Method for recycling process water in APT (ammonium paratungstate) production process

Abstract

The invention discloses a method for recycling process water in an APT (ammonium paratungstate) production process, and relates to the technical field of hydrometallurgy. Comprising the following steps: step a, recycling wastewater of an alkali extraction system; step b, evaporating strip liquor and recovering ammonia water; c, pure ammonium tungstate evaporation ammonia water is utilized in a graded mode; step d, ammonium molybdate evaporation ammonia water closed-loop utilization; and e, recycling ammonia gas in a crystallization section. According to the method for recycling the process water in the APT production process, the whole-process closed-loop design is realized, the discharged wastewater is thoroughly eliminated, and the requirements of environmental protection regulations are met; the waste water treatment cost and the fresh water consumption are reduced, and the comprehensive cost is reduced by 15%-30%; key components such as ammonia water and sodium ions are graded and recycled, so that the raw material consumption is reduced by more than 20%; the method is suitable for transformation of an existing scheelite APT production line, operation is easy, and large-scale equipment upgrading is not needed.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrometallurgy, and particularly relates to a method for recycling process water during the production of APT. Background Art

[0002] Scheelite is produced into APT by alkaline extraction using a hydrometallurgical process. A large amount of process wastewater containing ammonia, sodium ions, and sulfates is generated in each process. In the traditional process, such wastewater needs to be discharged after complex treatment, which not only increases the treatment cost but also is difficult to meet the increasingly strict environmental protection requirements. In the prior art, wastewater recycling schemes are mostly limited to a single link and lack systematic integration, resulting in low overall recycling efficiency. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for recycling process water during the production of APT. Through the closed-loop circulation of process water in multiple links, zero discharge of wastewater is achieved, with both economic and environmental benefits.

[0004] The technical solution adopted by the present invention is as follows: A method for recycling process water during the production of APT, comprising: Step a, wastewater recycling in the alkali extraction system: The wastewater in the alkaline extraction stage of the alkali extraction system includes raffinate and washing section wastewater. After the raffinate and washing wastewater are allowed to stand and precipitate, they are transferred to the decomposition workshop and then pumped into the decomposition pulping tank. Lime is added to the pulping tank and heated to 75 - 85°C, and then sodium carbonate is added to adjust the pH value to 8.0 - 8.5, and then ore powder is added for pulping operation; Step b, evaporation of stripping solution and recovery of ammonia water: During the evaporation process of the stripping solution in the alkali extraction system entering the continuous crystallizer, the generated ammonia gas is condensed into recovered ammonia water A through a shell-and-tube heat exchanger. The recovered ammonia water A is transported through a pipeline to the stripping agent preparation stirring tank, and ammonium bicarbonate is added and mixed, and then stirred and heated to 30 - 40°C to prepare the stripping agent, which is returned to the alkaline extraction stage for use; the evaporated solution is filtered to obtain crude ammonium tungstate crystals for use in the ammonia dissolution process, and the filtrate is prepared into ammonium molybdate solution and sent to the thickener; Step c, hierarchical utilization of ammonia water evaporated from pure ammonium tungstate: During the evaporation and concentration process of pure ammonium tungstate, the generated ammonia vapor is condensed to obtain recovered ammonia water B, which flows by gravity into the recovered ammonia water tank. Recovered ammonia water B is transferred from the recovered ammonia water tank to the ammonia flushing tank, and liquid ammonia is added to the ammonia flushing tank to increase the concentration of recovered ammonia water B to 5 - 8 mol / L, and then it is pumped into the ammonia dissolution kettle through a pump. The crude ammonium tungstate crystals prepared in step b are added to the ammonia dissolution kettle for dissolution, and the prepared ammonium tungstate solution is transported to the moving bed in the ion exchange process for use; Step d, Closed-loop utilization of ammonia water in ammonium molybdate evaporation: The ammonia vapor generated during the evaporation and concentration of ammonium molybdate solution in the thickener is condensed to obtain recycled ammonia water C. Recycled ammonia water C flows by gravity to the low-level ammonia water tank and is pumped into the high-level ammonia water tank by a pump, and then enters the alkaline extraction and washing tank by gravity to be used as washing water in the alkaline extraction section to remove sodium ions. Step e, Resource utilization of ammonia gas in the crystallization section: The residual ammonia gas during the evaporation processes in the continuous crystallizer and APT evaporation crystallizer is respectively drawn into the sulfuric acid absorption tower by a fan for spray absorption to generate ammonium sulfate wastewater. The ammonium sulfate wastewater is discharged into the ammonium sulfate solution tank and then pumped into a multi-effect evaporator for evaporation and concentration. After cooling by a condenser, it is filtered by suction to obtain ammonium sulfate salt.

[0005] Specifically, in step a, the static precipitation time of the wastewater in the alkaline extraction stage is 2 - 4 hours to facilitate the separation of oil and water; the addition amount of ore powder ensures that the tungsten metal content in the solution after pulping is 80 - 110 g / L.

[0006] Specifically, in step b, the temperature of the continuous crystallizer is controlled at 90 - 105 °C, and the temperature of the shell-and-tube heat exchanger is controlled at 20 - 30 °C to ensure the efficient recovery of ammonia water; when preparing the stripping agent, the amount of recycled ammonia water A added in each batch is 35 - 45 m³, and the addition amount of ammonium bicarbonate is 7 tons.

[0007] Specifically, in step c, the condensation temperature is controlled at 20 - 30 °C.

[0008] Specifically, in step d, the evaporation temperature of ammonium molybdate is controlled at 70 - 80 °C, and the condensation temperature is controlled at 20 - 30 °C.

[0009] Specifically, in step e, the absorption tower is a wet packed absorption tower with ring packing. Sulfuric acid is recycled in the absorption tower. When the sulfuric acid concentration is 1 mol / L and the pH of the circulating liquid reaches 6 - 7, the solution is discharged into the ammonium sulfate solution tank to replace the new sulfuric acid. The temperature of the multi-effect evaporator is controlled at 100 - 110 °C.

[0010] Due to the adoption of the above technical solution, the present invention has the following advantages: The method for recycling process water in the APT production process of the present invention realizes a full-process closed-loop design, completely eliminates the discharged wastewater, and meets the requirements of environmental protection regulations; reduces the wastewater treatment cost and the fresh water consumption, and the comprehensive cost is reduced by 15% - 30%; key components such as ammonia water and sodium ions are recycled at different levels, reducing the raw material consumption by more than 20%; it is applicable to the transformation of existing APT production lines for low-grade scheelite, with simple operation and no need for large-scale equipment upgrading. Brief Description of the Drawings

[0011] Figure 1 is the process flow diagram of the entire APT production process of the present invention. Detailed implementation mode

[0012] The present invention will be further explained and illustrated below in conjunction with the accompanying drawings and embodiments. The protection scope of the present invention cannot be limited thereby. The purpose of disclosing the present invention is to protect all technical improvements within the scope of the present invention. Embodiment 1

[0013] Combined with the attached Figure 1 A method for recycling process water in the APT production process as shown, including: Step a: Recycling of the wastewater from the alkali extraction system: The wastewater from the alkaline extraction stage of the alkali extraction system includes the raffinate with a tungsten content of 10 g / L and the washing section wastewater. Take 25 cubic meters of the raffinate and washing wastewater, after standing for 2 hours of precipitation, transfer it to the decomposition workshop, and then pump it into the decomposition pulping tank. Add 800 Kg of lime into the pulping tank, heat up to 75 °C, then add 250 Kg of sodium carbonate to adjust the pH value to 8.0 - 8.5, and then add 18.6 t of ore powder for pulping operation; the tungsten metal content in the solution after pulping is 80 - 110 g / L.

[0014] Step b: Recovery of ammonia water from the evaporation of the stripping solution: During the evaporation process of the stripping solution of the alkali extraction system in a continuous crystallizer with a temperature controlled at 90 °C, the generated ammonia gas is condensed by a shell-and-tube heat exchanger with a temperature of 20 °C to obtain the recovered ammonia water A with a concentration of 4 mol / L. Transfer 35 m³ of the recovered ammonia water A to the stripping agent preparation stirring tank through a pipeline, add 7 tons of ammonium bicarbonate and mix, then start stirring and heat up. After heating up to 35 °C, continue stirring for half an hour to obtain the stripping agent, and the stripping agent is returned to the alkaline extraction stage for use; the solution after evaporation is filtered to obtain the crude ammonium tungstate crystals for use in the ammonia dissolution process, and the filtrate is made into ammonium molybdate solution and sent to the thickener.

[0015] Step c: Hierarchical utilization of ammonia water from the evaporation of pure ammonium tungstate: During the evaporation and concentration process of pure ammonium tungstate, the generated ammonia vapor is condensed to obtain the recovered ammonia water B with a concentration of 5 mol / L, and the condensation temperature is controlled at 20 °C. The recovered ammonia water B flows into the recovered ammonia water tank by gravity. Transfer 5 m³ of the recovered ammonia water B from the recovered ammonia water tank into the ammonia flushing tank, add 0.5 m³ of liquid ammonia into the ammonia flushing tank, increase the concentration of the recovered ammonia water B to 8 mol / L, and then pump it into the ammonia dissolution kettle, and add 2.5 tons of crude ammonium tungstate crystals for dissolution to prepare ammonium tungstate solution; the ammonium tungstate solution is transported to the moving bed in the ion exchange process for use.

[0016] Step d, Closed-loop utilization of ammonia water in ammonium molybdate evaporation: The ammonia vapor generated during the evaporation and concentration of ammonium molybdate solution in a concentrator at 70°C is condensed to obtain recycled ammonia water C with a concentration of 2 mol / L, and the condensation temperature is controlled at 20°C; the recycled ammonia water C flows by gravity into the low-level ammonia water tank, is pumped into the high-level ammonia water tank by a pump, and then enters the alkaline extraction and washing tank by gravity. By controlling the valve opening, the flow rate is controlled at 1 m³ and used as washing water in the alkaline extraction and washing section to remove sodium ions.

[0017] Step e, Resource utilization of ammonia gas in the crystallization section: The residual ammonia gas during the evaporation processes in the continuous crystallizer and the APT evaporation crystallizer is respectively drawn into a sulfuric acid absorption tower by a fan for spray absorption to generate ammonium sulfate wastewater. The absorption tower is a wet packing absorption tower with annular packing, and sulfuric acid is recycled in the absorption tower with a concentration of 1 mol / L; when the pH of the circulating liquid reaches 6 - 7, the ammonium sulfate wastewater is discharged into the ammonium sulfate solution tank to replace the new sulfuric acid, and then the solution is pumped into a multi-effect evaporator for evaporation and concentration. After cooling through a condenser, it is filtered to obtain ammonium sulfate salt; the temperature of the multi-effect evaporator is controlled at 100°C. Example 2

[0018] Combined with the attached Figure 1 A method for recycling process water in the APT production process as shown, including: Step a, Recycling of wastewater in the alkali extraction system: The wastewater in the alkaline extraction stage of the alkali extraction system includes the raffinate with a tungsten content of 10 g / L and the washing section wastewater. Take 28.3 cubic meters of the raffinate and washing wastewater, after standing and precipitating for 4 hours, transfer it to the decomposition workshop, then pump it into the decomposition pulping tank. Add 730 Kg of lime, heat up to 85°C, add 263 Kg of sodium carbonate to adjust the pH value to 8.0 - 8.5, and then add 17.9 t of ore powder for pulping operation; the tungsten metal content in the pulped solution is 80 - 110 g / L.

[0019] Step b, Recovery of ammonia water from the stripping solution evaporation: During the evaporation process of the stripping solution in the alkali extraction system in a continuous crystallizer with a temperature controlled at 105°C, the generated ammonia gas is condensed by a shell-and-tube heat exchanger at a temperature of 30°C to obtain recycled ammonia water A with a concentration of 3 mol / L. Transfer 45 m³ of the recycled ammonia water A to the stripping agent preparation and stirring tank through a pipeline, add 7 tons of ammonium bicarbonate and mix, then start stirring and heat up. After heating up to 35°C, continue stirring for half an hour to obtain the stripping agent, and the stripping agent returns to the alkaline extraction stage for use; the evaporated solution is filtered to obtain crude ammonium tungstate crystals for use in the ammonia dissolution process, and the filtrate is made into ammonium molybdate solution and sent to the concentrator.

[0020] c. Hierarchical utilization of ammonia water in the evaporation of ammonium tungstate pure: During the evaporation and concentration of ammonium tungstate pure, the ammonia vapor generated is condensed to obtain recycled ammonia water B with a concentration of 5 mol / L. The condensation temperature is controlled at 30 °C. The recycled ammonia water B flows by gravity into the recycled ammonia water tank. 5 m³ of recycled ammonia water B is transferred from the recycled ammonia water tank into the ammonia flushing tank, and 0.7 m³ of liquid ammonia is added into the ammonia flushing tank. After the concentration of the recycled ammonia water B is increased to 5 mol / L, it is pumped into the ammonia dissolution kettle, and 2.3 tons of crude ammonium tungstate crystals are added for dissolution to prepare an ammonium tungstate solution. The ammonium tungstate solution is transported to the moving bed in the ion exchange process for use.

[0021] Step d. Closed-loop utilization of ammonia water in the evaporation of ammonium molybdate: The ammonia vapor generated during the evaporation and concentration of ammonium molybdate solution in a concentrator at 80 °C is condensed to obtain recycled ammonia water C with a concentration of 2.5 mol / L. The condensation temperature is controlled at 30 °C. The recycled ammonia water C flows by gravity into the low-level ammonia water tank, is pumped into the high-level ammonia water tank by a pump, and then enters the alkaline extraction and washing tank by gravity. By controlling the opening of the valve, the flow rate is controlled at 1 m³ and used as washing water in the alkaline extraction and washing section to remove sodium ions.

[0022] Step e. Resource utilization of ammonia gas in the crystallization section: The residual ammonia gas during the evaporation in the continuous crystallizer and the APT evaporation crystallizer is respectively drawn into the sulfuric acid absorption tower by a fan for spray absorption to generate ammonium sulfate wastewater. The absorption tower is a wet packing absorption tower with annular packing. Sulfuric acid is recycled in the absorption tower, and the concentration of sulfuric acid is 1 mol / L. When the pH of the circulating liquid reaches 6 - 7, the ammonium sulfate wastewater is discharged into the ammonium sulfate solution tank to replace the new sulfuric acid, and then the solution is pumped into a multi-effect evaporator for evaporation and concentration. After cooling by a condenser, it is filtered by suction to obtain ammonium sulfate salt. The temperature of the multi-effect evaporator is controlled at 110 °C.

[0023] The parts not detailed in the present invention are prior art.

[0024] The embodiments selected herein for disclosing the invention purpose of the present invention are currently considered appropriate. However, it should be understood that the present invention is intended to include all variations and improvements of all embodiments within the scope of this concept and invention.

Claims

1. A method for recycling process water in an APT production process, characterized in that: include: Step a, reuse of wastewater from alkali extraction system: the wastewater from the alkaline extraction stage of the alkali extraction system includes raffinate and washing stage wastewater. After static sedimentation, the raffinate and washing wastewater are transferred to the decomposition workshop and then pumped into the decomposition pulping tank. Lime is added to the pulping tank and heated to 75-85°C. Sodium carbonate is then added to adjust the pH value to 8.0-8.5, and then mineral powder is added to perform pulping operation; Step b, stripping liquid evaporation and ammonia recovery: during the stripping liquid of the alkali extraction system enters the continuous crystallizer for evaporation, the generated ammonia gas is condensed into recovered ammonia water A through a tube-in-tube heat exchanger, and the recovered ammonia water A is transported to the stripping agent configuration stirring tank through a pipeline, and after adding ammonium bicarbonate and mixing, the mixture is stirred and heated to 30-40°C to obtain a stripping agent, and the stripping agent is returned to the alkaline extraction stage for standby use; the evaporated solution is filtered to obtain crude ammonium tungstate crystals for use in the ammonia dissolution process, and the filtrate is used to obtain an ammonium molybdate solution and sent to a concentrator; Step c, graded utilization of ammonia water after evaporation of pure ammonium tungstate: During the evaporation and concentration process of pure ammonium tungstate, the generated ammonia vapor is condensed to obtain recovered ammonia water B, which flows into the recovered ammonia water tank by gravity, and then transferred from the recovered ammonia water tank to the ammonia flushing tank to recover the ammonia water B. Liquid ammonia is added to the ammonia flushing tank to increase the concentration of the recovered ammonia water B to 5-8 mol / L, and then the recovered ammonia water B is pumped into the ammonia dissolving kettle, and the crude ammonium tungstate crystals obtained in step b are added into the ammonia dissolving kettle for dissolution, and the prepared ammonium tungstate solution is transported to the moving bed of the ion exchange process for use; Step d, closed-loop utilization of ammonia water by evaporation of ammonium molybdate: ammonia vapor generated during the evaporation and concentration process of the ammonium molybdate solution in the concentrator is condensed to obtain recovered ammonia water C, which flows by gravity into the ammonia water low-level tank, is pumped into the ammonia water high-level tank, and then flows by gravity into the alkaline extraction washing tank, and is used as washing water in the alkaline extraction stage to remove sodium ions; Step e, ammonia resource utilization in the crystallization stage: the residual ammonia in the evaporation process of the continuous crystallizer and the APT evaporation crystallizer is respectively sucked into the sulfuric acid absorption tower through a fan for spray absorption to generate ammonium sulfate waste water; the ammonium sulfate waste water is discharged into the ammonium sulfate solution tank, and then pumped into the multi-effect evaporator for evaporation and concentration, and then cooled by the condenser and filtered to obtain ammonium sulfate salt.

2. The method for recycling process water in the APT production process according to claim 1, characterized in that: In the step a, the wastewater in the alkaline extraction stage is allowed to settle for 2-4 hours; the amount of mineral powder added ensures that the tungsten metal content of the solution after pulping is 80-110 g / L.

3. The method for recycling process water in the APT production process according to claim 1, characterized in that: In the step b, the temperature of the continuous crystallizer is controlled at 90-105°C, and the temperature of the shell and tube heat exchanger is controlled at 20-30°C; when preparing the stripping agent, the amount of recovered ammonia water A added in each batch is 35-45m³, and the amount of ammonium bicarbonate added is 7 tons.

4. The method for recycling process water in the APT production process according to claim 1, characterized in that: In the step c, the condensation temperature is controlled at 20-30°C.

5. The method for recycling process water in the APT production process according to claim 1, characterized in that: In the step d, the evaporation temperature of ammonium molybdate is controlled at 70-80°C, and the condensation temperature is controlled at 20-30°C.

6. The method for recycling process water in the APT production process according to claim 1, characterized in that: In the step e, the absorption tower is a wet packed absorption tower, annular packing is used, sulfuric acid is circulated in the absorption tower, the sulfuric acid concentration is 1 mol / L, and when the pH of the circulating liquid reaches 6-7, the solution is discharged into the ammonium sulfate solution tank to replace new sulfuric acid, and the temperature of the multiple-effect evaporator is controlled at 100-110°C.

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