Method for controlling the precipitation of zinc containing lead during crystallization cleaning of a zinc electrolysis system

Abstract

The present application belongs to the technical field of zinc electrolysis, and particularly relates to a control method for zinc lead content during crystallization cleaning of a zinc electrolysis system. The method comprises the following steps: S1: gradually stopping electrolyte circulation two hours before the tank is discharged, the zinc electrolysis system is continuously powered, and the current density is reduced; S2: two hours before the electrolyte circulation is stopped, the amount of strontium carbonate is increased, the tank temperature and the acid-zinc ratio are reduced; S3: after the circulation is completely stopped, the crystallization is cleaned; S4: after the crystallization cleaning is completed, strontium carbonate is added in one time immediately upstream of the electrolysis tank; and S5: slowly open the circulation pump valve, keep the liquid level in the electrolysis tank uniform, and increase until the circulation amount reaches that in normal operation of the zinc electrolysis system. The method can complete the crystallization cleaning under continuous power supply, and stably controls the normal production of the zinc electrolysis system, especially the lead content of the key quality index of precipitated zinc can be stably maintained below 0.0015%.

Description

Technical Field

[0001] This invention belongs to the field of zinc electrolysis technology, specifically relating to a method for controlling lead-containing zinc precipitation during the crystallization cleaning process of a zinc electrolysis system. Background Technology

[0002] Currently, crystallization cleaning in zinc electrolysis systems is all done manually during maintenance or overhauls. As the system's operating time increases, calcium and magnesium crystals become increasingly saturated, and the rate of crystal deposition in pipes or chutes accelerates. To ensure normal system circulation, power outages and frequent overhauls are common practices. However, power outages and overhauls not only lead to reduced output but also cause unstable lead content in the precipitated zinc, sometimes even exceeding the standard.

[0003] Patent application CN114686924A discloses a method for stopping and restarting a zinc electrolysis system. The method includes: gradually reducing the current density of the zinc electrolysis system while simultaneously performing a first pumping operation to gradually lower the level of the first electrolyte in the electrolytic cell; stopping the first pumping operation and disconnecting the power when the level of the first electrolyte in the electrolytic cell reaches a low level; performing a second pumping operation to remove the remaining first electrolyte in the electrolytic cell; removing the electrode plates from the electrolytic cell for cleaning; adding electrode plates and second electrolyte to the electrolytic cell, energizing the cell, and then adding more first electrolyte to restore normal production. Therefore, this invention can achieve rapid separation of the electrolyte from the cathode and anode plates in the electrolytic cell, effectively preventing zinc back dissolution from the cathode and excessive lead content in the electrolyte caused by anode dissolution. Summary of the Invention

[0004] To address the issues of reduced yield and unstable lead content in precipitated zinc during crystallization cleaning in existing zinc electrolysis systems, a control method is provided that enables crystallization cleaning without power interruption and effectively controls the lead content in precipitated zinc.

[0005] This invention is achieved through the following technical solution:

[0006] A method for controlling lead-containing zinc precipitation during crystallization cleaning in a zinc electrolysis system includes the following:

[0007] (1) Selection of the crystallization cleaning time point in the zinc electrolysis system:

[0008] The crystal clearing time should be selected within 2 hours before the item drops. However, the crystal clearing time is not limited to 2 hours before the item drops; depending on character resources, it can be shortened to within 2 hours.

[0009] The current density during the unloading period is half of the maximum power consumption during normal zinc electrolysis. This is because the unloading process involves the removal of the plate from the tank, which causes the current density to instantly double while the plate is still in the tank. For safety reasons, the current density must be reduced.

[0010] The process of removing the cathode plate from the electrolytic cell refers to the process where, after zinc has been adsorbed to a certain thickness on the cathode plate, the current efficiency decreases and the possibility of electrode short circuits occurs. To avoid wasting electrical energy, after a certain period of electrolysis, the cathode plate with a certain thickness of zinc adsorbed on it needs to be removed and peeled off in time before being reloaded into the electrolytic cell.

[0011] (2) Two hours before stopping the electrolyte circulation, increase the amount of strontium carbonate to three times that of the zinc electrolysis system during normal operation. The strontium carbonate is used to reduce the lead content in the cathode zinc.

[0012] Before stopping electrolyte circulation, control the electrolytic cell temperature at 30–32°C; adjust the acid-zinc ratio in the electrolytic cell to 1.8–2.0 (the acid-zinc ratio during normal operation of the zinc electrolysis system is 3.0–4.0). The requirements for cell temperature and acid-zinc ratio are not limited to "2 hours before stopping circulation," but should be met until the specified requirements are met.

[0013] The lead content in the zinc cathode increases with increasing electrolyte temperature. Therefore, the cell temperature is lowered to reduce the lead content in the zinc cathode. Furthermore, maintaining zinc-acid balance at different temperatures is crucial for maximizing production efficiency; therefore, the acid-zinc ratio needs to be adjusted.

[0014] Maintain stable liquid levels in the electrolytic cell and circulating tank during the shutdown process.

[0015] (3) After the cycle has completely stopped, begin cleaning up the crystals.

[0016] (4) After the crystallization cleaning is completed, strontium carbonate is added to the electrolytic cell in one go. The amount of strontium carbonate added is the same as the amount of strontium carbonate used in one hour when the zinc electrolysis system is running normally. Specifically, it can be added at the chute head upstream of the electrolytic cell.

[0017] During the crystallization cleaning process, the liquid circulation in the zinc electrolysis system is stopped, but precipitation continues normally, and the amount of divalent lead ions produced remains unchanged. After the crystallization cleaning is completed and the circulation is restarted, the lead ion concentration in the electrolysis system increases. Therefore, it is necessary to add strontium carbonate to enhance the lead reduction operation.

[0018] (5) Slowly open the circulation pump valve to keep the liquid level in the electrolytic cell rising evenly until it reaches the circulation volume when the zinc electrolysis system is running normally.

[0019] Electrolyte circulation start / stop requirements:

[0020] Stop the circulation: Gradually stop the circulation pump to keep the liquid level in the electrolytic cell and circulation tank stable.

[0021] Circulation: Adhere to the principle of slow pump start-up to maintain a uniform increase in liquid level within the electrolytic cell and sluice. Gradually increase the valve opening according to different pump types.

[0022] (6) Other time points outside the crystallization cleaning period of the first precipitation cycle shall be operated in accordance with the normal operation of the zinc electrolysis system; the amount of strontium carbonate used in the second cycle shall be uniformly increased to 1.2 times that of the normal operation of the zinc electrolysis system.

[0023] The second cycle is carried out sequentially after the first cycle. The zinc electrolysis system divides the cycle by the loading and unloading tank, and the liquid circulation is continuous. Based on years of experience in crystallization and cleaning, the amount of strontium carbonate replenished in the first cycle is insufficient to completely precipitate the lead content in the liquid of the zinc electrolysis system. However, in the second cycle, the amount is uniformly increased to 1.2 times that of the zinc electrolysis system during normal operation, which can well ensure the lead content of the cathode zinc.

[0024] The first cycle is counted as the day of crystallization and cleaning, and the second cycle follows in sequence.

[0025] In the above method, the system circulation is stopped during crystallization cleaning, but the zinc electrolysis system is kept powered on.

[0026] The beneficial effects of this invention are as follows:

[0027] This invention controls four aspects of the crystallization and cleaning period of the zinc electrolysis system: firstly, the timing of crystallization and cleaning; secondly, the frequency and amount of strontium carbonate added as an auxiliary material; thirdly, the control of process parameters such as the zinc acid content in the waste liquid and the tank temperature; and fourthly, ensuring a stable electrolyte circulation rate. Only in this way can the normal production of the zinc electrolysis system be stably controlled during the crystallization and cleaning period, especially ensuring that the lead content, a key quality indicator of precipitated zinc, is consistently maintained below 0.0015%. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the zinc electrolysis system in Example 1. Detailed Implementation

[0029] The present invention will now be described in more detail through specific embodiments to facilitate understanding of the technical solution of the present invention, but this is not intended to limit the scope of protection of the present invention.

[0030] Example 1

[0031] like Figure 1As shown, the zinc electrolysis system includes a fresh liquid tank for storing new solution, a cooling tower for cooling waste liquid, a strontium carbonate addition device (including a strontium carbonate silo and a strontium carbonate feeding screw), chutes (high-level chute and lower liquid tank) and pipelines for guiding liquid flow, parallel electrolytic cells (with anode and cathode plates arranged at intervals within the electrolytic cells), a circulation pool for storing waste liquid, and various pumps to ensure circulation. The circulation pumps and pipelines connect the circulation pool and the cooling tower. The high-level chute connects the distribution tank downstream of the cooling tower to the inlet end of the electrolytic cells, and the lower liquid tank connects the outlet end of the electrolytic cells to the circulation pool. The fresh solution pump replenishes the fresh solution needed by the electrolysis system. The strontium carbonate feeding screw ensures that strontium carbonate is added to the mixture uniformly and continuously using a screw feed method. The electrolytic cells complete the deposition of zinc at the cathode through direct current supplied by the power transmission system.

[0032] The operation process of the above zinc electrolysis system is as follows:

[0033] Waste liquid from the electrolyzer enters the circulation tank through the lower liquid tank. The circulation pump installed outside the circulation tank pumps the waste liquid to the cooling tower for cooling. The cooled waste electrolyte is mixed with the new liquid from the new liquid tank and enters the distribution tank. At the same time, the strontium carbonate feeding screw of the auxiliary material adding device adds strontium carbonate evenly to the new liquid and mixes it together. The mixture enters the distribution tank and is evenly distributed to each high-level chute and sent to each electrolyzer.

[0034] In the electrolytic cell, a lead-silver alloy plate is used as the anode, and a rolled pure aluminum plate is used as the cathode. Under the influence of direct current, zinc is deposited on the cathode (a reduction reaction), while oxygen is deposited on the anode (an oxidation reaction). To ensure the quality of the zinc deposited on the cathode, strontium carbonate is added to reduce lead content. The main reaction is CrCO3 + PbSO4 = CrSO4 + PbCO3. Strontium sulfate has lower solubility than lead sulfate (PbSO4), allowing some lead ions to be replaced and removed by forming isomorphous co-precipitates.

[0035] The operation of the pumps ensures the continuous circulation of the zinc electrolysis system, replenishing it with fresh solution and removing waste liquid. Most of the waste liquid is cooled by a cooling tower to ensure replenishment of the electrolytic cells and cooling of the mixed solution, while a small portion of the waste liquid is sent to the leaching process for zinc oxide leaching, thus maintaining the system balance of the electrolysis system.

[0036] The method for controlling lead-containing zinc precipitation during the crystallization cleaning process of the zinc electrolysis system in this embodiment includes the following steps:

[0037] (1) Two hours before the loading tank is opened, the electrolyte circulation is gradually stopped. The zinc electrolysis system is kept powered on and the current density is half of the current density when the zinc electrolysis system is running normally.

[0038] Two hours before stopping the circulation, perform the following steps:

[0039] 1.1: Increase the amount of strontium carbonate used to three times the amount used when the zinc electrolysis system is operating normally, specifically 6 bags / hour, each bag weighing 25 kg; the amount of strontium carbonate used when the zinc electrolysis system is operating normally is 2 bags / hour.

[0040] 1.2: Control the temperature of the electrolytic cell at 30-32℃; reduce the acid-zinc ratio of the electrolytic cell to 1.8-2.0.

[0041] Maintain stable liquid levels in the electrolytic cell and circulating tank during the shutdown process.

[0042] (2) After the circulation has completely stopped, start cleaning the crystals. The cleaned crystals can be temporarily bagged and stacked or discharged into the leaching system through the scouring system. The bagged crystals will be transported to the designated location after the system is turned on.

[0043] (3) After the crystallization cleaning is completed, strontium carbonate is added to the sluice head of the high-level sluice all at once. The amount of strontium carbonate used is the same as the amount of strontium carbonate used per hour when the zinc electrolysis system is running normally, specifically 2 bags / hour, each bag weighing 25 kg.

[0044] (4) Slowly open the circulation pump valve to keep the liquid level in the electrolytic cell and chute rising evenly until the circulation volume of the zinc electrolysis system is reached during normal operation.

[0045] (5) At other time points outside the crystallization and cleaning period of the first cycle, the addition of strontium carbonate shall be carried out in the same manner as when the zinc electrolysis system is running normally; the amount of strontium carbonate used in the second cycle shall be increased uniformly to 1.2 times that when the zinc electrolysis system is running normally, such as adding 6 bags (the amount used when the zinc electrolysis system is running normally is 30 bags, each bag is 25 kg).

[0046] The method of this invention can stably control the normal production of the electrolysis system, especially the lead content, a key quality indicator of zinc deposition, can be stably maintained at 0.001 to 0.0013%.

[0047] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the claims of the present invention should be included within the scope of the present invention.

Claims

1. A method for controlling lead-containing zinc precipitation during crystallization cleaning in a zinc electrolysis system, characterized in that, Includes the following steps: S1: Two hours before unloading from the tank, gradually stop the electrolyte circulation, keep the zinc electrolysis system powered on, and reduce the current density. S2: Two hours before stopping the electrolyte circulation, increase the amount of strontium carbonate to three times that of the zinc electrolysis system during normal operation, and control the temperature of the electrolytic cell at 30-32℃; reduce the acid-zinc ratio of the electrolytic cell to 1.8-2.0; S3: After the cycle has completely stopped, begin cleaning up the crystals; S4: After the crystallization cleaning is completed, strontium carbonate is added in one go upstream of the electrolytic cell; S5: Slowly open the circulation pump valve to maintain a uniform increase in the liquid level in the electrolytic cell until the circulation volume reaches the normal operating flow rate of the zinc electrolysis system.

2. The method according to claim 1, characterized in that, In S1, the current density is reduced to half that of the zinc electrolysis system at its highest power consumption.

3. The method according to claim 1, characterized in that, During the electrolyte circulation process, maintain a stable liquid level in the electrolytic cell and circulation tank.

4. The method according to claim 1, characterized in that, In S4, the amount of strontium carbonate added is the same as the amount of strontium carbonate added per hour during normal operation of the zinc electrolysis system.

5. The method according to claim 1, characterized in that, The zinc electrolysis system is divided into cycles based on the loading and unloading tank. The first cycle is counted as the day of crystallization and cleaning, and the second cycle follows in sequence. At other times outside the crystallization and cleaning period of the first cycle, strontium carbonate is added in the same way as when the zinc electrolysis system is running normally. In the second cycle, the amount of strontium carbonate is increased to 1.2 times that when the zinc electrolysis system is running normally.

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