Method for determining sulfides in wet-process phosphoric acid

Abstract

The invention relates to the technical field of chemical detection and analysis, and discloses a method for determining sulfides in wet-process phosphoric acid, which comprises the following steps: 1) fixing a phosphoric acid sample, adding a wet-process phosphoric acid sample to be detected into a reaction container containing a sulfur ion fixing agent solution, and fixing the sulfides in the phosphoric acid to obtain a solution to be detected; 2) conversion and release of sulfides: the to-be-detected liquid enters a reaction device, the sulfides are converted into hydrogen sulfide to be released through pH adjustment, heating and stirring, and the hydrogen sulfide enters an absorption liquid after condensation and gas dispersion absorption; 3) sulfide absorption and numerical value reading: after the absorption liquid fully absorbs hydrogen sulfide substances released from the sample, acquiring a sulfur ion concentration value of the absorption liquid; 4) calculating the real concentration of the sample according to the concentration of sulfur ions; the invention provides a method for quantitatively determining the content of hydrogen sulfide in phosphoric acid and intermediate products thereof, and a technical basis is provided for process control and product quality control of wet-process phosphoric acid production.

Description

Technical Field

[0001] The invention relates to the technical field of chemical detection and analysis, and in particular to a method for determining sulfide in wet-process phosphoric acid. Background Art

[0002] The methods used abroad to analyze sulfides mainly include: methylene blue spectrophotometry, flow injection-methylene blue spectrophotometry iodine titration, ion selective electrode method, etc., and there is no gas phase molecular absorption spectroscopy related method. Among them:

[0003] (1) In Standard Methods for the Examination of Water and Wastewater (20th Edition), "Method 4500-S2" recommends the use of methylene blue flow injection method to determine sulfide in water. After the sample is collected, it is treated with sulfuric acid to convert zinc sulfide into H 2 S is collected in a certain concentration of sodium hydroxide absorption solution and determined using the flow injection method.

[0004] (2) International Organization for Standardization (ISO) Method 10530-1992: Water quality-Determination of dissolved sulfide-Photometric method using methylene blue. This method uses methylene blue photometric method to determine soluble sulfide in water. The water sample is filtered through a 0.45μm filter membrane, then ascorbic acid is added for fixation, and then titanate buffer with pH = 4 is dripped into it. Ammonia gas is purged for 30 minutes, and then it is absorbed with zinc acetate solution. Finally, a color developer is added for 10 minutes for color comparison. The measurement range is 0.04mg / L~1.5mgL.

[0005] (3) International Organization for Standardization (ISO) Method 13358-1997: Water quality-Determination of easily released sulfide3 is to use methylene blue photometric method to determine the easily released sulfide in water quality. This method does not require filtration, directly add ascorbic acid to fix, then drip into pH = 4 titanate buffer, nitrogen purge for 30 minutes, absorb with zinc acetate solution, and finally add colorimetric reagent for 10 minutes. The measurement range is 0.04mg / L ~ 1.5mg / L.

[0006] (4) U.S. Environmental Protection Agency (EPA) Method 9030B: Acid-Soluble and Acid-Insoluble Sulfides: Distillation. is a pretreatment method. The method only provides semi-quantitative determination of sulfides and is mainly used to determine acid-soluble sulfides in liquid, solid waste and sewage. The sample is distilled under acidic conditions to produce H 2 The S gas is introduced into the zinc acetate absorption liquid through nitrogen and absorbed.

[0007] (5) U.S. Environmental Protection Agency (EPA) Method 9031: Extractable Sulfides uses the iodine titration method to determine sulfides in oils, soils, and matrices that cannot be treated using EPA Method 9030. The lower limit of sulfide determination in solid samples is 1 mg / kg.

[0008] (6) The U.S. Environmental Protection Agency (EPA) Method 9034: Titrimetric Procedure for Acid-Soluble and Acid-Insoluble Sulfides uses the iodine titration method to measure samples treated with EPA Method 9030B. The measurement range is 0.2 mg / kg to 50 mg / kg.

[0009] (7) American Society for Testing and Materials (ASTM) Method D4658-2015: Standard Test Method for Sulfide Ion in Water uses an ion selective electrode method to determine sulfide in water quality, with a measurement range of 0.04 g / L to 4000 mg / L.

[0010] Domestically, many departments have issued a number of technical methods for detecting sulfide content in soil and water, mainly including gas phase molecular absorption spectroscopy, methylene blue spectrophotometry, iodine titration, colorimetric method, etc. Among them:

[0011] Table 1 Main sulfide-related analysis standard methods published in China and their comparison

[0012]

[0013] In summary, there are many methods for the determination and analysis of sulfides, each with its own characteristics: the ion selective electrode method has a small footprint, is easy to carry, has a fast response speed, and is suitable for on-site sampling and determination of water samples; the gas phase molecular absorption spectroscopy, thin film diffusion technology, and flow injection method have simple pretreatment, fast analysis speed, high precision and accuracy, and are suitable for batch analysis, but require the use of large instruments, the equipment is complex and expensive, and requires long-term technical personnel to debug and maintain, and it is difficult to promote it widely; the iodine titration method has a high detection limit and is suitable for analyzing samples with relatively high sulfide concentrations, but its stability and accuracy are relatively poor; the direct colorimetric spectrophotometry method has a cumbersome operation process, large errors, and is less used; currently, the methylene blue spectrophotometry method has high sensitivity, is simple and fast, and is widely used, but its pretreatment is complex, there are many interference factors, and it is not suitable for situations with a large number of samples.

[0014] However, the above methods are basically applicable to water samples and soil samples, and there is no specific sulfide analysis method and standard for chemical products such as phosphoric acid. Rapid detection of sulfide in phosphoric acid can be used to understand the progress of wet-process phosphoric acid production based on the results, which is convenient for controlling the production process and product quality of wet-process phosphoric acid. Therefore, it is urgent to develop a method for determining sulfide in wet-process phosphoric acid. Summary of the invention

[0015] The object of the present invention is to provide a method for determining sulfide in wet-process phosphoric acid, by which the content of hydrogen sulfide in phosphoric acid can be quantitatively analyzed, thereby providing a technical basis for process control and product quality control of wet-process phosphoric acid production.

[0016] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0017] A method for determining the sulfide content in wet-process phosphoric acid comprises the following steps:

[0018] 1) Fixation of phosphoric acid sample: Add an appropriate amount of wet-process phosphoric acid sample to be tested into a reaction container containing a sulfide fixative (SAOB) solution, first fix the sulfide in the phosphoric acid to obtain a test solution;

[0019] 2) Sulfide conversion and release: The test liquid enters the reaction device and undergoes pH adjustment, heating, and stirring to convert the sulfide into hydrogen sulfide and release it, which then enters the absorption liquid after condensation and gas dispersion absorption;

[0020] 3) Sulfide absorption and numerical reading: After the absorption liquid fully absorbs the hydrogen sulfide released from the sample, the sulfur ion concentration value of the absorption liquid is obtained using a sulfur ion selective electrode;

[0021] 4) Calculate the true concentration of the sample: Sulfide ion (S 2- ) concentration ρ(S 2- ) is calculated according to the following formula:

[0022]

[0023] in:

[0024] is the sulfide ion concentration, in mg / L;

[0025] V (PA) To measure the volume of phosphoric acid, the unit is mL;

[0026] ρ (T) The electrode reading concentration is in mg / L;

[0027] V (W+SAOB) is the total volume of the mixed solution of water and SAOB measured, in mL.

[0028] As a preferred technical solution, the preparation requirements of the sulfide anti-oxidant buffer (SAOB) solution are as follows: add 550-650 mL of water to a 1000 mL beaker, then slowly add sodium hydroxide (NaOH), ascorbic acid (AA) and disodium ethylenediaminetetraacetate (EDTA-2Na) to the water in sequence, stir until all substances are dissolved and cooled to room temperature, and then transfer the solution to a 1000 mL volumetric flask and make up the volume with water; the concentration of sodium hydroxide in the sulfide fixative solution is 2 mol / L, the concentration of ascorbic acid is 0.2 mol / L, and the concentration of disodium ethylenediaminetetraacetate is 0.2 mol / L, and the water is one of deionized water or ultrapure water.

[0029] As a preferred technical solution, in step 1), the preparation requirements of the sulfide anti-Oxidant buffer (SAOB) solution are as follows: add 600 mL of deionized water or ultrapure water to a 1000 mL beaker, then slowly add 80 g of sodium hydroxide, 35 g of ascorbic acid and 67 g of disodium ethylenediaminetetraacetate in turn to the water, stir until all substances are dissolved and cooled to room temperature, and then transfer the solution to a 1000 mL volumetric flask and make up to volume with deionized water or ultrapure water. The NaOH concentration in this solution is 2 mol / L, the AA concentration is 0.2 mol / L, and the EDTA-2Na concentration is 0.2 mol / L.

[0030] As a preferred technical solution, in step 1), the volume ratio of the wet phosphoric acid sample (PA) and the sulfide fixative SAOB solution is 1:14, and the PA volume should be no less than 10mL. After mixing, the wet phosphoric acid sample is left to stand without shaking, and the wet phosphoric acid sample is naturally sunk to the bottom layer of the reactor as much as possible, and the upper layer is covered with SAOB solution to achieve the effect of alkali sealing oxygen. This step is mainly to convert the sulfide ions in the wet phosphoric acid sample into salt or ionic state by adding alkali solution to prevent the volatilization of gaseous hydrogen sulfide, and at the same time use ascorbic acid to prevent the oxidation of divalent sulfide ions by oxides in the environment.

[0031] As a preferred technical solution, in step 1), the reaction container is a glass three-necked flask with a capacity of ≥250 mL. The specific operation process can be to measure the sample according to the container capacity.

[0032] As a preferred technical solution, in step 2), the pH is adjusted using a hydrochloric acid solution, the hydrochloric acid solution is a 1+1 hydrochloric acid solution (the 1+1 hydrochloric acid solution is a solution prepared by diluting concentrated hydrochloric acid and pure water in equal proportions), and the amount of the solution added is 5.5 times the volume of the wet-process phosphoric acid sample. Its main purpose is to convert the fixed divalent sulfur in the mixed solution into hydrogen sulfide and release it, and the added acid solution makes the pH value of the mixed solution <6.0.

[0033] As a preferred technical solution, in step 2), the heating temperature of the reactor is 125°C (±5°C).

[0034] As a preferred technical solution, in step 2), the stirring rate should be ≥500r / min.

[0035] As a preferred technical solution, in step 2), the gas dispersion absorption is purged with nitrogen, and the nitrogen gas flow rate should be set to 60 / min.

[0036] As a preferred technical solution, in step 2), the condensation uses a serpentine condenser as a cooling channel, and the condensation temperature is -10°C ± 5°C, ensuring that the outlet gas temperature remains no higher than the room temperature of the day. The serpentine condenser is a 1.2m serpentine condenser.

[0037] As a preferred technical solution, in step 3), the absorption liquid is a mixed solution of equal volumes of ultrapure water and SAOB solution. (For example, 25.00 mL of ultrapure water and 25.00 mL of SAOB solution are mixed, and V (W+SAOB) is 50.00mL).

[0038] As a preferred technical solution, in step 3), the absorption liquid should use a magnetic stirring rotor to promote sulfide absorption, and the stirring rate should be ≥500r / min.

[0039] As a preferred technical solution, in step 3), the absorption liquid should be measured using a selective sulfide ion electrode, and the potential value and concentration value should be recorded when the electrode change rate is within the range of ±0.2mV / min. Since the phosphoric acid sample is unstable, the time for the numerical value to stabilize can be appropriately extended during actual operation before recording.

[0040] The main principles are:

[0041] After the sulfide in the phosphoric acid sample is acidified, heated and nitrogen-blown, the hydrogen sulfide produced is absorbed by the sulfide antioxidant buffer (SAOB) solution. The sulfide ion selective electrode measures the potential of the absorption liquid, converts the potential into the sulfide content, reads the absorption liquid content, and further converts it into the sulfide content in the actual sample. Within the measurement range, the potential and the sulfide content are inversely proportional and linear.

[0042] As a preferred technical solution, in step 2), to ensure that the interfaces between the connected unit devices are sealed during the reaction process, the straight pipe part in the gas delivery is made of silicone material, and the gas outlet position uses a glass or polytetrafluoroethylene gas dispersion pipe to cooperate with the magnetic stirring rotor in the absorption liquid to work as gas dispersion absorption.

[0043] The present invention also discloses a reaction device for a method for determining sulfide in wet-process phosphoric acid, comprising a nitrogen gas supply device, the outlet of the nitrogen gas supply device is connected to a rotor flowmeter through a gas passage, the rotor flowmeter is connected to an air guide tube through the gas passage, the air guide tube extends from one end of a three-mouth reaction bottle into the three-mouth reaction bottle, the other end of the three-mouth reaction bottle is provided with a glass bottle stopper, a magnetic rotor is provided in the three-mouth reaction bottle, a top central port of the three-mouth reaction bottle is connected to one end of an outer tube of a serpentine condenser, the other end of the outer tube of the serpentine condenser is connected to a gas diffusion tube through the gas passage; the gas diffusion tube is placed in a beaker, the beaker is provided with a magnetic rotor and a sulfur ion selective electrode of an ion meter; the beaker is placed on a magnetic stirrer, the magnetic stirrer is located on a lifting platform, the three-mouth reaction bottle is located on a magnetic stirrer with heating, the magnetic stirrer is located on the lifting platform, and the two ends of the inner tube of the serpentine condenser are respectively connected to the inlet and outlet of a cooling circulation device through a condensate passage.

[0044] Advantages of the present invention:

[0045] This method is currently applicable to the sulfide determination method of wet-process phosphoric acid products and some intermediate products. It can accurately determine samples with hydrogen sulfide concentrations within the range of 0.7 to 500 mg / L. This method can be adapted to phosphoric acid samples and intermediate products with relative water concentrations that are dozens of times higher. The determination time is relatively shorter, and pretreatment measures can effectively reduce interference. The actual measured values ​​of precision recovery rate are better than the currently publicly released and implemented water quality determination industry standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a schematic diagram of the structure of a reaction device used in the method for determining sulfide in wet-process phosphoric acid of the present invention;

[0047] Figure 2 It is a flow chart of the determination in the embodiment of the present invention;

[0048] Among them, 1-nitrogen gas supply device; 2-rotor flowmeter; 3-cooling circulation device; 4-lifting platform; 5-magnetic stirrer with heating; 6-magnetic rotor; 7-gas guide tube; 8-three-necked reaction bottle; 9-glass bottle stopper; 10-snake condenser; 11-magnetic stirrer; 12-gas diffusion tube; 13-ion selective electrode of ion meter; 14-gas passage; 15-condensate passage. DETAILED DESCRIPTION

[0049] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments.

[0050] Example 1

[0051] 1. Main instruments

[0052] 1) Mettler Toledo composite silver / sulfide ion electrode (BNC connector) perfectION

[0053] 2) Mettler Toledo Multi-parameter Tester S400-B

[0054] 3) Mettler Toledo ME204E electronic balance

[0055] like Figure 1As shown, a reaction device for determining sulfide in wet-process phosphoric acid comprises a nitrogen gas supply device 1, wherein the outlet of the nitrogen gas supply device 1 is connected to one end of a rotor flowmeter 2 through a gas passage 14, and the other end of the rotor flowmeter 2 is connected to an air guide tube 7 through the gas passage 14, and the air guide tube 7 extends from one end of a three-necked reaction bottle 8 into the three-necked reaction bottle 8, and the other end of the three-necked reaction bottle 8 is provided with a glass bottle stopper 9, and the three-necked reaction bottle 8 is provided with a magnetic rotor 6, and the top central port of the three-necked reaction bottle 8 is connected to one end of an outer tube of a serpentine condenser 10, The other end of the outer tube of the serpentine condenser 10 is connected to the gas diffusion tube 12 through the gas passage 14; the gas diffusion tube 12 is placed in a beaker, and the beaker is provided with a magnetic rotor 6 and a sulfur ion selective electrode 13 of an ion meter; the beaker is placed on a magnetic stirrer 11, and the magnetic stirrer 11 is located on a lifting platform 4, and the three-mouth reaction bottle 8 is located on a heated magnetic stirrer 5, and the magnetic stirrer 5 is located on a lifting platform 4, and the two ends of the inner tube of the serpentine condenser 10 are respectively connected to the inlet and outlet of the cooling circulation device 3 through the condensate passage 15. The serpentine condenser 10 and the cooling circulation device 3 and their corresponding connected pipelines constitute a condensation system.

[0056] 2. Main Reagents

[0057] 1) Deoxygenated deionized water: Deionized water with a resistivity ≥ 18MΩ·cm (25°C) must be deoxygenated first.

[0058] 2) Hydrochloric acid solution: 1+1. Take 50 ml of ultrapure water and slowly add 50 ml of hydrochloric acid to 100 ml.

[0059] 3) Sodium hydroxide solution: c(NaOH) = 2 mol / L. Weigh 80 g of sodium hydroxide, dissolve it in water and dilute to 1 L.

[0060] 4) Sulfide Anti-Oxidant Buffer (SAOB) solution: Add 600 ml of experimental water to a 1000 ml beaker, add 80 g of sodium hydroxide, 35 g of ascorbic acid and 67 g of disodium ethylenediaminetetraacetate, stir until completely dissolved and cool to near room temperature, and transfer the mixed solution to a 1000 ml volumetric flask. The final concentration of sodium hydroxide in the sulfide fixative solution is 2 mol / L, the concentration of ascorbic acid is 0.2 mol / L, and the concentration of disodium ethylenediaminetetraacetate is 0.2 mol / L.

[0061] 3. Experimental Methods

[0062] First, calibrate the sulfur ion selective electrode according to the instrument requirements and establish a concentration curve.

[0063] Use a pipette to transfer 25 mL of SAOB and 25 mL of deionized water into a 100 mL beaker as the absorption solution and add it to the magnetic rotor.

[0064] Add 140mL of SAOB solution to a 250mL three-necked reaction bottle for later use. Shake and mix phosphoric acid sample A evenly, then quickly measure 10mL and transfer it to the reaction bottle and let it stand without stirring. Then add 55mL of hydrochloric acid solution until the pH value is less than 6, and close the bottle stopper.

[0065] according to Figure 1 Connect the absorption device as shown, maintain the condensation cycle temperature at -10°C, connect nitrogen and adjust the flow rate to 60mL / min, heat the reactor to 125°C, maintain the rotation speed of the reactor and the absorption liquid at 500r / min, and perform a leak test to confirm that there is no leakage.

[0066] Record the highest concentration point when the electrode change rate of the sample is within the range of ±0.2mV / min, and record the potential value and concentration value at this time;

[0067] The concentration of divalent sulfide ions in acid sample A was calculated according to the following formula:

[0068]

[0069] in:

[0070] ——Sulfide ion concentration, unit: mg / L;

[0071] V (PA) ——Measure the volume of phosphoric acid, in mL;

[0072] ρ (T) ——Electrode reading concentration, unit: mg / L;

[0073] V (W+SAOB) ——Total volume of the mixed solution of water and SAOB measured, unit: mL.

[0074] The same sample was tested six times, and the average, standard deviation, and relative standard deviation were calculated. The results are shown in Table 2 below.

[0075] Table 2

[0076]

[0077] Example 2

[0078] Example 1 was repeated, except that the sample was replaced with phosphoric acid sample B having a relatively higher concentration. The test results are shown in Table 3 below:

[0079] Table 3

[0080]

[0081] Example 3

[0082] Example 1 was repeated, except that a standard water sample with a total content of 0.02 mg (corresponding to a hydrogen sulfide concentration of 0.4 mg / L) was added to the phosphoric acid sample A, and the measurement was repeated 5 times.

[0083] The test results are shown in Table 4 below:

[0084] Table 4

[0085]

[0086] Example 4

[0087] Example 1 was repeated, except that a standard water sample with a total content of 1 mg (corresponding to a hydrogen sulfide concentration of 20 mg / L) was added to the phosphoric acid sample B, and the measurement was repeated 5 times.

[0088] The test results are shown in Table 5 below:

[0089] Table 5

[0090]

[0091] It can be seen from the above examples that the precision determined by this method can reach 80% to 120%, and the spike recovery rate can reach 80% to 120%, which is better than the index requirements in the "Determination of Sulfide in Water by Methylene Blue Spectrophotometry" (HJ 1226-2021). The present invention has significant effects. From the actual situation of phosphoric acid determination, it is obviously more appropriate to use this method as a detection method for wet-purified phosphoric acid and its intermediate product sulfide.

[0092] The selective ion electrode method is applied to actual production. By analyzing key samples, the test results are consistent with the logic of the production process, reflecting the accuracy of the analysis and test, which can provide a reference for H 2 It can accurately, quickly and effectively identify the effect of various production processes on the removal of sulfides in wet-process phosphoric acid, and help the production department find H 2 The trend of S is convenient for further material management. At the same time, the detection of intermediate products can effectively grasp the H in each process interval 2 The content range of S can be determined, so as to timely and effectively control the quality of wet-process phosphoric acid production products and raw materials.

[0093] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for determining sulfide in wet-process phosphoric acid, characterized in that: The following steps are involved: 1) Fixation of phosphoric acid sample: Add an appropriate amount of wet-process phosphoric acid sample to be tested into a reaction container containing a sulfide ion fixative solution, first fix the sulfide in the phosphoric acid, and obtain a solution to be tested; 2) Sulfide conversion and release: The test liquid enters the reaction device and undergoes pH adjustment, heating, and stirring to convert the sulfide into hydrogen sulfide and release it, which then enters the absorption liquid after condensation and gas dispersion absorption; 3) Sulfide absorption and numerical reading: After the absorption liquid fully absorbs the hydrogen sulfide released from the sample, the sulfur ion concentration value of the absorption liquid is obtained using a sulfur ion selective electrode; 4) Calculate the true concentration of the sample: Based on the concentration of sulfur ions, calculate according to the following formula: in, is the sulfide ion concentration, in mg / L; V (PA) To measure the volume of phosphoric acid, the unit is mL; ρ (T) is the electrode reading concentration, in mg / L; V (W+SAOB) The total volume of the mixed solution of water and sulfide ion fixative measured, in mL.

2. The method for determining sulfide in wet-process phosphoric acid according to claim 1, characterized in that: The preparation method of the sulfide ion fixing agent solution is: Add 550-650 mL of water to a 1000 mL beaker, then slowly add sodium hydroxide, ascorbic acid and disodium ethylenediaminetetraacetate to the water in sequence, stir until all substances are dissolved and cooled to room temperature, then transfer the solution to a 1000 mL volumetric flask and make up to volume with water; the concentration of sodium hydroxide in the sulfide ion fixative solution is 2 mol / L, the concentration of ascorbic acid is 0.2 mol / L, and the concentration of disodium ethylenediaminetetraacetate is 0.2 mol / L, and the water is one of deionized water or ultrapure water.

3. The method for determining sulfide in wet-process phosphoric acid according to claim 1, characterized in that: In the step 1), the mixed volume ratio of the wet-process phosphoric acid sample and the sulfide ion fixative solution is 1:14, and the volume of the wet-process phosphoric acid sample is ≥10 mL; the reaction container should be a glass three-necked flask with a capacity of ≥250 mL.

4. The method for determining sulfide in wet-process phosphoric acid according to claim 1, characterized in that: In the step 2), a hydrochloric acid solution is used for pH adjustment. The hydrochloric acid solution is a solution prepared by diluting concentrated hydrochloric acid and pure water in equal proportions, and the amount of the solution is 5.5 times the volume of the wet-process phosphoric acid sample.

5. The method for determining sulfide in wet-process phosphoric acid according to claim 1, characterized in that: The reaction device is a heated magnetic stirring device, the heating temperature is 120-130° C.; the stirring rate is ≥500 r / min; the gas dispersion absorption is purged with nitrogen, and the nitrogen gas flow rate should be set to 60 / min.

6. The preparation method of the method for determining sulfide in wet-process phosphoric acid according to claim 1, characterized in that: In the step 2), the condensation adopts a serpentine condenser as a cooling channel, and the condensation temperature is -15 to -5°C.

7. The method for determining sulfide in wet-process phosphoric acid according to claim 1, characterized in that: In the step 3), the absorption liquid includes ultrapure water and a sulfide ion fixative solution, and the ultrapure water and the sulfide ion fixative solution are mixed in a volume ratio of 1:

1.

8. The method for determining sulfide in wet-process phosphoric acid according to claim 1, characterized in that: In the step 3), the absorption liquid uses a magnetic stirring rotor to promote sulfide absorption, and the stirring rate should be ≥500r / min.

9. The method for determining sulfide in wet-process phosphoric acid according to claim 1, characterized in that: In the step 3), the absorption liquid is measured using a sulfur ion selective electrode, and the potential value and concentration value are recorded when the electrode change rate is observed to be within the range of ±0.2 mV / min.

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