Device and method for detecting metal ions in solution based on ice water liquid-solid phase change

Abstract

The invention discloses a device and method for detecting metal ions in a solution based on ice water liquid-solid phase change. A liquid drop shaping unit of the metal ion detection device is made of a transparent low-temperature-resistant material, and a liquid drop-shaped cavity with an opening in the bottom end is formed in the liquid drop shaping unit; the refrigeration unit is detachably connected to the bottom end of the liquid drop shaping unit in a sealing manner and is used for cooling the to-be-detected solution so as to manufacture a two-dimensional liquid drop-shaped slice of the to-be-detected solution; the image acquisition system and the liquid drop shaping unit are oppositely arranged along the horizontal direction, are focused on the liquid drop-shaped solution to be detected and are used for recording the ice water liquid-solid phase change process of the solution to be detected; and the image analysis system is used for analyzing the ice water liquid solid phase change process of the to-be-detected solution obtained by the image acquisition system to obtain ice water liquid solid phase change characteristics, and speculating the ion species or concentration of the to-be-detected solution according to the ice water liquid solid phase change characteristics. The detection device has the characteristics of high detection efficiency, low cost, no pollution, high environmental adaptability and simple and convenient structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion detection in solution, and particularly relates to a device and method for detecting metal ions in solution based on the liquid-solid phase change of ice water. Background Art

[0002] Solutions generated from industrial wastewater discharge, mining, agricultural pollution, electronic waste dismantling, domestic sewage, etc. may contain metal ions such as calcium, magnesium, lead, cadmium, etc. Such ions have had a significant impact on ecological environment, human health, industrial production and other fields due to their characteristics of being difficult to degrade and easy to enrich. In terms of the ecological environment, heavy metals such as lead and cadmium can cause soil degradation, acute poisoning of aquatic organisms and loss of biodiversity; in terms of human health, long-term exposure to mercury- and arsenic-containing water bodies will lead to cancer, nervous system damage and liver and kidney organ diseases; in industrial production, metal ions will cause product defects, equipment corrosion and even safety accidents, and incomplete treatment of industrial wastewater is more likely to cause secondary pollution. Achieving rapid detection and accurate quantification of metal ions in solution has become the core technical challenge in pollution prevention and control, disease prevention and resource recycling.

[0003] Current metal ion detection mainly uses atomic absorption spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS), electroanalytical methods, spectrophotometry, etc. For example, in the Chinese invention patent application with the patent application number 201510495087.9 and the invention title "Method for Determining Trace Copper, Zinc and Iron in Mineral Water by Ion Pair-Cloud Point Extraction-Flame Atomic Absorption Spectrometry", the detection of metal ions is realized by using the absorption principle of specific elements for characteristic wavelength light. This method relies on large-scale precision instruments and has problems such as high equipment cost, complex operation process, and long detection cycle. In the Chinese invention patent application with the patent application number 201510076553.X and the invention title "Method for Detecting the Morphology of Trace Metal Particles in Flue Gas Based on Inductively Coupled Plasma Atomic Absorption Spectrometry", high-temperature plasma is generated by high-frequency inductive coupling to ionize the sample, and then it is separated and detected by a mass spectrometer according to the mass-to-charge ratio to achieve qualitative and quantitative analysis of metal ions. This method also has disadvantages such as high equipment cost, complex maintenance, limitations in sample pretreatment and applicability, and insufficient portability. In the Chinese invention patent application with the patent application number 202010389232.6 and the invention title "Composite Electrode for Heavy Metal Ion Detection and Its Preparation Method", a composite electrode that can be used for electrochemically detecting heavy metal lead and cadmium ions in a solution containing heavy metal ions is prepared. This method has disadvantages such as being sensitive to the solution matrix, easy contamination or passivation of the electrode resulting in insufficient stability. In the Chinese invention patent application with the patent application number 202111611159.3 and the invention title "Method for Detecting Ferrous Ions in Water Body", spectrophotometry is used for ferrous ion detection. This method has relatively low accuracy, is easily interfered by coexisting substances, and has problems such as limited detection sensitivity and insufficient result stability.

[0004] The deficiencies of existing methods for detecting metal ions in solutions can be summarized as follows: (1) Existing atomic absorption spectrometry requires frequent replacement of element-specific light sources, cannot achieve multi-element synchronous detection, and the detection sensitivity is significantly affected by matrix effects. Trace analysis relies on complex sample pretreatment; (2) Inductively coupled plasma mass spectrometry has high equipment purchase and maintenance costs. High-salt or high-dissolved solid samples easily cause cone blockage, and isotope interference and memory effects require additional correction techniques to eliminate; (3) Electroanalytical methods are easily interfered by coexisting ions, the electrode surface modification process is complex, and the long-term stability is poor and the repeatability is insufficient; (4) The detection sensitivity of spectrophotometry is limited by the specificity of the chromogenic agent, turbidity or coexisting chromogenic substances easily introduce errors, and complex pretreatment steps are required. These defects lead to significant limitations in the detection efficiency, cost control, and on-site adaptability of existing methods. Summary of the Invention

[0005] To overcome the limitations of existing metal ion detection technologies in solutions, the present invention provides a device and method for detecting metal ions in solutions based on the liquid-solid phase change of ice water. The detection device and method are characterized by high detection efficiency, low cost, no pollution, strong environmental adaptability, and simple structure, effectively solving the problems of high efficiency, portability, and economy in the prior art, and providing a pollution-free and highly universal innovative solution for detecting metal ions in solutions.

[0006] To achieve the above object, the present invention adopts the following specific technical solutions: The present invention provides a device for detecting metal ions in solutions based on the liquid-solid phase change of ice water. The metal ion detection device includes a droplet shaping unit, a refrigeration unit, an image acquisition system, and an image analysis system; the droplet shaping unit is made of a transparent low-temperature resistant material and has a droplet-shaped cavity with an open bottom inside, and the droplet-shaped cavity is used to accommodate the solution to be measured; the solution to be measured is a metal ion solution with unknown type and concentration. The refrigeration unit is detachably and hermetically connected to the bottom end of the droplet shaping unit and is used to cool the solution to be measured to produce a two-dimensional droplet-shaped slice of the solution to be measured. The image acquisition system is disposed opposite to the droplet shaping unit in the horizontal direction and focuses on the droplet-shaped solution to be measured, and is used to record the liquid-solid phase change process of the ice water of the solution to be measured. The image analysis system is signal-connected to the image acquisition system and is used to analyze the liquid-solid phase change process of the ice water of the solution to be measured obtained by the image acquisition system, obtain the liquid-solid phase change characteristics of the ice water, and infer the ion type or concentration of the solution to be measured according to the liquid-solid phase change characteristics.

[0007] Furthermore, the image acquisition system is used to record in real time the growth process of dendrites in the re-illumination stage and ice in the freezing stage during the liquid-solid phase change process of the solution to be measured.

[0008] Furthermore, the image analysis system calculates the average growth rate of dendrites by the final height of the dendrites and the dendrite growth time, calculates the average freezing rate by the final height of the ice and the time required for the complete solidification of the solution to be measured, and then infers the ion type or concentration of the solution to be measured according to the average growth rate of dendrites and the average freezing rate of the solution to be measured.

[0009] Furthermore, the droplet shaping unit is composed of a first layer of transparent acrylic plate, a polydimethylsiloxane sandwich layer, and a second layer of transparent acrylic plate that are sequentially hermetically connected; The droplet-shaped cavity is arranged in the polydimethylsiloxane sandwich layer; The polydimethylsiloxane sandwich layer is provided with a communicating liquid injection channel at the top of the droplet-shaped cavity.

[0010] Further, the refrigeration unit is a compression refrigeration device, an absorption refrigeration device or a semiconductor refrigeration device; When the refrigeration unit is a semiconductor refrigeration device, it includes a semiconductor refrigeration chip, a heat exchanger, a copper plate, a low-temperature constant temperature bath, a heat insulation material and a control unit; The hot end of the semiconductor refrigeration chip is attached to the heat exchanger, and the cold end is attached to the copper plate for transferring heat; a refrigerant circulates between the heat exchanger and the low-temperature constant temperature bath; the control unit is connected to the semiconductor refrigeration chip for controlling the temperature of the semiconductor refrigeration chip; The top end of the copper plate is inserted into the gap between the first-layer transparent acrylic plate and the second-layer transparent acrylic plate and is in close contact with the polydimethylsiloxane sandwich layer to ensure that the solution to be measured does not leak; the outside of the copper plate is pasted with the heat insulation material to reduce the loss of cold quantity.

[0011] Further, it also includes a liquid injection system; The liquid injection system is used to inject the solution to be measured into the droplet-shaped cavity of the droplet shaping unit through the liquid injection channel.

[0012] Further, the liquid injection system is a micro syringe or a micro injection pump; The control unit is a digital thermostat; The image acquisition system is a high-speed camera; The image analysis system is a computer.

[0013] In addition, the present invention also provides a detection method using the above metal ion detection device, and the detection method includes the following steps: First step, tightly connect the droplet shaping unit and the refrigeration unit; Second step, inject the solution to be measured into the droplet shaping unit; Third step, adjust the image acquisition system to focus on the droplet-shaped solution to be measured; Fourth step, adjust the temperature of the refrigeration unit T n Lower it below the freezing point of the solution to be measured to cause an ice-water liquid-solid phase change of the solution to be measured; Fifth step, calculate the specific value of the dendrite growth model coefficient related to the metal ion type and concentration ξ Under the condition of knowing the ion type, infer the concentration of the solution to be measured according to the dendrite growth model coefficient ξ Or under the condition of knowing the ion concentration, infer the ion type of the solution to be measured according to the dendrite growth model coefficient ξ Sixth step, calculate the freezing model coefficient related to the metal ion type and concentration ζ ​The specific value, under the condition of known ion species, according to the freezing model coefficient ζ infer the ion concentration of the solution to be measured, or under the condition of known ion concentration, according to the freezing model coefficient ζ infer the ion species of the solution to be measured; The seventh step is to achieve mutual verification of the detection results through the collaborative analysis of the average dendritic growth rate and the average freezing rate.

[0014] Furthermore, in the second step, a liquid injection system is used to inject the solution to be measured into the droplet shaping unit; In the fifth step, calculate the dendritic growth model coefficient ξ The specific process is as follows: Use the image analysis system to measure the final height of the dendrites in the solution to be measured during the recalescence stage H d and the dendritic growth time t d , the actual average dendritic growth rate v d The calculation formula is: v d = H d / t d (1); The theoretical average dendritic growth rate The calculation formula is: (2); In the above formula, k i is the thermal conductivity of ice, ρ i is the density of ice, L is the latent heat of solidification phase change of the solution, υ is the kinematic viscosity of the solution, γ is the ice-water interface energy, A is the ice-water interface temperature gradient constant, T f is the solidification phase change temperature of the solution, v is the solution flow rate; The simplified theoretical average dendritic growth rate The calculation formula is: (3); In the above formula, ξ is the dendritic growth model coefficient, which is related to the ion species and concentration; Substitute the actual average dendritic growth rate calculated using formula (1) into formula (3), and use formula (3) to fit the actual average dendritic growth rate obtained through calculation to obtain the dendritic growth model coefficient ξ for its specific value.

[0015] Furthermore, in the sixth step, the process of calculating the freezing model coefficient ζ is as follows: Use an image analysis system to measure the final height of ice after the solution to be measured has completely solidified H f and the time required for complete solidification t f Calculate the average freezing rate, the actual average freezing rate v f is calculated by the formula: v f = H f / t f (4); The theoretical average freezing rate is calculated by the formula: (5); In the above formula, L w is the latent heat of solidification phase change of water, C p is the specific heat capacity of water at constant pressure, ζ is the freezing model coefficient associated with the ion type and concentration; Substitute the actual average freezing rate calculated using formula (4) into formula (5), and use formula (5) to fit the actual average freezing rate obtained through calculation to obtain the specific value of the freezing model coefficient ζ for its specific value.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The above metal ion detection device and method are based on the ice-water liquid-solid phase change, and utilize the physical phenomenon of the difference in the ice-water liquid-solid phase change characteristics of different metal ion solutions to realize the detection of metal ions in the solution to be measured. By adjusting the temperature of the refrigeration unit, the solution to be measured is solidified, and the visualization observation of the ice-water liquid-solid phase change characteristics of the solution to be measured and the detection of metal ions are realized through the droplet shaping unit, the image acquisition system and the image analysis system. Compared with the existing methods for detecting metal ions in solution, using the ice-water liquid-solid phase change characteristics of the solution to detect metal ions is simple to operate, has a wide range of applicable ion types and concentrations, high detection efficiency, low cost, no pollution and strong environmental adaptability.

[0017] The material of the above-mentioned droplet shaping unit and the shape and volume of the droplet-shaped cavity inside it can be adjusted to obtain higher metal ion detection accuracy; the refrigeration temperature provided by the above-mentioned refrigeration unit can be adjusted to obtain higher metal ion detection efficiency; the above-mentioned droplet shaping unit and the refrigeration unit can be flexibly disassembled, enabling efficient and continuous detection of metal ions in multiple test solutions; the above-mentioned test solution has multiple ice-water liquid-solid phase change characteristic parameters that can be used for ion detection, and the detection results are mutually verified through multi-parameter collaborative analysis, significantly improving the detection accuracy and result reliability. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the principle of the metal ion detection device of the present invention; Figure 2 It is a schematic diagram of the ice-water liquid-solid phase change process of metal ion solution droplets; Figure 3 It is a graph showing the relationship between metal ion species and concentration and dendrite growth rate; Figure 4 It is a graph showing the relationship between metal ion species and concentration and freezing rate; Figure 5 It is a schematic diagram of the specific structure of the metal ion detection device in Embodiment 1 of the present invention; Figure 6 It is an experimental photo of the final dendrite morphology during the reheating stage of different concentrations of MgCl2 solution; Figure 7 It is a graph showing the relationship between MgCl2 solution concentration and dendrite growth rate; Figure 8 It is the relationship between ion species and concentration and the coefficients of the mathematical model.

[0019] Among them, 1 - test solution, 2 - droplet shaping unit, 3 - refrigeration unit, 4 - liquid injection system, 5 - image acquisition system, 6 - image analysis system, 101 - dendrite, 102 - ice, 201 - first layer of transparent acrylic plate, 202 - second layer of transparent acrylic plate, 203 - polydimethylsiloxane sandwich, 301 - copper plate, 302 - semiconductor refrigeration sheet, 303 - control unit, 304 - heat exchanger, 305 - low-temperature constant temperature bath, 306 - thermal insulation material. Detailed Embodiments

[0020] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0021] The object of the present invention is to utilize the differences in the ice-water liquid-solid phase change characteristics of different metal ion solutions, such as ice crystal growth rate, freezing rate, etc., induce phase change through a temperature control device and monitor characteristic parameters, and realize the detection of metal ions in the solution according to the quantitative correlation model between the ion type and concentration and the phase change characteristic parameters. According to the ice-water liquid-solid phase change characteristics of the target metal ion solution, detect the ion type and concentration, and realize the integration of "sampling-detection-analysis".

[0022] Example 1 This example provides a device for detecting metal ions in a solution based on the ice-water liquid-solid phase change, Figure 1 which is a schematic diagram of the principle of the metal ion detection device, Figure 2 and is a schematic diagram of the ice-water liquid-solid phase change process of the metal ion solution droplet, Figure 2 which shows the initial state, recalescence stage, freezing stage and final state of the melt; the metal ion detection device includes a droplet shaping unit 2, a refrigeration unit 3, an image acquisition system 5 and an image analysis system 6; among them: The droplet shaping unit 2 is made of a transparent low-temperature resistant material and has a droplet-shaped cavity with an open bottom inside. The droplet-shaped cavity is used to accommodate the solution to be measured 1; the solution to be measured 1 is a metal ion solution with unknown type and concentration. The refrigeration unit 3 is detachably and hermetically connected to the bottom end of the droplet shaping unit 2, so that the solution to be measured 1 in the droplet shaping device can be directly in close contact with the refrigeration unit 3, and is used to supply cold to the solution to be measured 1 to make a two-dimensional droplet-shaped slice of the solution to be measured 1; the refrigeration unit 3 is a compression refrigeration device, an absorption refrigeration device or a semiconductor refrigeration device.

[0023] The image acquisition system 5 is arranged horizontally opposite to the droplet shaping unit 2 and focuses on the droplet-shaped solution to be measured 1, and is used to record the ice-water liquid-solid phase change process of the solution to be measured 1 in real time; the image acquisition system 5 is used to record the growth process of dendrite 101 in the recalescence stage and ice 102 in the freezing stage of the solution to be measured 1 during the ice-water liquid-solid phase change process in real time. The image acquisition system 5 is a high-speed camera.

[0024] The image analysis system 6 is connected to the image acquisition system 5 by signal, and is used to analyze the ice-water liquid-solid phase change process of the solution to be measured 1 obtained by the image acquisition system 5, obtain the ice-water liquid-solid phase change characteristics, and infer the ion type or concentration of the solution to be measured 1 according to the ice-water liquid-solid phase change characteristics. The image analysis system 6 calculates the average dendrite growth rate through the final height of the dendrite 101 and the dendrite growth time, and calculates the average freezing rate through the final height of the ice 102 and the time required for the complete solidification of the solution to be measured 1, and then infers the ion type or concentration of the solution to be measured 1 according to the average dendrite growth rate and the average freezing rate of the solution to be measured 1. The image analysis system 6 is a computer.

[0025] In the above metal ion detection device, as Figure 5 shown, the droplet shaping unit 2 is composed of a first-layer transparent acrylic plate 201, a polydimethylsiloxane sandwich layer 203, and a second-layer transparent acrylic plate 202 that are hermetically connected in sequence; a droplet-shaped cavity is arranged in the polydimethylsiloxane sandwich layer 203; the polydimethylsiloxane sandwich layer 203 is provided with a communicating liquid injection channel at the top of the droplet-shaped cavity.

[0026] As Figure 5 shown, when the refrigeration unit 3 is a semiconductor refrigeration device, it includes a copper plate 301, a semiconductor refrigeration chip 302, a control unit 303, a heat exchanger 304, a low-temperature constant temperature bath 305, and a heat insulation material 306; the hot end of the semiconductor refrigeration chip 302 is attached to the heat exchanger 304, and the cold end is attached to the copper plate 301 for heat transfer; there is a refrigerant circulating between the heat exchanger 304 and the low-temperature constant temperature bath 305; the control unit 303 is connected to the semiconductor refrigeration chip 302 for controlling the temperature of the semiconductor refrigeration chip 302, and the control unit 303 is a digital thermostat; the top of the copper plate 301 is inserted into the gap between the first-layer transparent acrylic plate 201 and the second-layer transparent acrylic plate 202 and is in close contact with the polydimethylsiloxane sandwich layer 203 to ensure that the test solution 1 does not leak; a heat insulation material 306 is attached to the outside of the copper plate 301 to reduce cold loss.

[0027] The above metal ion detection device further includes a liquid injection system 4; the liquid injection system 4 is used to inject a predetermined volume of the test solution 1 into the droplet-shaped cavity of the droplet shaping unit 2 through the liquid injection channel. The liquid injection system 4 is a micro syringe or a micro injection pump.

[0028] Embodiment 2 This embodiment provides a detection method using the metal ion detection device in the above Embodiment 1. The detection method includes the following steps: First step, tightly connect the droplet shaping unit 2 and the refrigeration unit 3; Second step, use the liquid injection system 4 to inject a predetermined volume of the test solution 1 into the droplet shaping unit 2; Third step, adjust the image acquisition system 5 to focus on the droplet-shaped test solution 1; Fourth step, adjust the temperature of the refrigeration unit 3 T n to drop below the freezing point of the test solution 1, causing the test solution 1 to undergo an ice-water liquid-solid phase change; Fifth step, use the image analysis system 6 to measure the final height H d of the dendrite 101 and the dendrite growth time t d in the remelting stage of the test solution 1 vd The calculation formula for v d = H d / t d (1); The theoretical average growth rate of dendrites The calculation formula for (2); In the above formula, k i is the thermal conductivity of ice 102, ρ i is the density of ice 102, L is the latent heat of solidification phase change of the solution, υ is the kinematic viscosity of the solution, γ is the ice-water interface energy, A is the ice-water interface temperature gradient constant, T f is the solidification phase change temperature of the solution, v is the solution flow rate; The simplified theoretical average growth rate of dendrites The calculation formula for (3); In the above formula, ξ is the dendrite growth model coefficient, which is related to the ion species and concentration; for example, Figure 3 is the relationship diagram between the metal ion species and concentration and the average growth rate of dendrites, where v d,0 is the ion concentration C 0 is the average growth rate of dendrites when it is 0. Solutions with different metal ion species and concentrations all correspond to a ξ value, and then a correlation formula between ξ and the metal ion species and concentration can be established. The relationship diagram between the metal ion species and concentration and the average growth rate of dendrites can be obtained through experiments.

[0029] Substitute the actual average growth rate of dendrites calculated by formula (1) into formula (3), and the actual average growth rate of dendrites obtained by calculation is used to fit by formula (3) to obtain the specific value of the dendrite growth model coefficient ξ Under the condition of known ion species, the concentration of the test solution 1 can be inferred according to the dendrite growth model coefficient ξ or under the condition of known ion concentration, the ion species of the test solution 1 can be inferred according to the dendrite growth model coefficient ξ ; Step 6: Use the image analysis system 6 to measure the final height of the ice 102 in the solution to be measured 1 after complete solidification H f and the time required for complete solidification t f Calculate the average freezing rate. The calculation formula for the actual average freezing rate is: v f = H f / t f (4); The theoretical average freezing rate The calculation formula is: (5); In the above formula, L w is the latent heat of solidification phase change of water, C p is the specific heat capacity of water at constant pressure, ζ is the freezing model coefficient associated with the ion type and concentration; Substitute the actual average freezing rate calculated by formula (4) into formula (5), and the specific value of the freezing model coefficient ζ is obtained by fitting the actual average freezing rate calculated by formula (5). Under the condition of known ion type, the ion concentration of the solution to be measured 1 is inferred according to the freezing model coefficient ζ or under the condition of known ion concentration, the ion type of the solution to be measured 1 is inferred according to the freezing model coefficient ζ ; Figure 4 is the relationship diagram between the metal ion type and concentration and the average freezing rate. Among them, v f,0 is the ion concentration C 0 is the average freezing rate when it is 0. Solutions with different metal ion types and concentrations all correspond to a ζ value, and then a correlation formula between ζ and the metal ion type and concentration can be established. The relationship diagram between the metal ion type and concentration and the average freezing rate can be obtained through experiments.

[0030] Step 7: Realize the mutual verification of the detection results through the collaborative analysis of the average dendrite growth rate and the average freezing rate.

[0031] Example 3 This example provides a device for detecting metal ions in a solution based on the liquid-solid phase change of ice water, as Figure 5As shown, the test solution 1 in the device is an MgCl2 ionic solution with an unknown concentration; the droplet shaping unit 2 is fixedly connected and composed of a first transparent acrylic plate 201 with a thickness of 5 mm, a second transparent acrylic plate 202 with a thickness of 5 mm, and a polydimethylsiloxane sandwich layer 203 with a thickness of 0.3 mm. The first transparent acrylic plate 201, the second transparent acrylic plate 202, and the polydimethylsiloxane sandwich layer 203 can be fixedly connected through bonding or bolts and nuts; the polydimethylsiloxane sandwich layer 203 is provided with a liquid injection channel and a droplet-shaped cavity with a diameter of 2 mm and a contact angle of 90°; the refrigeration unit 3 uses a semiconductor refrigeration device, and the semiconductor refrigeration device includes a copper plate 301, a semiconductor refrigeration chip 302, a control unit 303, a heat exchanger 304, and a low-temperature constant-temperature bath 305; the specification of the semiconductor refrigeration chip 302 is 40 mm × 40 mm × 10 mm, and the hot end of the semiconductor refrigeration chip 302 is attached to the heat exchanger 304 with a specification of 40 mm × 40 mm × 20 mm; there is a refrigerant circulating between the heat exchanger 304 and the low-temperature constant-temperature bath 305, and heat dissipation of the heat exchanger 304 is achieved through the refrigerant; the semiconductor refrigeration chip 302 is connected to the control unit 303; the control unit 303 is a digital thermostat for controlling the temperature of the semiconductor refrigeration chip 302; the cold end of the semiconductor refrigeration chip 302 is attached to the copper plate 301 with a thickness of 0.3 mm for heat transfer; the top of the copper plate 301 is inserted into the gap between the first transparent acrylic plate 201 and the second transparent acrylic plate 202 and is in close contact with the polydimethylsiloxane sandwich layer 203 to ensure that the test solution 1 does not leak; a heat insulation material 306 is pasted on the outside of the copper plate 301 to reduce the cold loss of the copper plate 301 through the heat insulation material 306; the liquid injection system 4 is a micro syringe, and 2 μL of the test solution 1 is injected into the droplet-shaped cavity through the liquid injection channel at the top of the polydimethylsiloxane sandwich layer 203; the image acquisition system 5 is a high-speed camera for capturing the ice-water phase change process of the test solution 1; the image acquisition system 5 is connected to the image analysis system 6, and the image analysis system 6 is a computer.

[0032] Example 4 The detection method for metal ion detection using the metal ion detection device in the above Example 3 includes the following steps: First step, insert the copper plate 301 into the gap between the first transparent acrylic plate 201 and the second transparent acrylic plate 202 and make close contact with the bottom end of the polydimethylsiloxane sandwich layer 203; Second step, inject 2 μL of the test solution 1 into the droplet-shaped cavity in the polydimethylsiloxane sandwich layer 203 by the liquid injection system 4; Third step, adjust the image acquisition system 5 to focus on the droplet-shaped test solution 1; Fourth step, regulate the temperature of the semiconductor refrigeration chip 302 to be reduced to -10 °C through the control unit 303 to cause an ice-water liquid-solid phase change in the solution; In the fifth step, use the image analysis system 6 to measure the final dendrite height of the solution 1 to be measured during the remelting stage H d and the dendrite growth time t d ; In the sixth step, substitute the actual average dendrite growth rate calculated by the formula v d = H d / t d into the formula , and use the actual average dendrite growth rate to replace the theoretical average dendrite growth rate , calculate the coefficient related to the ion concentration and type ξ , and infer the concentration of the solution 1 to be measured based on the coefficient ξ under the condition of known ion types.

[0033] Figure 6 Figure 30 is the experimental photo of the final dendrite morphology during the remelting stage of MgCl2 solutions with different concentrations. The height and growth time of the dendrite 101 are different at different ion concentrations. The relationship between the Mg 2+ ion concentration in the solution and the dendrite growth rate is as shown in Figure 7 . A relational formula between the Mg 2+ ion concentration and the dendrite growth rate v d can be established as: (6); In the above formula, C is the ion concentration, with the unit of ppm; based on the obtained actual average dendrite growth rate, the concentration of Mg 2+ ions in the solution 1 to be measured can be detected according to the above formula.

[0034] Based on the dendrite growth rate results under multiple different metal ion types and concentrations, a coefficient ξ related to the metal ion type and concentration can be obtained, and its relational formula is: (7); As shown in Figure 8 , a relational formula for the dendrite growth rate v d under the coupling effect of ion type and concentration can be established as: (8); In the above formula, C is the ion concentration, with the unit of ppm; Rwhere \(r_i\) is the ionic radius in pm (picometers); according to the above formula, the concentration of metal ions in a solution with a known type of metal ions can be detected, and the type of metal ions in a solution with a known metal ion concentration can also be detected.

[0035] The above metal ion detection device and method are based on the ice - water liquid - solid phase change, and utilize the physical phenomenon of the difference in the ice - water liquid - solid phase change characteristics of different metal ion solutions to detect the metal ions in the solution to be measured 1. By adjusting the temperature of the refrigeration unit 3, the solution to be measured 1 is solidified, and through the droplet shaping unit 2, the image acquisition system 5 and the image analysis system 6, the visualization observation of the ice - water liquid - solid phase change characteristics of the solution to be measured 1 and the detection of metal ions are realized. Compared with the existing methods for detecting metal ions in solutions, such as spectroscopic method, electrochemical method and chemical colorimetric method, the method of detecting metal ions by using the ice - water liquid - solid phase change characteristics of the solution is simple to operate, has a wide range of applicable ion types and concentrations, high detection efficiency, low cost, no pollution and strong environmental adaptability.

[0036] The material of the above droplet shaping unit 2 and the shape and volume of the internal droplet - shaped cavity can be adjusted to obtain higher metal ion detection accuracy; the refrigeration temperature provided by the above refrigeration unit 3 can be adjusted to obtain higher metal ion detection efficiency; the droplet shaping unit 2 and the refrigeration unit 3 can be flexibly disassembled, and the efficient and continuous detection of metal ions in multiple solutions to be measured 1 can be realized; the above solution to be measured 1 has multiple ice - water liquid - solid phase change characteristic parameters for ion detection, and the mutual verification of detection results is realized through multi - parameter collaborative analysis, significantly improving the detection accuracy and result reliability.

[0037] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A metal ion detection device in a solution based on the liquid-solid phase change of ice water, characterized in that, It includes a droplet shaping unit, a refrigeration unit, an image acquisition system, and an image analysis system; The droplet shaping unit is made of a transparent low-temperature resistant material and has a droplet-shaped cavity with an open bottom inside. The droplet-shaped cavity is used to hold the solution to be tested; the solution to be tested is a metal ion solution with unknown type and concentration; The refrigeration unit is detachably and hermetically connected to the bottom end of the droplet shaping unit and is used to supply cold to the solution to be tested to make a two-dimensional droplet-shaped slice of the solution to be tested; The image acquisition system is arranged opposite to the droplet shaping unit in the horizontal direction and focuses on the droplet-shaped solution to be tested, and is used to record the ice-water liquid-solid phase change process of the solution to be tested; The image analysis system is connected to the image acquisition system by signal and is used to analyze the ice-water liquid-solid phase change process of the solution to be tested obtained by the image acquisition system, obtain the ice-water liquid-solid phase change characteristics, and infer the ion type or concentration of the solution to be tested according to the ice-water liquid-solid phase change characteristics.

2. The metal ion detection device according to claim 1, wherein The image acquisition system is used to record in real time the growth process of dendrites in the re-illumination stage and ice in the freezing stage during the ice-water liquid-solid phase change process of the solution to be tested.

3. The metal ion detection device according to claim 2, wherein The image analysis system calculates the average growth rate of dendrites by the final height of dendrites and the dendrite growth time, calculates the average freezing rate by the final height of ice and the time required for the complete solidification of the solution to be tested, and then infers the ion type or concentration of the solution to be tested according to the average growth rate of dendrites and the average freezing rate of the solution to be tested.

4. The metal ion detection device according to claim 1, wherein The droplet shaping unit is composed of a first-layer transparent acrylic plate, a polydimethylsiloxane sandwich layer, and a second-layer transparent acrylic plate that are hermetically connected in sequence; The droplet-shaped cavity is arranged in the polydimethylsiloxane sandwich layer; The polydimethylsiloxane sandwich layer is provided with a communicating liquid injection channel at the top of the droplet-shaped cavity.

5. The metal ion detection device according to claim 4, wherein The refrigeration unit is a compression refrigeration device, an absorption refrigeration device, or a semiconductor refrigeration device; When the refrigeration unit is a semiconductor refrigeration device, it includes a semiconductor refrigeration chip, a heat exchanger, a copper plate, a low-temperature constant temperature bath, a heat insulation material, and a control unit; The hot end of the semiconductor refrigeration chip is attached to the heat exchanger, and the cold end is attached to the copper plate for heat transfer; a refrigerant circulates between the heat exchanger and the low-temperature constant temperature bath; the control unit is connected to the semiconductor refrigeration chip and is used to control the temperature of the semiconductor refrigeration chip; The top end of the copper plate is inserted into the gap between the first-layer transparent acrylic plate and the second-layer transparent acrylic plate and is in close contact with the polydimethylsiloxane sandwich layer to ensure that the solution to be tested does not leak; the outside of the copper plate is pasted with the heat insulation material to reduce cold loss.

6. The metal ion detection device according to claim 5, wherein It further includes a liquid injection system; The liquid injection system is used to inject the solution to be tested into the droplet-shaped cavity of the droplet shaping unit through the liquid injection channel.

7. The metal ion detection device according to claim 6, characterized in that, The liquid injection system is a micro syringe or a micro injection pump; The control unit is a digital constant temperature instrument; The image acquisition system is a high-speed camera; The image analysis system is a computer.

8. A detection method using the metal ion detection device according to any one of claims 1-7, characterized in that, It includes the following steps: The first step is to tightly connect the droplet shaping unit and the refrigeration unit; The second step is to inject the solution to be tested into the droplet shaping unit; The third step is to adjust the image acquisition system so that it focuses on the droplet-shaped solution to be tested; Step 4, adjust the temperature of the refrigeration unit T n Lower it below the freezing point of the solution to be measured, causing an ice-water liquid-solid phase change in the solution to be measured; Step 5: Calculate the dendrite growth model coefficients related to the type and concentration of metal ions ξ to obtain the specific values. Under the condition of known ion types, infer the concentration of the solution to be measured based on the dendrite growth model coefficients ξ or, under the condition of known ion concentrations, infer the ion types of the solution to be measured based on the dendrite growth model coefficients ξ ; Step 6: Calculate the specific values of the freezing model coefficients related to the type and concentration of metal ions. Under the condition of known ion types, infer the ion concentration of the solution to be measured based on the freezing model coefficients ζ ; or under the condition of known ion concentrations, infer the ion types of the solution to be measured based on the freezing model coefficients ζ ; ζ ​ Step 7: Mutual verification of the detection results is achieved through the collaborative analysis of the average dendritic growth rate and the average freezing rate.

9. The detection method according to claim 8, characterized in that, In Step 2, a liquid injection system is used to inject the solution to be measured into the droplet shaping unit. In the fifth step, calculate the dendrite growth model coefficients ξ The specific process is as follows: Measuring the final height of dendrites in the recalescence stage of the solution to be measured using an image analysis system H d and the dendrite growth time t d The calculation formula for the actual average dendrite growth rate v d is as follows: v d = H d / t d （1）； Theoretical average dendrite growth rate The calculation formula is as follows: （2）； In the above formula, k i is the thermal conductivity of ice, ρ i is the density of ice, L is the latent heat of solidification phase change of the solution, υ is the kinematic viscosity of the solution, γ is the ice-water interfacial energy, A is the ice-water interface temperature gradient constant, T f is the solidification phase change temperature of the solution, v is the solution flow rate; Simplified theoretical average dendrite growth rate The calculation formula is as follows: （3）； In the above formula, ξ is the dendrite growth model coefficient, which is associated with the ion type and concentration; Substitute the actual average dendrite growth rate calculated by formula (1) into formula (3), and use formula (3) to fit the actual average dendrite growth rate obtained through calculation to obtain the dendrite growth model coefficient ξ for the specific value.

10. The detection method according to claim 9, wherein In the sixth step, calculate the coefficients of the frozen model ζ The specific process is as follows: Measure the final height of ice after the test solution has completely solidified using an image analysis system H f and the time required for complete solidification t f Calculate the average freezing rate and the actual average freezing rate v f The calculation formula is as follows: v f = H f / t f （4）； Theoretical average freezing rate The calculation formula is as follows: （5）； In the above formula, L w is the latent heat of solidification phase change of water, C p is the specific heat capacity of water at constant pressure, ζ is the freezing model coefficient associated with the ion species and concentration; Substitute the actually calculated average freezing rate obtained by formula (4) into formula (5), and use formula (5) to fit the actually calculated average freezing rate to obtain the coefficients of the freezing model ζ for the specific values.

Images