Method and system for removing fluorine and chlorine from electrolytic circulation liquid in wet zinc refining

Abstract

This invention relates to the field of hydrometallurgical technology, and in particular to a method and system for removing fluorine and chlorine from a circulating electrolyte in a hydrometallurgical zinc smelting process. It provides a method and system for removing only fluorine and chlorine without altering other components of the waste electrolyte. The method includes the following steps: (1) pumping the waste electrolyte to a concentration tower for concentration and heating; (2) sending the waste electrolyte to a defluorination and chlorination circulating tank; (3) pumping the waste electrolyte from the tank to a defluorination and chlorination tower, where the waste electrolyte falls in a spray-like manner. Hot air at 160-220°C is introduced into the defluorination and chlorination tower to strip the fluorine and chloride ions from the falling droplets. Simultaneously, a) the falling droplets are returned to the defluorination and chlorination circulating tank and pumped back to the defluorination and chlorination tower for stripping. After several cycles, when the sulfuric acid content in the acid reaches 65-75%, it becomes the finished acid; b) the rising flue gas containing fluorine and chloride ions is introduced into an alkaline scrubbing tower, where sodium hydroxide solution is introduced to scrub the flue gas. The generated sodium salt solution is discharged to a wastewater treatment plant, and the scrubbed gas is vented into the atmosphere.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, and in particular to a method and system for removing fluorine and chlorine from the circulating liquid in a hydrometallurgical zinc smelting process. Background Technology

[0002] Hydrometallurgical zinc refining involves dissolving zinc in zinc-containing materials (such as zinc roasted sand, zinc dust, and zinc oxide ore) with dilute sulfuric acid to form zinc sulfate. The clarified zinc sulfate solution enters an electrodeposition cell, where zinc ions are reduced to metallic zinc under the influence of electric current and gradually deposited on the aluminum cathode. The electrolyte in the electrodeposition cell is recycled as a solvent to dissolve zinc-containing materials. This process allows naturally occurring fluorine and chloride in the zinc-containing materials to accumulate to a harmful level. The greatest harm is the corrosion of the electrode plates, which reduces the quality of zinc ingots. It also affects current efficiency and increases energy consumption. Therefore, it is generally required that the concentration of fluoride ions in the electrolyte not exceed 50 mg / L and the concentration of chloride ions not exceed 100 mg / L.

[0003] Chinese Patent Publication No. CN112877736A discloses a method for removing fluoride and chlorine from a wet zinc smelting electrolytic circulating solution. Calcium oxide is added to the circulating solution, and the reaction is heated to obtain calcium fluoride precipitate and a fluoride-free liquid. Copper slag is then added to the fluoride-free liquid, and the reaction is heated to obtain copper chloride precipitate and a fluoride- and chlorine-free circulating solution. This method utilizes copper from the slag, but the composition of the slag is complex, and it cannot be guaranteed that no new pollutants will be introduced into the electrolyte. This includes the addition of calcium oxide to the circulating solution. Therefore, this process of adding reactants to the electrolyte is not a purely fluoride- and chlorine-removing process. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for removing fluorine and chlorine from wet zinc smelting electrolytic circulating liquid without changing other components of the waste electrolyte, and to provide a corresponding removal system.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] A method for removing fluoride and chlorine from a wet zinc smelting electrolytic circulating solution, wherein the method involves collecting the waste electrolyte and then centrally removing fluoride and chlorine, and includes the following steps:

[0007] (1) The waste electrolyte is pumped to the concentration tower, and hot gas is introduced into the concentration tower to evaporate the water so that the mass content of sulfuric acid in the waste electrolyte rises to 15-25% and the temperature of the waste electrolyte rises to 60-65℃.

[0008] (2) The waste electrolyte is transported to the defluorination and chlorination circulation tank;

[0009] (3) The waste electrolyte in the defluorination and chlorination circulation tank is pumped to the defluorination and chlorination tower. The waste electrolyte falls in a spray pattern inside the defluorination and chlorination tower. Hot air at 160-220°C is introduced into the defluorination and chlorination tower to strip the fluoride and chloride ions from the falling droplets. This process simultaneously has the following effects:

[0010] a. The falling droplets flow back to the defluorination and chlorination circulation tank. The waste electrolyte in the defluorination and chlorination circulation tank is pumped back to the defluorination and chlorination tower for stripping. After several cycles, when the sulfuric acid mass content in the acid solution of the defluorination and chlorination circulation tank reaches 65-75%, it becomes the finished acid for use in the wet process workshop.

[0011] b. The rising flue gas containing fluoride and chloride ions is fed into the alkaline scrubbing tower. Sodium hydroxide solution is introduced into the alkaline scrubbing tower to wash the flue gas. The resulting sodium salt solution is discharged to the sewage treatment plant, and the washed gas is vented into the air.

[0012] Specifically, in order to save energy, the hot gas introduced into the thickening tower in process (1) is the hot flue gas discharged from the rotary kiln introduced into the thickening tower.

[0013] Specifically, between processes (1) and (2), there is also a process of connecting the waste electrolyte to a filter press for filtration. The filtered waste electrolyte enters process (2), and the filtered residue is sent back to the rotary kiln.

[0014] Similarly, in order to save energy, the hot air at 160-220°C introduced into the defluorination and chlorination tower in process (3) is the hot air from the acid conversion section that has been reheated by a reheating furnace before being introduced into the defluorination and chlorination tower.

[0015] Specifically, the sodium hydroxide solution introduced into the alkaline washing tower in process (3) has a sodium hydroxide content of 8-12% by mass.

[0016] Correspondingly, a system for removing fluorine and chlorine from the circulating liquid of wet zinc smelting electrolysis is provided. The system is a system for collecting waste electrolyte and centrally removing fluorine and chlorine. It has a concentration tower, a defluorination and chlorine circulation tank, a defluorination and chlorine tower and an alkaline washing tower, and also has a sodium hydroxide preparation tank connected to the pipeline of the alkaline washing tower.

[0017] The concentration tower is equipped with a heating device for concentrating the evaporated water in the waste electrolyte, and the concentration tower is connected to the defluorination and chlorination circulation tank;

[0018] The defluorination and chlorination tower is equipped with a first spray device, which is connected to the defluorination and chlorination circulation tank via a first circulation pump outside the defluorination and chlorination tower. A hot air inlet is provided on the defluorination and chlorination tower below the first spray device, and the hot air inlet is connected to a hot air device. A fluorine and chlorine stripping port is provided at the top of the defluorination and chlorination tower above the first spray device, and a first reflux port is provided at the bottom of the defluorination and chlorination tower, which is connected to the pipeline of the defluorination and chlorination circulation tank.

[0019] The alkaline washing tower has a flue gas inlet, which is connected to the fluorine and chlorine stripping port pipe of the defluorination and chlorine removal tower. A second spray device is provided above the flue gas inlet. The second spray device is connected to the second return port pipe at the bottom of the alkaline washing tower via a second circulation pump outside the alkaline washing tower. The top of the alkaline washing tower has an air vent.

[0020] The first circulating pump has two states: one leading to the first spray device and the other leading to the finished acid tank. The second circulating pump has two states: one leading to the second spray device and the other leading to the sewage outlet.

[0021] Specifically, in order to save energy, the heating device is a heat exchange tube connected to the external rotary kiln exhaust system.

[0022] Specifically, a filter press and a storage tank are connected in sequence by pipelines between the concentration tower and the defluorination and chlorination circulation tank, and a pump is installed between the storage tank and the defluorination and chlorination circulation tank.

[0023] Specifically, the system also includes a clean water supply device that supplies clean water to the sodium hydroxide preparation tank, rinse clean water to the defluorination and chlorination tower, and rinse clean water to the alkali washing tower.

[0024] Also for the purpose of saving energy, the hot air device includes a reheating furnace, a fan, and a pipeline connected to the hot air exhaust system of the external acid conversion section.

[0025] The beneficial effects of this invention are as follows: This invention uses a method of one-point spray stripping and one-point spray washing to remove fluorine and chlorine from the electrolytic circulating liquid and to collect only the removed fluorine and chlorine. No substances are added to the electrolyte, so no new pollution is caused to the electrolytic circulating liquid. The amount of sodium salt produced by the spray washing reaction is small, which reduces the burden of wastewater treatment. Both spraying processes are in a circulating treatment mode, which saves production costs. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the system connection relationship of the present invention. Detailed Implementation

[0027] The technical features of this invention are further illustrated by the following embodiments, but the scope of protection of this invention is not limited to the following embodiments.

[0028] Appendix Figure 1 This is a schematic diagram of a system for removing fluorine and chlorine from a circulating electrolyte in a wet zinc smelting process. This system diagram can also be used to illustrate a method for removing fluorine and chlorine from the circulating electrolyte. First, the method involves collecting waste electrolyte and then centrally removing fluorine and chlorine. Second, it includes the following specific processes:

[0029] (1) The waste electrolyte is pumped to the concentration tower, and hot gas is introduced into the concentration tower. The hot gas is introduced into the concentration tower by the hot flue gas discharged from the rotary kiln. The water evaporates and the mass content of sulfuric acid in the waste electrolyte increases from 3-10% to about 20%, and the temperature of the waste electrolyte rises to 60-65℃.

[0030] Waste electrolyte is fed into a filter press for filtration. The filtered waste electrolyte enters process (2), and the filtered residue is sent back to the rotary kiln.

[0031] (2) The waste electrolyte is transported to the defluorination and chlorination circulation tank;

[0032] (3) The waste electrolyte in the defluorination and chlorination circulation tank is pumped to the defluorination and chlorination tower. The waste electrolyte falls in a spray pattern inside the defluorination and chlorination tower. Hot air at 160-220°C is introduced into the defluorination and chlorination tower to strip the fluoride and chloride ions from the falling droplets. This 160-220°C hot air is the hot air at about 90°C from the acid conversion section, which is then reheated by a supplementary heating electric furnace. Direct contact with hot air at 120°C or higher can cause fluoride and chloride ions to escape from the electrolyte. This process also has the following effects:

[0033] a. The falling droplets flow back to the defluorination and chlorination circulation tank. The waste electrolyte in the defluorination and chlorination circulation tank is pumped back to the defluorination and chlorination tower for stripping. After several cycles, when the sulfuric acid content in the acid solution of the defluorination and chlorination circulation tank reaches 70%, it becomes the finished acid used in the wet process workshop. During the circulation process, as the temperature of the waste electrolyte increases and the concentration of sulfuric acid increases, the sulfuric acid destroys the hydration force of hydrogen fluoride and hydrogen chloride, and the volatility of hydrogen fluoride and hydrogen chloride is greatly enhanced. In this way, fluorine and chlorine are separated from the waste electrolyte.

[0034] b. The rising flue gas containing hydrogen fluoride and hydrogen chloride is fed into the alkaline scrubbing tower. A sodium hydroxide solution with a sodium hydroxide mass content of 10% is introduced into the alkaline scrubbing tower to fully contact and scrub the flue gas. A baffle device can be installed in the alkaline scrubbing tower to increase the residence time of the flue gas. The sodium salt solution generated in the reaction is discharged to the sewage treatment plant, and the scrubbed gas is vented.

[0035] The system used in the above method is still listed in the appendix. Figure 1 This system is a system for collecting waste electrolyte and centrally removing fluorine and chlorine. It has a concentration tower, a defluorination and chlorine circulation tank, a defluorination and chlorine tower and an alkaline washing tower, as well as a sodium hydroxide preparation tank connected to the pipeline of the alkaline washing tower.

[0036] The thickening tower is equipped with a heating device for concentrating the evaporated water in the waste electrolyte. This heating device is a heat exchange tube that is connected to the external rotary kiln exhaust system. The thickening tower is connected to the defluorination and chlorination circulation tank. A filter press and a storage tank are connected in sequence between the thickening tower and the defluorination and chlorination circulation tank. A pump is installed between the storage tank and the defluorination and chlorination circulation tank.

[0037] The defluorination and chlorination tower is equipped with a first spray device, which is connected to the defluorination and chlorination circulation tank via a first circulation pump outside the defluorination and chlorination tower. A hot air inlet is located below the first spray device on the defluorination and chlorination tower and is connected to a hot air device. The hot air device includes a supplementary heating furnace, a fan, and a pipe connected to the hot air exhaust system of the external acid conversion section. A fluorine and chlorine stripping port is located at the top of the defluorination and chlorination tower above the first spray device, and a first reflux port connected to the pipe of the defluorination and chlorination circulation tank is located at the bottom of the defluorination and chlorination tower.

[0038] The alkaline scrubbing tower has a flue gas inlet, which is connected to the fluorine and chlorine stripping port pipe of the defluorination and chlorine removal tower. A second spray device is installed above the flue gas inlet. The second spray device is connected to the second return port pipe at the bottom of the alkaline scrubbing tower via a second circulation pump outside the alkaline scrubbing tower. A blocking device can be installed inside the alkaline scrubbing tower to increase the residence time of the flue gas. The top of the alkaline scrubbing tower has an exhaust port.

[0039] Since this system is a centralized treatment mode for a certain amount of waste electrolyte rather than a continuous treatment mode, the first circulation pump has two states: one leading to the first spray device and the other leading to the finished acid tank. The second circulation pump has two states: one leading to the second spray device and the other leading to the wastewater outlet. The switching between these two states can be achieved by a reversing valve, or by using multiple valves as shown in the figure.

[0040] This system also has a clean water supply device, which supplies clean water to the sodium hydroxide preparation tank, rinse clean water to the defluorination and chlorination tower, and rinse clean water to the alkaline washing tower. The defluorination and chlorination tower and the alkaline washing tower are both spray towers, so a drip trap is installed above their spray devices. The drip trap, also known as a water collector, is to prevent water droplets from being carried out by the gas. The drip trap needs to be rinsed with clean water in stages.

[0041] Based on the above-described preferred embodiments of the present invention, and through the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for removing fluorine and chlorine from a circulating electrolyte in a wet zinc smelting process, characterized in that: The method described is a process for collecting waste electrolyte and then centrally removing fluorine and chlorine, and includes the following steps: (1) The waste electrolyte is pumped to the concentration tower, and hot gas is introduced into the concentration tower to evaporate the water so that the mass content of sulfuric acid in the waste electrolyte rises to 15-25% and the temperature of the waste electrolyte rises to 60-65℃. (2) The waste electrolyte is transported to the defluorination and chlorination circulation tank; (3) The waste electrolyte in the defluorination and chlorination circulation tank is pumped to the defluorination and chlorination tower. The waste electrolyte falls in a spray pattern inside the defluorination and chlorination tower. Hot air at 160-220°C is introduced into the defluorination and chlorination tower to strip the fluoride and chloride ions from the falling droplets. This process simultaneously has the following effects: a. The falling droplets flow back to the defluorination and chlorination circulation tank. The waste electrolyte in the defluorination and chlorination circulation tank is pumped back to the defluorination and chlorination tower for stripping. After several cycles, when the sulfuric acid mass content in the acid solution of the defluorination and chlorination circulation tank reaches 65-75%, it becomes the finished acid for use in the wet process workshop. b. The rising flue gas containing fluoride and chloride ions is fed into the alkaline scrubbing tower. Sodium hydroxide solution is introduced into the alkaline scrubbing tower to wash the flue gas. The washed gas is then discharged into the air. After several cycles, the sodium salt solution generated is discharged to the sewage treatment plant. (4) Set up a clean water supply device to periodically rinse the drip traps in the defluorination and chlorination tower and the alkaline washing tower with clean water.

2. The method for removing fluoride and chlorine from the circulating solution of wet zinc smelting electrolysis according to claim 1, characterized in that: In process (1), hot gas is introduced into the thickening tower by introducing the hot flue gas discharged from the rotary kiln into the thickening tower.

3. The method for removing fluoride and chlorine from the circulating solution of wet zinc smelting electrolysis according to claim 1, characterized in that: Between processes (1) and (2), there is also a process of connecting the waste electrolyte to a filter press for filtration. The filtered waste electrolyte enters process (2), and the filtered residue is sent back to the rotary kiln.

4. The method for removing fluoride and chlorine from the circulating solution of wet zinc smelting electrolysis according to claim 1, characterized in that: In process (3), the hot air at 160-220°C introduced into the defluorination and chlorination tower is obtained by heating the hot air from the acid conversion section through a supplementary heating furnace before it is introduced into the defluorination and chlorination tower.

5. The method for removing fluoride and chlorine from the circulating solution of wet zinc smelting electrolysis according to claim 1, characterized in that: In process (3), the sodium hydroxide solution introduced into the alkaline washing tower has a sodium hydroxide content of 8-12% by mass.

6. A system for removing fluorine and chlorine from a circulating electrolyte in a wet zinc smelting process, characterized in that: The system is a system for collecting waste electrolyte and centrally removing fluorine and chlorine. It has a concentration tower, a defluorination and chlorine circulation tank, a defluorination and chlorine tower and an alkaline washing tower, and also has a sodium hydroxide preparation tank connected to the pipeline of the alkaline washing tower. The concentration tower is equipped with a heating device for concentrating the evaporated water in the waste electrolyte, and the concentration tower is connected to the defluorination and chlorination circulation tank; The defluorination and chlorination tower is equipped with a first spray device, which is connected to the defluorination and chlorination circulation tank via a first circulation pump outside the defluorination and chlorination tower. A hot air inlet is provided on the defluorination and chlorination tower below the first spray device, and the hot air inlet is connected to a hot air device. A fluorine and chlorine stripping port is provided at the top of the defluorination and chlorination tower above the first spray device, and a first reflux port is provided at the bottom of the defluorination and chlorination tower, which is connected to the pipeline of the defluorination and chlorination circulation tank. The alkaline washing tower has a flue gas inlet, which is connected to the fluorine and chlorine stripping port pipe of the defluorination and chlorine removal tower. A second spray device is provided above the flue gas inlet. The second spray device is connected to the second return port pipe at the bottom of the alkaline washing tower via a second circulation pump outside the alkaline washing tower. The top of the alkaline washing tower has an air vent. The first circulating pump has two states: one leading to the first spray device and the other leading to the finished acid tank. The second circulating pump has two states: one leading to the second spray device and the other leading to the wastewater outlet. The system also has a clean water supply device that supplies clean water to the sodium hydroxide preparation tank, rinses clean water to the drip trap of the defluorination tower, and rinses clean water to the drip trap of the alkaline washing tower.

7. The system for removing fluoride and chlorine from the circulating liquid in the wet zinc smelting electrolysis process according to claim 6, characterized in that: The heating device is a heat exchange tube that is connected to the external rotary kiln exhaust system.

8. The system for removing fluoride and chlorine from the circulating liquid in the wet zinc smelting electrolysis process according to claim 6, characterized in that: in A filter press and a storage tank are connected in sequence by pipelines between the concentration tower and the defluorination and chlorination circulation tank, and a pump is installed between the storage tank and the defluorination and chlorination circulation tank.

9. The system for removing fluoride and chlorine from the circulating liquid in the wet zinc smelting electrolysis process according to claim 6, characterized in that: The hot air device includes a reheating furnace, a blower, and a pipeline connected to the hot air exhaust system of the external acid conversion section.

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