A method for determining sulfides in an environmental water body

Abstract

A kind of method for determining sulfide in environmental water body is determined by using X-ray fluorescence spectrometry.In environmental water body, slightly excessive copper chloride solution and sodium hydroxide solution are added to convert unstable sulfide into extremely difficultly soluble copper sulfide precipitate, 0.23 μm PTFE filter membrane is used to filter sample preparation technology to enrich and separate copper sulfide precipitate in environmental water body, dilute hydrochloric acid is used to wash the precipitate to remove Cu (OH) 2 and Cu 2+ Residue, the microporous filter membrane that is naturally dried is pressed into sheet in the middle of two polyethylene sheets under high pressure condition, the copper element content in difficultly soluble copper sulfide is determined by WDXRF, and then the concentration of sulfide in environmental water body is obtained according to the conversion of equal molar quantity.The present application has the advantages of low detection limit, high accuracy, good precision, wide linear range and short analysis time.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ecological environment quality detection, and particularly relates to a method for determining sulfide in environmental water. BACKGROUND

[0002] The sulfide in water refers to the dissolved inorganic sulfide and acid-soluble metal sulfide in water, including dissolved H2S, HS - and S 2- , and soluble sulfide and acid-soluble metal sulfide existing in suspended solids. The sulfide in environmental water mainly has two sources, one is the sulfide produced by the reduction of sulfate or the decomposition of sulfur-containing organic matter in nature, and the other is the sulfide contained in the wastewater discharged into the environment by human activities. Generally, the concentration of sulfide in environmental water is low, and its existing form is related to water temperature and pH. At 25℃, when pH≥11.96, the main existing form of sulfide is S 2- ; when pH<7.04, the sulfide is almost completely converted into H2S which is highly toxic. When the concentration of sulfide in water is 0.094-1.9mg / L, it will cause the activity of most aquatic organisms to decrease, organs to be damaged, and even death. The sulfide also plays an important role in the biogeochemical processes of many elements, such as affecting the occurrence form and bioavailability of heavy metals by complexing with heavy metal ions in anaerobic environment, inducing the release of phosphorus and aggravating the eutrophication of water body, etc. Therefore, accurately and reliably determining the content of sulfide in water is of great significance to water environment protection and related scientific research.

[0003] Water sample collection and pretreatment is one of the important links affecting the accuracy of water quality monitoring results. Since the sulfide is easy to escape from water and be oxidized by oxygen, the sample disturbance and air exposure should be minimized during sampling. The usual practice is to pre-add a certain amount of zinc acetate solution into the sampling bottle, then add the collected water sample into the bottle, and finally add sodium hydroxide solution and mix well. The added zinc acetate and sodium hydroxide solution can convert the unstable sulfide into stable zinc sulfide for preservation. After the water sample collected on site is brought back to the laboratory, it is pretreated before determination. The commonly used pretreatment methods are acidification-blowing-absorption method and acidification-distillation-absorption method. The acidification-blowing-absorption method is to first acidify the water sample to convert the sulfide in the sample into H2S, then use high-purity nitrogen gas to blow off H2S, absorb it with alkaline absorption liquid, and finally calculate the concentration of sulfide in the sample by determining the content of sulfide in the absorption liquid. The acidification-distillation-absorption method is to transfer the H2S generated by acidifying the water sample to the absorption liquid through distillation. Both of the two pretreatment methods need at least 30min to process a single sample. Moreover, since the nitrogen gas used in the acidification-blowing-absorption method often contains a small amount of oxygen, the sulfide will be oxidized and lost during the experiment.

[0004] The determination methods of sulfide content in environmental water bodies mainly include iodometric method (HJ / T 60-2000 “Determination of sulfide in water - iodometric method”) and spectrophotometric method (HJ 1226-2021 “Determination of sulfide in water - methylene blue spectrophotometric method”). The iodometric method has the advantages of fast speed and low cost, but also has unavoidable disadvantages, such as difficulty in determining trace and trace sulfide, and large subjective error of the operator. When the spectrophotometric method is used to determine the sulfide in environmental water bodies, it is easy to be interfered by NO2 - , SO3 2- , S2O3 2- , SCN - , NO3 - , I - , CN - and part of heavy metal ions. When the sulfide content is 0.3 mg / L, the maximum allowable content of the interfering substances in the sample is SO3 2- 700 mg / L, S2O3 2- 900 mg / L, SCN - 900 mg / L, NO3 - 200 mg / L, I - 400 mg / L, CN - 5 mg / L, Cu 2+ 2 mg / L, Pb 2+ 25 mg / L, Hg 2+ 4 mg / L. NO2 - can react with methylene blue, resulting in a lower determination result. When the concentration of NO2 - (N) is higher than 2.0 mg / L, the method is not applicable.

[0005] In X-ray spectrum analysis, the filter membrane filtering sample preparation method has the advantages of simple operation process, small matrix effect, high signal-to-noise ratio of the element to be measured, less sample and reagent consumption, green environmental protection and the like. The present application adopts the micro-porous filter membrane filtering sample preparation technology to enrich and separate the sulfide in environmental water bodies, determines the copper element content in the insoluble copper sulfide by WDXRF, and then realizes quantitative analysis of the sulfide concentration in the environmental water bodies. The present application can solve the problems of the current analysis method of the sulfide in environmental water bodies, such as complicated process, long analysis period and high analysis cost. SUMMARY

[0006] The present application provides a method for determining the sulfide concentration in environmental water bodies, which has low detection limit, high accuracy, good precision, wide linear range and short analysis time.

[0007] The environmental water bodies according to the present application refer to surface water, underground water, domestic sewage, industrial wastewater and seawater.

[0008] The inventor, through long-term exploration and trial, and multiple experiments and efforts, constantly reforms and innovates, and provides a technical scheme for solving the above technical problems, which is a method for determining sulfide in environmental water, comprising the following steps:

[0009] Step 1) Collecting environmental water samples, adding a protective reagent to facilitate the preservation of sulfide components;

[0010] Step 2) Filtering the water sample using a microporous filter membrane to obtain a precipitate A;

[0011] Step 3) Washing the precipitate A with dilute hydrochloric acid to obtain a precipitate B;

[0012] Step 4) Pressing the microporous filter membrane carrying the precipitate B into a sheet;

[0013] Step 5) Indirectly determining the concentration of sulfide in the environmental water by means of an X-ray fluorescence spectrometer.

[0014] According to a preferred embodiment of the method for determining sulfide in environmental water according to the present application, in step 1), collecting environmental water samples specifically includes: collecting a certain volume of water sample, and sequentially adding copper chloride solution and sodium hydroxide solution to convert unstable sulfide into stable copper sulfide for preservation.

[0015] According to a preferred embodiment of the method for determining sulfide in environmental water according to the present application, in step 2), filtering the water sample using a microporous filter membrane specifically includes: filtering the water sample through a 0.23 μm filter membrane and an oil-free vacuum sand core filtering device to obtain a precipitate A.

[0016] According to a preferred embodiment of the method for determining sulfide in environmental water according to the present application, in step 3), washing the precipitate with dilute hydrochloric acid specifically includes: washing the precipitate with dilute hydrochloric acid to remove Cu(OH)2 and Cu 2+ residues to obtain a precipitate B.

[0017] According to a preferred embodiment of the method for determining sulfide in environmental water according to the present application, in step 4), pressing the microporous filter membrane into a sheet specifically includes: naturally drying the microporous filter membrane carrying the precipitate B, clamping it in the middle of two polyethylene films (or sheets), and placing it in a high-pressure sample pressing machine under a pressure of 30 MPa for 3 seconds to press and solidify it into a sheet.

[0018] According to a preferred embodiment of the method for determining sulfide in environmental water according to the present application, in step 5), indirect determination by an X-ray fluorescence spectrometer specifically includes: determining the content of Cu in the sample sheet by means of an X-ray fluorescence spectrometer, and then calculating the concentration of sulfide in the environmental water according to the equivalent molar quantity.

[0019] Calculate the concentration of sulfide in the environmental water. The calculation formula is

[0020]

[0021] wherein:

[0022] p 硫化物 - concentration of sulfide in the environmental water body, mg / L;

[0023] ω 铜 - measured copper content, mg;

[0024] V - volume of water sample collected, 1 L.

[0025] According to a preferred embodiment of the method for determining sulfide in an environmental water body, the protective agent is a 134 g / L copper chloride solution and a 20 g / L sodium hydroxide solution.

[0026] According to an alternative embodiment of the method for determining sulfide in an environmental water body, the amount of copper chloride solution and sodium hydroxide solution added to the sample of environmental water body should each be in excess. That is, no more black-brown precipitate is produced when the copper chloride solution is added dropwise (indicating that the copper chloride solution has been added in excess); no more blue precipitate is produced when the sodium hydroxide solution is added dropwise (indicating that the sodium hydroxide solution has been added in excess).

[0027] According to a preferred embodiment of the method for determining sulfide in an environmental water body, the microporous filter membrane is a 0.23 μm PTFE filter membrane (diameter R = 25 mm).

[0028] According to a preferred embodiment of the method for determining sulfide in an environmental water body, the dilute hydrochloric acid is a dilute hydrochloric acid solution with pH = 3.0.

[0029] According to a preferred embodiment of the method for determining sulfide in an environmental water body, the polyethylene sheet is a polyethylene sheet with diameter R = 40 mm and thickness d = 1 mm.

[0030] According to a preferred embodiment of the method for determining sulfide in an environmental water body, the X-ray fluorescence spectrometer is Axios PW4400.

[0031] Compared with the prior art, one of the above technical solutions has the following advantages:

[0032] a) In one embodiment of the method for determining sulfide in an environmental water body, the copper chloride solution is added dropwise, so that the sulfide in the water body reacts with Cu2+ to form copper sulfide (CuS) which is extremely difficult to dissolve in water and concentrated hydrochloric acid (Ksp = 1.27 x 10-36 at 25°C). 2+ sp b) In one embodiment of the method for determining sulfide in an environmental water body, the sodium hydroxide solution is added dropwise, so that the copper sulfide (CuS) is converted into copper hydroxide (Cu(OH)2) which is insoluble in water and concentrated hydrochloric acid (Ksp = 4.8 x 10-19 at 25°C).​-36 ), which is conducive to the physical separation of sulfides and other valence state sulfur components, and fully ensures the precision and accuracy of the detection results.

[0033] b) In an embodiment of the method for determining sulfides in environmental water bodies according to the present application, the copper sulfide precipitate is washed with dilute hydrochloric acid at pH = 3.0, which not only eliminates the interference of matrix impurities (such as high salt components in seawater and wastewater), but also avoids the influence of other copper-containing compounds and sulfur-containing compounds on the determination results.

[0034] c) In an embodiment of the method for determining sulfides in environmental water bodies according to the present application, an acid and alkali resistant PTFE filter membrane with a pore size of 0.23 μm is used as the filter material, which is more conducive to the rapid and effective separation of the precipitate and the solution, while not affecting the detection limit, precision and accuracy of the determination results, and improves the detection efficiency and quality.

[0035] d) In an embodiment of the method for determining sulfides in environmental water bodies according to the present application, the microporous filter membrane is clamped in the middle of two pieces of polytetrafluoroethylene sheets, and is pressed at a pressure of 30 MPa for 3 s, which ensures the flatness and consolidation degree of the sample sheet, and the sample sheet can be used for repeated determination after being dried and stored.

[0036] e) In an embodiment of the method for determining sulfides in environmental water bodies according to the present application, the X-ray fluorescence analyzer Axios PW4400 is selected, which is equipped with a ceramic thin beryllium end window (75 μm) ultra-sharp rhodium-palladium X-ray tube, LiF200 crystal, Flow detector and Al200 spectral filter, which makes the determination work smoothly.

[0037] f) The detection limit of the method for determining sulfides in environmental water bodies according to the present application is 0.006 mg / L, which is lower than the detection limit of the national environmental protection standard HJ 1226-2021 "Determination of sulfides in water - methylene blue spectrophotometric method" (detection limit is 0.01 mg / L), indicating that the method has high sensitivity.

[0038] g) The present application provides a determination technology and solution for sulfides in environmental water bodies, which is different from the national environmental protection standard determination method. The existing standard detection method needs to acidify, heat and nitrogen blow or distill the sulfides in the sample, and then absorb the generated hydrogen sulfide with sodium hydroxide solution, and the generated sulfur ions react with N,N-dimethyl-p-phenylenediamine in ferric ammonium sulfate acid solution to generate methylene blue square which can be used for spectrophotometric determination. The pretreatment of a single sample takes about 6 hours. The pretreatment time of the present application is significantly shortened, and has the characteristics of safety, high efficiency, high precision and high accuracy, and has very practical value. DETAILED DESCRIPTION

[0039] The following will be described in conjunction with specific embodiments.

[0040] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work belong to the scope of protection of the present application. Therefore, the following detailed description of the embodiments of the present application is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application.

[0041] Example 1

[0042] Reagents: copper chloride solution 134 g / L, sodium hydroxide solution 20 g / L, hydrochloric acid solution (adjusting pH = 3.0), sodium sulfide solution (10 g / L), copper standard stock solution 1000 mg / L.

[0043] Water sample collection: accurately collect 1 L of water sample into a brown ground glass bottle, slowly drop 134 g / L of copper chloride solution while shaking, when there is no black precipitate produced (indicating that the copper chloride solution has been added in excess), stop adding the copper chloride solution; then add 20 g / L of sodium hydroxide solution and shake until there is no blue precipitate produced (indicating that the sodium hydroxide solution has been added in excess). Seal the water sample with a plug and store it in the dark. Transfer it to the analysis laboratory for detection within 7 days.

[0044] Water sample filtration: use a full-glass vacuum suction filter with a 0.23 μm PTFE filter membrane (diameter R = 25 mm) to filter. Pour the water sample into the filter cup in batches, and under negative pressure difference, the precipitate is enriched on the filter membrane, and the filtrate is collected in the collection bottle. When the liquid in the water sample collection bottle is completely transferred to the filter, about 60 mL of filtrate is used to shake and wash the water sample collection bottle to ensure that there is no precipitate remaining on the wall of the collection bottle, and the washing liquid is filtered through the aforementioned filter membrane. The filtered precipitate is collected to obtain precipitate A. The full-glass vacuum suction filter is prior art, and the present application does not make any innovation to the suction filter. Generally, the suction filter includes a filter cup, a sand core filter head, a liquid collection bottle, a clamp, a conduit and a vacuum pump. In this embodiment, a full-glass vacuum suction filter with a filter membrane of diameter R = 25 mm is selected. The suction filter needs to be airtight, and the water sample can only flow into the receiving bottle after being filtered through the filter membrane.

[0045] Washing the precipitate: use a hydrochloric acid solution with pH = 3.0 to wash the precipitate A three times (each time about 30 mL. If the filtrate still appears blue after the last washing, the number of washing times can be appropriately increased); then use deionized water to wash the precipitate three times (each time about 30 mL). Finally, precipitate B is obtained.

[0046] Pressing sample: the microporous filter membrane carrying the precipitate B was naturally air-dried, clamped in the middle of two polyethylene films (or sheets, diameter R = 40 mm), and placed in a high-pressure sample pressing machine under a pressure of 30 MPa for 3 s to press and solidify into a sheet for determination of sulfide.

[0047] Standard series preparation: 0.01 mg, 0.05 mg, 0.10 mg, 0.50 mg, 1.0 mg, 5.0 mg, 10.0 mg, 50.0 mg, and 100.0 mg of copper ions were respectively taken into a 100 mL beaker, and 15 mL of 10 g / L sodium sulfide solution was added, and stirred to completely precipitate. The above-mentioned steps of "water sample filtration", "precipitate washing", and "sample pressing" were sequentially performed to obtain standard series samples for calibration curve.

[0048] Instrument determination: the X-ray fluorescence spectrometer selected Axios PW4400, with a ceramic thin beryllium end window (75 μm) ultra-sharp rhodium-palladium X-ray tube, LiF200 crystal, Flow detector, and Al200 spectral filter. Test conditions: element: Cu; analysis line: K α ; crystal: LiF200; collimator: 300 nm; detector: Flow; spectral filter: Al200; X-ray tube voltage: 60 kV; X-ray tube current: 60 mA; 2θ: analysis line 45.0202°, background 1.6830°; time: analysis line 25 s, background 10 s; PHD: LL20, UL66; sulfide concentration conversion factor: λ = 32.066 / 63.546 = 0.5046.

[0049] Using the method, different sources of environmental water samples were determined.

[0050] Table 1 Detection limit and determination lower limit test

[0051]

[0052] As can be seen from the results in Table 1, the detection limit of sulfide in environmental water determined by the method is 0.006 mg / L, which is lower than the detection limit (0.01 mg / L) of "Determination of Sulfide in Water - Methylene Blue Spectrophotometric Method" (HJ 1226-2021), indicating that the method has high sensitivity.

[0053] Table 2 Precision test data.

[0054]

[0055] It can be seen from the results in Table 2 that the relative standard deviations of the determination of sulfides in four different environmental water samples, including surface water, seawater, domestic sewage and industrial wastewater, are 2.50%, 7.86%, 1.74% and 1.42% respectively. It meets the requirement of the relative standard deviation of sulfides being less than 30% in the “Determination of Sulfides in Water - Methylene Blue Spectrophotometric Method” (HJ 1226-2021).

[0056] Table 3 Accuracy test data

[0057]

[0058] It can be seen from the results in Table 3 that the recoveries of sulfides in three different environmental water samples in the method are 106.0%, 98.8% and 96.0%. It meets the requirement of the standard addition recovery of sulfides being controlled between 60% and 120% in the “Determination of Sulfides in Water - Methylene Blue Spectrophotometric Method” (HJ 1226-2021).

[0059] The above is only the preferred embodiment of the present application, it should be pointed out that the above preferred embodiment should not be regarded as limiting the present application, the protection scope of the present application should be limited by the scope defined by the claims. For ordinary skilled in the art, without departing from the spirit and scope of the present application, a number of improvements and refinements can also be regarded as the protection scope of the present application.

Claims

1. A method for determining sulfides in an environmental water body, comprising a water body sample pretreatment step and an X-ray fluorescence spectroscopy analysis determination step, characterized by, It comprises the following steps: Step 1) collecting environmental water sample: collect a certain volume of water sample, add a little excess copper chloride solution and sodium hydroxide solution in turn to convert unstable sulfide into stable copper sulfide for preservation, no more black-brown precipitate is produced when adding copper chloride solution dropwise, which indicates that the copper chloride solution has been added in excess; no more blue precipitate is produced when adding sodium hydroxide solution dropwise, which indicates that the sodium hydroxide solution has been added in excess; Step 2) filtering the water sample through microporous filter membrane: filter the water sample through 0.23 μm filter membrane and oil-free vacuum sand core filtering device to obtain Cu(OH)2+CuS composite precipitate A; Step 3) Washing of the precipitate A: The precipitate A is washed at least 5 times with 20 mL of dilute hydrochloric acid each time to remove Cu(OH)2and Cu 2+ residues, resulting in a CuS precipitate B which is insoluble in dilute hydrochloric acid; Step 4) pressing the microporous filter membrane into a sheet: naturally air dry the microporous filter membrane carrying the precipitate B, clamp it in the middle of two polyethylene sheets, and place it in a high-pressure sample pressing machine under a pressure of 30 MPa for 2 s to press and solidify into a sheet; Step 5) determining the content of Cu in the sample sheet by X-ray fluorescence spectrometer, and then calculating the concentration of sulfide in the environmental water body according to the equivalent molar mass conversion.

2. The method of determining sulfides in an environmental water body according to claim 1, wherein, In the step 1), the concentration of the copper chloride solution is 134 g / L, and the concentration of the sodium hydroxide solution is 20 g / L.

3. The method of determining sulfides in an environmental water body according to claim 1, wherein, In the step 2), the microporous filter membrane is a PTFE filter membrane with a sheet diameter R=25 mm and a pore size of 0.23 μm.

4. The method of determining sulfides in an environmental water body according to claim 1, wherein, In the step 3), the dilute hydrochloric acid is a hydrochloric acid solution with pH=2.

0.

5. The method of determining sulfides in an environmental water body according to claim 1, wherein, The polyethylene sheet is a polyethylene sheet with a diameter R=40 mm and a thickness d=1 mm.

6. The method of determining sulfides in an environmental water body of claim 1, wherein, The X-ray fluorescence spectrometer is Axios PW4400.

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