Method for stably fixing sulfide in water for long time

Abstract

The invention discloses a method for stably fixing sulfides in water for a long time. The method comprises the following operation steps: step 1, preparing a composite reagent; 2, fixing the water sample; 2, fixing the water sample; step 4, automatic detection; step 5, quality control; the invention has the following beneficial effects: through steric hindrance effect and electrostatic repulsion effect of sodium carboxymethyl cellulose, zinc sulfide is uniformly dispersed in the form of 50-200nm nanoscale particles, particle aggregation and sedimentation are effectively inhibited, long-acting preservation of more than or equal to 7 days is realized, pH value adjustment or addition of other chemical reagents is not needed during preservation, and the method is simple and convenient to operate. A dynamic equilibrium system is established through coordination competition of disodium ethylene diamine tetraacetate and zinc ions, and when the concentration of sulfide in a water sample changes in a range of 0.1 mg / L-50 mg / L, the release rate of the zinc ions can be adaptively adjusted, so that complete generation of zinc sulfide precipitates is ensured, and a wider concentration detection range is covered.

Description

Technical Field

[0001] This invention relates to the field of xx technology, and in particular to a method for long-term stable fixation of sulfides in water. Background Technology

[0002] Sulfur is widely distributed in nature and is a basic component of biomass. Sulfur can change between -2 and +6 oxidation states and exists in various inorganic and organic forms. Its transformation process is complex. Sulfur is present in water bodies, the atmosphere, and sediments. The migration, transformation, and biological metabolism of sulfur play a significant role in global biogeochemical cycles and have a major impact on the global ecological environment.

[0003] China is a major aquaculture country. When the sulfide content in water bodies is too high, oxidation reactions occur, consuming oxygen and leading to oxygen deficiency. Sulfides also induce the release of phosphorus from sediments, further exacerbating eutrophication. Furthermore, sulfides irritate and corrode the gill tissues of aquatic organisms and combine with hemoglobin to produce sulfohhemoglobin, reducing the blood's oxygen-carrying capacity and causing fish mortality. This also leads to excessive nitrogen oxide levels, further aggravating water pollution and posing a severe threat to aquatic life. Studies have shown that when the concentration of volatile sulfur in water sediments exceeds 1.7 mg / g, aquatic life is essentially unable to survive. Therefore, this case study was developed to address these issues. Summary of the Invention

[0004] The technical solution of the present invention to achieve the above objectives is: a method for long-term stable fixation of sulfides in water, characterized by comprising the following operational steps: Step 1: Preparation of compound reagents Accurately weigh 50g of zinc acetate ( ), 5g disodium ethylenediaminetetraacetate ( ) and 10g sodium carboxymethyl cellulose ( Add the first 800 mL of deionized water to the second 800 mL of water and stir continuously at 300 rpm on a magnetic stirrer until completely dissolved. Then, bring the volume up to 1000 mL with deionized water to form a homogeneous and stable sulfide fixative. Step 2: Water sample fixation Collect 500 mL of water sample into a polyethylene sampling bottle, immediately add 2 mL of the sulfide fixative prepared in step 1, and manually shake for 30 seconds to ensure that the reagent and water sample are fully mixed, ensuring that the sulfide and zinc acetate react completely to form zinc sulfide precipitate; Step 3: Long-term preservation Once fixed, the sample is directly sealed in a light-protected environment and stored at a temperature range of 4℃~25℃. The effective storage period is ≥7 days, during which no pH value needs to be adjusted or other chemical reagents need to be added. Step 4: Automated Detection The fixed sample is directly injected into a spectrophotometric or gas phase molecular absorption spectrometry detection system: Spectrophotometry: The absorbance is measured at a wavelength of 665 nm, and the sulfide concentration is calculated through a standard curve; Gas phase molecular absorption spectrometry: The sulfide content is quantified based on the peak area at a wavelength of 205 nm. Step 5: Quality Control The following quality control measures are implemented for each batch of analysis: Blank experiment: Insert one ultrapure water blank for every 10 samples, with a blank value ≤0.02mg / L; Parallel sample determination: Repeat the determination of the same water sample 3 times, with a relative standard deviation (RSD) ≤3%; Standard reference comparison: Insert a sulfide standard solution with a concentration of 1.0mg / L for each batch, with a deviation between the measured value and the standard value ≤5%.

[0005] In step 1, the chelating agent is disodium ethylenediaminetetraacetate, the thickener is sodium carboxymethyl cellulose, and the mass ratio of each component in the reagent formula is zinc acetate: disodium ethylenediaminetetraacetate: sodium carboxymethyl cellulose = 10:1:2.

[0006] During the preservation process in step 3, zinc sulfide is uniformly dispersed in the form of nanoparticles. The steric hindrance effect and electrostatic repulsion of sodium carboxymethyl cellulose inhibit particle aggregation and sedimentation, ensuring the sampling uniformity of the automatic sampling system. The particle size distribution range is 50 nm to 200 nm.

[0007] During the preservation process in step 3, zinc sulfide is uniformly dispersed in the form of nanoparticles. The steric hindrance effect and electrostatic repulsion of sodium carboxymethyl cellulose inhibit particle aggregation and sedimentation, ensuring the sampling uniformity of the automatic sampling system. The particle size distribution range is 50 nm to 200 nm.

[0008] In the detection process of step 4, the chelating agent has pre-bound calcium and magnesium ions in the water sample to avoid the formation of carbonates or hydroxides that interfere with precipitation during detection. The detection limit of spectrophotometry is ≤0.005 mg / L, and the detection limit of gas phase molecular absorption spectroscopy is ≤0.001 mg / L.

[0009] The fixative formulation in step 1 establishes a dynamic equilibrium system through coordination competition between disodium ethylenediaminetetraacetate and zinc ions. When the sulfide concentration in the water sample varies within the range of 0.1 mg / L to 50 mg / L, the zinc ion release rate is adaptively adjusted to ensure complete formation of zinc sulfide precipitate.

[0010] The fixation process in step 2 can be completed at the sampling site or in the laboratory. The fixed sample can be directly used for portable detection equipment, meeting the dual needs of emergency monitoring in the field and routine laboratory analysis. The equipment response time is ≤30 seconds.

[0011] This invention provides a method for long-term stable fixation of sulfides in water. Through the steric hindrance and electrostatic repulsion of sodium carboxymethyl cellulose, zinc sulfide is uniformly dispersed into nanoparticles of 50nm~200nm, effectively inhibiting particle aggregation and sedimentation, achieving long-term preservation for ≥7 days (compared to only 24 hours using traditional methods). Furthermore, no pH adjustment or addition of other chemical reagents is required during preservation. A dynamic equilibrium system is established through coordination competition between disodium ethylenediaminetetraacetate and zinc ions. When the sulfide concentration in the water sample varies within the range of 0.1mg / L~50mg / L, the zinc ion release rate can be adaptively adjusted. This ensures complete zinc sulfide precipitation, covering a wider concentration detection range. A neutral formula (pH=6~8) avoids EDTA dissociation and metal hydroxyl precipitation caused by the introduction of NaOH in traditional alkaline fixation methods, maintaining chelation stability. It also preferentially binds to calcium and magnesium ions in the water sample, blocking interference from carbonates or hydroxides during detection. The composite reagent integrates the functions of zinc acetate, disodium ethylenediaminetetraacetate, and sodium carboxymethyl cellulose, simplifying the operation process. No experience-based adjustments are required; the fixation process can be completed on-site or in the laboratory. It is compatible with portable detection equipment, meeting the dual needs of emergency field monitoring and routine laboratory analysis. Detailed Implementation

[0012] The present invention will now be described in detail, including embodiments. Therefore, this application protects a method for the long-term stable fixation of sulfides in water, based on the precipitation reaction of zinc acetate with sulfides ( By innovatively introducing thickeners (such as sodium carboxymethyl cellulose) and chelating agents (such as disodium EDTA), a long-lasting fixation system under neutral conditions was constructed. In practice, zinc acetate, chelating agents, and thickeners are dissolved and mixed in a specific ratio to form a composite reagent, which is then quantitatively added to the water sample to complete the fixation.

[0013] Its improvement mechanism is reflected in four aspects: 1) The thickener, through electrostatic adsorption, steric hindrance, and viscosity control, ensures that the generated ZnS is uniformly dispersed in molecular particles, avoiding agglomeration and sedimentation, and improving the uniformity of automatic sample injection; 2) The chelating agent and excess Formation of stable chelates (such as ), achieving dynamic equilibrium through coordination competition and precipitation reaction, adapting to different concentrations of sulfides, and achieving long-term fixation for over 7 days (traditional methods only last 24 hours); 3) The neutral formula avoids the introduction of NaOH, preventing EDTA dissociation at high pH. form( ) and metal hydroxyl precipitates (such as ), maintain chelation stability; 4) The compound reagent integrates the functions of zinc acetate, thickener, and chelating agent, simplifying the operation process and eliminating the need for experience-based control.

[0014] Working principle: Based on the precipitation reaction of zinc acetate with sulfides, sulfides are fixed through two pathways: under acidic or neutral conditions, zinc acetate reacts with dissolved hydrogen sulfide (… A neutralization reaction occurs, producing sparingly soluble zinc sulfide (Zn(sulfide)). solubility product In alkaline or neutral water, zinc ions react directly with sulfur ions ( ); The reaction combines to form zinc sulfide precipitate, and the reaction equilibrium constant reaches... This indicates a strong tendency for the reaction to produce a precipitate. To address the problem of zinc hydroxide precipitation caused by excess zinc ions in traditional methods, disodium ethylenediaminetetraacetate (EDTA disodium) is introduced as a chelating agent. It binds to zinc ions through a hexadectic coordination structure (2 nitrogen atoms and 4 carboxylic acid oxygen atoms). ) forms a five-membered ring chelate ( The stability constant lgK = 16.5, far exceeding the solubility product of zinc hydroxide ( The chelation and precipitation reactions reach a dynamic equilibrium, and the concentration of free zinc ions is maintained at a certain level by controlling the amount of EDTA used. to The mol / L range ensures both sulfide precipitation efficiency and prevents excessive zinc ions.

[0015] Neutral conditions (pH = 6~8) are the key innovation of this system: at this temperature, EDTA mainly functions as... It exists in a form that has a higher chelation efficiency with zinc ions than under acidic conditions. The morphology has been improved by three orders of magnitude, through the formula. This ensures that zinc ions are effectively chelated without forming precipitates. Simultaneously, EDTA preferentially binds to calcium ions, which are commonly found in water. ), magnesium ions ( This forms a more stable chelate (with a stability constant of lgK=10.7 for calcium ions and lgK=8.8 for magnesium ions), blocking the formation of hydroxides and avoiding turbidity interference caused by calcium and magnesium ion precipitation in the traditional alkaline fixation method.

[0016] To address the issue of zinc sulfide particle agglomeration, sodium carboxymethyl cellulose (CMC-Na) was introduced as a thickener: its carboxymethyl groups ( Adsorbed onto the zinc sulfide surface, the particles are given an additional negative charge (zeta potential increases from -15mV to -35mV), meeting the electrostatic stability requirements of DLVO theory; the polymer chains form a physical barrier between particles (molecular rotation radius approximately 50nm), generating entropic repulsion to inhibit aggregation caused by van der Waals forces; a 0.5% CMC-Na solution increases the system viscosity to 15mPa·s, reducing Brownian motion velocity (particle collision frequency from...). The frequency / (s·cm²) decreased to (times / (s·cm²)); The hydrophilic groups reduce the contact angle of zinc sulfide particles from 120° to 45°, enhancing compatibility with the aqueous phase and preventing aggregation caused by hydrophobic interactions.

[0017] Finally, a composite reagent was formed by compounding zinc acetate, disodium EDTA, and CMC-Na in a mass ratio of 2:1:0.5, achieving multiple synergistic effects: CMC-Na delays the release of zinc ions, extending the precipitation reaction time from 2 hours in traditional methods to more than 7 days; the molar ratio of EDTA to zinc sulfide is controlled at 0.8~1.2 to ensure that more than 95% of zinc ions are in a chelated or precipitated state; the composite reagent forms a weak gel network, maintaining structural stability when standing and rapidly restoring fluidity after shaking, making it suitable for automated sample introduction systems. This system, through the combination of chemical equilibrium regulation and physical dispersion technology, achieves a comprehensive improvement in sulfide fixation efficiency, stability, and ease of operation.

[0018] The above technical solutions only embody the preferred technical solutions of the present invention. Any modifications that may be made by those skilled in the art to certain parts thereof embody the principles of the present invention and fall within the protection scope of the present invention.

Claims

1. A method for long-term stable fixation of sulfides in water, characterized in that, The following steps are included: Step 1: Preparation of compound reagents Accurately weigh 50g zinc acetate, 5g disodium ethylenediaminetetraacetate and 10g sodium carboxymethyl cellulose, add them sequentially to 800mL of deionized water, and stir continuously at 300rpm on a magnetic stirrer until completely dissolved. Then, bring the volume to 1000mL with deionized water to form a homogeneous and stable sulfide fixative. Step 2: Water sample fixation Collect 500 mL of water sample into a polyethylene sampling bottle, immediately add 2 mL of the sulfide fixative prepared in step 1, and manually shake for 30 seconds to ensure that the reagent and water sample are fully mixed, ensuring that the sulfide and zinc acetate react completely to form zinc sulfide precipitate; Step 3: Long-term preservation Once fixed, the sample is directly sealed in a light-protected environment and stored at a temperature range of 4℃~25℃. The effective storage period is ≥7 days, during which no pH value needs to be adjusted or other chemical reagents need to be added. Step 4: Automated Detection The fixed sample is directly injected into a spectrophotometric or gas phase molecular absorption spectrometry detection system: Spectrophotometry: The absorbance is measured at a wavelength of 665 nm, and the sulfide concentration is calculated through a standard curve; Gas phase molecular absorption spectrometry: The sulfide content is quantified based on the peak area at a wavelength of 205 nm. Step 5: Quality Control The following quality control measures are implemented for each batch of analysis: Blank experiment: Insert one ultrapure water blank for every 10 samples, with a blank value ≤0.02mg / L; Parallel sample determination: Repeat the determination of the same water sample 3 times, with a relative standard deviation (RSD) ≤3%; Standard reference comparison: Insert a sulfide standard solution with a concentration of 1.0mg / L for each batch, with a deviation between the measured value and the standard value ≤5%.

2. The method for long-term stable fixation of sulfides in water according to claim 1, characterized in that, In step 1, the chelating agent is disodium ethylenediaminetetraacetate, the thickener is sodium carboxymethyl cellulose, and the mass ratio of each component in the reagent formula is zinc acetate: disodium ethylenediaminetetraacetate: sodium carboxymethyl cellulose = 10:1:

2.

3. The method for long-term stable fixation of sulfides in water according to claim 2, characterized in that, During the preservation process in step 3, zinc sulfide is uniformly dispersed in the form of nanoparticles. The steric hindrance effect and electrostatic repulsion of sodium carboxymethyl cellulose inhibit particle aggregation and sedimentation, ensuring the sampling uniformity of the automatic sampling system. The particle size distribution range is 50 nm to 200 nm.

4. The method for long-term stable fixation of sulfides in water according to claim 3, characterized in that, During the preservation process in step 3, zinc sulfide is uniformly dispersed in the form of nanoparticles. The steric hindrance effect and electrostatic repulsion of sodium carboxymethyl cellulose inhibit particle aggregation and sedimentation, ensuring the sampling uniformity of the automatic sampling system. The particle size distribution range is 50 nm to 200 nm.

5. The method for long-term stable fixation of sulfides in water according to claim 4, characterized in that, In the detection process of step 4, the chelating agent has pre-bound calcium and magnesium ions in the water sample to avoid the formation of carbonates or hydroxides that interfere with precipitation during detection. The detection limit of spectrophotometry is ≤0.005 mg / L, and the detection limit of gas phase molecular absorption spectroscopy is ≤0.001 mg / L.

6. The method for long-term stable fixation of sulfides in water according to claim 5, characterized in that, The fixative formulation in step 1 establishes a dynamic equilibrium system through coordination competition between disodium ethylenediaminetetraacetate and zinc ions. When the sulfide concentration in the water sample varies within the range of 0.1 mg / L to 50 mg / L, the zinc ion release rate is adaptively adjusted to ensure complete formation of zinc sulfide precipitate.

7. The method for long-term stable fixation of sulfides in water according to claim 6, characterized in that, The fixation process in step 2 can be completed at the sampling site or in the laboratory. The fixed sample can be directly used for portable detection equipment, meeting the dual needs of emergency monitoring in the field and routine laboratory analysis. The equipment response time is ≤30 seconds.