Method for recovering sodium carbonate and removing phosphorus, arsenic and silicon from tungsten-molybdenum leaching solution

Abstract

The invention discloses a method for recovering sodium carbonate and removing phosphorus, arsenic and silicon from tungsten and molybdenum leachate, which comprises the following steps: (1) adding a solvating-out agent and / or a regenerated solvating-out agent recovered in the step (3) into the tungsten and molybdenum leachate obtained by decomposing tungsten and molybdenum resources with sodium carbonate, reacting for 10-30 minutes, and carrying out solid-liquid separation to obtain sodium carbonate crystals and crystallization mother liquor; (2) adding an acid solution into the crystallization mother liquor obtained in the step (1), adjusting the pH value of the system to 9-10, and adding a magnesium precipitator in a stirring state; and (3) carrying out evaporation operation on the system after the precipitation reaction in the step (2) is completed, carrying out solid-liquid separation after the evaporation is completed to obtain a purified liquid and impurity-removed slag, condensing and recycling evaporated solventing-out agent steam to obtain a regenerated solventing-out agent, and returning to the step (1) for recycling. The crystallization rate of sodium carbonate can reach 90% or above, and phosphorus, arsenic and silicon can be deeply removed.

Description

Technical Field

[0001] This invention relates to the field of compound purification technology, and specifically to a method for recovering sodium carbonate and removing phosphorus, arsenic and silicon from tungsten-molybdenum leachate. Background Technology

[0002] Sodium carbonate decomposition is a classic method for processing various tungsten minerals and secondary tungsten and molybdenum resources. It includes roasting and pressure cooking. Sodium carbonate roasting was one of the earliest tungsten smelting technologies introduced to my country, characterized by its wide adaptability to raw materials and its ability to process various tungsten mineral resources and secondary resources. Simultaneously, the roasting process decomposes residual organic matter in flotation reagents and spent catalysts, eliminating interference from organic matter in subsequent processes. Sodium carbonate pressure cooking is an important method for processing scheelite, offering advantages such as high decomposition efficiency and low tungsten content in the slag. Since the 1980s, the tungsten smelting process of sodium carbonate pressure cooking-acidic extraction-evaporation crystallization to produce ammonium paratungstate has been in use. Because this process does not require dilution of the leachate before conversion, its wastewater discharge is significantly lower than that of the sodium hydroxide pressure cooking-alkaline ion exchange-evaporation crystallization process, thus its production capacity has continued to expand in recent years.

[0003] To ensure efficient decomposition of tungsten resources by sodium carbonate, excess sodium carbonate is required in production practices. For example, when decomposing scheelite using the sodium carbonate pressure cooking method, the amount of sodium carbonate consumed can be 4 to 6 times the amount of tungsten material; while when treating waste SCR denitration catalyst using the sodium carbonate roasting method, the amount consumed can be 35 to 87 times the amount of tungsten material. If the excess sodium carbonate is not recovered during the subsequent acidic extraction process after entering the leachate, more acid will be needed to adjust it to a weakly acidic state. Therefore, current processes use freeze crystallization to recover some sodium carbonate before extraction. However, the crude sodium tungstate solution or crude sodium carbonate solution obtained from freeze crystallization needs to be further treated by magnesium salt precipitation to remove impurities such as phosphorus, arsenic, and silicon. This causes the system temperature to drop from a high temperature to about 5°C, and then rise to about 80°C. This cooling and heating process significantly increases energy consumption. Therefore, there is an urgent need to develop a technology that is compatible with both upstream and downstream processes and can efficiently recover sodium carbonate from tungsten-molybdenum leachates. Summary of the Invention

[0004] The purpose of this invention is to provide a method for recovering sodium carbonate and removing phosphorus, arsenic and silicon from tungsten-molybdenum leachate. The method aims to use a dissolution crystallization method to separate sodium carbonate from the tungsten-molybdenum leachate, and then promote the precipitation of phosphorus, arsenic and silicon during the magnesium salt precipitation process, and recover the solvent by evaporation and condensation.

[0005] To achieve the above objectives, the present invention provides a method for recovering sodium carbonate and removing phosphorus, arsenic, and silicon from tungsten-molybdenum leachate, comprising the following steps: (1) Add the solvent and / or the regenerated solvent recovered in step (3) to the tungsten-molybdenum leachate obtained by decomposing tungsten-molybdenum resources with sodium carbonate, react for 10 to 30 minutes, and obtain sodium carbonate crystals and crystallization mother liquor by solid-liquid separation. The solvent includes one or more of methanol, ethanol and propanol.

[0006] (2) Add acid to the crystallization mother liquor obtained in step (1) to adjust the pH of the system to 9-10, and then add magnesium precipitant while stirring. The residual solvent in the system weakens the hydration of magnesium ions, and promotes the formation of precipitates of magnesium salt with phosphorus, arsenic and silicon impurities.

[0007] (3) Evaporate the system after the precipitation reaction in step (2) to completely remove the solvent from the system. The evaporated solvent vapor is condensed and recovered to obtain regenerated solvent, which is then returned to step (1) for recycling. The evaporation process, while removing the solvent, provides a high-temperature aging environment for the precipitate generated in step (2), promoting its transformation into a more easily filterable crystalline or condensed form. After evaporation, solid-liquid separation is performed to obtain purified liquid and removed residue.

[0008] Preferably, the volume of the solvent added in step (1) is 0.8 to 2 times the volume of the tungsten-molybdenum leaching solution.

[0009] Preferably, the acid solution in step (2) includes one or more of hydrochloric acid, sulfuric acid and nitric acid.

[0010] Preferably, the magnesium precipitant in step (2) includes one or more of magnesium chloride, magnesium sulfate, magnesium nitrate, magnesium oxide, and magnesium hydroxide.

[0011] Preferably, the amount of magnesium precipitant added in step (2) is 1.5 to 2.5 times the total molar amount of phosphorus, arsenic and silicon in the tungsten-molybdenum leachate.

[0012] Preferably, the evaporation operation temperature in step (3) is 70~100℃.

[0013] The technical principles employed in this invention are as follows: This invention utilizes the superior solubility of alcohols in sodium carbonate compared to sodium tungstate, thus preferentially crystallizing out sodium carbonate. On the other hand, magnesium ions exhibit strong hydration properties, and the solution system for magnesium salt precipitation and impurity removal has a certain degree of supersaturation. The residual solvent in the solution after sodium carbonate recovery weakens the hydration of magnesium ions, promoting the formation of precipitates between magnesium ions and impurity ions such as phosphate, arsenate, and silicate. The subsequent evaporation process not only recovers the solvent but also creates a high-temperature aging environment for the magnesium salt precipitate, thereby transforming it into a precipitate form that is easily filtered.

[0014] The beneficial effects that this invention can achieve are as follows: This invention fully utilizes the selective dissolution and crystallization effect of the solvent on sodium carbonate in tungsten-molybdenum leaching solutions. The crystallization rate of sodium carbonate can reach over 90%, and the crystallization reaction reaches equilibrium in 5-10 minutes, achieving rapid and efficient recovery of sodium carbonate. For the mother liquor from the dissolution and crystallization process, the magnesium salt precipitation and impurity removal process is coupled with the solvent recovery process. This allows the solvent to play a promoting role in the removal of phosphorus, arsenic, and silicon by magnesium salt precipitation, improving the precipitation efficiency of magnesium salts and achieving deep removal of the aforementioned impurities. Detailed Implementation

[0015] The present invention will be further illustrated by the following examples, but is not limited thereto.

[0016] Example 1 Take 1 liter of tungsten leaching solution, with a tungsten content of 12.7 g / L and a sodium carbonate concentration of 281 g / L. Add 1.5 liters of ethanol while stirring. Take samples at different time points, extract a small amount of solution, and determine the concentrations of sodium carbonate and sodium tungstate, and calculate their precipitation rates. The experimental results are shown in Table 1.

[0017] Table 1. Experimental results of dissolution and crystallization at different reaction times. Example 2 Take 2 liters of tungsten leaching solution, with a tungsten content of 15.1 g / L, a sodium carbonate concentration of 296 g / L, and impurities of phosphorus, arsenic, and silicon concentrations of 1.3, 0.2, and 3.7 g / L, respectively. Add 1.9 liters of ethanol while stirring, and after reacting for 15 minutes, perform solid-liquid separation. The precipitation rate of sodium carbonate is 96.4%, and the precipitation rate of sodium tungstate is 4.3%. Add hydrochloric acid to the above filtrate to adjust the pH to 9.9. Then divide the solution into two equal portions, labeled A and B.

[0018] Magnesium chloride was added to solution A, at a concentration 2.0 times the total molar amount of phosphorus, arsenic, and silicon in the solution. The impurity removal reaction was carried out at 85°C, while simultaneously evaporating and condensing the ethanol in the solution. After one hour of reaction, solid-liquid separation was performed. The removal rates of phosphorus, arsenic, and silicon were determined to be 98%, 91%, and 96%, respectively, with a magnesium residue rate of 0.6% in the solution.

[0019] For solution B, ethanol was first evaporated at 85°C until completely evaporated. Then, magnesium chloride was added to the solution, with the amount of magnesium chloride being 2.0 times the total molar amount of phosphorus, arsenic, and silicon in the solution. A purification reaction was carried out at 85°C for 1 hour, followed by solid-liquid separation. The removal rates of phosphorus, arsenic, and silicon were determined to be 93%, 87%, and 88%, respectively, with a magnesium residue rate of 2.1% in the solution.

[0020] Example 3 One liter of molybdenum leaching solution was taken, containing 18.2 g / L of molybdenum, 235 g / L of sodium carbonate, and impurities of 3.6 g / L of phosphorus, 0.3 g / L of arsenic, and 2.2 g / L of silicon. One liter of methanol was added under stirring, and after reacting for 10 minutes, solid-liquid separation was performed. The precipitation rate of sodium carbonate was 98.3%, and that of sodium molybdate was 5.9%. Sulfuric acid was added to the filtrate to adjust the pH to 9.5. Magnesium sulfate was then added to the solution, at a concentration 2.5 times the total molar amount of phosphorus, arsenic, and silicon. The impurity removal reaction was carried out at 70°C, while the methanol in the solution was volatilized and condensed for recovery. After reacting for one hour, solid-liquid separation was performed again. The removal rates of phosphorus, arsenic, and silicon were determined to be 98%, 95%, and 93%, respectively, with a magnesium residue rate of 1.1% in the solution.

[0021] Example 4 One liter of tungsten-molybdenum leachate was taken, containing 21.9 g / L of tungsten, 10.4 g / L of molybdenum, and 196 g / L of sodium carbonate. The concentrations of impurities phosphorus and silicon were 1.3 g / L and 2.9 g / L, respectively. Two liters of propanol were added under stirring, and after reacting for 15 minutes, solid-liquid separation was performed. The precipitation rate of sodium carbonate was 91.6%, while the precipitation rates of sodium tungstate and sodium molybdate were 6.4% and 2.3%, respectively. Nitric acid was added to the filtrate to adjust the pH to 9.0. Magnesium oxide was then added to the solution at a concentration 1.9 times the total molar amount of phosphorus and silicon. The impurity removal reaction was carried out at 100°C, while the propanol in the solution was volatilized and condensed for recovery. After reacting for one hour, solid-liquid separation was performed again. The removal rates of phosphorus and silicon were determined to be 95% and 93%, respectively, with a magnesium residue rate of 0.8% in the solution.

[0022] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for recovering sodium carbonate and removing phosphorus, arsenic, and silicon from tungsten-molybdenum leachate, characterized in that, Includes the following steps: (1) Add the solvent and / or the regenerated solvent recovered in step (3) to the tungsten-molybdenum leachate obtained by decomposing tungsten-molybdenum resources with sodium carbonate, react for 10 to 30 minutes, and obtain sodium carbonate crystals and crystallization mother liquor by solid-liquid separation. The solvent includes one or more of methanol, ethanol and propanol. (2) Add acid to the crystallization mother liquor obtained in step (1), adjust the pH of the system to 9-10, and then add magnesium precipitant while stirring. (3) Evaporate the system after the precipitation reaction in step (2). After evaporation, perform solid-liquid separation to obtain purified liquid and impurity-free residue. The evaporated solvent vapor is condensed and recovered to obtain regenerated solvent, which is then returned to step (1) for recycling.

2. The method as described in claim 1, characterized in that, The volume of the solvent added in step (1) is 0.8 to 2 times the volume of the tungsten-molybdenum leaching solution.

3. The method as described in claim 1, characterized in that, The acid solution in step (2) includes one or more of hydrochloric acid, sulfuric acid, and nitric acid.

4. The method as described in claim 1, characterized in that, The magnesium precipitant in step (2) includes one or more of magnesium chloride, magnesium sulfate, magnesium nitrate, magnesium oxide, and magnesium hydroxide.

5. The method as described in claim 1, characterized in that, The amount of magnesium precipitant added in step (2) is 1.5 to 2.5 times the total molar amount of phosphorus, arsenic and silicon in the tungsten-molybdenum leachate.

6. The method as described in claim 1, characterized in that, The evaporation operation temperature in step (3) is 70~100℃.

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