A method for cooling indium electrolyte

Abstract

The present invention discloses a method for cooling indium electrolyte, which relates to the technical field of hydrometallurgy. The method for cooling indium electrolyte of the present invention comprises the following steps: (1) pumping the indium electrolyte from the electrolytic cell into the elevated tank, and exchanging heat with the water-cooled coil in the elevated tank; (2) after the temperature of the indium electrolyte in the elevated tank drops to the target value, conveying the indium electrolyte back to the electrolytic cell. By performing heat exchange between the water-cooled coil and the plate heat exchanger, between the plate heat exchanger and the cold water tank, between the cold water tank and the refrigerator, and between the refrigerator and the cooling water tower, and gradually cooling down, it can ensure that the temperature of the indium electrolyte is relatively stable, without large fluctuations, the prepared indium product has good quality, and the cooling by the said method is relatively energy-saving.

Description

Technical Field

[0001] The invention relates to the technical field of hydrometallurgy, and in particular to a method for cooling an indium electrolyte. Background Art

[0002] With the rapid development of modern technology, the application fields of high-purity rare metals are becoming more and more extensive. As high-purity indium for the production of liquid crystal screens, its consumption is increasing day by day, and the requirements for product purity are constantly improving. As a purification process, electrolytic refining is used by most factories to prepare high-purity indium. In the process of electrolytic refining to prepare high-purity indium, the factors affecting the quality of indium products mainly include electrolyte composition, cell voltage, current density, electrolysis temperature and other factors. Among them, the electrolysis temperature in production is generally controlled at 20-30°C. Within this range, it can effectively prevent anode passivation, control the diffusion rate of various ions and the conductivity of the electrolyte, reduce the cell voltage, and make indium precipitate densely at the cathode. At the same time, it can reduce the possibility of impurities discharging and precipitating at the cathode, thereby improving the quality of indium products. When the electrolysis temperature is too low, it will not only increase the viscosity of the electrolyte, but also In 3+ The mass transfer conditions deteriorate, resulting in a decrease in both production and quality, and even causing the sodium sulfate in the electrolyte to precipitate and adhere to the cathode plate, the wall of the electrolytic cell and the inside of the pipe, causing safety accidents such as pipe blockage and cell bubbling. When the electrolyte temperature is too high, it will cause the discharge potential of metals such as Zn, Pb, Sn, Cd, Tl and hydrogen to decrease, reduce the quality of indium products, increase the evaporation loss of the electrolyte, cause changes in the electrolyte composition, and the evaporated electrolyte acid gas will cause workshop environmental pollution, damage equipment and endanger human health. Therefore, in order to produce qualified and stable products, it is very necessary to ensure a stable indium electrolyte temperature.

[0003] In the existing data, there are cases where the temperature is controlled by adding air conditioners in the factory, but there are problems such as insufficient cooling capacity and corrosion of electrical components, and the key point that the control of electrolysis temperature is mainly to control the electrolyte temperature in the electrolytic cell is not grasped. This is because the indium electrolytic cell is composed of a cell body, an anode and a cathode. When direct current passes through the electrolytic cell, at the interface between the anode and the solution, indium metal undergoes an oxidation reaction to form indium ions that enter the solution. At the interface between the cathode and the solution, indium ions undergo a reduction reaction to form indium metal elements to obtain the desired indium product. During the electrolysis process, due to the continuous heat generation during the reaction process, heat will be released into the electrolyte, causing the electrolyte temperature to rise. If the heat is not dissipated in time, it is easy to cause heat accumulation, causing the impurities in the electrolyte to dissolve faster, affecting product quality.

[0004] Chinese patent document CN211771590 mentions a cooling device for the electrolytic cell solution in an alkaline wet process. This device can achieve heat exchange outside the cell for the electrolyte inside the electrolytic cell through an acid-base pump and then return it to the electrolytic cell, enabling timely heat dissipation. The cooling water in the heat exchanger realizes continuous input of the refrigerant through circulating heat dissipation. Compared with simple air conditioning heat dissipation, this method has the effect of fast heat dissipation, but it is only suitable for alkaline electrolytes that are difficult to volatilize and have weak corrosiveness, and is not applicable to acidic solutions such as indium electrolytes that are easy to volatilize and have strong corrosiveness. Moreover, its cooling degree is low, only using a simple cooling tower for air cooling, which is greatly affected by the ambient temperature and it is difficult to obtain a temperature below 30°C.

[0005] Therefore, to solve the problems of poor heat exchange degree, large heat exchange temperature fluctuations, equipment corrosion, high energy consumption, etc. in the current cooling of indium electrolytes, the present invention proposes a method for cooling indium electrolytes, with high temperature control accuracy, small temperature fluctuation range, high degree of automatic control and convenient maintenance of a stable electrolyte concentration. Summary of the Invention

[0006] The object of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a method for cooling indium electrolytes. The method has small heat exchange temperature fluctuations, low energy consumption, stable electrolyte concentration, good quality of the prepared indium products, low energy consumption during the cooling process, and no pollution to the environment.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for cooling indium electrolytes, the method comprising the following steps:

[0009] (1) Pump the indium electrolyte from the electrolytic cell into the elevated tank and exchange heat with the water-cooled coil in the elevated tank; the elevated tank and the water-cooled coil can be one or multiple;

[0010] (2) After the temperature of the indium electrolyte in the elevated tank drops to the target value, transport the indium electrolyte back to the electrolytic cell; the target value is 20 - 30°C.

[0011] The outlet of the electrolytic cell is connected to the inlet of the elevated tank, and the outlet of the elevated tank is connected to the inlet of the electrolytic cell; the outlet of the water-cooled coil is connected to the first inlet of the plate heat exchanger, and the first outlet of the plate heat exchanger is connected to the inlet of the water-cooled coil; the second outlet of the plate heat exchanger is connected to the first inlet of the cold water tank, and the first outlet of the cold water tank is connected to the second inlet of the plate heat exchanger; the second outlet of the cold water tank is connected to the first inlet of the refrigerator, and the first outlet of the refrigerator is connected to the second inlet of the cold water tank; the second outlet of the refrigerator is connected to the inlet of the cooling water tower, and the outlet of the cooling water tower is connected to the second inlet of the refrigerator. The first inlet of the cold water tank is located below the second inlet, and the first outlet of the cold water tank is located above the second outlet.

[0012] Through step-by-step cooling by the water-cooled coil, the plate heat exchanger, the cold water tank, the refrigerator and the cooling water tower, stable heat transfer and heat exchange can be achieved, maintaining the temperature of the indium electrolyte within a small range of fluctuations, and having little impact on the quality of indium products.

[0013] Preferably, in step (1), an acid-resistant pump is used to pump the indium electrolyte into the elevated tank.

[0014] Preferably, the plate heat exchanger conveys the first cooling water into the water-cooled coil, and the water-cooled coil conveys the first cooling return water into the plate heat exchanger. The temperature of the first cooling water is 10-15 °C, and the temperature of the first cooling return water is 15-20 °C.

[0015] Preferably, the cold water tank conveys the second cooling water into the plate heat exchanger, and the plate heat exchanger conveys the second cooling return water into the cold water tank. The temperature of the second cooling water is 5-10 °C, and the temperature of the second cooling return water is 10-15 °C.

[0016] Preferably, the refrigerator conveys the chilled water into the cold water tank, and the cold water tank conveys the chilled return water into the refrigerator. The temperature of the chilled water is 0-5 °C.

[0017] By controlling the temperature reduction range of each stage within 5-10 °C, the temperature of the indium electrolyte can be basically kept constant.

[0018] Preferably, the cooling water tower conveys the third cooling water into the refrigerator, and the refrigerator conveys the third cooling return water into the cooling water tower. The temperature of the third cooling water is 30-35 °C, and the temperature of the third cooling return water is 40-50 °C. In the present invention, by setting the cooling water tower to perform air-cooling on the circulating water and then conveying it back to the refrigerator for refrigeration, energy can be saved.

[0019] Preferably, in step (1), after the temperature of the indium electrolyte reaches the set value, the pump is started to pump the indium electrolyte into the high-level tank; the volume of the indium electrolyte in the high-level tank is smaller than that in the electrolytic cell; the set value is 20-30°C. Through the above solution, the temperature of the electrolyte can be reduced slowly and stably, without sharp changes affecting the electrolysis effect.

[0020] Preferably, the present invention controls the opening and closing and operating speed of the pump through a temperature feedback control cabinet. When the temperature of the electrolyte in the electrolytic cell is higher than 30°C, the pump is started for heat exchange.

[0021] Preferably, the liquid level of the indium electrolyte in the high-level tank is higher than that in the electrolytic cell; the position of the liquid outlet in the high-level tank is higher than that of the water-cooled coil. Through the above solution, the electrolyte in the high-level tank can automatically flow into the electrolytic cell to achieve automatic control.

[0022] Preferably, the material of the water-cooled coil is at least one of titanium, titanium alloy, Hastelloy, Inconel alloy, graphite, and silicon carbide. The above materials have good thermal conductivity and are acid corrosion resistant.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] The present invention gradually cools the indium electrolyte through a water-cooled coil, a plate heat exchanger, a cold water tank, a refrigerator, and a cooling water tower, so that the temperature of the indium electrolyte is stable, improving the quality of indium products. And the temperature control operation can be automated, carried out under normal temperature and pressure. The cooling method is simple, safe, and efficient. In addition, the cooling method of the present invention can realize the recycling of cooling water, without generating waste water, and consumes less electric energy, being more energy-saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a process flow chart for cooling the indium electrolyte. DETAILED DESCRIPTION OF THE INVENTION

[0026] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with the drawings and specific embodiments.

[0027] Example 1

[0028] An embodiment of the cooling method for the indium electrolyte of the present invention. The specific cooling method in this embodiment is as follows:

[0029] (1) The indium electrolyte at a temperature of 30°C is pumped from the electrolytic cell into the high-level tank through an acid-resistant pump and exchanges heat with the water-cooled titanium coil arranged in the high-level tank.

[0030] (2) After the temperature of the indium electrolyte in the high-level tank drops to 20 °C, it is returned to the electrolytic cell for electrolysis;

[0031] In this embodiment, the opening and closing of the pump are controlled by a temperature feedback control cabinet. When the temperature of the electrolyte in the electrolytic cell is higher than 20 °C, the pump is started to work, and the indium electrolyte is input from the electrolytic cell into the high-level tank through an acid-resistant pump and exchanges heat with the water-cooled titanium coil in the high-level tank; the water-cooled titanium coil is located below the liquid level of the water outlet in the high-level tank; the volume of the indium electrolyte in the high-level tank is smaller than the volume of the indium electrolyte in the electrolytic cell; the liquid level of the indium electrolyte in the high-level tank is higher than the liquid level of the indium electrolyte in the electrolytic cell.

[0032] The above cooling process is controlled by the following method:

[0033] S1: The first cooling return water in the water-cooled titanium coil in the high-level tank enters the plate heat exchanger for heat exchange after confluence. The temperature of the first cooling return water flowing into the plate heat exchanger is controlled to be 15 °C, and the temperature of the first cooling water after heat exchange is 10 °C. The first cooling water is input into the water-cooled titanium coil;

[0034] S2: The second cooling return water in the plate heat exchanger is input into the cold water tank and mixed with the chilled water generated by the chiller to form the second cooling water, which is then input into the plate heat exchanger. The temperature of the second cooling return water is 10 °C, the temperature of the chilled water is 0 °C, and the temperature of the second cooling water is 5 °C;

[0035] S3: The water at the bottom of the cold water tank is input into the chiller for heat exchange and cooling, and the chilled water formed after heat exchange and cooling is input into the cold water tank for storage;

[0036] S4: The third cooling return water at 40 °C in the chiller is transported to the cooling tower, cooled by air cooling to 30 °C to obtain the third cooling water, and then the third cooling water is transported to the chiller. The refrigeration unit consists of an evaporator, a compressor, a condenser, and a throttle valve (expansion valve). The first inlet of the chiller is connected to the evaporator. The cooling return water of the cold water tank exchanges heat with the refrigerant in the evaporator and cools down, and the chilled water is produced from the first outlet of the chiller. In the evaporator, the refrigerant expands in volume due to heat absorption and is then transported to the compressor for compression. The compressed refrigerant has a higher temperature, and in the condenser, the high-temperature refrigerant exchanges heat with the third cooling water transported from the cooling tower to form a low-temperature refrigerant, which enters the evaporator through the throttle valve, and the formed third cooling return water is transported to the cooling tower for cooling.

[0037] After electrolysis for one cycle using the above method, the power consumption for cooling is 0.8 kW·h / kg of indium. Compared with the power consumption of 1.5 kW·h / kg of indium when using an air conditioner to cool the electrolyte to 20°C, 0.7 kW·h / kg of indium is saved. After electrolysis for one cycle, the surface of the cathode is flat and no obvious large dendrites are produced. The lead content of the impurity in the indium product is 1 ppm, and the tin content of the impurity is 2 ppm, meeting the standard of 4.5N indium (lead content < 5 ppm, tin content < 10 ppm).

[0038] Figure 1 It is a process flow chart for cooling the indium electrolyte. The outlet of the electrolytic cell is connected to the inlet of the elevated tank, and the outlet of the elevated tank is connected to the inlet of the electrolytic cell; the outlet of the water-cooled coil is connected to the first inlet of the plate heat exchanger, and the first outlet of the plate heat exchanger is connected to the inlet of the water-cooled coil; the second outlet of the plate heat exchanger is connected to the first inlet of the cold water tank, and the first outlet of the cold water tank is connected to the second inlet of the plate heat exchanger; the second outlet of the cold water tank is connected to the first inlet of the refrigerator, and the first outlet of the refrigerator is connected to the second inlet of the cold water tank; the second outlet of the refrigerator is connected to the inlet of the cooling water tower, and the outlet of the cooling water tower is connected to the second inlet of the refrigerator. The first outlet of the cold water tank is higher than the second outlet of the cold water tank, and the first inlet of the cold water tank is higher than the second inlet of the cold water tank.

[0039] Example 2

[0040] An embodiment of the method for cooling the indium electrolyte of the present invention. The difference between the cooling method of this embodiment and that of Example 1 is that: in step (1), the temperature of the indium electrolyte is 35°C; in step (2), after the temperature of the indium electrolyte in the elevated tank drops to 25°C, it is returned to the electrolytic cell for electrolysis;

[0041] When the temperature of the indium electrolyte in the electrolytic cell is higher than 25°C, the pump is started to work; during the cooling process, the temperature of the first cooling return water is controlled at 17°C, the temperature of the first cooling water is 12°C, the temperature of the second cooling return water is 12°C, the temperature of the second cooling water is 7°C, the temperature of the chilled water is 3°C, the temperature of the third cooling return water is 45°C, and the temperature of the third cooling water is 33°C.

[0042] After electrolysis for one cycle using the above method, the power consumption for cooling is 0.7 kW·h / kg of indium. Compared with the power consumption of 1.3 kW·h / kg of indium when using an air conditioner to cool the electrolyte to 25°C, 0.6 kW·h / kg of indium is saved. After electrolysis for one cycle, the surface of the cathode is flat and no obvious large dendrites are produced. The lead content of the impurity in the indium product is 3 ppm, and the tin content of the impurity is 5 ppm, meeting the standard of 4.5N indium.

[0043] Example 3

[0044] An embodiment of the method for cooling indium electrolyte according to the present invention. The difference between the cooling method of this embodiment and that of Embodiment 1 is as follows: In step (1), the temperature of the indium electrolyte is 38°C; in step (2), after the temperature of the indium electrolyte in the high-level tank drops to 30°C, it is returned to the electrolytic cell for electrolysis.

[0045] When the temperature of the indium electrolyte in the electrolytic cell is higher than 30°C, the pump is started to work; during the cooling process, the temperature of the first cooling return water is controlled at 20°C, the temperature of the first cooling water is 15°C, the temperature of the second cooling return water is 15°C, the temperature of the second cooling water is 7°C, the temperature of the chilled water is 5°C, the temperature of the third cooling return water is 50°C, and the temperature of the third cooling water is 35°C.

[0046] After electrolysis for one cycle using the above method, the power consumption for cooling is 0.65 kW·h / kg of indium. Compared with the power consumption of 1.2 kW·h / kg of indium when using an air conditioner to cool the electrolyte to 30°C, 0.55 kW·h / kg of indium is saved. After electrolysis for one cycle, the surface of the cathode is flat, with a small amount of large dendrites produced. The lead content of impurities in the indium product is 4 ppm, and the tin content of impurities is 9 ppm, meeting the standard of 4.5N indium.

[0047] Embodiment 4

[0048] An embodiment of the method for cooling indium electrolyte according to the present invention. The difference between the cooling method of this embodiment and that of Embodiment 3 is as follows: During the cooling process, the temperature of the first cooling return water is controlled at 25°C, the temperature of the first cooling water is 20°C, the temperature of the second cooling return water is 20°C, the temperature of the second cooling water is 10°C, the temperature of the chilled water is 3°C, the temperature of the third cooling return water is 50°C, and the temperature of the third cooling water is 35°C.

[0049] After electrolysis for one cycle using the above method, the power consumption for cooling is 0.72 kW·h / kg of indium. Compared with the power consumption of 1.2 kW·h / kg of indium when using an air conditioner to cool the electrolyte to 30°C, 0.5 kW·h / kg of indium is saved. After electrolysis for one cycle, the surface of the cathode is relatively flat, with a small amount of large dendrites visible. The lead content of impurities in the indium product is 4 ppm, and the tin content of impurities is 11 ppm, not meeting the standard of 4.5N indium.

[0050] Comparative Example 1

[0051] A method for cooling indium electrolyte, the method comprising the following steps:

[0052] (1) Transfer the indium electrolyte at a temperature of 30°C from the electrolytic cell to the high-level tank through an acid-resistant pump for heat exchange with the water-cooled coil arranged in the high-level tank.

[0053] (2) After the temperature of the indium electrolyte in the high-level tank drops to 20 °C, it is returned to the electrolytic cell for electrolysis;

[0054] A temperature feedback control cabinet is used to control the opening and closing of the pump. When the temperature of the indium electrolyte in the electrolytic cell is higher than 20 °C, the pump is started to work, and the indium electrolyte is pumped from the electrolytic cell into the high-level tank through an acid-resistant pump for heat exchange with the water-cooled titanium coil in the high-level tank; the water-cooled titanium coil is located below the liquid level of the water outlet in the high-level tank; the volume of the indium electrolyte in the high-level tank is smaller than that in the electrolytic cell; the liquid level of the indium electrolyte in the high-level tank is higher than that in the electrolytic cell.

[0055] The above cooling process is controlled by the following method:

[0056] The first cooling return water at 10 °C in the water-cooled titanium coil is transported into the cold water tank, and the first cooling water at 5 °C in the cold water tank is transported into the water-cooled titanium coil; the water at the bottom of the cold water tank flows into the refrigerator and is mixed with the 0 °C water produced in the refrigerator to form the second cooling water at 5 °C, which is transported into the cold water tank for storage; the third cooling return water at 40 °C in the refrigerator is transported into the cooling tower and air-cooled to 30 °C to obtain the third cooling water, which is then transported into the refrigerator.

[0057] After electrolysis for one cycle using the above method, the power consumption for cooling is 1 kW·h / kg of indium. Compared with the power consumption of 1.5 kW·h / kg of indium when using an air conditioner to cool the electrolyte to 20 °C, 0.5 kW·h / kg of indium is saved. After electrolysis for one cycle, some large dendrites can be seen on the surface of the cathode. The impurity lead content of the product indium is 6 ppm, and the impurity tin content is 15 ppm, which does not meet the standard of 4.5N indium.

[0058] Comparative Example 2

[0059] A method for cooling an indium electrolyte, the method comprising the following steps:

[0060] (1) The indium electrolyte at 30 °C is pumped from the electrolytic cell into a plate heat exchanger through an acid-resistant pump for heat exchange;

[0061] (2) When the temperature of the indium electrolyte in the plate heat exchanger is 20 °C, it is returned to the electrolytic cell for electrolysis.

[0062] A temperature feedback control cabinet is used to control the opening and closing and operating speed of the acid-resistant pump. When the temperature of the indium electrolyte in the electrolytic cell is higher than 20 °C, the pump is started for heat exchange.

[0063] The above cooling process is controlled by the following method:

[0064] The first cooling return water at 10°C in the plate heat exchanger is transported into the cold water tank, and the first cooling water at 5°C in the cold water tank is transported into the plate heat exchanger; the second cooling return water at the bottom of the cold water tank is transported into the refrigerator, where it is mixed with the water at 0°C produced in the refrigerator to form the second cooling water, which is then returned to the cold water tank for storage. The third cooling return water at 40°C in the refrigerator is transported into the cooling tower, where it is air-cooled to 30°C to obtain the third cooling water, and the third cooling water is then transported into the refrigerator. The connection modes of the plate heat exchanger, the cold water tank, the refrigerator, and the cooling tower are the same as those in Embodiment 1.

[0065] After electrolyzing for one cycle using the above method, the electricity consumption for cooling is 0.93 kW·h / kg indium. Compared with the power consumption of 1.5 kW·h / kg indium when using an air conditioner to cool the electrolyte to 20°C, 0.57 kW·h / kg indium is saved. After electrolyzing for one cycle, some large dendrites can be seen on the surface of the cathode. The impurity lead content in the indium product is 7 ppm, and the impurity tin content is 19 ppm, which does not meet the standard of 4.5N indium.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for cooling indium electrolyte, characterized in that, It includes the following steps: (1) Pump indium electrolyte from the electrolytic cell into the elevated tank and exchange heat with the water-cooled coil in the elevated tank; (2) After the temperature of the indium electrolyte in the elevated tank drops to the target value of 20 - 30 °C, transport the indium electrolyte back to the electrolytic cell; The outlet of the electrolytic cell is connected to the inlet of the elevated tank, and the outlet of the elevated tank is connected to the inlet of the electrolytic cell; the outlet of the water-cooled coil is connected to the first inlet of the plate heat exchanger, and the first outlet of the plate heat exchanger is connected to the inlet of the water-cooled coil; the second outlet of the plate heat exchanger is connected to the first inlet of the cold water tank, and the first outlet of the cold water tank is connected to the second inlet of the plate heat exchanger; The second outlet of the cold water tank is connected to the first inlet of the chiller, and the first outlet of the chiller is connected to the second inlet of the cold water tank; the second outlet of the chiller is connected to the inlet of the cooling water tower, and the outlet of the cooling water tower is connected to the second inlet of the chiller; The plate heat exchanger transports the first cooling water into the water-cooled coil, and the water-cooled coil transports the first cooling return water into the plate heat exchanger. The temperature of the first cooling water is 10 - 15 °C, and the temperature of the first cooling return water is 15 - 20 °C; The cold water tank transports the second cooling water into the plate heat exchanger, and the plate heat exchanger transports the second cooling return water into the cold water tank. The temperature of the second cooling water is 5 - 10 °C, and the temperature of the second cooling return water is 10 - 15 °C; The chiller transports the chilled water into the cold water tank, and the cold water tank transports the chilled return water into the chiller. The temperature of the chilled water is 0 - 5 °C; The cooling water tower transports the third cooling water into the chiller, and the chiller transports the third cooling return water into the cooling water tower. The temperature of the third cooling water is 30 - 35 °C, and the temperature of the third cooling return water is 40 - 50 °C.

2. The method for cooling indium electrolyte according to claim 1, characterized in that, In step (1), when the temperature of the indium electrolyte reaches the set value, start the pump and pump the indium electrolyte into the elevated tank; the volume of the indium electrolyte in the elevated tank is less than the volume of the indium electrolyte in the electrolytic cell.

3. The method for cooling indium electrolyte according to claim 1, characterized in that, The liquid level of the indium electrolyte in the elevated tank is higher than the liquid level of the indium electrolyte in the electrolytic cell; the position of the liquid outlet in the elevated tank is higher than the water-cooled coil.

4. The method for cooling indium electrolyte according to claim 1, characterized in that, The material of the water-cooled coil is at least one of titanium, titanium alloy, Hastelloy, Inconel alloy, graphite, and silicon carbide.

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