Method for testing concentration of ferric ions in citric acid cleaning solution

Abstract

The invention discloses a method for testing the concentration of ferric ions in a citric acid cleaning solution, when the cleaning solution is combined with a color developing agent, namely a potassium thiocyanate solution, the cleaning solution is acidized in advance, firstly, citric acid is easy to form a stable complex with Fe < 3 + > at a relatively high pH value to hinder a subsequent color developing reaction and titration, and the concentration of ferric ions in the citric acid cleaning solution is not influenced; the protonated citric acid is subjected to pre-acidification treatment, so that the complexing ability of the protonated citric acid is destroyed, free Fe < 3 + > is released, hydrolysis of Fe < 3 + > is inhibited, and Fe < 3 + > is ensured to participate in subsequent reaction in an ionic state; besides, the acid environment can reduce the oxidation rate of Fe < 2 + >, avoid the introduction of additional errors due to the fact that Fe < 2 + > is oxidized into Fe < 3 + >, and improve the accuracy of a Fe < 3 + > concentration test result, so that the citric acid complexing effect is eliminated through the pre-acidification treatment, meanwhile, the oxidation interference of Fe < 2 + > is inhibited, and the detection precision is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron ion analysis and detection, and relates to a method for testing the concentration of ferric ions in a citric acid cleaning solution. Background Art

[0002] With the use of power station boilers, iron oxide scale (mainly composed of Fe2O3, Fe3O4, etc.) will be generated inside. The existence of iron oxide scale will affect the heat transfer efficiency of power station boilers and the safety of unit operation. Therefore, it is necessary to regularly clean the iron oxide scale inside the power station boilers. In the prior art, due to the high complexing ability and low corrosiveness of citric acid, it is widely used in the chemical cleaning of power station boilers. The principle of using citric acid to clean iron oxide scale is that citric acid (pH value between 3.5 and 4.0) forms a soluble ferric citrate complex with iron oxide scale. In this process, since free Fe 3+ has a significant impact on metal corrosion, so the real-time determination of Fe 3+ concentration in the cleaning solution can effectively control the corrosion risk.

[0003] For the determination of Fe 3+ content in the system, the existing methods include ion chromatography (IC), inductively coupled plasma mass spectrometry (ICP-MS), and redox titration. Among the above methods, redox titration is widely used for the determination of Fe 3+ because of its simplicity, rapidity, and easy realization of on-site real-time determination. Chinese Patent Application CN106770920A discloses a rapid determination method for the content of ferric ions in the acidolysis titanium liquid of sulfuric acid process titanium white. This method first dilutes the acidolysis titanium liquid, then adjusts the pH value of the dilution, then heats the system, uses sodium sulfosalicylic acid indicator, and finally titrates with EDTA to achieve the quantitative determination of ferric ions. However, this method prepares the solution by first diluting and then adjusting the acidity. Since the cleaning solution of power station boilers contains Fe 2 +, it is extremely easy to be oxidized to Fe 3+ . Therefore, during the sampling and dilution process, Fe 2+ in the cleaning solution is easily oxidized to Fe 3+ , resulting in a higher determination result and lower test accuracy, and unable to reflect the true Fe 3+ content. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a method for testing the concentration of ferric ions in a citric acid cleaning solution, so as to solve the problem of using redox titration method in the prior art for Fe3+ When measuring the content, there is a technical problem of low accuracy of the test results.

[0005] The present invention is realized by the following technical solutions:

[0006] A method for testing the concentration of ferric ions in a citric acid cleaning solution, comprising the following steps:

[0007] S1: Add the cleaning solution to an acidifying reagent for pre-acidification treatment;

[0008] S2: Add a potassium thiocyanate solution to the pre-acidified cleaning solution to make the Fe in the cleaning solution 3+ fully react with potassium thiocyanate;

[0009] S3: Use an EDTA solution as a titrant to titrate the system that has completed step S2 at room temperature until the titration end point, and obtain the concentration of ferric ions in the citric acid cleaning solution according to the concentration of the EDTA solution, the volume of the EDTA solution consumed during titration, and the volume of the cleaning solution.

[0010] Preferably, in step S1, the acidifying reagent is a sulfuric acid solution with a molar concentration of 0.5 - 2.0 mol / L.

[0011] Preferably, in step S1, the pre-acidification treatment is carried out until the pH value of the system is 1.5 - 2.0.

[0012] Preferably, in step S1, the cleaning solution is first filtered and then added to the acidifying reagent for pre-acidification treatment.

[0013] Preferably, in step S2, the pre-acidified cleaning solution is first diluted, and then a potassium thiocyanate solution is added to the obtained system to make the Fe in the cleaning solution 3+ fully react with potassium thiocyanate.

[0014] Preferably, in step S2, the mass percentage concentration of the potassium thiocyanate solution is 20% - 60%, and the volume ratio of the potassium thiocyanate solution to the diluted pre-acidified cleaning solution is 1:(10 - 50).

[0015] Preferably, in step S3, the molar concentration of the EDTA solution is 0.05 - 0.3 mol / L.

[0016] Preferably, in step S3, when approaching the titration end point, the EDTA solution is added drop by drop.

[0017] Preferably, in step S3, the titration treatment is carried out under the protection of an inert atmosphere.

[0018] Preferably, in step S3, during the titration treatment process, sufficient stirring is maintained.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] The invention discloses a method for testing the concentration of trivalent iron ions in a citric acid cleaning solution. When the cleaning solution is combined with a color developer, namely a potassium thiocyanate solution, the cleaning solution is acidified in advance. First, citric acid (C6H8O7) is easy to react with Fe at a higher pH value. 3+ Forming a stable complex (such as FeCit-), which hinders the subsequent color development reaction and titration. Pre-acidification can protonate citric acid, destroy its complexing ability, and release free Fe 3+ , while inhibiting Fe 3+ Hydrolysis of (Fe 3+ When pH>2, Fe(OH)3 precipitation is likely to occur. 3+ Participate in subsequent reactions in an ionic state; in addition, the acidic environment can reduce Fe 2+ The oxidation rate of Fe 2+ Oxidized to Fe 3+ The introduction of additional errors increases the Fe 3+ The accuracy of the concentration test results; more importantly, during the addition process, the cleaning solution is directly added to the acidifying agent. At this time, the acidifying agent is in excess compared to the added cleaning solution, which can fully inhibit Fe 2+ oxidation, fully ensuring the accuracy of the test results; in addition, the titration is carried out at room temperature in this application, which effectively ensures the stability of the acidity of the system and further avoids Fe 2+ Therefore, the present invention eliminates the citric acid complexing effect through pre-acidification treatment, and inhibits Fe 2 +Oxidation interference improves the accuracy of detection.

[0021] Furthermore, in step S1, the acidifying agent is a sulfuric acid solution with a molar concentration of 0.5 to 2.0 mol / L. First, Fe 3+ When pH>2, it is easy to hydrolyze to form Fe(OH)3 precipitate, which makes it unable to participate in subsequent reactions. Under this acidity condition, avoid Fe 3+ Hydrolysis loss. Citric acid (C6H8O7) easily reacts with Fe under near-neutral or weakly acidic conditions. 3+ Forming stable complexes (such as FeCit - ), hindering Fe 3+ The color reaction with potassium thiocyanate (KSCN) causes the strong acidic environment of sulfuric acid to protonate citric acid (convert to H3Cit), significantly reducing its complexing ability and releasing free Fe 3+ , ensuring the high efficiency of subsequent reactions; an acidic environment (pH < 2) can reduce Fe 2+ The oxidation rate (Fe2+ →Fe 3+ ) to avoid introducing additional Fe due to the oxidation reaction 3+ resulting in a falsely high measured value; additionally, regarding the control of the concentration of the acidifying reagent, if the concentration of the acidifying reagent is too low, the acidification rate is slow, and it cannot effectively inhibit the complexation of citric acid and the oxidation of Fe 2+ . If the concentration of the acidifying reagent is too high, it will lead to the introduction of too much SO4 2- , which causes interference in the measurement. Within this concentration range, sulfuric acid has sufficient reaction activity to quickly complete the acidification of the citric acid cleaning solution, avoiding the complexation of citric acid and the oxidation of Fe 2+ .

[0022] Furthermore, in step S1, the pre-acidification treatment is carried out until the pH value of the system is 1.5 - 2.0. This acidity range can effectively avoid the complexation of citric acid and the oxidation of Fe 2+ .

[0023] Furthermore, in step S1, the cleaning solution is first filtered and then added to the acidifying reagent for pre-acidification treatment. First, the cleaning solution may contain particulate impurities, and these particles may adsorb or encapsulate Fe 3+ , resulting in incomplete dissolution during acidification and causing the detection result to be on the low side. Additionally, the suspended particles will increase the turbidity of the solution, interfering with the visual judgment of the subsequent potassium thiocyanate color reaction and affecting the test result. After filtration, the solution is clearer, and the visual end point (the disappearance of red) judgment is more intuitive. This operation, through the synergistic effect of physical separation and chemical treatment, significantly improves the accuracy and reliability of the Fe 3+ concentration measurement.

[0024] Furthermore, in step S2, the pre-acidified cleaning solution is first diluted, and then potassium thiocyanate solution is added to the resulting system to allow the Fe 3+ in the cleaning solution to fully react with potassium thiocyanate. The red complex formed by potassium thiocyanate (KSCN) and Fe 3+ . If the Fe 3+ concentration in the original solution is too high, the color reaction is prone to reach a supersaturated state, resulting in the absorbance deviating from the linear relationship and causing a concentration measurement error. The dilution treatment can adjust the Fe 3+ to a concentration range suitable for visual colorimetry. Additionally, in the EDTA titration, the disappearance of the red color in the color reaction is used as the end point indication. If the Fe 3+ concentration is too high, the intense coloration may cause a delay in end point judgment. After dilution, the color intensity is moderate, the end point color change is more sensitive, reducing the subjective error and improving the accuracy of the test result; additionally, the cleaning solution may contain high concentrations of citric acid and other metal ions (such as Al 3+ , Ca 2+) or organic matter, dilution can reduce the concentration of these substances, thereby reducing the potential re-complexation risk of citric acid to Fe 3+ , reducing the competitive consumption of the titrant by coexisting metal ions. Moreover, high ionic strength can cause changes in the stability of the complex. After dilution treatment, the ionic strength is reduced, making the reaction of Fe 3+ with KSCN and EDTA closer to the ideal state and improving the accuracy of the stoichiometric relationship.

[0025] Further, in step S2, the mass percentage concentration of the potassium thiocyanate solution is 20% - 60%. When the concentration of potassium thiocyanate (KSCN) is too low, it cannot react fully with Fe 3+ to form a stable red complex Fe(SCN) n 3-n , resulting in insufficient color development intensity and affecting the detection sensitivity of low-concentration Fe 3+ . Too high a concentration of KSCN will trigger side reactions, leading to color over-saturation or background interference; the volume ratio of the potassium thiocyanate solution to the diluted pre-acidified cleaning solution is 1:(10 - 50). The concentration of Fe 3+ in the diluted pre-acidified cleaning solution is usually low. By controlling the addition amount of KSCN, the excess or deficiency of the color reagent can be avoided, ensuring complete reaction and uniform color development. In addition, the high volume ratio can reduce the ionic strength of the system, reduce the influence of the salt effect on the stability of the complex, and improve the repeatability of the color reaction.

[0026] Further, in step S3, the molar concentration of the EDTA solution is 0.05 - 0.3 mol / L. High-concentration EDTA (such as 0.3 mol / L) can quickly form a stable 1:1 complex with metal ions, reducing the equilibrium time after each drop addition, especially suitable for the rapid detection of high-concentration samples. For low-concentration samples, using 0.05 mol / L EDTA can avoid waste of excessive reagents, and at the same time adjust the titration volume to a reasonable range by dilution, improving the economy of trace component detection.

[0027] Further, in step S3, near the titration end point, the EDTA solution is added drop by drop. First, in the back titration method of EDTA titrating Fe 3+ , there is a jump region near the stoichiometric point (end point) of the titration curve. Near the end point, the concentration of Fe 3+ is extremely low. At this time, a small excess of EDTA can cause significant changes in the solution pH or complex concentration. Adding drop by drop can narrow the span of the jump region, making the end point judgment closer to the true stoichiometric point; in addition, the end point indicated by potassium thiocyanate is judged by the fading of the red color. Near the end point, the residual trace red color may fade slowly. Adding drop by drop and shaking well can avoid the operator from adding too much due to rapid dropping. Through this operation, the accuracy of the titration is improved.

[0028] Further, in step S3, the titration treatment is carried out under the protection of an inert atmosphere. During the titration process, if there are reactive gases such as oxygen in the system, it may cause Fe 2+ to be oxidized to Fe 3+ , thus interfering with the stoichiometric relationship of the titration reaction. The inert atmosphere can isolate oxygen and moisture, maintain a stable redox state of the system, and avoid the occurrence of non-target reactions. In addition, the inert gas can also prevent CO2 from dissolving into the solution and causing pH fluctuations. The stability of pH directly affects the formation of complexes and the clarity of the end-point jump. Therefore, by controlling the titration atmosphere, the accuracy of the titration result is improved.

[0029] Further, in step S3, during the titration treatment, sufficient stirring is maintained. Stirring breaks the concentration stratification of the reactants in the solution through forced convection, reduces the diffusion resistance, and enables the titrant to quickly contact the ions to be measured. In addition, rapid stirring can reduce the time required for the reaction to reach equilibrium. Especially in redox titration, it can avoid the error in end-point judgment caused by reaction lag, effectively improving the accuracy of the test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0031] Figure 1 is a schematic flow chart of a method for testing the concentration of ferric ions in a citric acid cleaning solution in the present invention;

[0032] Figure 2 is a schematic flow chart of the determination of the Fe 2+ concentration in the cleaning solution in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] In order to enable those skilled in the art to understand the features and effects of the present invention, the following will generally explain and define the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. When there are conflicts, the definition in this specification shall prevail.

[0034] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not in any way limit the scope of the present invention, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0035] Herein, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0036] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0037] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0038] The present invention provides a method for testing the concentration of trivalent iron ions in a citric acid cleaning solution, comprising the following steps:

[0039] S1: The cleaning liquid is first filtered and then quickly added into an acidifying agent for pre-acidification.

[0040] Wherein, the acidifying agent is a sulfuric acid solution with a molar concentration of 0.5 to 2.0 mol / L.

[0041] Pre-acidification treatment is performed until the pH value of the system is 1.5-2.0.

[0042] S2: Dilute the cleaning solution after pre-acidification treatment, and then add potassium thiocyanate solution to the diluted system to make the Fe 3+ It fully reacts with potassium thiocyanate, Fe 3+ The reaction product with potassium thiocyanate is red.

[0043] The mass percentage concentration of the potassium thiocyanate solution is 20% to 60%, and the volume ratio of the potassium thiocyanate solution to the diluted system is 1:(10 to 50).

[0044] S3: Using an EDTA solution with a molar concentration of 0.05 to 0.3 mol / L as a titrant, the system after completing step S2 is titrated at room temperature under the protection of an inert atmosphere. During the titration process, sufficient stirring is maintained. When approaching the titration endpoint, the EDTA solution is added dropwise. After titrating to the titration endpoint, the concentration of trivalent iron ions in the citric acid cleaning solution is obtained according to the concentration of the EDTA solution, the volume of the EDTA solution consumed during the titration, and the volume of the cleaning solution. Specifically,

[0045]

[0046] In the formula:

[0047] Mass percentage of Fe in the pickling solution 3+ / mg / L;

[0048] A: Concentration of the EDTA solution;

[0049] a: Volume of the consumed EDTA solution / mL;

[0050] 56: Molar mass of iron / g / mol;

[0051] V: Volume of the taken cleaning solution sample / mL.

[0052] In step S3, the titration end point is the disappearance of the red color.

[0053] If no red color appears in the system when adding potassium thiocyanate solution, add 2 mL of dilute sulfuric acid to verify the existence of Fe 3+ Specifically, if no red color appears in the system after adding potassium thiocyanate (KSCN) (i.e., no red Fe(SCN) n 3-n complex is formed), there may be two cases: 1. Fe does not actually exist in the cleaning solution 3+ ; 2. Fe 3+ does not combine with SCN- to show color due to reactions such as complexation, hydrolysis, or reduction. The functions of adding dilute sulfuric acid are as follows: 1. Adjust the pH to inhibit the hydrolysis of Fe 3+ , Fe 3+ is prone to hydrolysis to form Fe(OH)3 precipitate at pH > 2, resulting in the inability to react with SCN - . Adding dilute sulfuric acid (H2SO4) can lower the system pH (<2), dissolve the Fe(OH)3 precipitate, and release free Fe 3+ , enabling it to combine with SCN - to show red. 2. Destroy the complex state of Fe 3+ . Citric acid (C6H8O7) can form a stable complex with Fe 3+ at a relatively high pH (such as FeCit - ), hindering its reaction with SCN - . After adding dilute sulfuric acid for acidification, citric acid is protonated (converted to H3Cit), and its complexing ability is weakened. Fe 3+ is released and reacts with SCN - to show red. If red color appears after adding dilute sulfuric acid, it indicates that Fe 3+ was originally "hidden" due to hydrolysis or complexation and returns to the free state after acidification, reacting with SCN- to show color, proving the existence of Fe 3+Exists. If it does not turn red after adding dilute sulfuric acid, it indicates that the cleaning solution actually does not contain Fe 3+ .

[0054] As Figure 2 shown, further, the present invention can also realize the determination of the concentration of Fe 2+ in the cleaning solution, specifically:

[0055] S4: Add 3 - 5 mL of ammonium persulfate ((NH4)2S2O8) oxidant to the system that has completed step S3, heat to 60°C - 70°C, and oxidize Fe 2+ to Fe 3+ , and the generated Fe 3+ reacts with the thiocyanate in the system, causing the reaction system to turn red again; heating to 60°C - 70°C here accelerates the oxidation efficiency of ammonium persulfate and avoids the hydrolysis of Fe 3+ due to long - time heating.

[0056] S5: Titrate again with the EDTA solution until the titration end - point, which is the disappearance of the red color, and obtain the concentration of ferrous ions in the citric acid cleaning solution through the concentration of the EDTA solution, the volume of the EDTA solution consumed during titration, and the volume of the cleaning solution.

[0057] The specific calculation process is as follows:

[0058]

[0059] In the formula:

[0060] Mass percentage content of Fe 2+ in the pickling solution / mg / L;

[0061] A: Concentration of the EDTA solution;

[0062] b: Volume of the EDTA solution consumed in step S5 / mL;

[0063] 56: Molar mass of iron / g / mol;

[0064] V: Volume of the cleaning solution sample taken / mL.

[0065] In the present invention, the acidification pretreatment effectively inhibits the oxidation of Fe 2+ , improves the accuracy of Fe 3+ determination, has strong anti - interference ability, and effectively improves the precision of Fe 3+ testing in the cleaning solution.

[0066] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0067] In the following embodiments, conventional instruments and equipment in the art are used. For the experimental methods without specific conditions noted in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are the conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0068] Example 1

[0069] This example discloses a method for testing the concentration of ferric ions in a citric acid cleaning solution, which includes the following steps:

[0070] S1: Take a 250 mL Erlenmeyer flask, add 5 mL of dilute sulfuric acid (H2SO4) solution (add acid in advance to reduce the exposure time of the sample in the air); pipette 5 mL of a citric acid cleaning solution from a certain power plant boiler (total iron is about 8903 mg / L, pH = 4.2); dilute it to 100 mL with distilled water and shake well;

[0071] S2: Add 5 mL of potassium thiocyanate solution to the pre-acidified cleaning solution to make the Fe 3+ in the cleaning solution react fully with potassium thiocyanate;

[0072] S3: Use an EDTA solution as the titrant and titrate the system completed in step S2 at room temperature until the titration end point is reached. Obtain the concentration of ferric ions in the citric acid cleaning solution according to the concentration of the EDTA solution, the volume of the EDTA solution consumed during titration, and the volume of the cleaning solution. Specifically, in this example, the volume a of EDTA consumed for titrating Fe 3+ is 0.9 mL, and the molar concentration of the EDTA solution is 0.1104 mol / L;

[0073] S4: Add 5 mL of ammonium persulfate ((NH4)2S2O8) oxidant to the system completed in step S3, heat it to 60 °C to 70 °C, oxidize Fe 2+ to Fe 3+ , and the generated Fe 3+ reacts with the thiocyanate in the system to make the reaction system turn red again;

[0074] S5: Titrate again with EDTA solution to the titration endpoint, where the red color disappears, and obtain the concentration of divalent iron ions in the citric acid cleaning solution by the concentration of EDTA solution, the volume of EDTA solution consumed during titration, and the volume of cleaning solution. Specifically, in this embodiment, the volume of EDTA consumed in the titration of total iron after oxidation is b=6.3mL, where the molar concentration of EDTA solution is 0.1104mol / L;

[0075] calculate:

[0076]

[0077] Compared with the atomic absorption spectrometry, the error is less than 3%. Therefore, the technical solution of the present invention has higher detection accuracy, convenient test operation and broad application prospects.

[0078] Example 2

[0079] A method for testing the concentration of ferric iron ions in a citric acid cleaning solution comprises the following steps:

[0080] S1: Firstly, the cleaning solution is quickly filtered, and then 5 mL of the filtered citric acid cleaning solution is quickly added to the acidifying agent for pre-acidification treatment;

[0081] The acidifying agent is a sulfuric acid solution with a molar concentration of 0.5 mol / L, and the pre-acidification treatment is performed to a pH value of 2.0;

[0082] S2: Dilute the pre-acidified cleaning solution to 100 mL with distilled water, then add potassium thiocyanate solution to the diluted system to make the Fe 3+ It fully reacts with potassium thiocyanate, Fe 3+ The reaction product with potassium thiocyanate is red;

[0083] Wherein, the mass percentage concentration of the potassium thiocyanate solution is 20%, and the volume ratio of the potassium thiocyanate solution to the diluted system is 1:10;

[0084] S3: Using an EDTA solution with a molar concentration of 0.0502 mol / L as a titrant, under the protection of an inert atmosphere, the system that completes step S2 is titrated at room temperature. During the titration process, sufficient stirring is maintained. When approaching the titration endpoint, the EDTA solution is added dropwise. After titrating to the titration endpoint, the concentration of trivalent iron ions in the citric acid cleaning solution is obtained according to the concentration of the EDTA solution, the volume of the EDTA solution consumed during the titration, and the volume of the cleaning solution. Specifically, the volume of the EDTA solution consumed in step S3 in this embodiment is 2.7 mL.

[0085] calculate:

[0086]

[0087] Furthermore, this embodiment can also measure the concentration of Fe in the citric acid cleaning solution, specifically as follows: 2+ Concentration measurement, specifically:

[0088] S4: Add 3 mL of ammonium persulfate ((NH4)2S2O8) oxidant to the system that has completed step S3, heat to 60 °C, and oxidize Fe 2+ to Fe 3+ Moreover, the generated Fe 3+ reacts with the thiocyanate in the system, causing the reaction system to turn red again;

[0089] S5: Titrate again with the EDTA solution until the titration end point, which is the disappearance of the red color. Obtain the concentration of ferrous ions in the citric acid cleaning solution through the concentration of the EDTA solution, the volume of the EDTA solution consumed during titration, and the volume of the cleaning solution. Specifically, in this embodiment, the volume of the EDTA solution consumed in step S3 is 5.2 mL.

[0090] Calculation:

[0091]

[0092] Example 3

[0093] A method for testing the concentration of ferric ions in a citric acid cleaning solution, comprising the following steps:

[0094] S1: First, perform a rapid filtration treatment on the cleaning solution, and then quickly add 2 mL of the filtered citric acid cleaning solution to the acidifying reagent for pre-acidification treatment.

[0095] Among them, the acidifying reagent is a sulfuric acid solution with a molar concentration of 0.5 mol / L, and the pre-acidification treatment is carried out until the pH value of the system is 1.5.

[0096] S2: Dilute the pre-acidified cleaning solution to 100 mL with distilled water, and then add potassium thiocyanate solution to the diluted system to allow the Fe 3+ in the cleaning solution to react fully with potassium thiocyanate, and the reaction product of Fe 3+ with potassium thiocyanate is red;

[0097] Among them, the mass percentage concentration of the potassium thiocyanate solution is 60%, and the volume ratio of the potassium thiocyanate solution to the diluted system is 1:50.

[0098] S3: Use an EDTA solution with a molar concentration of 0.1305 mol / L as the titrant. Under the protection of an inert atmosphere, titrate the system that has completed step S2 at room temperature. During the titration process, keep stirring thoroughly. When approaching the titration end point, add the EDTA solution drop by drop. After titrating to the titration end point, obtain the concentration of ferric ions in the citric acid cleaning solution based on the concentration of the EDTA solution, the volume of the EDTA solution consumed during titration, and the volume of the cleaning solution. Specifically, in this embodiment, the volume of the EDTA solution consumed in step S3 is 0.5 mL.

[0099] Calculation:

[0100]

[0101] Furthermore, this embodiment can also measure the concentration of Fe in the citric acid cleaning solution, specifically: 2+ Concentration measurement:

[0102] S4: Add 4 mL of ammonium persulfate ((NH4)2S2O8) oxidant to the system that has completed step S3, heat to 65 °C, and oxidize Fe 2+ to Fe 3+ , and the generated Fe 3+ reacts with the thiocyanate ions in the system, causing the reaction system to turn red again;

[0103] S5: Titrate with the EDTA solution again until the titration end point. The titration end point is when the red color disappears, and obtain the concentration of ferrous ions in the citric acid cleaning solution based on the concentration of the EDTA solution, the volume of the EDTA solution consumed during titration, and the volume of the cleaning solution. Specifically, in this embodiment, the volume of the EDTA solution consumed in step S3 is 2.6 mL.

[0104] Calculation:

[0105]

[0106] Example 4

[0107] A test method for the concentration of ferric ions in a citric acid cleaning solution, comprising the following steps:

[0108] S1: First, perform a rapid filtration treatment on the cleaning solution, and then quickly add 5 mL of the filtered citric acid cleaning solution to the acidifying reagent for pre-acidification treatment.

[0109] Among them, the acidifying reagent is a sulfuric acid solution with a molar concentration of 2.0 mol / L, and the pre-acidification treatment is carried out until the pH value of the system is 1.7.

[0110] S2: Dilute the pre-acidified cleaning solution to 100 mL with distilled water, then add potassium thiocyanate solution to the diluted system to make the Fe 3+ It fully reacts with potassium thiocyanate, Fe 3+ The reaction product with potassium thiocyanate is red;

[0111] The mass percentage concentration of the potassium thiocyanate solution is 40%, and the volume ratio of the potassium thiocyanate solution to the diluted system is 1:25.

[0112] S3: Using an EDTA solution with a molar concentration of 0.3005 mol / L as a titrant, under the protection of an inert atmosphere, the system that completes step S2 is titrated at room temperature. During the titration process, sufficient stirring is maintained. When approaching the titration endpoint, the EDTA solution is added dropwise. After titrating to the titration endpoint, the concentration of trivalent iron ions in the citric acid cleaning solution is obtained according to the concentration of the EDTA solution, the volume of the EDTA solution consumed during the titration, and the volume of the cleaning solution. Specifically, the volume of the EDTA solution consumed in step S3 in this embodiment is 0.2 mL.

[0113] calculate:

[0114]

[0115] Furthermore, this embodiment can also achieve the Fe 2+ The concentration is determined as follows:

[0116] S4: Add 5 mL of ammonium persulfate ((NH4)2S2O8) oxidant to the system after step S3, heat to 65°C, and 2+ Oxidized to Fe 3+ , and the generated Fe 3+ Reacts with the thiocyanate in the system, making the reaction system appear red again;

[0117] S5: Titrate again with EDTA solution to the titration endpoint, the titration endpoint is the disappearance of red, and obtain the concentration of divalent iron ions in the citric acid cleaning solution by the concentration of EDTA solution, the volume of EDTA solution consumed during titration, and the volume of cleaning solution. Specifically, the volume of EDTA solution consumed in step S3 in this embodiment is 1.8 mL.

[0118] calculate:

[0119]

[0120] Example 5

[0121] A method for testing the concentration of ferric iron ions in a citric acid cleaning solution comprises the following steps:

[0122] S1: Firstly, the cleaning solution is quickly filtered, and then 3 mL of the filtered citric acid cleaning solution is quickly added to the acidifying agent for pre-acidification.

[0123] The acidifying agent is a sulfuric acid solution with a molar concentration of 1.5 mol / L, and the system is pre-acidified to a pH value of 1.8.

[0124] S2: Dilute the pre-acidified cleaning solution to 100 mL with distilled water, then add potassium thiocyanate solution to the diluted system to make the Fe 3+ It reacts fully with potassium thiocyanate, Fe 3+ The reaction product with potassium thiocyanate is red;

[0125] The mass percentage concentration of the potassium thiocyanate solution is 55%, and the volume ratio of the potassium thiocyanate solution to the diluted system is 1:30.

[0126] S3: Using an EDTA solution with a molar concentration of 0.1710 mol / L as a titrant, under the protection of an inert atmosphere, the system that completes step S2 is titrated at room temperature. During the titration process, sufficient stirring is maintained. When approaching the titration endpoint, the EDTA solution is added dropwise. After titrating to the titration endpoint, the concentration of trivalent iron ions in the citric acid cleaning solution is obtained according to the concentration of the EDTA solution, the volume of the EDTA solution consumed during the titration, and the volume of the cleaning solution. Specifically, the volume of the EDTA solution consumed in step S3 in this embodiment is 0.3 mL.

[0127] calculate:

[0128]

[0129] Furthermore, this embodiment can also achieve the Fe 2+ The concentration is determined as follows:

[0130] S4: Add 4 mL of ammonium persulfate ((NH4)2S2O8) oxidant to the system after step S3, heat to 65°C, and 2+ Oxidized to Fe 3+ , and the generated Fe 3+ Reacts with the thiocyanate in the system, making the reaction system appear red again;

[0131] S5: Titrate again with EDTA solution to the titration endpoint, the titration endpoint is the disappearance of red, and obtain the concentration of divalent iron ions in the citric acid cleaning solution by the concentration of EDTA solution, the volume of EDTA solution consumed during titration, and the volume of cleaning solution. Specifically, the volume of EDTA solution consumed in step S3 in this embodiment is 1.3 mL.

[0132] Calculation:

[0133]

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for testing the concentration of ferric ions in a citric acid cleaning solution, characterized in that, It includes the following steps: S1: Add the cleaning solution to the acidifying reagent for pre-acidification treatment; S2: Add the potassium thiocyanate solution to the pre-acidified cleaning solution to allow the Fe3+ in the cleaning solution to fully react with the potassium thiocyanate; S3: Use the EDTA solution as the titrant, and perform titration on the system that has completed step S2 at room temperature until the titration end point is reached. Obtain the concentration of ferric ions in the citric acid cleaning solution based on the concentration of the EDTA solution, the volume of the EDTA solution consumed during titration, and the volume of the cleaning solution.

2. The testing method for the concentration of ferric ions in a citric acid cleaning solution according to claim 1, characterized in that In step S1, the acidifying reagent is a sulfuric acid solution with a molar concentration of 0.5 - 2.0 mol / L.

3. The testing method for the concentration of ferric ions in a citric acid cleaning solution according to claim 1, characterized in that, In step S1, the pre-acidification treatment is carried out until the pH value of the system is 1.5 - 2.

0.

4. The testing method for the concentration of ferric ions in a citric acid cleaning solution according to claim 1, characterized in that, In step S1, the cleaning solution is first filtered and then added to the acidifying reagent for pre-acidification treatment.

5. The test method for the concentration of ferric ions in a citric acid cleaning solution according to claim 1, wherein In step S2, the pre-acidified cleaning solution is first diluted, and then the potassium thiocyanate solution is added to the resulting system to allow the Fe3+ in the cleaning solution to fully react with the potassium thiocyanate.

6. The test method for the concentration of ferric ions in a citric acid cleaning solution according to claim 5, characterized in that, In step S2, the mass percentage concentration of the potassium thiocyanate solution is 20% - 60%, and the volume ratio of the potassium thiocyanate solution to the diluted pre-acidified cleaning solution is 1:(10 - 50).

7. The test method for the concentration of ferric ions in the citric acid cleaning solution according to claim 1, characterized in that, In step S3, the molar concentration of the EDTA solution is 0.05 - 0.3 mol / L.

8. The testing method for the concentration of ferric ions in a citric acid cleaning solution according to claim 1, wherein In step S3, when approaching the titration end point, the EDTA solution is added drop by drop.

9. The test method for the concentration of ferric ions in a citric acid cleaning solution according to claim 1, characterized in that, In step S3, the titration treatment is carried out under the protection of an inert atmosphere.

10. The test method for the concentration of ferric ions in the citric acid cleaning solution according to claim 1, characterized in that, In step S3, during the titration treatment, sufficient stirring is maintained.

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