession.

[0068] Specifically, the tungstate solution described in S1 is an ammonium tungstate solution or a sodium tungstate solution, and the concentration of the solution calculated based on WO3 is 100 g / L to 250 g / L, and the molybdenum concentration is less than 100 mg / L.

[0069] Specifically, the sulfurizing agent is either sodium sulfide or ammonium sulfide.

[0070] Specifically, the soluble copper salt is one or more of copper sulfate, copper nitrate, and copper chloride.

[0071] Specifically, there is an excess of sulfurizing agent in the sulfurization process, and there is S in the solution. 2- Since there is an excess of soluble copper salts, after copper reacts with sulfided molybdenum ions to form a precipitate, S 2- The presence of copper causes S 2- This allows for the possibility of controlling the copper content in solution by controlling the amount of soluble copper salt used.

[0072] Preferably, in S3, the sequential processing according to S1 and S2 may be repeated 3 to 5 times.

[0073] It should be noted that the tungstate needs to be sampled to detect the molybdenum content before sulfurization. After one round of sulfurization and impurity removal, sampling is carried out again to dynamically adjust the conditions for the next stage according to the impurity removal effect, or to determine whether sulfide-molybdenum removal is required in the next stage.

[0074] Specifically, the method for removing molybdenum from tungstate further includes a step of crystallizing and concentrating the purified tungstate solution to prepare high-purity tungstate.

[0075] Specifically, in the method for removing molybdenum from tungstate, the molybdenum removal rate reaches ≧80%, and the yield of tungstate reaches ≧80%.

[0076] Preferably, in the method for removing molybdenum from tungstate, the molybdenum removal rate reaches ≧90%.

[0077] Compared with the current technology of purifying tungstate by multiple crystallizations, the present invention employs a stepwise sulfurization process, and when the molybdenum removal process does not reach the required concentration, the next step is started. No matter how many times the molybdenum removal process is performed, the tungstate remains in solution, and the loss of tungsten element is very small, which can be seen to guarantee a high yield of ammonium paratungstate.

[0078] Another aspect of the present invention provides a high-purity tungstate produced by the method for removing molybdenum from a tungstate, in which the content of molybdenum impurities in the tungstate is suppressed to 0.05 ppm to 15 ppm.

[0079] Preferably, the molybdenum impurity content in the tungstate is kept to <0.1 ppm.

[0080] We provide the following examples and comparative examples to further illustrate the technical solutions of the present invention. [Example]

[0081] In this example, commercially available ammonium paratungstate (with a molybdenum impurity content of 120 ppm) is used to prepare an ammonium tungstate solution (with a WO concentration of 150 g / L and a molybdenum concentration of 18 mg / L), and the molybdenum impurity is removed to produce high-purity ammonium paratungstate. The steps are as follows:

[0082] S1: Select 200 ml of ammonium tungstate solution, select ammonium sulfide as the sulfurizing agent, add the sulfurizing agent in an amount equivalent to 1000 times the molar concentration of molybdenum in the tungstate solution, set the sulfurizing time to 24 hours, and set the sulfurizing temperature to 60°C.

[0083] S2: Add copper chloride to the sulfurized ammonium tungstate solution to remove molybdenum. The amount of copper salt added is equivalent to four times the molar concentration of molybdenum in the tungstate solution. The molybdenum removal time is set to 8 hours, and the impurity removal temperature is set to 60°C. After impurity removal, a high-purity ammonium paratungstate solution is obtained, which is then evaporated and crystallized to produce ammonium paratungstate. Calculations show that under these conditions, a single sulfide-molybdenum removal process results in a molybdenum removal rate of 89% and a tungstate yield of 83%. After a single step of sulfurization-molybdenum impurity removal, the molybdenum content in the ammonium paratungstate solution reaches 1.98 mg / L, and the molybdenum content in the ammonium paratungstate reaches 13.2 ppm. [Example]

[0084] In this example, commercially available sodium tungstate (with a molybdenum impurity content of 200 ppm) is used to prepare a sodium tungstate solution (with a WO concentration of 200 g / L and a molybdenum concentration of 40 mg / L), and the molybdenum impurity is removed to produce high-purity sodium tungstate. The steps are as follows:

[0085] S1: Select 100ml of sodium tungstate solution, select sodium sulfide as the sulfurizing agent, add the sulfurizing agent in an amount equivalent to 800 times the molar concentration of molybdenum in the tungstate solution, set the sulfurizing time to 20h, and set the sulfurizing temperature to 60°C.

[0086] S2: Add copper sulfate to the sodium tungstate solution after sulfurization to remove molybdenum. The amount of copper salt added is equivalent to four times the molar concentration of molybdenum in the tungstate solution. The molybdenum removal time is set to 8 hours, and the impurity removal temperature is set to 50°C. After impurity removal, high-purity sodium tungstate is obtained, which is then evaporated and crystallized to produce sodium tungstate. Calculations show that under these conditions, a single sulfide-molybdenum removal process achieves a molybdenum removal rate of 94% and a tungstate yield of 82%. After a single step of sulfurization-molybdenum impurity removal, detection reveals that the molybdenum content in the sodium tungstate solution is 2.4 mg / L, and the molybdenum content in the sodium tungstate is 12 ppm. [Example]

[0087] In this example, commercially available ammonium paratungstate (with a molybdenum impurity content of 20 ppm) is used to prepare an ammonium tungstate solution (with a WO concentration of 250 g / L and a molybdenum concentration of 5 mg / L), and the molybdenum impurity is removed to produce high-purity ammonium paratungstate. The steps are as follows:

[0088] S1: Select 100 ml of ammonium tungstate solution, select ammonium sulfide as the sulfurizing agent, add the sulfurizing agent in an amount equivalent to 4000 times the molar concentration of molybdenum in the tungstate solution, set the sulfurizing time to 26 hours, and set the sulfurizing temperature to 60°C.

[0089] S2: Add copper sulfate to the sulfurized ammonium tungstate solution to remove molybdenum. The amount of copper salt added is equivalent to 8 times the molar concentration of molybdenum in the tungstate solution. The molybdenum removal time is set to 10 hours, and the impurity removal temperature is set to 60°C. After impurity removal, a high-purity ammonium paratungstate solution is obtained, which is then evaporated and crystallized to produce ammonium paratungstate. Calculations show that under these conditions, a single sulfide-molybdenum removal process achieves a molybdenum removal rate of 89% and a tungstate yield of 82.5%. After a single step of sulfurization-molybdenum impurity removal, detection reveals that the molybdenum content in the ammonium paratungstate solution is 0.55 mg / L, and the molybdenum content in the ammonium paratungstate is 2.42 ppm. [Example]

[0090] In this example, the ammonium tungstate solution (molybdenum content 1.98 mg / L) obtained after purification in Example 1 is selected as the pre-treatment raw material to remove molybdenum impurities so as to purify high-purity ammonium paratungstate, and the steps are as follows:

[0091] S1: Select 100 ml of ammonium tungstate solution, select ammonium sulfide as the sulfurizing agent, add the sulfurizing agent in an amount equivalent to 6000 times the molar concentration of molybdenum in the tungstate solution, set the sulfurization time to 24 hours, and set the sulfurization temperature to 60°C.

[0092] S2: Copper nitrate is added to the sulfurized ammonium tungstate solution to remove molybdenum. The amount of copper salt added is equivalent to 6 times the molar concentration of molybdenum in the tungstate solution. The molybdenum removal time is set to 8 hours, and the impurity removal temperature is set to 60°C. After impurity removal, a high-purity ammonium paratungstate solution is obtained, which is then evaporated and crystallized to produce ammonium paratungstate. Calculations show that under these conditions, a single sulfide-molybdenum removal process achieves a molybdenum removal rate of 88%. After two rounds of stepwise sulfurization-molybdenum impurity removal, the tungstate yield reaches 83.5%. In this example, the tungstate solution from Example 1 after one round of stepwise sulfurization-molybdenum impurity removal is used as the pretreatment raw material, so two rounds of stepwise sulfurization-molybdenum impurity removal are actually performed. Through detection, the molybdenum content in the ammonium paratungstate solution reached 0.238 mg / L, and the molybdenum content in ammonium paratungstate reached 1.584 ppm. [Example]

[0093] In this example, the sodium tungstate solution (molybdenum content is 2.4 mg / L) obtained after purification in Example 2 is selected as the pre-treatment raw material to remove molybdenum impurities so as to purify high-purity sodium paratungstate, and the steps are as follows:

[0094] S1: 100 ml of sodium tungstate solution is selected, and sodium sulfide is selected as the sulfurizing agent. The amount of sulfurizing agent added is equivalent to 5,500 times the molar concentration of molybdenum in the tungstate solution. The sulfurizing time is set to 24 hours, and the sulfurizing temperature is set to 60°C.

[0095] S2: Copper nitrate is added to the sodium tungstate solution after sulfurization to remove molybdenum. The amount of copper salt added is equivalent to 6 times the molar concentration of molybdenum in the tungstate solution. The molybdenum removal time is set to 8 hours, and the impurity removal temperature is set to 60°C. After impurity removal, a high-purity sodium paratungstate solution is obtained, which is then evaporated and crystallized to produce sodium paratungstate. Calculations show that under these conditions, a single sulfide-molybdenum removal process achieves a molybdenum removal rate of 87.2%. After two rounds of stepwise sulfurization-molybdenum impurity removal, the tungstate yield reaches 82%. In this example, the tungstate solution after one round of stepwise sulfurization-molybdenum impurity removal in Example 2 is used as the pretreatment raw material, so the stepwise sulfurization-molybdenum impurity removal is actually performed twice. Through detection, the molybdenum content in the sodium paratungstate solution was found to be 0.253 mg / L, and the molybdenum content in the sodium paratungstate was found to be 2.16 ppm. [Example]

[0096] In this example, the ammonium tungstate solution (molybdenum content 0.238 mg / L) obtained after purification in Example 4 is selected as the pre-treatment raw material to remove molybdenum impurities so as to purify high-purity ammonium paratungstate, and the steps are as follows:

[0097] S1: Select 100 ml of ammonium tungstate solution, select ammonium sulfide as the sulfurizing agent, add the sulfurizing agent in an amount equivalent to 40,000 times the molar concentration of molybdenum in the tungstate solution, set the sulfurization time to 28 hours, and set the sulfurization temperature to 60°C.

[0098] S2: Copper nitrate is added to the sulfurized ammonium tungstate solution to remove molybdenum. The amount of copper salt added is equivalent to 8 times the molar concentration of molybdenum in the tungstate solution. The molybdenum removal time is set to 10 hours, and the impurity removal temperature is set to 60°C. After impurity removal, a high-purity ammonium paratungstate solution is obtained, which is then evaporated and crystallized to produce ammonium paratungstate. Calculations show that under these conditions, a single sulfide-molybdenum removal process achieves a molybdenum removal rate of 86.1%. After three rounds of stepwise sulfurization-molybdenum removal, the tungstate yield reaches 81%. In this example, the tungstate solution from Example 4 that underwent two rounds of stepwise sulfurization-molybdenum removal is used as the pretreatment raw material, so the stepwise sulfurization-molybdenum removal process is actually performed three times. Through detection, the molybdenum content in the ammonium paratungstate solution reaches 0.033 mg / L, and the molybdenum content in ammonium paratungstate reaches 0.300 ppm. [Example]

[0099] In this example, the sodium tungstate solution (molybdenum content is 0.253 mg / L) obtained after purification in Example 5 is selected as the pre-treatment raw material to remove molybdenum impurities so as to purify high-purity sodium paratungstate, and the steps are as follows:

[0100] S1: 100 ml of sodium tungstate solution is selected, and sodium sulfide is selected as the sulfurizing agent. The amount of sulfurizing agent added is equivalent to 37,000 times the molar concentration of molybdenum in the tungstate solution. The sulfurizing time is set to 28 hours, and the sulfurizing temperature is set to 60°C.

[0101] S2: Copper sulfate is added to the sodium tungstate solution after sulfurization to remove molybdenum. The amount of copper salt added is equivalent to 8 times the molar concentration of molybdenum in the tungstate solution. The molybdenum removal time is set to 10 hours, and the impurity removal temperature is set to 60°C. After impurity removal, a high-purity sodium paratungstate solution is obtained, which is then evaporated and crystallized to produce sodium paratungstate. Calculations show that under these conditions, a single sulfide-molybdenum removal process achieves a molybdenum removal rate of 85.2%. After three rounds of stepwise sulfurization-molybdenum removal, the tungstate yield reaches 80.6%. In this example, the tungstate solution after two rounds of stepwise sulfurization-molybdenum removal in Example 5 is used as the pretreatment raw material, so the stepwise sulfurization-molybdenum removal is actually performed three times. Through detection, the molybdenum content in the sodium paratungstate solution reaches 0.038 mg / L, and the molybdenum content in the sodium paratungstate reaches 0.419 ppm. [Example]

[0102] In this example, the ammonium tungstate solution (molybdenum content is 0.033 mg / L) obtained after purification in Example 6 is selected as the pre-treatment raw material to remove molybdenum impurities so as to purify high-purity ammonium paratungstate, and the steps are as follows:

[0103] S1: Select 100 ml of ammonium tungstate solution, select ammonium sulfide as the sulfurizing agent, add the sulfurizing agent in an amount equivalent to 380,000 times the molar concentration of molybdenum in the tungstate solution, set the sulfurization time to 32 hours, and set the sulfurization temperature to 60°C.

[0104] S2: Copper nitrate is added to the sulfurized ammonium tungstate solution to remove molybdenum. The amount of copper salt added is equivalent to 12 times the molar concentration of molybdenum in the tungstate solution. The molybdenum removal time is set to 12 hours, and the impurity removal temperature is set to 60°C. After impurity removal, a high-purity ammonium paratungstate solution is obtained, which is then evaporated and crystallized to produce ammonium paratungstate. Calculations show that under these conditions, a single sulfide-molybdenum removal process achieves a molybdenum removal rate of 79.8%. After four rounds of stepwise sulfurization-molybdenum impurity removal, the tungstate yield reaches 80.4%. In this example, the tungstate solution from Example 6 that underwent three rounds of stepwise sulfurization-molybdenum impurity removal is used as the pretreatment raw material, so four rounds of stepwise sulfurization-molybdenum impurity removal are actually performed. Through detection, the molybdenum content in the ammonium paratungstate solution reached 0.0067 mg / L, and the molybdenum content in ammonium paratungstate reached 0.061 ppm. [Example]

[0105] In this example, the sodium tungstate solution (molybdenum content is 0.038 mg / L) obtained after purification in Example 7 is selected as the pre-treatment raw material to remove molybdenum impurities so as to purify high-purity sodium paratungstate, and the steps are as follows:

[0106] S1: 100 ml of sodium tungstate solution is selected, and sodium sulfide is selected as the sulfurizing agent. The amount of sulfurizing agent added is equivalent to 400,000 times the molar concentration of molybdenum in the tungstate solution. The sulfurizing time is set to 32 hours, and the sulfurizing temperature is set to 60°C.

[0107] S2: Copper sulfate is added to the sulfurized sodium tungstate solution to remove molybdenum. The amount of copper salt added is equivalent to 12 times the molar concentration of molybdenum in the tungstate solution. The molybdenum removal time is set to 12 hours, and the impurity removal temperature is set to 60°C. After impurity removal, a high-purity sodium paratungstate solution is obtained, which is then evaporated and crystallized to produce sodium paratungstate. Calculations show that under these conditions, a single sulfide-molybdenum removal process achieves a molybdenum removal rate of 80.4%. After four rounds of stepwise sulfurization-molybdenum removal, the tungstate yield reaches 80%. In this example, the tungstate solution from Example 7 that underwent three rounds of stepwise sulfurization-molybdenum removal is used as the pretreatment raw material, so four rounds of stepwise sulfurization-molybdenum removal are actually performed. Through detection, the molybdenum content in the sodium paratungstate solution was found to be 0.0074 mg / L, and the molybdenum content in the sodium paratungstate was found to be 0.082 ppm.

[0108] The difference from Example 1 is that the amount of sulfurizing agent added corresponds to a molar concentration 80 times that of the molybdenum molar concentration in the tungstate solution. The remaining conditions are the same. Calculations show that under these conditions, a single sulfide-molybdenum removal process achieves a molybdenum removal rate of 5% and a tungstate yield of 85%. Detection revealed that the molybdenum content in the molybdenum-removed ammonium paratungstate was 114 ppm. Comparative Example 2

[0109] The difference from Example 1 is that the sulfurization time is set to 12 hours. The remaining conditions are the same. Calculations show that under these conditions, a single sulfide-molybdenum removal process results in a molybdenum removal rate of 58% and a tungstate yield of 84.6%. Detection reveals that the molybdenum content in the molybdenum-removed ammonium paratungstate is 50.4 ppm. Comparative Example 3

[0110] The difference from Example 1 is that the molybdenum removal time is set to 6 hours. The remaining conditions are the same. Calculations show that under these conditions, for a single sulfide-molybdenum removal process, the molybdenum removal rate reaches 72% and the tungstate yield reaches 84.5%. Detection reveals that the molybdenum content in the molybdenum-removed ammonium paratungstate reaches 33.6 ppm. Comparative Example 4

[0111] The difference from Example 4 is that the amount of sulfurizing agent added corresponds to a molar concentration 800 times that of the molybdenum molar concentration in the tungstate solution. The remaining conditions are the same. Calculations show that under these conditions, a single sulfide-molybdenum removal step results in a molybdenum removal rate of 39%, and after two stepwise sulfurization-molybdenum impurity removal steps, the yield of tungstate reaches 83.2%. Detection revealed that the molybdenum content in the molybdenum-removed ammonium paratungstate was 8.052 ppm. Comparative Example 5

[0112] The difference from Example 4 is that the sulfurization time is set to 12 hours. The remaining conditions are the same. Calculations show that under these conditions, the molybdenum removal rate for a single sulfide-molybdenum removal process reaches 48%, and the yield of tungstate after two stages of sulfurization-molybdenum impurity removal reaches 82.9%. Detection reveals that the molybdenum content in the molybdenum-removed ammonium paratungstate reaches 6.864 ppm. Comparative Example 6

[0113] The difference from Example 4 is that the amount of copper salt added is equivalent to three times the molar concentration of molybdenum in the tungstate solution. The remaining conditions are the same. Calculations show that under these conditions, a single sulfide-molybdenum removal step results in a molybdenum removal rate of 71.2%, and after two stages of sulfide-molybdenum impurity removal, the yield of tungstate reaches 81.7%. Detection reveals that the molybdenum content in the molybdenum-removed ammonium paratungstate is 3.802 ppm. Comparative Example 7

[0114] The difference from Example 4 is that the molybdenum removal time is set to 6 hours. The remaining conditions are the same. Calculations show that under these conditions, the molybdenum removal rate for a single sulfide-molybdenum removal process reaches 70%, and the yield of tungstate after two stages of sulfide-molybdenum impurity removal reaches 82.4%. Detection reveals that the molybdenum content in the molybdenum-removed ammonium paratungstate reaches 3.96 ppm. Comparative Example 8

[0115] The difference from Example 6 is that the amount of sulfurizing agent added corresponds to a molar concentration 4000 times higher than the molar concentration of molybdenum in the tungstate solution. The remaining conditions are the same. Calculations show that under these conditions, a single sulfide-molybdenum removal step results in a molybdenum removal rate of 16%, and after three stepwise sulfurization-molybdenum impurity removal steps, the yield of tungstate reaches 81.6%. Detection revealed that the molybdenum content in the molybdenum-removed ammonium paratungstate reached 1.813 ppm. Comparative Example 9

[0116] The difference from Example 6 is that the sulfurization time is set to 12 hours. The remaining conditions are the same. Calculations show that under these conditions, the molybdenum removal rate for a single sulfide-molybdenum removal process reaches 45%, and the yield of tungstate after three stages of sulfurization-molybdenum impurity removal reaches 82.4%. Detection reveals that the molybdenum content in the molybdenum-removed ammonium paratungstate reaches 1.187 ppm. Comparative Example 10

[0117] The difference from Example 6 is that the amount of copper salt added is equivalent to a molar concentration five times that of the molybdenum in the tungstate solution. The remaining conditions are the same. Calculations show that under these conditions, a single sulfide-molybdenum removal step results in a molybdenum removal rate of 65%, and after three stages of sulfide-molybdenum impurity removal, the yield of tungstate reaches 80.4%. Detection revealed that the molybdenum content in the molybdenum-removed ammonium paratungstate reached 0.755 ppm. Comparative Example 11

[0118] The difference from Example 6 is that the molybdenum removal time is set to 6 hours. The remaining conditions are the same. Calculations show that under these conditions, the molybdenum removal rate for a single sulfide-molybdenum removal process reaches 57%, and the yield of tungstate after three stages of sulfide-molybdenum impurity removal reaches 80.8%. Detection reveals that the molybdenum content in the molybdenum-removed ammonium paratungstate reaches 0.928 ppm. Comparative Example 12

[0119] The difference from Example 8 is that the amount of sulfurizing agent added corresponds to a molar concentration 55,000 times the molar concentration of molybdenum in the tungstate solution. The remaining conditions are the same. Calculations show that under these conditions, a single sulfide-molybdenum removal step results in a molybdenum removal rate of 18%, and after four stages of sulfurization-molybdenum impurity removal, the yield of tungstate reaches 80.5%. Detection revealed that the molybdenum content in the molybdenum-removed ammonium paratungstate was 0.248 ppm. Comparative Example 13

[0120] The difference from Example 8 is that the sulfurization time is set to 12 hours. The remaining conditions are the same. Calculations show that under these conditions, the molybdenum removal rate for a single sulfide-molybdenum removal process reaches 39.6%, and the yield of tungstate after four stages of sulfurization-molybdenum impurity removal reaches 81.1%. Detection reveals that the molybdenum content in the molybdenum-removed ammonium paratungstate reaches 0.182 ppm. Comparative Example 14

[0121] The difference from Example 8 is that the amount of copper salt added is equivalent to a molar concentration seven times that of the molybdenum in the tungstate solution. The remaining conditions are the same. Calculations show that under these conditions, a single sulfide-molybdenum removal step results in a molybdenum removal rate of 52.5%, and after four stages of sulfide-molybdenum impurity removal, the yield of tungstate reaches 80.7%. Detection revealed that the molybdenum content in the molybdenum-removed ammonium paratungstate was 0.143 ppm. Comparative Example 15

[0122] The difference from Example 8 is that the molybdenum removal time was set to 6 hours. The remaining conditions were the same. Calculations showed that under these conditions, the molybdenum removal rate for a single sulfide-molybdenum removal step reached 47.8%, and the yield of tungstate after four stages of sulfide-molybdenum impurity removal reached 80.4%. Detection showed that the molybdenum content in the molybdenum-removed ammonium paratungstate reached 0.158 ppm.

[0123] According to the results of Examples 1 to 9, the present invention can purify soluble tungstic acid with a molybdenum impurity content of 0.05 ppm to 15 ppm, and the yield of tungstate can reach ≥ 80%, which combines excellent separation effect and high yield. Preferably, the molybdenum content in the purified tungstate can reach < 0.1 ppm.

[0124] Comparing the Examples with the Comparative Examples, it can be seen that the removal rate of molybdenum impurities can be effectively improved by the reaction conditions outside the limited ranges of the raw material ratio and reaction time in the sulfurization process and the molybdenum removal process from soluble copper salts.

[0125] The above content is merely a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto, and any modifications or substitutions that a person skilled in the art can easily think of within the technical scope disclosed by the present invention should be included in the protection scope of the present invention.

Claims

1. A method for removing molybdenum from tungstate based on a stepwise sulfurization process, comprising: sulfurizing the tungstate solution based on soluble sulfides; performing molybdenum removal on a sulfided tungstate solution based on a soluble copper salt; a step of obtaining a high-purity tungstate by sequentially performing the sulfurization step and the molybdenum removal step multiple times, By adopting the molybdenum removal technology based on stepwise sulfurization, the sulfurization reaction of molybdenum and the coprecipitation reaction with copper salts reach a reversible equilibrium, thereby obtaining sulfurized molybdenum sulfide; Soluble copper salts are used as molybdenum removal agents, and the amount of copper salt used is adjusted to achieve the removal of extremely low concentrations of molybdenum. Excess copper is removed by reacting with excess sulfurizing reagent during sulfurization treatment; The method for removing molybdenum from tungstate based on a stepwise sulfurization process includes the following steps: Step S1: adding a sulfurizing agent to a tungstate solution to perform sulfurization treatment; Step S2: adding a soluble copper salt to the sulfurized tungstate solution to remove molybdenum, thereby obtaining a molybdenum-removed tungstate solution; Step S3: sequentially treating the tungstate solution from which molybdenum has been removed in Step S2 as a pre-treatment raw material in Step S1 three or more times in the order of Step S1-Step S2; In the step S1, an excess of sulfurizing agent is added, and MoS in the sulfurization product is 4 2- The molar ratio of the sulfurization agent is adjusted to 3.8 × 10 of the molar concentration of molybdenum in the tungstate solution. 4 Times to 4 x 10 5 It fulfills the condition of doubling, In the step S2, the molar concentration of the soluble copper salt is adjusted to the molar concentration of the tungstate solution. The molybdenum concentration must be 12 to 14 times higher than the molybdenum concentration, and the reaction must be carried out at 60 to 65°C for 8 to 12 hours to remove the molybdenum. A method for removing molybdenum from tungstate based on a stepwise sulfurization process, characterized in that the molybdenum impurity content in the produced high-purity tungstate is less than 0.1 ppm, and the total yield of the molybdenum-removed tungstate reaches 80% or more.

2. The step of removing molybdenum from the sulfurized tungstate solution includes adding an excess of soluble copper salt to achieve a molybdenum removal rate of 80% or more in the tungstate solution.

2. The method for removing molybdenum from tungstate based on a stepwise sulfurization process according to claim 1.

3. 2. The method for removing molybdenum from tungstate based on a stepwise sulfurization process according to claim 1, wherein the sulfurization agent is either sodium sulfide or ammonium sulfide.

4. 2. The method for removing molybdenum from tungstate based on a stepwise sulfurization process according to claim 1, wherein the soluble copper salt is one or more of copper sulfate, copper nitrate, and copper chloride.

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