Method for preparing refined molybdic acid by low-grade molybdenum oxide alkali leaching and acid precipitation

Abstract

This invention discloses a method for preparing refined molybdic acid by alkaline leaching and acid precipitation of low-grade molybdenum oxide, belonging to the technical field of hydrometallurgy and comprehensive resource utilization. The method includes: mixing low-grade molybdenum oxide raw material with an alkaline leachate containing a specific composite alkaline leaching stabilizer (sodium gluconate, sodium hexametaphosphate, sodium polyaspartate, and sodium sulfide), and performing alkaline leaching at pH=11.0±0.2 and 80-85℃ to achieve efficient dissolution and preliminary purification of molybdenum; the resulting crude solution is then subjected to high-temperature, high-pH stripping to remove ammonia, thus removing NH4+. + The concentration was reduced to ≤50 mg / L; the purified solution was subjected to high-temperature acid precipitation at 85-95℃ using a mixture of concentrated nitric acid and concentrated hydrochloric acid, with the final pH controlled at 0.5±0.1, to obtain wet molybdic acid solid. After washing and drying, refined molybdic acid product was obtained. This invention effectively solves the problems of high impurities in low-grade raw materials, large molybdenum loss, and low product purity by synergistically combining stabilizer complexation-precipitation in the alkaline leaching stage with high-temperature enhancement and precise acid control in the acid precipitation stage. The total molybdenum recovery rate is high, the product purity and physical properties are good, and the process is stable and efficient.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgy and comprehensive utilization of mineral resources, specifically relating to a method for efficiently and cleanly extracting and preparing high-purity molybdic acid from low-grade, high-impurity oxidized molybdenum ore (or its intermediate products). Background Technology

[0002] Molybdenum is a rare metal with advantages such as high strength, high melting point, abrasion resistance, and corrosion resistance, and is widely used in metallurgy, aerospace, optoelectronic materials, and other fields. With the continuous exploitation of molybdenum resources, high-grade molybdenum resources are becoming increasingly scarce, and high-quality resources are far from meeting market demand. Therefore, lean, fine, and impurity-laden ores have gradually become the main raw materials for molybdenum extraction. Low-grade molybdenum concentrate, due to its low molybdenum content (mostly 30%–45%), falls below the grade requirement of standard molybdenum concentrate (containing ≥45% molybdenum), and its high content of impurities such as SiO2, CaO, MgO, Cu, and Fe presents many problems in industrial applications.

[0003] Currently, research on wet processing of low-grade molybdenum oxide feedstock mainly focuses on the leaching stage, aiming to selectively dissolve molybdenum. Mainstream processes include: Alkaline leaching: This method uses sodium hydroxide or sodium carbonate solution for leaching under normal pressure. However, while highly efficient at dissolving molybdenum, strong alkaline leaching also leads to the co-dissolution of large amounts of impurities such as silica, aluminum, and phosphorus, resulting in a very heavy subsequent purification load. Furthermore, high alkalinity conditions are difficult to control precisely; excessive alkalinity in certain areas may exacerbate impurity leaching, while insufficient alkalinity affects the molybdenum leaching rate. This contradiction restricts the leaching selectivity and the purity of the final product.

[0004] Acid leaching: For example, using 30% sulfuric acid at 80℃ to leach low-grade oxidized molybdenum ore can achieve a leaching rate of 84.15%. However, acid leaching will dissolve a large amount of impurities such as iron, aluminum, and calcium, resulting in a complex composition of the leachate. Subsequent separation and purification steps are cumbersome, acid consumption is high, and the requirements for equipment corrosion protection are stringent.

[0005] Other leaching methods include sodium hypochlorite oxidative leaching and oxygen pressure boiling. Although the sodium hypochlorite method has a mild reaction, the reagent is easily decomposed and the cost is high. The oxygen pressure boiling method is highly efficient and has no SO2 emissions, but it requires large equipment investment, has high requirements for operating conditions, and still faces the common problems of complex leachate and the need for deep purification.

[0006] Meanwhile, low-grade oxidized molybdenum ore (with a Mo content typically <2%) must first undergo flotation enrichment to obtain smeltable molybdenum concentrate (with a Mo content typically >25%). During the flotation process, ammonium-containing chemical agents such as ammonium carbonate, ammonium bicarbonate, ammonium phosphate, NH4Cl, or (NH4)2SO4 are often used to adjust the pulp pH, disperse slime, and suppress gangue. This results in a high ammonium ion content in the final product of traditional processes, leading to low purity of molybdic acid.

[0007] Therefore, it is of great significance to develop a method for preparing refined molybdic acid by alkaline leaching and acid precipitation of low-grade molybdenum oxide. Summary of the Invention

[0008] This invention provides a method for preparing refined molybdic acid by alkaline leaching and acid precipitation of low-grade molybdenum oxide, which solves the problems of low recovery rate and low purity of molybdic acid prepared by alkaline leaching and acid precipitation of low-grade molybdenum oxide.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing refined molybdic acid by alkaline leaching and acid precipitation of low-grade molybdenum oxide includes the following steps: S1. Alkali leaching: Low-grade molybdenum oxide raw material is mixed with alkaline leaching solution at a solid-liquid ratio of 1:3-4, and an alkaline leaching reaction is carried out at 80-85℃ under stirring. The alkaline solution consists of 20-30 g / L NaOH, 20-30 g / L Na2CO3, and an alkaline leaching stabilizer. The pH of the reaction system is controlled at 11.0±0.2, and the reaction time is 1-2 hours. Solid-liquid separation yields a crude sodium molybdate solution. The alkaline leaching stabilizer, by weight, includes 10-15 parts sodium gluconate, 0.3-0.8 parts sodium hexametaphosphate, 0.1-0.3 parts sodium polyaspartate, and 0.5-1 parts sodium sulfide. The amount added is 1-3‰ of the mass of the molybdenum oxide raw material. S2. Ammonia Removal and Purification: The crude sodium molybdate solution obtained in S1 is heated to 85-90℃, the pH is adjusted to 11.5-12.0 with NaOH, and steam or air is introduced for stripping for 30-60 minutes to remove NH4+ from the solution. + Concentration ≤ 50 mg / L; S3. High-temperature acid precipitation: The purified solution obtained in S2 is heated to 90-95℃, and acid is slowly added while stirring. The final pH value is controlled to be 0.5±0.1. The solution is kept at this temperature for 1-2 hours and then separated into wet molybdic acid solid. S4. Washing and drying: Wash the wet molybdic acid solid obtained in S3 with hot deionized water, and then dry it at 100-120℃ to obtain the refined molybdic acid product.

[0010] Further, preferably: the low-grade molybdenum oxide raw material is a molybdenum oxide raw material containing residual ammonium ion impurities, wherein the molybdenum content is 35%-45%, the molybdenum trioxide content is 52.5%-67.5%, and the particle size is 200-300 mesh.

[0011] Further, preferably: the acid solution is a mixture of concentrated nitric acid and concentrated hydrochloric acid, with a volume ratio of HNO3:HCl = 2-3:1, and the addition rate is controlled so that the pH value of the system drops from the initial value to the final value in 30-60 minutes.

[0012] Further, preferably: the acid precipitation step further includes adding an acid precipitation stabilizer, which, by weight, includes 10-20 parts of diammonium hydrogen phosphate, 1-3 parts of disodium ethylenediaminetetraacetate, and 1-2 parts of polyethylene glycol with a molecular weight of 600-1000, and the amount added is 1-2‰ of the acid solution.

[0013] The beneficial effects of this invention are: This invention effectively solves the problems of high impurities in low-grade raw materials, large molybdenum loss, and low product purity by synergistically combining stabilizer complexation-precipitation in the alkaline leaching stage with high-temperature enhancement and precise acid control in the acid precipitation stage. It achieves high total molybdenum recovery rate, good product purity and physical properties, stable and efficient process, and the refined molybdic acid prepared has high purity and few impurities. Detailed Implementation

[0014] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative effort are also described.

[0015] The low-grade molybdenum oxide raw material used in this invention has an ammonia ion content of 356 mg / L, Mo: 38.6%; Fe: 6.38%; CaO: 4.36%; Mg: 5.01%; SiO2: 9.67%; Al2O3: 1.36%; Na2O: 2.68%; S: 0.13%; P: 0.48%; Cu: 0.72%; and a particle size of 200-300 mesh.

[0016] Example 1: Investigating the effect of alkali-soluble stabilizers on molybdenum leaching rate Low-grade molybdenum oxide raw material was mixed with alkaline leachate at a solid-liquid ratio of 1:4 and subjected to an alkaline dissolution reaction at 85°C under stirring at 400 r / min. The alkaline solution consisted of 30 g / L NaOH, 20 g / L Na2CO3, and an alkaline dissolution stabilizer. The pH of the reaction system was controlled at 11.0 ± 0.2, and the reaction time was 1.5 hours. After solid-liquid separation, a crude sodium molybdate solution was obtained. The alkaline dissolution stabilizer, by weight, included 10-15 parts sodium gluconate, 0.3-0.8 parts sodium hexametaphosphate, 0.1-0.3 parts sodium polyaspartate, and 0.5-1 parts sodium sulfide. The addition amount was 2‰ of the mass of the molybdenum oxide raw material. The specific raw material ratio of the alkaline dissolution stabilizer is shown in Table 1.

[0017] Table 1 Raw material ratios for different alkali-soluble stabilizers

[0018] The leaching rates of chemical elements in the crude sodium molybdate solution were determined, as detailed in Table 2.

[0019] Molybdenum leaching rate (%) = (Molybdenum content in crude sodium molybdate solution × Volume of crude sodium molybdate solution) / (Molybdenum content in low-grade molybdenum oxide feedstock × Mass of molybdenum oxide) × 100

[0020] The leaching rates of other elements are calculated in the same way as for molybdenum, and will not be listed in detail here.

[0021] Table 2. Element leaching rates of alkali-soluble stabilizers with different ratios

[0022] As shown in Table 2, the alkaline stabilizer used in this invention effectively improves the molybdenum leaching rate, inhibits the leaching rate of other metals, and effectively improves the purity of the crude sodium molybdate solution, providing favorable conditions for the subsequent preparation of molybdic acid. The composite stabilizer composed of sodium gluconate, sodium hexametaphosphate, sodium polyaspartate, and sodium sulfide in this invention, through a mechanism of spatial complementarity and chemical coupling, simultaneously eliminates molybdenum loss pathways from three dimensions: liquid phase, solid phase, and colloidal interface, ultimately achieving a significant increase in molybdenum recovery rate. Sodium gluconate chelates the dissolved Ca... 2+ This prevents it from interacting with MoO4. 2- By combining, sodium hexametaphosphate effectively reduces the loss of CaMoO4 formation. It adsorbs onto the surface of calcium carbonate (CaCO3) particles, forming a hydrophilic film that slows down the dissolution rate, thus reducing the loss of Ca from the source. 2+ Upon entering the solution, it reduces the consumption load of sodium gluconate; the two combine, releasing free Ca into the solution. 2+ The significantly reduced concentration effectively decreased the loss of CaMoO4 formation and improved the molybdenum leaching rate. The carboxyl groups on the polyaspartic acid sodium chain adsorbed onto the silica gel surface, and steric hindrance prevented their cross-linking and growth, maintaining an oligomeric state and preventing the silica gel from adsorbing MoO4. 2- Simultaneously, sodium polyaspartate disperses Fe(OH)3, Al(OH)3, and other hydroxide colloids, preventing them from precipitating and co-aggregating with sulfides, and avoiding the adsorption and suspension of heavy metal sulfides by the colloids, thus allowing them to settle smoothly into the tailings. Meanwhile, sodium gluconate also helps to disperse Ca... 2+ The chelation process creates a calcium-free environment for sodium sulfide, allowing it to focus on precipitating heavy metals without triggering new molybdenum loss pathways. Sodium sulfide forms highly insoluble precipitates such as CuS, PbS, and ZnS, directionally removing heavy metals from the solution and preventing them from contaminating molybdate in the acid precipitation stage. The four raw materials mutually eliminate each other's interference, allowing each component to function optimally under its own conditions. This creates a non-interfering leaching environment encompassing the entire spectrum of impurities from calcium ions to clay particles, silica gel, and heavy metals, ultimately achieving the free dissolution, non-destructive separation, and efficient recovery of molybdate ions.

[0023] Example 2: Investigating the effect of acid precipitation stabilizer on molybdenum leaching rate A method for preparing refined molybdic acid by alkaline leaching and acid precipitation of low-grade molybdenum oxide includes the following steps: S1. Alkali leaching: Low-grade molybdenum oxide raw material is mixed with alkaline leaching solution at a solid-liquid ratio of 1:4, and an alkaline leaching reaction is carried out at 85°C with stirring at 400 r / min. The alkaline solution consists of 30 g / L NaOH, 20 g / L Na2CO3, and an alkaline leaching stabilizer. The pH of the reaction system is controlled at 11.0 ± 0.2, and the reaction time is 1.5 hours. Solid-liquid separation yields a crude sodium molybdate solution. The alkaline leaching stabilizer, by weight, includes 10 parts sodium gluconate, 0.5 parts sodium hexametaphosphate, 0.3 parts sodium polyaspartate, and 0.7 parts sodium sulfide, and the addition amount is 2‰ of the mass of the molybdenum oxide raw material. S2. Ammonia Removal and Purification: The crude sodium molybdate solution obtained in S1 is heated to 90℃, the pH is adjusted to 11.8±0.2 with NaOH, and steam is introduced for stripping for 60 minutes to remove NH4+ from the solution. + Concentration ≤ 50 mg / L; S3. High-temperature acid precipitation: The purified solution obtained in S2 is heated to 95°C, and acid is slowly added while stirring. The final pH value is controlled to be 0.5±0.1. The solution is kept at this temperature for 2 hours and then separated into solid and wet molybdic acid. The acid is a mixture of concentrated nitric acid and concentrated hydrochloric acid with a volume ratio of HNO3:HCl = 2:1. The addition rate is controlled so that the pH value of the system drops from the initial value to the final value in 60 minutes. The acid precipitation step also includes the addition of an acid precipitation stabilizer. The acid precipitation stabilizer, by weight, includes 10-20 parts of diammonium hydrogen phosphate, 1-3 parts of disodium ethylenediaminetetraacetate, and 1-2 parts of polyethylene glycol (molecular weight 800). The amount added is 2‰ of the acid solution. S4. Washing and drying: Wash the wet molybdic acid solid obtained in S3 with hot deionized water, and then dry it at 70°C to obtain the refined molybdic acid product.

[0024] The specific raw material ratios for the acid precipitation stabilizer are shown in Table 3.

[0025] Table 3 Raw material ratios for different acid precipitation stabilizers

[0026] The molybdenum content in the purified molybdic acid was determined, and the molybdenum recovery rate was calculated. See Table 4 for details.

[0027] Molybdenum recovery rate (%) = (Molybdenum content in refined molybdic acid × Weight of refined molybdic acid) / (Molybdenum content in low-grade molybdenum oxide feedstock × Mass of molybdenum oxide) × 100

[0028] Table 4. Elemental leaching rates of acid precipitation stabilizers with different ratios

[0029] As shown in Table 4, the method of the present invention effectively improves the molybdenum recovery rate by adding a suitable acid precipitation stabilizer.

[0030] In a strongly acidic environment with a pH of 0.5, phosphate ions mainly exist in the form of H3PO4, but very low concentrations of HPO4 are still present. 2- / H2PO4 - These trace amounts of phosphate ions can react with residual alkaline earth metals (Ca) in the solution. 2+ Mg 2+ Molybdenum acid (H2MoO4) and some heavy metal ions form phosphate precipitates with very low solubility (such as Ca3(PO4)2, FePO4). By fixing these most difficult-to-remove impurity ions in phosphate form simultaneously with or before the precipitation of molybdenum acid, co-precipitation of these impurities with molybdenum acid is effectively prevented, which is key to obtaining high-purity molybdenum acid. EDTA is a broad-spectrum strong complexing agent. Although its complexing ability decreases under strongly acidic conditions (pH 0.5), it remains effective against Fe... 3+ Cu 2+ Pb 2+ Heavy metal ions still possess strong complexing properties, "locking" soluble heavy metal ions within the complex and preventing their hydrolysis and precipitation or co-crystallization with molybdate, thus further reducing the heavy metal impurity content in the product. EDTA treats soluble complexed impurities, while phosphate treats precipitable ions, forming a dual impurity removal barrier of complexation and precipitation, ensuring more thorough impurity removal.

[0031] PEG is a nonionic surfactant that adsorbs onto the surface of molybdate crystal nuclei, slowing down crystal growth, promoting the formation of larger and denser crystal particles, reducing the formation of fine crystals, increasing the repulsive force between particles, preventing excessive crystal aggregation, and avoiding impurities being encapsulated in agglomerates. The resulting large, easily filterable crystals greatly reduce the filtration loss of molybdate and the entrainment loss of filter cake during solid-liquid separation, directly improving the molybdenum recovery rate.

[0032] The acid precipitation stabilizer formulation of this invention solves two core problems in the acid precipitation process—deep removal of impurities and control of crystal morphology—through a design that combines complementary functions and synergistic effects, thereby significantly improving molybdenum recovery rate and product purity.

[0033] Example 3 A method for preparing refined molybdic acid by alkaline leaching and acid precipitation of low-grade molybdenum oxide includes the following steps: S1. Alkali leaching: Low-grade molybdenum oxide raw material is mixed with alkaline leaching solution at a solid-liquid ratio of 1:4, and an alkaline leaching reaction is carried out at 85°C with stirring at 400 r / min. The alkaline solution consists of 30 g / L NaOH, 20 g / L Na2CO3, and an alkaline leaching stabilizer. The pH of the reaction system is controlled at 11.0 ± 0.2, and the reaction time is 1.5 hours. Solid-liquid separation yields a crude sodium molybdate solution. The alkaline leaching stabilizer, by weight, includes 10 parts sodium gluconate, 0.5 parts sodium hexametaphosphate, 0.3 parts sodium polyaspartate, and 0.7 parts sodium sulfide, and the addition amount is 2‰ of the mass of the molybdenum oxide raw material. S2. Ammonia Removal and Purification: The crude sodium molybdate solution obtained in S1 is heated to 90℃, the pH is adjusted to 11.8±0.2 with NaOH, and steam is introduced for stripping for 60 minutes to remove NH4+ from the solution. + Concentration ≤ 50 mg / L; S3. High-temperature acid precipitation: The purified solution obtained in S2 is heated to 95°C, and acid is slowly added while stirring. The final pH value is controlled to be 0.5±0.1. The solution is kept at this temperature for 2 hours and then separated into solid and wet molybdic acid. The acid is a mixture of concentrated nitric acid and concentrated hydrochloric acid with a volume ratio of HNO3:HCl = 2:1. The addition rate is controlled so that the pH value of the system drops from the initial value to the final value in 60 minutes. The acid precipitation step also includes the addition of an acid precipitation stabilizer. The acid precipitation stabilizer, by weight, includes 15 parts of diammonium hydrogen phosphate, 1 part of disodium ethylenediaminetetraacetate, and 1.5 parts of polyethylene glycol (molecular weight 800). The amount added is 2‰ of the acid solution. S4. Washing and drying: Wash the wet molybdic acid solid obtained in S3 with hot deionized water, then dry and pulverize it at 70°C, and pass it through a 60-mesh sieve to obtain a refined molybdic acid product, which is a light yellow powder with fine, dry particles, good flowability, and a residue of <0.2g on a 60-mesh sieve.

[0034] The product measurement data of refined molybdic acid obtained from the determination are shown in Table 5.

[0035] Table 5. Product Measurement Data of Refined Molybdic Acid

[0036] As shown in Table 5, the refined molybdic acid prepared by this invention has high purity and meets relevant industrial standards.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing refined molybdic acid by alkaline leaching and acid precipitation of low-grade molybdenum oxide, characterized in that, Includes the following steps: S1. Alkali leaching: Low-grade molybdenum oxide raw material is mixed with alkaline leaching solution at a solid-liquid ratio of 1:3-4, and an alkaline leaching reaction is carried out at 80-85℃ under stirring. The alkaline solution consists of 20-30 g / L NaOH, 20-30 g / L Na2CO3, and an alkaline leaching stabilizer. The pH of the reaction system is controlled at 11.0±0.2, and the reaction time is 1-2 hours. Solid-liquid separation yields a crude sodium molybdate solution. The alkaline leaching stabilizer, by weight, includes 10-15 parts sodium gluconate, 0.3-0.8 parts sodium hexametaphosphate, 0.1-0.3 parts sodium polyaspartate, and 0.5-1 parts sodium sulfide. The amount added is 1-3‰ of the mass of the molybdenum oxide raw material. S2. Ammonia Removal and Purification: The crude sodium molybdate solution obtained in S1 is heated to 85-90℃, the pH is adjusted to 11.5-12.0 with NaOH, and steam or air is introduced for stripping for 30-60 minutes to remove NH4+ from the solution. + Concentration ≤ 50 mg / L; S3. High-temperature acid precipitation: The purified solution obtained in S2 is heated to 90-95℃, and acid is slowly added while stirring. The final pH value is controlled to be 0.5±0.

1. The solution is kept at this temperature for 1-2 hours and then separated into wet molybdic acid solid. S5. Washing and drying: Wash the wet molybdic acid solid obtained in S3 with hot deionized water, and then dry it at 100-120℃ to obtain the refined molybdic acid product.

2. The method according to claim 1, characterized in that: The low-grade molybdenum oxide raw material is a molybdenum oxide raw material containing residual ammonium ion impurities, wherein the molybdenum content is 35%-45% and the particle size is 200-300 mesh.

3. The method according to claim 1, characterized in that: The acid solution is a mixture of concentrated nitric acid and concentrated hydrochloric acid, with a volume ratio of HNO3:HCl = 2-3:

1. The addition rate is controlled so that the pH value of the system drops from the initial value to the final value in 30-60 minutes.

4. The method according to claim 1, characterized in that: The acid precipitation step further includes adding an acid precipitation stabilizer, which, by weight, comprises 10-20 parts diammonium hydrogen phosphate, 1-3 parts disodium ethylenediaminetetraacetate, and 1-2 parts polyethylene glycol with a molecular weight of 600-1000, and the amount added is 1-2‰ of the acid solution.

Images