Calcium ion content detection method based on desulfurization gypsum dissolution experiment

Abstract

The invention discloses a calcium ion content dynamic detection method based on a desulfurization gypsum dissolution experiment. The method comprises the following steps: establishing a standard working curve of calcium ion concentration and absorbance value in advance; building an online detection system consisting of a reaction container, a microporous filter head, a precise peristaltic pump, a dynamic mixer and a flow-type detection pool; the method comprises the following steps: continuously pumping out clear liquid in a reaction container by using a precision peristaltic pump in a desulfurization gypsum dissolving process, mixing the clear liquid with a mixed color developing reagent on line, and enabling the mixed liquid to flow into a flow-type detection pool of an ultraviolet and visible spectrophotometer for real-time dual-wavelength absorbance detection; and finally, converting the absorbance value subjected to background correction into calcium ion concentration through a standard working curve, and drawing a dissolution kinetics curve. According to the method, in-situ, continuous and high-precision monitoring of the calcium ion concentration in the desulfurization gypsum dissolving process is achieved, and the defects that a traditional interruption sampling method is tedious in operation, large in system disturbance and poor in anti-interference capacity are overcome.

Description

Technical Field

[0001] This invention relates to the field of analytical chemistry, and in particular to a method for detecting calcium ion content in a desulfurized gypsum dissolution experiment. Background Technology

[0002] Desulfurized gypsum is a byproduct of the flue gas desulfurization process in coal-fired power plants, and its main component is calcium sulfate dihydrate. In the resource utilization of desulfurized gypsum, such as as a cement retarder or in the production of building gypsum powder, its solubility characteristics are a key parameter affecting its application performance. Accurately determining the calcium ion dissolution kinetics of desulfurized gypsum in specific solutions (such as water or simulated acid rain environments) is crucial for evaluating its reactivity, purity, and suitability.

[0003] Currently, common methods for determining calcium ion content in solutions include ethylenediaminetetraacetic acid (EDTA) titration, atomic absorption spectrometry, and electrochemical methods based on calcium ion selective electrodes. However, in the specific application scenario of desulfurized gypsum dissolution kinetics experiments, these existing technologies all have significant limitations. First, while EDTA titration is simple to operate, it is an endpoint detection method and cannot achieve real-time, online monitoring of the dissolution process. To plot a complete dissolution kinetic curve, researchers must interrupt the dissolution process multiple times at different time points, take samples, and perform manual titration. This process is cumbersome, time-consuming, and prone to human error. More seriously, each sampling changes the liquid-solid ratio of the reaction system, disrupting the continuity and consistency of the dissolution process and leading to distorted kinetic data. Second, although atomic absorption spectrometry is highly accurate, the equipment is expensive, and it has high requirements for the operating environment and personnel. It also struggles to achieve in-situ, continuous, real-time detection, and its complex sample pretreatment makes it unsuitable for monitoring rapid, dynamic dissolution processes. Furthermore, while the calcium ion selective electrode method can theoretically be used for real-time monitoring, in practical applications, especially in complex systems such as desulfurized gypsum dissolution, the electrode is susceptible to interference from other coexisting ions in the solution, such as magnesium and strontium ions, leading to a decrease in measurement accuracy. Simultaneously, the electrode's response time, drift issues, and potential membrane fouling or physical damage in high-solids-content suspensions all limit its reliability and durability in this scenario.

[0004] Therefore, there is an urgent need in this field for a method that can be applied to desulfurized gypsum dissolution experiments and achieve in-situ, continuous, high-precision, and highly interference-resistant dynamic detection of calcium ion content, so as to overcome the inherent defects of existing technologies in process monitoring, data accuracy, and ease of operation. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides a method for detecting calcium ion content in a desulfurized gypsum dissolution experiment, the method comprising the following steps: Step 1: Establish a standard working curve for calcium ion concentration versus absorbance value; Step 2: Construct a dynamic dissolution and online detection system for desulfurized gypsum. The system includes a reaction vessel, a microporous filter head, a first precision peristaltic pump, a mixed colorimetric reagent storage container, a second precision peristaltic pump, a dynamic mixer, a flow-through detection cell, and a UV-Vis spectrophotometer. The microporous filter head is submerged below the liquid surface of the reaction vessel. The outlet of the microporous filter head is connected to the inlet of the first precision peristaltic pump via a fluid conduit. The outlet of the first precision peristaltic pump and the mixed colorimetric reagent storage container are connected to the inlet of the dynamic mixer via a fluid conduit. The second precision peristaltic pump is used to pump the mixed colorimetric reagent from the mixed colorimetric reagent storage container into the dynamic mixer. The outlet of the dynamic mixer is connected to the inlet of the flow-through detection cell via a fluid conduit. The flow-through detection cell is fixedly installed in the sample chamber of the UV-Vis spectrophotometer. Step 3: Conduct a desulfurized gypsum dissolution experiment and simultaneously implement online calcium ion detection. Add the desulfurized gypsum sample and dissolving solvent to the reaction vessel, start the dissolution process, and simultaneously start the first precision peristaltic pump and the second precision peristaltic pump. The filtered clear liquid and the mixed colorimetric reagent are mixed and reacted in the dynamic mixer according to a preset ratio and flow into the flow-through detection cell. The UV-Vis spectrophotometer continuously measures the absorbance value at the maximum absorption wavelength and the reference wavelength, and calculates the real-time absorbance data after background correction. Step 4: Substitute the background-corrected real-time absorbance data into the standard working curve to calculate the calcium ion concentration before dilution, and plot the calcium ion dissolution kinetic curve.

[0006] Preferably, in step 2, the filter medium of the microporous filter head is sintered metal or sintered polymer, and the average pore size of the microporous filter head ranges from 0.2 micrometers to 0.8 micrometers.

[0007] Preferably, in step 2, the ratio of the flow rate of the first precision peristaltic pump to the flow rate of the second precision peristaltic pump is configured as a fixed dilution ratio; the process of determining the dilution ratio includes: calculating the required dilution factor based on the upper limit of the linear range of the standard working curve and the expected calcium ion saturation concentration in the desulfurized gypsum solution, thereby setting the flow rate ratio of the first precision peristaltic pump to the second precision peristaltic pump.

[0008] Preferably, in step 1, the step of establishing a standard working curve of calcium ion concentration versus absorbance value includes: Step 1.1: Prepare a series of calcium ion standard solutions of known concentrations, wherein the matrix solvent of the calcium ion standard solutions is exactly the same as the dissolving solvent used in Step 3; Step 1.2: Add a masking agent, a pH buffer solution, and a calcium ion colorimetric reagent sequentially to each of the calcium ion standard solutions. The masking agent is triethanolamine, the pH buffer solution is an ammonia-ammonium chloride buffer solution or a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution, and the calcium ion colorimetric reagent is a calcium carboxylic acid indicator. Step 1.3: Use a UV-Vis spectrophotometer to measure the absorbance of each standard solution after the reaction at the maximum absorption wavelength; Step 1.4: Plot the standard working curve with calcium ion concentration on the x-axis and absorbance value on the y-axis.

[0009] Preferably, in step 1.2, the mixed colorimetric reagent is prepared by pre-mixing the masking agent, the pH buffer solution, and the calcium ion colorimetric reagent, and stored in the mixed colorimetric reagent storage container; the pH buffer solution maintains the pH of the colorimetric reaction environment in the range of 9.5 to 12.5.

[0010] Preferably, in step 3, the UV-Vis spectrophotometer adopts a dual-wavelength detection mode, wherein the maximum absorption wavelength is the characteristic absorption peak wavelength of the complex formed by the calcium ions and the colorimetric agent, and the reference wavelength is the wavelength at which the complex has virtually no absorption while the system background has absorption; the real-time absorbance data after background correction is obtained by subtracting the absorbance value measured at the reference wavelength from the absorbance value measured at the maximum absorption wavelength.

[0011] Preferably, the process of determining the reference wavelength includes: scanning the absorption spectrum of the complex formed by the calcium ions and the colorimetric agent in the fully reacted state, and selecting a region wavelength with low and flat absorbance on the long-wavelength side or short-wavelength side of the maximum absorption peak as the reference wavelength.

[0012] Preferably, in step 2, the dynamic mixer is a spiral tube mixer or a microchannel mixer, and the internal volume of the dynamic mixer is designed such that the residence time of the mixed liquid is sufficient to complete the colorimetric reaction between the calcium ions and the colorimetric agent.

[0013] Preferably, in step 3, the reaction vessel is placed in a constant temperature water bath shaker, and the dissolution process is carried out at a constant temperature and oscillation speed; the start-up of the first precision peristaltic pump and the second precision peristaltic pump is synchronized with the start of the dissolution process.

[0014] Preferably, in step 2, the waste liquid flowing out of the outlet of the flow-through detection cell is guided to a separate waste liquid collection container, or selectively returned to the reaction vessel through a three-way valve to maintain a constant total volume of the reaction system.

[0015] The beneficial effects of this invention are: 1. This invention constructs a closed online detection loop through the linkage design of "microporous filter head - precision peristaltic pump - dynamic mixer - flow-through detection cell". It can automatically and continuously extract and analyze the solution during the continuous oscillation and dissolution of desulfurized gypsum, completely avoiding the changes in the liquid-solid ratio and human operation errors caused by the need to interrupt the reaction and take multiple samples in traditional methods. Thus, complete and continuous data that can truly reflect the dissolution kinetics are obtained. 2. The online filtration of this invention removes suspended solid particles immediately before analysis, fundamentally eliminating the influence of turbidity on photometric analysis; dual-wavelength detection effectively eliminates interference from sample substrate color, reagent background, and microbubbles by subtracting background absorption from characteristic absorption signals. Furthermore, the pre-addition of a masking agent and pH buffer solution to the mixed colorimetric reagent ensures the specificity and stability of the colorimetric reaction, making the method highly reliable even in complex systems. 3. The entire detection process of this invention, from sample extraction and processing to signal acquisition and data processing, is fully automated without any manual intervention. A single setup allows for monitoring of the entire dissolution cycle, freeing researchers from tedious repetitive operations, significantly reducing human error, and improving the reproducibility and throughput of experimental data. This provides an efficient means for rapid, batch evaluation of the dissolution performance of desulfurized gypsum. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of the steps of the method of the present invention; Figure 2 A flowchart illustrating the steps involved in establishing a standard working curve of calcium ion concentration versus absorbance value using the method of this invention. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0019] Please see Figures 1-2This invention provides a method for detecting calcium ion content in a desulfurized gypsum dissolution experiment. In step 1, a series of calcium ion standard solutions of known concentrations are first prepared. The matrix solvent of the standard solutions should be the same as the dissolving solvent used in the experiment to ensure that no external interference is introduced during the experiment. A masking agent, pH buffer solution, and calcium ion colorimetric agent are added to each standard solution to form a reaction solution, which effectively stabilizes the colorimetric reaction and provides good optical absorption. The absorbance of each standard solution is measured at the maximum absorption wavelength using a UV-Vis spectrophotometer, and the absorbance value is recorded. By repeatedly measuring the absorbance of these standard solutions of known concentrations, a standard working curve between calcium ion concentration and absorbance can be plotted.

[0020] In step 2, a complex online detection system is constructed, comprising key components such as a reaction vessel, a microporous filter head, a precision peristaltic pump, a dynamic mixer, a flow-through detection cell, and a UV-Vis spectrophotometer. The reaction vessel holds the desulfurized gypsum sample and the dissolving solvent; the microporous filter head removes solid impurities from the solution, ensuring the purity of the sample dissolution process. First and second precision peristaltic pumps control the flow rate of the solution and the chromogenic reagent, delivering them to the dynamic mixer via fluid conduits to ensure thorough mixing of the reaction liquids. The dynamic mixer ensures sufficient reaction between the chromogenic reagent and calcium ions in the solution. The flow-through detection cell is fixedly installed in the sample chamber of the UV-Vis spectrophotometer, facilitating continuous monitoring of absorbance changes in the solution and reflecting real-time changes in calcium ion concentration.

[0021] In step 3, the desulfurized gypsum sample and dissolving solvent are added to the reaction vessel to initiate the dissolution process. Simultaneously, the first and second precision peristaltic pumps begin operation, feeding the filtered clarified liquid and colorimetric reagent into a dynamic mixer at a preset ratio for mixing. The mixed liquid flows into a flow-through detection cell, where a UV-Vis spectrophotometer continuously measures the absorbance value using a dual-wavelength detection mode at both the maximum absorption wavelength and the reference wavelength. Real-time absorbance values ​​are background-corrected to eliminate external optical interference and ensure measurement accuracy. Through this continuous data acquisition, the dynamic changes in calcium ion concentration can be accurately tracked.

[0022] Finally, in step 4, the background-corrected real-time absorbance data is substituted into the standard working curve, and the calcium ion concentration before dilution is calculated based on the linear relationship of the curve. By plotting these concentration data into a calcium ion dissolution kinetic curve, the rate of calcium ion release and dissolution characteristics during the dissolution of desulfurized gypsum can be understood in detail.

[0023] The online detection method for calcium ion content of the present invention can not only effectively monitor the calcium ion dissolution process, but also provide reliable data support for the optimization of the desulfurized gypsum dissolution process.

[0024] In one possible implementation, the design of the microporous filter head and the filter media used in step 2 are crucial. To effectively remove solid impurities from the solution and prevent particulate matter from interfering with calcium ion measurement, it is necessary to select appropriate filter materials and pore size ranges.

[0025] Microporous filter heads use sintered metal or sintered polymer as the filter medium. Sintered metal has high strength and corrosion resistance, making it suitable for high-temperature and complex chemical reaction environments. Sintered polymer has good chemical inertness and low weight, making it suitable for experimental conditions with lower temperatures or high requirements for chemical stability. Both materials can effectively withstand the flow pressure of liquids during experiments, ensuring long-term stable use.

[0026] The average pore size of the microporous filter head is set to range from 0.2 micrometers to 0.8 micrometers. This pore size range can effectively filter out tiny solid particles that may be generated during the dissolution of desulfurized gypsum, such as precipitates and incompletely dissolved impurities. A pore size that is too large may fail to remove smaller particles, while a pore size that is too small may slow down the solution flow rate, affecting experimental efficiency. Therefore, selecting an appropriate pore size range can balance the filtration effect with the experimental flow rate, ensuring the efficiency and accuracy of the experiment.

[0027] Choosing sintered metal or sintered polymer as the filter medium for the microporous filter head and setting an appropriate pore size range can effectively improve the sample purity and experimental efficiency in the desulfurized gypsum dissolution experiment, while ensuring high accuracy and stability of calcium ion content detection.

[0028] In one possible implementation, in step 2, the flow rate ratio of the first precision peristaltic pump to the second precision peristaltic pump is set to a fixed dilution ratio. The determination of this ratio is crucial to ensure the accuracy of calcium ion content measurement in the experiment.

[0029] Specifically, the determination of the dilution ratio is first based on the upper limit of the linear range of the standard working curve. The standard working curve is a curve plotted using calcium ion standard solutions of known concentrations; the upper limit of the linear range is the highest value in the interval within which calcium ion concentration can be accurately measured. Secondly, considering the expected saturation concentration of calcium ions in the desulfurized gypsum solution, the required dilution factor is calculated. The saturation concentration represents the maximum concentration of calcium ions in the solution; exceeding this concentration may cause supersaturation precipitation, affecting the experimental results. By calculating the required dilution factor, the flow rate ratio of the first and second precision peristaltic pumps is determined to achieve a suitable dilution effect during the mixing of the colorimetric reagent and the solution, ensuring that the calcium ion concentration falls within the linear range of the standard working curve, thereby obtaining accurate absorbance values.

[0030] Based on the dilution factor calculated above, the flow rate ratio of the two pumps is adjusted. Specifically, the first precision peristaltic pump is responsible for delivering the filtered solution to the mixer through a fluid conduit, while the second precision peristaltic pump is responsible for delivering the chromogenic reagent to the mixer. Adjusting the flow rate ratio directly affects the mixing ratio of the chromogenic reagent and the solution, as well as the reaction concentration, which is crucial for the effectiveness of the calcium ion colorimetric reaction. By setting a fixed dilution ratio, the colorimetric reaction is ensured to proceed within a controllable concentration range, avoiding the impact of excessively high or low calcium ion concentrations on the accuracy of the measurement results.

[0031] The design using a fixed flow rate ratio and a reasonable dilution ratio not only ensures that the calcium ion concentration is controlled within an accurate range, but also improves experimental efficiency and system stability, thus providing strong support for the accurate measurement of calcium ion concentration.

[0032] In one possible implementation, a series of calcium ion standard solutions of known concentrations are prepared. The matrix solvent of this series of solutions must be exactly the same as the solvent of the desulfurized gypsum solution used in step 3 to ensure that the physicochemical properties of the solutions remain consistent during actual measurements, avoiding interference or errors caused by different solvents.

[0033] A masking agent, a pH buffer solution, and a calcium ion colorimetric reagent are added sequentially to each standard calcium ion solution. The masking agent, triethanolamine, prevents other ions in the solution from reacting with calcium ions and interfering with the determination. The pH buffer solution maintains a stable pH; either an ammonia-ammonium chloride buffer solution or a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution can be used to ensure that the pH value remains within a suitable range during the calcium ion reaction. The calcium ion colorimetric reagent is a calcium carboxylic acid indicator that forms a colored complex with calcium ions, facilitating absorbance measurement using a UV-Vis spectrophotometer.

[0034] Using a UV-Vis spectrophotometer, the absorbance value at the maximum absorption wavelength after the reaction of each standard solution was measured. This wavelength is the maximum wavelength of light absorbed by the complex after the calcium ion chromogenic agent reacts with calcium ions. By accurately measuring the absorbance, the correlation between calcium ion concentration and absorbance can be obtained.

[0035] Based on the calcium ion concentration and absorbance values ​​obtained in step 1.3, a standard working curve is plotted. In this curve, the horizontal axis represents the known calcium ion concentration, and the vertical axis represents the corresponding absorbance value. Using this curve, the calcium ion concentration in an unknown solution can be calculated in subsequent experiments by measuring the absorbance value.

[0036] By carefully designing and strictly implementing the above steps, the establishment of the standard working curve not only improves the accuracy and reliability of the measurement, but also provides a reliable reference for subsequent experiments, ensuring the efficiency and stability of the calcium ion concentration determination process.

[0037] In one possible implementation, the mixed colorimetric reagent is prepared by pre-mixing a masking agent, a pH buffer solution, and a calcium ion colorimetric reagent in a specific ratio. The masking agent, triethanolamine, prevents unnecessary reactions between other ions and calcium ions, ensuring the accuracy of the detection results. The pH buffer solution stabilizes the pH value during the colorimetric reaction; an ammonia-ammonium chloride buffer solution or a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution can be selected to effectively maintain the acidity or alkalinity of the reaction environment. The calcium ion colorimetric reagent is a calcium carboxylic acid indicator that can form a colored complex with calcium ions, facilitating absorbance measurement with a UV-Vis spectrophotometer.

[0038] Prepared mixed colorimetric reagents should be stored in dedicated storage containers. These containers must be tightly sealed to prevent changes in external environmental factors such as temperature, humidity, or light from affecting the reagent's stability. Contamination must be avoided during storage to ensure consistent reaction results.

[0039] The purpose of the pH buffer solution is to maintain the pH of the colorimetric reaction environment within the range of 9.5 to 12.5. The calcium ion colorimetric reaction is highly sensitive to pH; excessively low or high pH levels will affect the reaction's effectiveness, leading to insufficient color development or incomplete binding of the colorimetric reagent with calcium ions. Precise pH control ensures optimal reaction between the colorimetric reagent and calcium ions, guaranteeing reliable results.

[0040] By pre-mixing the colorimetric reagent and storing it under strictly controlled pH conditions, the consistency of reaction conditions and the stability of the reagents in the experiment were ensured, thereby improving the reliability, accuracy and operational efficiency of the calcium ion content detection method.

[0041] In one possible implementation, the characteristic absorption peak wavelength of the complex formed by calcium ions and the colorimetric agent is first determined. This wavelength corresponds to the point where the absorbance of the complex is maximum, reflecting the change in calcium ion concentration in the solution. During the measurement, the photometer is adjusted to this maximum absorption wavelength, and the absorbance value of the complex is recorded.

[0042] The selection of a reference wavelength should meet two conditions: first, the complex should absorb almost no light at this wavelength; second, the system background should have some absorption. By measuring the absorbance at the reference wavelength, the background interference signal of the system can be obtained, such as solvent absorption, impurity interference, or baseline drift caused by optical path inhomogeneity.

[0043] Real-time background correction is performed using dual-wavelength measurement data. The absorbance value measured at the reference wavelength is subtracted from the absorbance value measured at the maximum absorption wavelength to obtain the background-corrected absorbance data. This data eliminates the influence of system background and reflects only the actual absorbance of the complex formed by the reaction of calcium ions with the chromogenic agent, thereby improving measurement accuracy.

[0044] During the solution reaction, the UV-Vis spectrophotometer continuously collects absorbance data at the maximum absorption wavelength and the reference wavelength. After real-time background correction, a stable and reliable absorbance curve is generated, providing an accurate basis for the calculation of calcium ion concentration.

[0045] Through the above implementation methods, the dual-wavelength background correction technology can significantly improve the accuracy and reliability of calcium ion detection, providing a stable and accurate technical guarantee for calcium ion analysis in desulfurized gypsum dissolution experiments.

[0046] In one possible implementation, under fully reactive conditions, the absorption spectrum of the complex formed by the calcium ions and the chromogenic agent is first scanned. This process involves acquiring the absorption spectrum data of the complex across the entire visible light region (typically 300 to 800 nanometers) using a UV-Vis spectrophotometer. During the scan, the absorbance changes of the complex at different wavelengths are recorded.

[0047] The maximum absorption peak of the complex in the absorption spectrum was determined by scanning the results. This peak wavelength represents the strongest absorption region of the reaction between the complex and calcium ions, and usually corresponds to the wavelength at which the calcium ion concentration is most sensitive to changes in the colorimetric reaction.

[0048] Choose a wavelength with low absorbance and a flat spectrum from either the long-wavelength or short-wavelength side of the maximum absorption peak as the reference wavelength. The absorbance in this region should be as close to zero as possible, and there should be no significant absorption peaks in this wavelength range to avoid other components or background affecting the absorbance measurement. The selected reference wavelength should have good stability and repeatability, ensuring low sensitivity to background interference.

[0049] After determining the reference wavelength, multiple measurements are performed to verify its effectiveness, ensuring that it provides consistent background data under different experimental conditions, serving as a standard wavelength for calibration. In practice, it is necessary to ensure that the absorbance data measured at the reference wavelength reflects only the background signal and is not affected by the absorbance of the complex.

[0050] Precise determination of the reference wavelength helps eliminate systematic errors, optimizes the background correction process of the calcium ion content detection method, improves the accuracy and stability of experimental results, and provides a more reliable technical guarantee for the accurate measurement of calcium ions in the desulfurized gypsum dissolution experiment.

[0051] In one possible implementation, the dynamic mixer is a helical mixer or a microchannel mixer. A helical mixer, through its helical structure within the pipe, effectively guides the fluid to rotate along the helical direction, thereby increasing shear forces and turbulence between the fluids and promoting uniform mixing. A microchannel mixer, on the other hand, employs a microchannel design, allowing liquids to mix rapidly and uniformly as they flow through the narrow space of the microchannels, utilizing high flow rates.

[0052] The internal volume of a dynamic mixer needs to be precisely designed based on the liquid's flow rate and velocity to ensure a sufficiently long residence time within the mixer. Residence time refers to the time the liquid flows within the mixer, sufficient for calcium ions to react with the colorimetric reagent to form a colorimetric complex. Insufficient residence time may lead to incomplete reaction, affecting the accuracy of measurement results. The design must ensure that the mixer volume matches the liquid flow rate at a given flow rate to guarantee complete reaction of the reactants.

[0053] Mixers, through efficient fluid dynamics, facilitate uniform and thorough contact between calcium ions and the reactants in a short time, thereby forming stable colorimetric complexes. In spiral tube mixers, the fluid is forced to rotate and tumble along the pipe walls, increasing the interaction forces between the fluids and improving the reaction rate. In microchannel mixers, due to the high shear force as the fluid flows through narrow channels, the liquid can be rapidly and uniformly mixed, further enhancing reaction efficiency.

[0054] The mixed liquid enters the next detection stage. At this point, the reaction between calcium ions and the colorimetric reagent is basically complete, and the colorimetric properties of the complex are fully activated, allowing for subsequent absorbance measurements or other analyses.

[0055] In one possible implementation, the reaction vessel containing the dissolution reaction solution is first placed in a constant-temperature water bath shaker. The constant-temperature water bath shaker provides a stable temperature control environment, allowing the dissolution process to proceed at a constant temperature, thereby ensuring the stability of the reaction between calcium ions and the colorimetric reagent. Temperature stability is crucial for the dissolution process because temperature fluctuations can lead to inconsistent reaction rates, thus affecting dissolution efficiency and the accuracy of subsequent measurements.

[0056] In a water bath shaker, the temperature is set within a constant range (e.g., the commonly used 30°C to 40°C) to ensure consistent reaction conditions. Simultaneously, the shaking speed is also set to a constant value to ensure thorough and uniform mixing of the solution within the container. This shaking not only helps to increase the dissolution reaction rate but also effectively promotes uniform distribution of reactants, reducing localized temperature or concentration differences.

[0057] Simultaneously with the start of the dissolution process, a first and a second precision peristaltic pump are activated. The first pump supplies the calcium ion source or colorimetric reagent solution to the reaction vessel, while the second pump controls the flow rate and precise dosage of the solution. The activation of these two precision peristaltic pumps is perfectly synchronized with the start of the dissolution process, ensuring that reactants are added to the reaction vessel precisely in the preset proportions during the initial stages of the reaction. This synchronization guarantees the accuracy of reactant addition and avoids any errors during the dissolution process.

[0058] Under constant temperature and oscillation, the dissolution process continues. The flow rate of the precision peristaltic pump can be adjusted as needed to ensure that the concentration and flow rate of the added solution meet the experimental requirements. As the reaction proceeds, calcium ions in the solution react with the colorimetric reagent to form a stable colorimetric complex, which ultimately proceeds to the subsequent detection steps.

[0059] The combined operation of a constant temperature water bath shaker and a precision peristaltic pump ensures that the dissolution process is carried out under stable temperature and precise solution flow conditions, thereby significantly improving the accuracy of calcium ion content detection and the repeatability of the experiment.

[0060] In one possible implementation, during step 2, the waste liquid from the flow-through detection cell needs to be properly treated during the calcium ion content dissolution experiment. The specific steps are as follows: Waste liquid flowing out of the flow-through testing tank is first guided through pipes or a diversion system to a separate waste liquid collection container. The waste liquid collection container is designed as a sealed container to effectively collect and store the waste liquid generated during the experiment, preventing leakage and environmental pollution. This step ensures that the waste liquid collection process is undisturbed by external factors, providing conditions for subsequent waste liquid treatment or recycling.

[0061] In addition to directing the waste liquid to a waste liquid collection container, a three-way valve can be used to achieve selective reflux of the waste liquid. The three-way valve can guide the waste liquid back to the reaction vessel when needed, ensuring that the total volume of the reaction system remains constant. During the experiment, the volume of the solution may change due to the discharge of waste liquid; the reflux design can compensate for this change and avoid excessive fluctuations in the system volume.

[0062] The opening and closing of the three-way valve can be regulated by an automated control system to ensure that the reflux operation occurs at the appropriate time. Specifically, when the volume of the reaction system decreases, the three-way valve automatically switches to reflux mode, guiding the waste liquid back to the reaction vessel to maintain the total volume of the system. The refluxed solution is usually the portion that has participated in the reaction but has not been completely consumed, which effectively reduces the waste of experimental materials while ensuring the continuity of the reaction.

[0063] Without the need for backflow, the waste liquid is piped to a waste liquid collection container for collection. The collection container is typically equipped with a level monitoring device that automatically alarms or triggers equipment to discharge or treat the waste liquid when the volume reaches a set value. The collected waste liquid can then be safely treated or recycled, minimizing its environmental impact.

[0064] Through the embodiments of the present invention, the effective guidance and reflux control of waste liquid not only optimizes the stability of the reaction system, but also improves the utilization rate of experimental resources, while ensuring environmental protection and experimental safety.

[0065] Example: Detection of calcium ion dissolution kinetics in desulfurized gypsum in water 1. Preparation of experimental materials and equipment; Desulfurized gypsum sample: Taken from the flue gas desulfurization system of a coal-fired power plant, dried, ground, and passed through a 100-mesh sieve, then stored in a desiccator for later use. Its main component is calcium sulfate dihydrate, with a content of approximately 95%.

[0066] Dissolving solvent: deionized water, used to simulate the aqueous environment of desulfurized gypsum in cement hydration or building applications.

[0067] Chemical reagents: calcium ion standard solution (1000 mg / L, national standard substance), triethanolamine (analytical grade, as a masking agent), ammonia-ammonium chloride buffer solution (pH=10.0, used to maintain the acidity and alkalinity of the colorimetric reaction), calcium carboxylic acid indicator (analytical grade, as a calcium ion colorimetric agent).

[0068] equipment: Reaction vessel: 500mL stoppered conical flask.

[0069] Microporous filter head: A sintered stainless steel filter head with an average pore size of 0.45 micrometers, which is fixed below the liquid surface inside the conical flask via a threaded interface.

[0070] Peristaltic pumps: Two precision peristaltic pumps (the first precision peristaltic pump is used to extract the clarified liquid, and the second precision peristaltic pump is used to pump the mixed colorimetric reagent), and the pump tubing is made of chemically resistant silicone tubing.

[0071] Dynamic mixer: Spiral tube mixer, 1mm inner diameter, 2m length, made of polytetrafluoroethylene.

[0072] Flow-through detection cell: a quartz flow-through cell with an optical path of 10 mm and a volume of 80 μL.

[0073] UV-Vis spectrophotometer: equipped with a dual-beam detection system and automatic data acquisition software.

[0074] Constant temperature water bath shaker: temperature control accuracy ±0.1°C, oscillation speed adjustable.

[0075] 2. Establishment of standard working curves; First, a series of calcium ion standard solutions were prepared: a 1000 mg / L calcium standard solution was diluted with deionized water to obtain standard solutions with concentrations of 0 mg / L, 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, and 25 mg / L. For each standard solution, 50 mL was taken, and 1 mL of triethanolamine masking agent, 5 mL of ammonia-ammonium chloride buffer solution (pH=10.0), and 1 mL of calcium carboxylic acid indicator solution (1 g / L) were added sequentially. After mixing, the mixture was allowed to stand for 5 minutes to ensure complete colorimetric reaction. The absorbance of each solution was measured using a UV-Vis spectrophotometer at the maximum absorption wavelength of 575 nm (the characteristic absorption peak of the calcium carboxylic acid complex). A standard working curve was plotted with calcium ion concentration on the x-axis and absorbance on the y-axis. The fitting equation was obtained through linear regression: Y = 0.025X + 0.002 (Y is absorbance, X is calcium ion concentration, mg / L), and the linear correlation coefficient R0 was [value missing]. 2 =0.999. This curve is used for quantitative calculations in subsequent real-time detection.

[0076] 3. Setup and parameter settings of the online detection system; The system setup process is as follows: A 500 mL Erlenmeyer flask was fixed in a constant temperature water bath shaker, with the temperature set at 25°C and the shaking speed at 150 rpm to simulate standard dissolution conditions.

[0077] The microporous filter head is installed on the side wall of the conical flask through a sealed interface, ensuring that it is always submerged below the liquid surface. The filter head pore size is selected as 0.45 micrometers, which is determined based on the particle size distribution of desulfurized gypsum particles (mainly between 1-50 micrometers), effectively trapping solid particles while allowing the liquid phase to pass through.

[0078] Connect the outlet of the microporous filter head to the inlet of the first precision peristaltic pump using a silicone tube. The flow rate of the first precision peristaltic pump is set to 2.0 mL / min, a value optimized through preliminary experiments: too low a flow rate will cause detection delay, while too high a flow rate may cause filter head clogging.

[0079] The mixed colorimetric reagent is prepared by pre-mixing triethanolamine, ammonia-ammonium chloride buffer solution and calcium carboxylic acid indicator in a volume ratio of 1:5:1, and is stored in a brown reagent bottle (as a storage container for the mixed colorimetric reagent) to avoid photodegradation.

[0080] The second precision peristaltic pump is used to pump the mixed colorimetric reagent at a flow rate of 0.2 mL / min. The flow rate ratio of the first to the second peristaltic pump (10:1) is used as the dilution ratio. This ratio is calculated based on the upper limit of the linear range of the standard working curve (25 mg / L) and the saturated solubility of desulfurized gypsum (approximately 2.1 g / L, equivalent to approximately 600 mg / L of calcium ions). The dilution factor needs to ensure that the detection concentration falls within the linear range, so the dilution factor is set to 10 times (i.e., the volume ratio of the clarified solution to the reagent is 10:1).

[0081] The dynamic mixer adopts a spiral tube design with an inner diameter of 1 mm and a length of 2 m, ensuring a residence time of approximately 30 seconds for the mixed liquid (calculated based on a total flow rate of 2.2 mL / min and mixer volume). This time is sufficient to complete the colorimetric reaction between calcium ions and the calcium carboxylic acid indicator (the literature shows that the reaction is completed within 10-20 seconds).

[0082] The inlet of the flow-through detection pool is connected to the outlet of the dynamic mixer, and the outlet is guided through a silicone tube to an independent waste liquid collection container (non-backflow) to avoid possible contamination and volume changes.

[0083] The UV-Vis spectrophotometer is set to dual-wavelength detection mode: the maximum absorption wavelength is 575 nm, and the reference wavelength is selected as 650 nm. The reference wavelength is determined based on the absorption spectrum scan: the calcium carboxylic acid complex has strong absorption at 575 nm, while the absorption is almost zero at 650 nm, but the system background (such as reagents or microbubbles) has slight absorption, so the background interference can be eliminated by the difference.

[0084] 4. Dissolution experiment and online detection execution; The specific steps are as follows: Add 5.00g of desulfurized gypsum sample and 400mL of deionized water to the conical flask (the liquid level should be such that the microporous filter head is completely submerged). Immediately seal the system and start the constant temperature water bath shaker, while simultaneously starting the timer.

[0085] The first and second precision peristaltic pumps are started simultaneously. After the clarified solution and mixed colorimetric reagent are mixed in a dynamic mixer, they flow continuously into the flow-through detection cell.

[0086] The UV-Vis spectrophotometer records absorbance values ​​at 575 nm and 650 nm every 10 seconds, and the software automatically calculates the real-time absorbance after background correction (A_corrected = A_575nm - A_650nm). The detection lasts for 120 minutes to ensure coverage of the dissolution equilibrium process.

[0087] Throughout the process, the system remained closed, the temperature was kept stable at 25°C, and the oscillation speed was 150 rpm to ensure consistent dissolution conditions.

[0088] 5. Data conversion and dynamic curve plotting; Substituting real-time absorbance data into the standard working curve equation Y = 0.025X + 0.002, the diluted calcium ion concentration was calculated. Since the system dilution ratio was 10 times, the actual calcium ion concentration was calculated as: C_real = C_diluted × 10, where C_diluted is the concentration calculated from the curve. A calcium ion dissolution kinetic curve was plotted with time on the x-axis and C_real on the y-axis. The curve shows that the calcium ion concentration rises rapidly in the initial dissolution phase (0-30 minutes) and gradually reaches equilibrium in the later stages, consistent with the dissolution kinetics theory of desulfurized gypsum.

[0089] 6. Comparison of proportions and verification of effects; To demonstrate the advantages of this invention, two comparative examples were set up, comparing the conventional interrupted sampling-EDTA titration method and the calcium ion selective electrode method. All experiments used the same desulfurized gypsum sample and were conducted under the same dissolution conditions (25°C, 150 rpm).

[0090] Comparative Example 1 (Interrupted Sampling-EDTA Titration): Shaking was interrupted at 10, 20, 30, 60, 90, and 120 minutes after the start of dissolution. 5 mL of the suspension was drawn using a syringe and immediately filtered through a 0.45 μm filter membrane. The calcium ion concentration of the filtrate was titrated with EDTA standard solution. Resampling was required at each time point, resulting in a cumulative decrease in system volume of 30 mL.

[0091] Comparative Example 2 (Calcium Ion Selective Electrode Method): The calcium ion selective electrode was directly inserted into the reaction vessel, and the potential values ​​were continuously recorded and converted to concentration using a standard curve. The electrode was calibrated according to the instructions before use, but drift occurred during the experiment, requiring recalibration after 60 minutes.

[0092] The table below compares the calcium ion concentration, operational complexity, data continuity, and robustness to interference measured by the three methods at 120 minutes:

[0093] Results Analysis: The concentration values ​​measured by the method of this invention are closer to the theoretical saturation concentration (approximately 210 mg / L), with a small standard deviation, demonstrating high precision and reproducibility. Comparative Example 1 showed a lower concentration due to volume changes and human error; Comparative Example 2 experienced large data fluctuations due to electrode drift and interference. This invention achieves fully automated continuous monitoring, avoids system disturbances, and effectively eliminates interference through dual wavelengths and masking agents.

[0094] 7. Detailed explanation of key features; Microporous filter head pore size selection: In this embodiment, 0.45 micrometers is selected. This value is based on a balance between the minimum particle size of desulfurized gypsum particles (approximately 1 micrometer) and filtration efficiency: pores that are too small are prone to clogging, while pores that are too large cannot effectively trap particles. 0.45 micrometers is an industry standard for suspension filtration, ensuring a clear liquid phase.

[0095] Dilution ratio calculation: First, estimate the maximum leaching concentration of desulfurized gypsum (approximately 600 mg / L). The upper limit of linearity of the standard curve is 25 mg / L, therefore the required dilution factor is at least 24 times (600 / 25). However, to allow for margin and consider detection sensitivity, a 10-fold dilution is selected and achieved by adjusting the pump speed.

[0096] Dual-wavelength detection principle: The selection of the reference wavelength of 650nm is based on full-band scanning. At 575nm, the calcium carboxylic acid complex exhibits the strongest absorption; at 650nm, its absorption is negligible, but there is slight absorption due to reagent and system background. After background reduction, the absorbance only reflects the concentration of the target complex, thus eliminating turbidity or color interference.

[0097] Dynamic mixer design: The helical mixer achieves efficient mixing through laminar and secondary flow. A 30-second residence time is based on reaction kinetics: calcium carboxylic acid and calcium ions react within 10 seconds at pH 10.0, and 30 seconds ensures complete reaction.

[0098] Waste liquid treatment: Waste liquid is not recirculated because the dissolution of desulfurized gypsum may produce trace impurities, and recirculation would introduce cumulative errors. Independent collection is more conducive to data accuracy.

[0099] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0100] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for detecting calcium ion content in a desulfurized gypsum dissolution experiment, characterized in that, The method includes the following steps: Step 1: Establish a standard working curve for calcium ion concentration versus absorbance value; Step 2: Construct a dynamic dissolution and online detection system for desulfurized gypsum. The system includes a reaction vessel, a microporous filter head, a first precision peristaltic pump, a mixed colorimetric reagent storage container, a second precision peristaltic pump, a dynamic mixer, a flow-through detection cell, and a UV-Vis spectrophotometer. The microporous filter head is submerged below the liquid surface of the reaction vessel. The outlet of the microporous filter head is connected to the inlet of the first precision peristaltic pump via a fluid conduit. The outlet of the first precision peristaltic pump and the mixed colorimetric reagent storage container are connected to the inlet of the dynamic mixer via a fluid conduit. The second precision peristaltic pump is used to pump the mixed colorimetric reagent from the mixed colorimetric reagent storage container into the dynamic mixer. The outlet of the dynamic mixer is connected to the inlet of the flow-through detection cell via a fluid conduit. The flow-through detection cell is fixedly installed in the sample chamber of the UV-Vis spectrophotometer. Step 3: Conduct a desulfurized gypsum dissolution experiment and simultaneously implement online calcium ion detection. Add the desulfurized gypsum sample and dissolving solvent to the reaction vessel, start the dissolution process, and simultaneously start the first precision peristaltic pump and the second precision peristaltic pump. The filtered clear liquid and the mixed colorimetric reagent are mixed and reacted in the dynamic mixer according to a preset ratio and flow into the flow-through detection cell. The UV-Vis spectrophotometer continuously measures the absorbance value at the maximum absorption wavelength and the reference wavelength, and calculates the real-time absorbance data after background correction. Step 4: Substitute the background-corrected real-time absorbance data into the standard working curve to calculate the calcium ion concentration before dilution, and plot the calcium ion dissolution kinetic curve.

2. The method for detecting calcium ion content in a desulfurized gypsum dissolution experiment according to claim 1, characterized in that, In step 2, the filter medium of the microporous filter head is sintered metal or sintered polymer, and the average pore size of the microporous filter head ranges from 0.2 micrometers to 0.8 micrometers.

3. The method for detecting calcium ion content in a desulfurized gypsum dissolution experiment according to claim 1, characterized in that, In step 2, the ratio of the flow rate of the first precision peristaltic pump to the flow rate of the second precision peristaltic pump is configured as a fixed dilution ratio. The process of determining the dilution ratio includes: calculating the required dilution factor based on the upper limit of the linear range of the standard working curve and the expected calcium ion saturation concentration in the desulfurized gypsum solution, thereby setting the flow rate ratio of the first precision peristaltic pump to the second precision peristaltic pump.

4. The method for detecting calcium ion content in a desulfurized gypsum dissolution experiment according to claim 1, characterized in that, In step 1, the step of establishing a standard working curve of calcium ion concentration versus absorbance value includes: Step 1.1: Prepare a series of calcium ion standard solutions of known concentrations, wherein the matrix solvent of the calcium ion standard solutions is exactly the same as the dissolving solvent used in Step 3; Step 1.2: Add a masking agent, a pH buffer solution, and a calcium ion colorimetric reagent sequentially to each of the calcium ion standard solutions. The masking agent is triethanolamine, the pH buffer solution is an ammonia-ammonium chloride buffer solution or a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution, and the calcium ion colorimetric reagent is a calcium carboxylic acid indicator. Step 1.3: Use a UV-Vis spectrophotometer to measure the absorbance of each standard solution after the reaction at the maximum absorption wavelength; Step 1.4: Plot the standard working curve with calcium ion concentration on the x-axis and absorbance value on the y-axis.

5. The method for detecting calcium ion content in a desulfurized gypsum dissolution experiment according to claim 4, characterized in that, In step 1.2, the mixed colorimetric reagent is prepared by pre-mixing the masking agent, the pH buffer solution and the calcium ion colorimetric reagent, and stored in the mixed colorimetric reagent storage container; the pH buffer solution maintains the pH of the colorimetric reaction environment in the range of 9.5 to 12.

5.

6. The method for detecting calcium ion content in a desulfurized gypsum dissolution experiment according to claim 1, characterized in that, In step 3, the UV-Vis spectrophotometer adopts a dual-wavelength detection mode. The maximum absorption wavelength is the characteristic absorption peak wavelength of the complex formed by the calcium ions and the colorimetric agent, and the reference wavelength is the wavelength at which the complex has almost no absorption while the system background has absorption. The real-time absorbance data after background correction is obtained by subtracting the absorbance value measured at the reference wavelength from the absorbance value measured at the maximum absorption wavelength.

7. The method for detecting calcium ion content in a desulfurized gypsum dissolution experiment according to claim 6, characterized in that, The process of determining the reference wavelength includes: scanning the absorption spectrum of the complex formed by the calcium ions and the colorimetric agent in the fully reacted state, and selecting a region wavelength with low and flat absorbance on the long-wavelength side or short-wavelength side of the maximum absorption peak as the reference wavelength.

8. The method for detecting calcium ion content in a desulfurized gypsum dissolution experiment according to claim 1, characterized in that, In step 2, the dynamic mixer is a spiral tube mixer or a microchannel mixer, and the internal volume of the dynamic mixer is designed such that the residence time of the mixed liquid is sufficient to complete the colorimetric reaction between the calcium ions and the colorimetric agent.

9. The method for detecting calcium ion content in a desulfurized gypsum dissolution experiment according to claim 1, characterized in that, In step 3, the reaction vessel is placed in a constant temperature water bath shaker, and the dissolution process is carried out at a constant temperature and oscillation speed; the start-up of the first precision peristaltic pump and the second precision peristaltic pump is synchronized with the start of the dissolution process.

10. The method for detecting calcium ion content in a desulfurized gypsum dissolution experiment according to claim 1, characterized in that, In step 2, the waste liquid flowing out of the outlet of the flow-through detection cell is guided to a separate waste liquid collection container, or selectively returned to the reaction vessel through a three-way valve to maintain a constant total volume of the reaction system.

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