Chroma relative concentration detection sensor and application thereof in phosphoric acid detection

Abstract

The invention discloses a chroma relative concentration detection sensor and application thereof in phosphoric acid detection, and belongs to the technical field of phosphoric acid detection. The sensor is integrated with the chromaticity detection unit, the comparison detection unit and the concentration detection unit, so that the chromaticity, the comparison and the concentration of refined phosphoric acid can be synchronously and quickly detected; the sensor completes signal acquisition by combining a differential pulse voltammetry and an alternating-current impedance method, and eliminates detection deviation caused by a high-temperature working condition through a temperature compensation formula. The method is fast in response, high in precision and strong in stability, can effectively reduce the risk of manual operation, is suitable for production process control of workshop sections such as wet-process phosphoric acid extraction, decoloration and concentration, and fills the industry blank of multi-parameter synchronous detection.

Description

Technical Field

[0001] This invention relates to the field of phosphoric acid detection technology, and more specifically to a phosphoric acid colorimetric concentration detection sensor. Background Technology

[0002] Refined phosphoric acid is a key product in the phosphorus chemical industry, widely used in food, electronics, and fertilizer sectors. The wet process for preparing phosphoric acid uses phosphate rock as raw material, undergoing a series of steps including acid hydrolysis, purification, refining, and concentration to ultimately obtain a refined phosphoric acid product with a concentration of 85%. Color, phase ratio, and concentration are core parameters for evaluating product quality and the stability of the extraction process. Color directly determines the product grade; it is a direct indicator of the appearance and purity of phosphoric acid. Excessive levels of color-causing organic groups will cause the product to turn yellow, failing to meet food-grade / electronic-grade standards, directly impacting market access and selling price. It also reflects the effectiveness of the decolorization process, preventing substandard products from entering downstream industries. Concentration relates to product purity and suitability for application scenarios. Insufficient concentration will affect downstream applications such as fertilizer production and electronic material preparation. Concentration should be avoided as it can lead to crystallization blockage if too high or increase production costs if too low.

[0003] The ratio, a standard term in the chemical industry, refers to the volume ratio of one liquid phase to another in an extraction system. In wet phosphoric acid extraction, it is usually expressed as the A / O ratio, i.e., the volume of the phosphoric acid phase / the volume of the organic phase. It is a key parameter for solvent extraction and impurity removal, directly affecting the impurity removal efficiency and phosphoric acid recovery rate. Ratio detection accurately reflects the current actual ratio in the extraction tank. If the detection result deviates from the optimal range, it can be adjusted immediately to quickly bring the ratio back to the best value, ensuring that phosphoric acid extraction and impurity separation remain in a highly efficient and stable state, and preventing the extraction imbalance from continuing to expand. If slow phase separation, emulsification, or interface turbidity occurs during ratio detection, the process of this section can be adjusted immediately to prevent the overall operating conditions of the extraction tank from deteriorating. By detecting the amount of organic phase entrainment in the ratio, the aging and contamination level of the circulating organic phase can be determined, allowing for timely cleaning and regeneration of the organic phase, ensuring the extraction efficiency of the circulating extractant, and maintaining long-term stable operation of the section. Traditional manual sampling has a strong lag, and after ratio imbalance, the organic phase is easily over-added or lost with the aqueous phase. Rapid ratio detection can eliminate the ineffective consumption of organic phase, reduce the waste of expensive extractants, and directly reduce raw material costs. Imbalance in the ratio directly leads to incomplete impurity removal, resulting in substandard phosphate that needs to be returned to the extraction stage for rework. Timely ratio adjustment can prevent substandard products from being produced at the source, saving on steam, water, electricity, labor, and material costs associated with rework. Timely detection of phase separation anomalies can prevent emulsion from clogging pipelines and corroding extraction equipment, reducing the frequency and cost of equipment maintenance and downtime, and increasing the effective operating time of the unit. Adjusting the ratio to its optimal value in a timely manner ensures efficient extraction and separation of impurities such as metal ions, fluorine, sulfur, and organic matter, enabling the product to consistently meet industrial-grade, food-grade, and even electronic-grade standards. A stable ratio means a stable amount of organic phase entrainment, preventing product yellowing and concentration fluctuations caused by residual organic phase.

[0004] Currently, the industry mostly uses offline sampling methods to detect the color, phase, and concentration of refined phosphoric acid.

[0005] The colorimetric determination method for refined phosphoric acid adopts the platinum-cobalt standard colorimetric method, i.e., the visual colorimetric method, as specified in GB / T605-2006 "General Methods for Measurement of Colorimetry of Chemical Reagents". The core principle of this method is visual colorimetry. It simulates the yellow hue of the sample by preparing a series of acidic standard solutions of potassium chloroplatinate and cobalt chloride of known concentrations. The operational steps are as follows: First, prepare standard color scales. A series of standard colorimetric solutions ranging from 5 Hazen to 500 Hazen are prepared strictly according to the standard method and sealed in Nessler tubes. Second, prepare the sample. The phosphoric acid sample to be tested is injected into another colorimetric tube of the same specifications as the standard tube, with the liquid level matching that of the standard tube. Third, perform visual colorimetry. Under a standard light source box or sufficient diffused light environment, the sample tube and the standard tube are placed side-by-side upright, and the sample is observed vertically downwards from the tube opening. Through repeated comparisons, the standard tube with the closest color depth to the sample is found. Finally, the result is read; the Hazen unit of the standard tube is the colorimetric value of the phosphoric acid. If the sample color falls between the two standards, the median value is taken.

[0006] The standard detection methods for industrial phosphoric acid concentration are based on national standards (GB / T), including the quinoline phosphomolybdate gravimetric method and the acid-base titration volumetric method. Both methods have the following drawbacks: manual sampling and analysis have long cycles, making it difficult to promptly reflect process fluctuations, leading to increased defect rates; phosphoric acid is highly corrosive, and manual contact can easily cause safety accidents, and sampling in high-temperature, high-acid environments may lead to equipment leaks; the platinum-cobalt standard colorimetric method for colorimetric detection relies on manual visual judgment, resulting in large errors; the quinoline phosphomolybdate gravimetric method for concentration detection is cumbersome to operate, requiring the use of hazardous reagents such as quinoline phosphomolybdate, and demands high levels of operational proficiency from personnel; the acid-base titration volumetric method is easily affected by other acidic impurities; existing online detection technologies are mostly designed for single parameters and are easily interfered with in high-temperature, high-viscosity phosphoric acid media, making it difficult to meet the needs of simultaneous monitoring of multiple parameters.

[0007] Methods for detecting industrial phosphoric acid include direct measurement and density methods. The direct measurement method involves placing the mixed two-phase solution in a separatory funnel or graduated cylinder, allowing it to stand and separate into layers, and then directly reading the volume scales of the organic and phosphoric acid phases to calculate the volume ratio. This method is simple to operate, requires no complex instruments, and only basic glassware such as separatory funnels and graduated cylinders. However, it requires waiting for complete separation, is affected by the system's viscosity and degree of emulsification, and is susceptible to human error. The scale readings are affected by the observation angle of the liquid surface and the clarity of the phase interface, and it is only suitable for offline sampling analysis. The density method works on the principle that the densities of the organic phase (tributyl phosphate (TBP) + kerosene) and the phosphoric acid phase (phosphoric acid solution) are ρ and ρ, respectively. O and ρ ABy measuring the total mass m and total volume V of the mixture, the volume ratio can be calculated using the law of conservation of mass: m = ρ O ×V O +ρ A ×V A V=V O +V A Compared to =V A / V O The advantages are that no stratification is required, and the mixture can be measured directly; the density can be calculated by weighing with an electronic balance and using a volume scale. The disadvantages are that the density is significantly affected by temperature, phosphoric acid concentration, and organic phase composition, requiring real-time calibration; if emulsification occurs, the density of the mixture cannot reflect the true phase volume.

[0008] Therefore, developing an online detection method and sensor for real-time, accurate, and synchronous detection of the color-to-concentration ratio of refined phosphoric acid is of great significance for improving production efficiency and reducing safety risks. Summary of the Invention

[0009] This invention provides a phosphoric acid colorimetric concentration detection sensor to achieve online synchronous detection of the colorimetric concentration of refined phosphoric acid, thereby improving detection efficiency and accuracy and reducing operational risks.

[0010] The phosphoric acid colorimetric concentration detection sensor of the present invention includes a colorimetric detection unit, a contrast detection unit, and a concentration detection unit; The colorimetric detection unit consists of a working electrode I, a reference electrode I, and an auxiliary electrode I. The working electrode I is a platinum electrode with a surface-modified organic selective chelating coating. The preparation of the platinum electrode with the surface-modified organic selective chelating coating is as follows: (1) Select platinum sheets with a purity ≥99.99%, and polish them step by step with 800 mesh, 1200 mesh and 2000 mesh silicon carbide sandpaper. Then, clean them with anhydrous ethanol for 10-20 min and deionized water for 8-12 min. Finally, activate them in 0.5 mol / L sulfuric acid solution by cyclic voltammetry. The scanning range is -0.2~1.2 V, the scanning rate is 40-60 mV / s, and the cycle is 20 times. (2) Dissolve the organophosphorus chelating agent in an acetate-sodium acetate buffer solution at pH=3.0 at a ratio of 0.5-1.0 g / L. Immerse the activated platinum substrate in the solution and electropolymerize it at a constant potential of 0.9-1.2 V for 25-35 min. Then, cure it in a vacuum drying oven at 55-65℃ for 1-3 h to form an organic group selective chelating coating with a thickness of 20-50 nm. The organophosphorus chelating agent is aminotrimethylenephosphonic acid. The detection unit consists of a top hydrophobic electrode, a middle composite electrode, and a bottom hydrophilic electrode; the top hydrophobic electrode is fabricated as follows: (1) Using platinum sheets with a purity of ≥99.99% as the base, the substrate is ultrasonically cleaned with anhydrous ethanol for 8-12 min, rinsed with deionized water, and then dried at 110-130℃ for 25-35 min. (2) Place the pretreated substrate in a vapor deposition furnace and deposit polytetrafluoroethylene micro powder as raw material at 380-400℃ and vacuum degree ≤10Pa for 30-60 min, controlling the film thickness to be 50-100nm. (3) After deposition, allow the film to cool naturally to room temperature, then anneal at 200°C for 1 hour to ensure that the adhesion between the film and the substrate is ≥5 N / cm. 2 The contact angle reaches 110°±5°; The preparation of the central composite electrode is as follows: (1) Using a platinum sheet with a purity of ≥99.99% as the substrate, the substrate is polished to a mirror finish by successively using 800-mesh, 1200-mesh, and 2000-mesh silicon carbide sandpaper. Then, it is ultrasonically cleaned with anhydrous ethanol for 10-20 minutes, ultrasonically cleaned with deionized water for 8-12 minutes, and dried with nitrogen for later use. (2) The platinum sheet surface after step (1) is etched using femtosecond laser etching technology. The etching parameters are: laser power 10-15W, scanning rate 400-600mm / s, etching depth 15-25μm, trench width 40-60μm, and trench spacing 40-60μm to form a uniform mesh-like trench structure. After etching, the surface is ultrasonically cleaned with deionized water for 4-6 minutes to remove etching residue. (3) Place the etched platinum sheet in a 0.4-0.6 mol / L sulfuric acid solution and activate it using cyclic voltammetry. The scanning range is -0.2~1.2V, the scanning rate is 40-60mV / s, and the cycle is 20 times. After activation, rinse it with deionized water and blow it dry with nitrogen to obtain the middle composite electrode. The bottom hydrophilic electrode is prepared as follows: (1) Using a platinum sheet with a purity of ≥99.99% as the substrate, the substrate is polished to a mirror finish by successively using 800-mesh, 1200-mesh, and 2000-mesh silicon carbide sandpaper. Then, it is ultrasonically cleaned with acetone for 8-12 minutes, anhydrous ethanol for 8-12 minutes, and deionized water for 8-12 minutes to remove surface oil and impurities. It is then dried with nitrogen for later use. (2) Immerse the pretreated platinum sheet in a hydrogen peroxide solution with a mass concentration of 20-40% and soak it at room temperature in the dark for 25-35 minutes to form a uniform PtO / PtO2 mixed platinum oxide hydrophilic layer on the surface of the platinum sheet. After taking it out, rinse it repeatedly with deionized water to remove residual hydrogen peroxide. (3) Place the oxidized platinum sheet in a vacuum drying oven at 55-65℃ and dry for 1-2 hours. Then, soak it in a phosphoric acid solution with a mass concentration of 80-90% at room temperature for 70-75 hours for aging treatment. After taking it out, rinse and dry it to ensure that the contact angle of the electrode surface is ≤30° and the change in contact angle after soaking is ≤5°. The concentration detection unit consists of working electrode II, reference electrode II, and auxiliary electrode II. The working electrode II is prepared as follows: (1) Multi-walled carbon nanotubes and reduced graphene oxide were mixed at a mass ratio of 1:1-3, and deionized water was added for ultrasonic dispersion to form a suspension with a concentration of 1-3 mg / mL. The suspension was then coated onto the surface of a glassy carbon electrode using a drop-coating method, with a coating amount of 4-6 μL / cm. 2 Dry at 75-85℃ for 1 hour to obtain the substrate; (2) The substrate was placed in a 0.1 mol / L bismuth nitrate solution and a bismuth film with a thickness of 10-20 nm was formed by constant potential deposition at a potential of -0.6 V for 10 min. (3) The coating amount is 0.2-0.6 mg / cm². 2 Sodium molybdate was dispersed in a 2-3% (w / w) chitosan solution and ultrasonically dispersed to form a uniform slurry. This slurry was then coated onto the surface of a bismuth film by spraying and crosslinked and cured at 100°C for 1-2 hours to obtain working electrode II.

[0011] The colorimetric and concentration detection sensors of this invention also include a temperature compensation unit, which comprises a temperature sensor. This unit compensates for the reduced peak current signals detected by the colorimetric and concentration detection units based on a temperature-peak current correction formula, which is as follows:

[0012] Among them I corr To correct the current, I meas For measuring current, α = 0.003 / ℃ is the temperature coefficient, T is the measured temperature, and T0 = 25℃ is the reference temperature.

[0013] This detection device also includes a control module, which monitors for impedance abnormalities (R>200kΩ or R<500Ω) and temperature exceeding the limit (>120℃) to provide real-time early warning with a response time of ≤2s.

[0014] Another objective of this invention is to apply a colorimetric-concentration detection sensor to the detection of phosphoric acid colorimetric, contrast, and concentration. When using the concentration detection unit, the working electrode II, reference electrode II, and auxiliary electrode II are placed in a standard solution of phosphoric acid with a concentration of 0-600 μmol / L, using an acetate-sodium acetate buffer solution with pH=3.0 as the solvent. Differential pulse voltammetry is used for detection, with parameters of pulse width 50 ms, scan rate 10 mV / s, and scan voltage -0.2~1.0 V. The reduction peak current of the phosphomolybdic heteropoly acid is obtained. A standard curve of phosphoric acid concentration is plotted with phosphoric acid concentration on the x-axis and reduction peak current on the y-axis to obtain the regression equation and determine the linear relationship between phosphoric acid concentration and reduction peak current. The sample to be tested is placed in an electrolytic cell and detected using the above method to obtain the reduction peak current corresponding to phosphoric acid in the sample. This current is then substituted into the regression equation to calculate the phosphoric acid concentration in the sample.

[0015] When using the colorimetric detection unit, 85% industrial refined phosphoric acid (mass concentration) is used as the solvent to prepare a standard solution with a concentration gradient of 0.1-5.0 ppm for the chromogenic organic compounds. The composition and mass percentage of the chromogenic organic compounds are 40%-50% 2-ethylhexylphosphonic acid, 30%-40% tributyl phosphate, and 10%-20% phenylphosphonic acid. Working electrode I, reference electrode I, and one end of auxiliary electrode I are placed in the standard solution, and detection is performed using differential pulse voltammetry with the following parameters: pulse width 50 ms, scan rate 10 mV / s, and scan voltage... 0~0.8V; Obtain the reduction peak current of the chromogenic organic compound, convert the reduction peak current of phosphoric acid aqueous solution of different concentrations into phosphoric acid Hazen color value, plot the standard curve of phosphoric acid color with phosphoric acid Hazen color value on the x-axis and reduction peak current on the y-axis, obtain the regression equation, and determine the linear relationship between phosphoric acid color and reduction peak current; Place the sample to be tested in the electrolytic cell, and detect it through an electrochemical workstation according to the above method to obtain the reduction peak current corresponding to phosphoric acid in the sample to be tested, substitute it into the regression equation, and calculate the phosphoric acid color in the sample to be tested.

[0016] In contrast to the detection unit, the top hydrophobic electrode, the middle composite electrode, and the bottom hydrophilic electrode are arranged sequentially from top to bottom in the sample to be tested, with equal spacing between the three electrodes. Impedance signals are obtained using AC impedance spectroscopy, and the real part of the impedance, R, is automatically analyzed by an electrochemical workstation. The real parts of the impedance, Ra, are obtained for the top hydrophobic electrode, the middle composite electrode, and the bottom hydrophilic electrode, respectively. 顶 R 中 R 底 The sample to be tested The detection unit was placed in a 1:1 volume ratio mixture of tributyl phosphate (TBP) and kerosene. AC impedance spectroscopy was used for detection, and the stable real part of the impedance of the top hydrophobic electrode was scanned and taken as R. 有机The detection unit was placed in 50% industrial refined phosphoric acid by mass concentration, and the same AC impedance method was used for detection. The real part of the stable impedance of the bottom hydrophilic electrode was scanned and taken as R. 磷酸 ; Calculate the comparison according to the following formula : ; When the ratio is in the range of 0.17 to 0.5, the sample meets the production requirements.

[0017] The beneficial effects of this invention are: 1. Fast response: Adopting offline detection mode, the response time is ≤10 seconds, which can promptly reflect process fluctuations; 2. High precision: Colorimetric detection error ≤3Hazen, compared to a comparison detection error ≤3%, and concentration detection error ≤2.5%, with stability further improved through temperature compensation; 3. Multi-parameter integration: For the first time, differential pulse voltammetry and AC impedance spectroscopy are integrated to achieve simultaneous detection of color, contrast ratio, and concentration, filling a gap in the industry; 4. High safety: Reduces human contact with strong acid environments. Attached Figure Description

[0018] Figure 1 The graph shows the linear relationship between phosphoric acid concentration and reduction peak current in Example 1. Figure 2 The graph shows the linear relationship between Hazen color values ​​and organic group concentrations in Example 1. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, the scope of protection of the present invention is not limited to the contents described. Unless otherwise specified, the reagents and methods used in the embodiments are all commercially available reagents and conventional methods. Example

[0020] Fabrication of a colorimetric-to-concentration detection sensor The colorimetric contrast density detection sensor in this embodiment includes a colorimetric detection unit, a contrast detection unit, a density detection unit, a temperature compensation unit, and a control module; Colorimetric detection unit: consisting of working electrode I, reference electrode I, and auxiliary electrode I, wherein the reference electrode I is an Ag / AgCl electrode, and the auxiliary electrode I is a platinum wire electrode; the working electrode I is a platinum electrode with a selective chelation coating of organic groups on its surface, and the preparation method is as follows: (1) Select platinum sheets with a purity ≥99.99%, and polish them step by step with 800 mesh, 1200 mesh, and 2000 mesh silicon carbide sandpaper, then ultrasonically clean them with anhydrous ethanol for 15 min, ultrasonically clean them with deionized water for 10 min, and finally clean them with 0.5 mol / L sulfuric acid. The solution was activated by cyclic voltammetry with a scanning range of -0.2~1.2V and a scanning rate of 50mV / s for 20 cycles. The solution was then dried with nitrogen gas for later use. (2) At a ratio of 0.8g / L, aminotrimethylenephosphonic acid was dissolved in an acetate-sodium acetate buffer solution with a pH of 3.0. The activated platinum substrate was then immersed in the solution. After electropolymerization modification at a constant potential of 1.0V for 30 minutes, the substrate was cured in a vacuum drying oven at 60℃ for 2 hours to form an organic group selective chelating coating with a thickness of 35nm. The working electrode I was then prepared.

[0021] Compared to the detection unit: it consists of a top hydrophobic electrode, a middle composite electrode, and a bottom hydrophilic electrode. The three electrodes are arranged vertically with equal spacing. The electrode leads are all argon-arc welded to a platinum substrate using 0.5mm platinum wire. The weld joints are sealed with a high-temperature curing adhesive that can withstand temperatures up to 180℃, with a thickness of only 1cm. 2The working end face is exposed to the detection medium; the preparation methods of each electrode are as follows: (1) Top hydrophobic electrode: a platinum sheet (10mm×10mm×0.2mm) with a purity ≥99.99% is used as the substrate, which is ultrasonically cleaned with anhydrous ethanol for 10min, rinsed with deionized water, and dried at 120℃ for 30min; the pretreated substrate is placed in a vapor deposition furnace, and polytetrafluoroethylene micro powder is used as the raw material, and deposition is carried out at 390℃ and vacuum degree 8Pa for 45min, and the film thickness is controlled to be 80nm; after deposition, it is naturally cooled to room temperature and annealed at 200℃ for 1h. The final electrode surface contact angle is 112°, and the film and substrate are closely connected. The bottom bonding force is 6.2 N / cm²; (2) The middle composite electrode: a platinum sheet (10 mm × 10 mm × 0.2 mm) with a purity ≥ 99.99% is used as the substrate. The substrate is polished to a mirror finish by 800 mesh, 1200 mesh and 2000 mesh silicon carbide sandpaper, and then ultrasonically cleaned with anhydrous ethanol for 15 min and deionized water for 10 min. It is then dried with nitrogen gas for later use. The surface of the treated platinum sheet is etched by femtosecond laser etching technology. The etching parameters are laser power 12 W, scanning rate 500 mm / s, etching depth 20 μm, trench width 50 μm, and trench spacing 50 μm to form a uniform mesh. The grid-like groove structure was ultrasonically cleaned with deionized water for 5 minutes after etching to remove etching residue; the etched platinum sheet was placed in 0.5 mol / L sulfuric acid solution and activated by cyclic voltammetry with a scanning range of -0.2~1.2V, a scanning rate of 50mV / s, and 20 cycles. After activation, it was rinsed with deionized water and dried with nitrogen. (3) Bottom hydrophilic electrode: a platinum sheet (10mm×10mm×0.2mm) with a purity ≥99.99% was used as the substrate. The substrate was polished to a mirror finish by 800 mesh, 1200 mesh, and 2000 mesh silicon carbide sandpaper, and then ultrasonically cleaned with acetone for 10 minutes. The platinum sheet was ultrasonically cleaned with anhydrous ethanol for 10 minutes and then ultrasonically cleaned with deionized water for 10 minutes to remove surface oil and impurities. It was then dried with nitrogen gas for later use. The pretreated platinum sheet was then immersed in a 30% hydrogen peroxide solution at room temperature in the dark for 30 minutes to form a uniform PtO / PtO2 mixed platinum oxide hydrophilic layer on the surface of the platinum sheet. After removal, it was repeatedly rinsed with deionized water. The oxidized platinum sheet was then dried in a vacuum drying oven at 60°C for 1 hour, and then immersed in an 85% phosphoric acid solution at room temperature for 72 hours for aging treatment. After removal, it was rinsed and dried. The contact angle of the electrode surface was 28°, and the contact angle changed by 3° after aging.

[0022] Concentration detection unit: working electrode II, reference electrode II, and auxiliary electrode II, wherein the reference electrode II is an Ag / AgCl electrode and the auxiliary electrode II is a platinum wire electrode; the working electrode II is prepared by: (1) mixing multi-walled carbon nanotubes and reduced graphene oxide in a mass ratio of 1:2, adding deionized water and ultrasonically dispersing to form a suspension with a concentration of 2 mg / mL, coating the suspension onto the surface of a glassy carbon electrode by drop coating method, with a coating amount of 5 μL / cm², drying at 80℃ for 1 h to obtain a substrate; (2) placing the substrate in a 0.1 mol / L bismuth nitrate solution, using a constant potential deposition method at a potential of -0.6V for 10 min to form a bismuth film with a thickness of 15 nm; (3) dispersing sodium molybdate in a chitosan solution with a mass concentration of 2% in a coating amount of 0.4 mg / cm², ultrasonically dispersing to form a uniform slurry, coating it onto the surface of the bismuth film by spray coating method, and crosslinking and curing at 100℃ for 1.5 h to obtain the working electrode II.

[0023] Temperature Compensation Unit and Control Module: The temperature compensation unit includes a PT100 platinum resistance temperature sensor (accuracy ±0.1℃), based on... The temperature-peak current correction formula compensates for the detection signal; The control module uses a Siemens S7-1200 PLC, paired with an 8-channel synchronous acquisition card (timestamp accuracy ≤10μs), which can monitor impedance abnormalities (R>200kΩ or R<500Ω) and temperature over-limit (>120℃) and provide real-time early warnings with an early warning response time ≤2s.

[0024] II. Plotting Standard Curves To construct a standard curve for phosphoric acid concentration, the working electrode II, reference electrode II, and auxiliary electrode II were placed in a standard solution of phosphoric acid containing a concentration gradient of 0-600 μmol / L, using an acetate-sodium acetate buffer solution at pH 3.0 as the solvent. Differential pulse voltammetry was used for detection, with parameters of pulse width 50 ms, scan rate 10 mV / s, and scan voltage -0.2~1.0 V. The reduction peak current of phosphomolybdic acid was obtained. A standard curve for phosphoric acid concentration was plotted with phosphoric acid concentration on the x-axis and reduction peak current on the y-axis. The results are shown in [Figure number missing]. Figure 1 The regression equation obtained is: C = 0.093 × I + 4.225, and the correlation coefficient R is... 2 =0.987.

[0025] A standard curve for phosphoric acid colorimetry was plotted using 85% industrial refined phosphoric acid as solvent to prepare standard solutions with a total concentration gradient of chromogenic organic compounds ranging from 0.1 to 5.0 ppm. The composition and mass percentage of the chromogenic organic compounds were 45% 2-ethylhexylphosphonic acid, 35% tributyl phosphate, and 20% phenylphosphonic acid. Working electrode I, reference electrode I, and auxiliary electrode I were placed in the standard solutions, and differential pulse voltammetry was used for detection. The parameters were: pulse width 50 ms, scan rate 10 mV / s, and scan voltage 0–0.8 V. The reduction peak currents of the chromogenic organic compounds were obtained, and the reduction peak currents of the standard solutions at different concentrations were converted into Hazen colorimetric values ​​of phosphoric acid. A standard curve for phosphoric acid colorimetry was plotted with Hazen colorimetric values ​​on the x-axis and reduction peak currents on the y-axis. The regression equation was: Hazen = 22.99 × [organic compounds] + 5.09, with a correlation coefficient R0. 2 =0.994.

[0026] The comparison detection unit was placed in a 1:1 volume ratio mixture of tributyl phosphate (TBP) and kerosene, and detected using AC impedance spectroscopy (frequency range 1Hz~1kHz, sinusoidal amplitude 10mV). The real part of the stable impedance of the top hydrophobic electrode was taken as R_organic = 102.5kΩ. The comparison detection unit was placed in 50% industrial refined phosphoric acid, and detected using the same AC impedance spectroscopy parameters. The real part of the stable impedance of the bottom hydrophilic electrode was taken as R_phosphoric acid = 0.82kΩ. III. Internal Control Requirements for Extraction Production Line The sample tested in this embodiment came from the wet refining phosphoric acid solvent extraction section of Yunnan Tianan Chemical Co., Ltd. The internal control requirements for the products in this section are as follows: Color requirement: The Hazen color value of the phosphoric acid phase to be tested should be ≤15, meeting the industrial first-grade refined phosphoric acid standard; Concentration requirements: The feed phosphoric acid concentration in the extraction section is 45%~50%, corresponding to a detection concentration of 4.5~5.0 mol / L after dilution (4500~5000 μmol / L, which falls within the linear range of the standard curve after 1000-fold dilution). Compared to requirements: the extraction system is compared (V) 磷酸 / V 有机 The acceptable fluctuation range is 0.2~0.4, and the acceptable fluctuation range is 0.17~0.5. Any deviation from this range is considered a process abnormality.

[0027] IV. Testing of Single Batch of Samples This embodiment only tests the mixed solution samples from the same batch in the extraction section. The testing process is as follows: Sample pretreatment: Take 500 mL of the mixture sample from the extraction tank of this batch, let it stand for 2 min to remove large particulate impurities, take the uniform mixture in the middle layer as the sample to be tested, and divide it into 6 parallel samples for later use. Compared to detection: The top hydrophobic electrode, the middle composite electrode, and the bottom hydrophilic electrode were vertically immersed into the sample from top to bottom, with a fixed distance of 10 mm between the three electrodes. The impedance signal was obtained using AC impedance spectroscopy (frequency range 1Hz~1kHz, sinusoidal amplitude 10mV). The real part of the impedance was automatically analyzed and separated using an electrochemical workstation, where Rtop = 92.3kΩ, Rmiddle = 41.6kΩ, and Rbottom = 1.2kΩ. The calculated Rsample of the sample was (92.3 + 41.6 + 1.2) / 3 = 45.03kΩ. Substituting... The formula for calculating the ratio is as follows: For organic phosphoric acid samples, the calculated ratio for this batch of samples is 0.39, which meets the internal control requirement of 0.2~0.4. Color and concentration detection: The above-mentioned sample was centrifuged to obtain the phosphoric acid phase. After 1000-fold dilution, the color and concentration were detected using the same differential pulse voltammetry parameters plotted according to the standard curve. The reduction peak current was obtained and substituted into the corresponding regression equation to calculate that the measured color of this batch of samples was 12.4 Hazen, which meets the internal control requirement of ≤15 Hazen; the measured phosphoric acid mass concentration was 47.2%, which meets the internal control requirement of 45%~50%.

[0028] V. Verification of the function of the temperature compensation unit, compensation method and effect data 1. Temperature Compensation Principles and Methods The temperature compensation unit of this invention strictly follows The temperature-peak current correction formula is used to correct the reduction peak current signal of the colorimetric and concentration detection units, where: I corr To correct the current, I meas The measured current is given by α = 0.003 / ℃, the temperature coefficient is given by T, the measured medium temperature is given by T0 = 25℃, and the reference temperature is given by T0 = 25℃. Since the actual operating temperature of the extraction section is 60~75℃, there is a significant deviation from the 25℃ reference temperature. Increased temperature leads to a faster electrochemical reaction rate, causing the measured reduction peak current to deviate from the reference value, ultimately resulting in positive deviations in the color and concentration detection results. The temperature compensation unit, using the above formula, can correct the detection errors caused by temperature fluctuations in real time, ensuring detection accuracy under high-temperature conditions.

[0029] 2. Temperature Compensation Experiment Design Take the same batch of phosphate phase samples to be tested, and perform parallel detection using a colorimetric detection unit and a concentration detection unit at 25℃ (reference temperature), 35℃, 45℃, 55℃, 65℃, and 75℃ (extreme temperature of the extraction section). Repeat the detection three times at each temperature point and take the average value. First, record the uncompensated measured peak current and the corresponding calculated value. Then, perform temperature compensation using the above formula, record the compensated corrected peak current and the corresponding calculated value, and compare the relative error between the compensation and the 25℃ reference value.

[0030] 3. Test data before and after temperature compensation Table 1 Comparison of colorimetric detection data before and after temperature compensation. ; Table 2 Comparison of concentration detection data before and after temperature compensation. ;

[0031] 4. Data Explanation and Compensation Effect Without temperature compensation, as the detection temperature increases from 25℃ to 75℃, the maximum relative error of colorimetric detection reaches 19.35%, and the maximum relative error of concentration detection reaches 11.02%. Temperature fluctuations have a significant impact on the detection results, exceeding the allowable error range for industrial testing. After correction by the temperature compensation unit of this invention, the maximum relative error of colorimetric detection is reduced to 1.21%, the maximum relative error of concentration detection is reduced to 0.44%, and the detection error of all temperature points is controlled within 1.5%, which fully meets the high-precision detection requirements of industrial production. The test results prove that the temperature compensation unit of the present invention can effectively correct the detection deviation caused by the high temperature condition in the extraction process, significantly improve the stability and detection accuracy of the sensor in the actual production environment, and solve the industry pain point of distorted detection results under high temperature and high acid conditions.

[0032] VI. Overall Sensor Performance Verification In this embodiment, the sensor's detection response time for this batch of samples is ≤8s, the colorimetric detection error is ≤2.4 Hazen, the comparison detection error is ≤2.2%, and the concentration detection error is ≤2.0%, which meets the performance indicators of the invention.

[0033] Example 2: The sensor preparation and application methods in this embodiment are the same as in Embodiment 1, except that: only the concentration and color of the same batch of refined phosphoric acid samples in the oxidation and decolorization process are detected, and comparison is not detected; I. Sensor Fabrication Preparation of working electrode I for the colorimetric detection unit: Aminotrimethylenephosphonic acid was dissolved in an acetate-sodium acetate buffer solution at a ratio of 0.6 g / L, and after electropolymerization modification, a 28 nm organic group selective chelating coating was formed. Coating amount for working electrode II of the concentration detection unit: 4 μL / cm². 2 The bismuth film thickness is 12 nm; the sodium molybdate coating amount is 0.3 mg / cm². 2 Reference electrode II is a saturated calomel electrode.

[0034] II. Standard Curve The preparation method is the same as in Example 1. The colorimetric standard curve is: Hazen = 22.99 × [organic groups] + 5.09, R... 2 =0.994. Concentration standard curve: C=0.093×I+4.225, R 2 =0.987.

[0035] III. Internal Control Requirements for Oxidation and Decolorization Section The sample to be tested came from the wet phosphoric acid oxidation and decolorization section. The quality control requirements for this section are as follows: Colorimetric requirement: Hazen ≤ 20; Concentration requirement: Phosphoric acid mass concentration 84.0%~86.0%; This section does not require testing compared to other sections.

[0036] IV. Single Batch Sample Testing Take 500 mL of purified phosphoric acid sample from the same batch in the oxidation and decolorization section, let it stand and filter, and then perform color and concentration tests: For colorimetric detection, the reduction peak current was measured using the differential pulse voltammetry method. After temperature compensation, the current was input into the standard curve, and the measured colorimetric value was 16.8 Hazen, which meets the requirement of ≤20 Hazen.

[0037] Concentration detection was performed, and the reduction peak current was measured after dilution. After temperature compensation, the actual concentration was calculated to be 85.1 wt%, which meets the requirement of 84.0%~86.0%.

[0038] V. Function, Compensation Method, and Effect of Temperature Compensation Unit 1. Temperature compensation method The actual temperature in the oxidation and decolorization section is 50~80℃, which is much higher than the 25℃ benchmark, causing the peak current to be too high and the result to be too large. The temperature compensation unit collects the sample temperature T in real time, automatically corrects the reduction peak current according to the formula in claim 2, and then calculates the color and concentration to eliminate temperature drift.

[0039] 2. Experimental Design The same batch of samples were tested at 25℃, 40℃, 50℃, 60℃, 70℃ and 80℃, with three parallel tests for each group, and the error between the results before and after compensation and the baseline value (25℃) was compared.

[0040] 3. Temperature compensation test data Table 3 Comparison of Temperature Compensation for Colorimetric Detection

[0041] Table 4 Comparison of Temperature Compensation for Concentration Detection ; 4. Data Description Without compensation, the increase in temperature caused the maximum deviation of color to be as high as +19.64% and the concentration to be as high as +3.76%, which are close to exceeding the standard. After compensation, the color error is ≤0.83%, the concentration error is ≤0.16%, and the results are stable and accurate; The temperature compensation unit proves that it can effectively eliminate the interference of high temperature on electrical signals and ensure high-precision detection in the decolorization process.

[0042] VI. Test Results and Performance In this embodiment, the sensor can detect a single batch of samples in the oxidation and decolorization process with a response time of ≤9s, a color error of ≤1.8 Hazen, and a concentration error of ≤1.2%.

Claims

1. A colorimetric concentration detection sensor, characterized in that, Includes a colorimetric detection unit, a contrast detection unit, and a concentration detection unit; The colorimetric detection unit consists of a working electrode I, a reference electrode I, and an auxiliary electrode I. The working electrode I is a platinum electrode with a surface-modified organic selective chelating coating. The preparation of the platinum electrode with the surface-modified organic selective chelating coating is as follows: (1) Select platinum sheets with a purity ≥99.99%, and polish them step by step with 800 mesh, 1200 mesh and 2000 mesh silicon carbide sandpaper. Then, clean them with anhydrous ethanol for 10-20 min and deionized water for 8-12 min. Finally, activate them in 0.5 mol / L sulfuric acid solution by cyclic voltammetry. The scanning range is -0.2~1.2 V, the scanning rate is 40-60 mV / s, and the cycle is 20 times. (2) Dissolve the organophosphorus chelating agent in an acetate-sodium acetate buffer solution at pH=3.0 at a ratio of 0.5-1.0 g / L. Immerse the activated platinum substrate in the solution and electropolymerize it at a constant potential of 0.9-1.2 V for 25-35 min. Then, cure it in a vacuum drying oven at 55-65℃ for 1-3 h to form an organic group selective chelating coating with a thickness of 20-50 nm. The organophosphorus chelating agent is aminotrimethylenephosphonic acid. Compared to the detection unit which consists of a top hydrophobic electrode, a middle composite electrode, and a bottom hydrophilic electrode; the top hydrophobic electrode is fabricated as follows: (1) Using platinum sheets with a purity of ≥99.99% as the base, the substrate is ultrasonically cleaned with anhydrous ethanol for 8-12 min, rinsed with deionized water, and then dried at 110-130℃ for 25-35 min. (2) Place the pretreated substrate in a vapor deposition furnace and deposit polytetrafluoroethylene micro powder as raw material at 380-400℃ and vacuum degree ≤10Pa for 30-60 min, controlling the film thickness to be 50-100nm. (3) After deposition, allow the film to cool naturally to room temperature, then anneal at 200°C for 1 hour to ensure that the adhesion between the film and the substrate is ≥5 N / cm. 2 The contact angle reaches 110°±5°; The preparation of the central composite electrode is as follows: (1) Using a platinum sheet with a purity of ≥99.99% as the substrate, the substrate is polished to a mirror finish by successively using 800-mesh, 1200-mesh, and 2000-mesh silicon carbide sandpaper. Then, it is ultrasonically cleaned with anhydrous ethanol for 10-20 minutes, ultrasonically cleaned with deionized water for 8-12 minutes, and dried with nitrogen for later use. (2) The platinum sheet surface after step (1) is etched using femtosecond laser etching technology. The etching parameters are: laser power 10-15W, scanning rate 400-600mm / s, etching depth 15-25μm, trench width 40-60μm, and trench spacing 40-60μm to form a uniform mesh-like trench structure. After etching, the surface is ultrasonically cleaned with deionized water for 4-6 minutes to remove etching residue. (3) Place the etched platinum sheet in a 0.4-0.6 mol / L sulfuric acid solution and activate it using cyclic voltammetry. The scanning range is -0.2~1.2V, the scanning rate is 40-60mV / s, and the cycle is 20 times. After activation, rinse it with deionized water and blow it dry with nitrogen to obtain the middle composite electrode. The bottom hydrophilic electrode is prepared as follows: (1) Using a platinum sheet with a purity of ≥99.99% as the substrate, the substrate is polished to a mirror finish by successively using 800-mesh, 1200-mesh, and 2000-mesh silicon carbide sandpaper. Then, it is ultrasonically cleaned with acetone for 8-12 minutes, anhydrous ethanol for 8-12 minutes, and deionized water for 8-12 minutes to remove surface oil and impurities. It is then dried with nitrogen for later use. (2) Immerse the pretreated platinum sheet in a hydrogen peroxide solution with a mass concentration of 20-40% and soak it at room temperature in the dark for 25-35 minutes to form a uniform PtO / PtO2 mixed platinum oxide hydrophilic layer on the surface of the platinum sheet. After taking it out, rinse it repeatedly with deionized water to remove residual hydrogen peroxide. (3) Place the oxidized platinum sheet in a vacuum drying oven at 55-65℃ and dry for 1-2 hours. Then, soak it in a phosphoric acid solution with a mass concentration of 80-90% at room temperature for 70-75 hours for aging treatment. After taking it out, rinse and dry it to ensure that the contact angle of the electrode surface is ≤30° and the change in contact angle after soaking is ≤5°. The concentration detection unit consists of working electrode II, reference electrode II, and auxiliary electrode II. The working electrode II is prepared as follows: (1) Multi-walled carbon nanotubes and reduced graphene oxide were mixed at a mass ratio of 1:1-3, and deionized water was added for ultrasonic dispersion to form a suspension with a concentration of 1-3 mg / mL. The suspension was then coated onto the surface of a glassy carbon electrode using a drop-coating method, with a coating amount of 4-6 μL / cm. 2 Dry at 75-85℃ for 1 hour to obtain the substrate; (2) The substrate was placed in a 0.1 mol / L bismuth nitrate solution and a bismuth film with a thickness of 10-20 nm was formed by constant potential deposition at a potential of -0.6 V for 10 min. (3) The coating amount is 0.2-0.6 mg / cm². 2 Sodium molybdate was dispersed in a 2-3% (w / w) chitosan solution and ultrasonically dispersed to form a uniform slurry. This slurry was then coated onto the surface of a bismuth film by spraying and crosslinked and cured at 100°C for 1-2 hours to obtain working electrode II.

2. The colorimetric contrast density detection sensor according to claim 1, characterized in that: It also includes a temperature compensation unit, which comprises a temperature sensor and compensates for the reduction peak current signals detected by the colorimetry detection unit and the concentration detection unit based on a temperature-peak current correction formula, the formula being: ； Among them I corr To correct the current, I meas For measuring current, α = 0.003 / ℃ is the temperature coefficient, T is the measured temperature, and T0 = 25℃ is the reference temperature.

3. The colorimetric contrast density detection sensor according to claim 1, characterized in that: It also includes a control module, which monitors impedance abnormalities R>200kΩ or R<500Ω and temperature exceeding the limit>120℃, enabling real-time early warning with a response time ≤2s.

4. The application of the colorimetric concentration detection sensor according to claim 1 in the detection of phosphoric acid colorimetric, concentration, and concentration.

5. The application according to claim 4, characterized in that: When using the concentration detection unit, the working electrode II, reference electrode II, and auxiliary electrode II are placed in a standard solution of phosphoric acid with a concentration of 0-600 μmol / L, using an acetate-sodium acetate buffer solution with pH=3.0 as the solvent. Differential pulse voltammetry is used for detection, with parameters of pulse width 50 ms, scan rate 10 mV / s, and scan voltage -0.2~1.0 V. The reduction peak current of the phosphomolybdic heteropoly acid is obtained. A standard curve of phosphoric acid concentration is plotted with phosphoric acid concentration on the x-axis and reduction peak current on the y-axis to obtain the regression equation and determine the linear relationship between phosphoric acid concentration and reduction peak current. The sample to be tested is placed in an electrolytic cell and detected using the above method to obtain the reduction peak current corresponding to phosphoric acid in the sample. This current is then substituted into the regression equation to calculate the phosphoric acid concentration in the sample.

6. The application according to claim 4, characterized in that: When using the colorimetric detection unit, 85% industrial refined phosphoric acid is used as the solvent to prepare a standard solution with a concentration gradient of 0.1-5.0 ppm for the colorimetric organic compounds. The composition and mass percentage of the colorimetric organic compounds are 40%-50% 2-ethylhexylphosphonic acid, 30%-40% tributyl phosphate, and 10%-20% phenylphosphonic acid. The working electrode I, reference electrode I, and one end of the auxiliary electrode I are placed in the standard solution, and the detection is performed by differential pulse voltammetry with the following parameters: pulse width 50 ms, scan rate 10 mV / s, and scan voltage 0-0.8 V. The reduction peak current of the chromogenic organic compound was obtained, and the reduction peak currents of phosphoric acid aqueous solutions of different concentrations were converted into phosphoric acid Hazen color values. A standard curve of phosphoric acid color was plotted with the phosphoric acid Hazen color value on the x-axis and the reduction peak current on the y-axis to obtain the regression equation and determine the linear relationship between phosphoric acid color and reduction peak current. The sample to be tested was placed in an electrolytic cell and detected by an electrochemical workstation according to the above method to obtain the reduction peak current corresponding to phosphoric acid in the sample. The reduction peak current was then substituted into the regression equation to calculate the phosphoric acid color in the sample.

7. The application according to claim 4, characterized in that: In contrast to the detection unit, the top hydrophobic electrode, the middle composite electrode, and the bottom hydrophilic electrode are arranged sequentially from top to bottom in the sample to be tested, with equal spacing between the three electrodes. Impedance signals are obtained using AC impedance spectroscopy, and the real part of the impedance, R, is automatically analyzed by an electrochemical workstation. The real parts of the impedance, Ra, are obtained for the top hydrophobic electrode, the middle composite electrode, and the bottom hydrophilic electrode, respectively. 顶 R 中 R 底 The sample to be tested The detection unit was placed in a 1:1 volume ratio mixture of tributyl phosphate (TBP) and kerosene. AC impedance spectroscopy was used for detection, and the stable real part of the impedance of the top hydrophobic electrode was scanned and taken as R. 有机 The detection unit was placed in 50% industrial refined phosphoric acid by mass concentration, and the same AC impedance method was used for detection. The real part of the stable impedance of the bottom hydrophilic electrode was scanned and taken as R. 磷酸 ; Calculate the comparison according to the following formula : ； When the ratio is in the range of 0.17 to 0.5, the sample meets the production requirements.

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