CN107643206B - Pretreatment method for high-chlorine water before COD (chemical oxygen demand) determination and application thereof - Google Patents
Pretreatment method for high-chlorine water before COD (chemical oxygen demand) determination and application thereof Download PDFInfo
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Abstract
The invention discloses a pretreatment method for high-chlorine water before COD (chemical oxygen demand) measurement, H2SO4+Cl‑=HCl（g）+HSO4 ‑The sulfuric acid converts chloride ions in the solution into hydrogen chloride gas, the gas enters the flat-bottom separation absorption tube through the air holes, and the alkaline solution absorbs the hydrogen chloride gas. The reaction of sulfuric acid and chloride ion and the reaction of alkaline solution to absorb hydrogen chloride can be accelerated by magnetic stirring, and the reaction time can be greatly shortened. The beneficial effects are that: the device is simple, the preparation cost is low, and the operation is convenient; the method has the advantages of high speed and high removal rate for removing the chloride ions in the high-chlorine water.
Description
Technical Field
The invention relates to the field of water quality determination, in particular to a pretreatment method before high-chlorine water COD determination and application thereof.
Background
COD, also known as chemical oxygen demand, is an important chemical indicator of water quality. The COD is generally determined by oxidizing the organic matter in the water sample with an excessive amount of a strong oxidizing agent, and determining the excessive amount of the strong oxidizing agent by back titration with a reducing agent with a calibrated concentration, or by spectrophotometry after oxidizing the organic matter in the water sample with the excessive amount of the strong oxidizing agent. The commonly used strong oxidants include potassium dichromate and potassium permanganate, the potassium dichromate is used as an oxidant to determine COD under an acidic condition, is suitable for fresh water or low-chlorine water samples, and cannot be directly used for determining seawater or high-chlorine water samples. The direct determination of seawater or high-chlorine water samples by potassium dichromate oxidation results in excessive COD results due to excessive oxidation caused by the presence of chloride ions, which deviate from the actual values. The potassium permanganate is generally used as an oxidant for measuring COD under an alkaline condition, is suitable for measuring seawater or a high-chlorine water sample, and the result obtained when the potassium permanganate is used for measuring a fresh water sample is customarily called the permanganate index. However, potassium permanganate has relatively weak oxidation effect under alkaline conditions, and has a low COD result, and the result is seriously deviated from the true value when the potassium permanganate is particularly applied to the determination of oil-polluted seawater or high-chlorine water samples. At present, the main method for solving the problems is to determine COD by an acid potassium dichromate oxidation method after seawater or high-chlorine water is subjected to dechlorination pretreatment.
The method for removing the chloride ions in the seawater or the high-chlorine water comprises the following steps: silver salt precipitation method, adding silver ion into water, and forming silver chloride precipitate with chloride ion to remove. The method is high in cost, and nitrate radicals in a water sample are not eliminated after silver chloride precipitates are removed, so that the method is equivalent to adding nitric acid, the nitric acid and sulfuric acid are mixed to form a strong oxidant, reducing substances can be oxidized, and the determination result is inaccurate.
Polytetrafluoroethylene (PTFE) is a typical representative of polymer materials, and the chemical structures of fluorine atoms and carbon atoms in the molecular structure of PTFE enable PTFE to exhibit extremely high chemical stability, insulation, flame retardancy, self-lubricating properties, strong corrosion resistance, wide temperature adaptability, almost no water solubility and the like, so that PTFE gains the reputation of "the king of plastics". Although PTFE, a solid self-lubricating material, has many advantages, its low hardness, high load capacity, easy creep, poor wear resistance and other disadvantages limit its application range in engineering plastics.
Disclosure of Invention
One of the purposes of the invention is to provide a pretreatment method before COD (chemical oxygen demand) determination of high-chlorine water, which has the advantages of high chloride ion removal speed, high removal rate, simple operation and long service life of the device;
the invention also aims to provide the application of the pretreatment method before the high-chlorine water COD determination for removing chloride ions in the water before the high-chlorine water COD determination.
Aiming at the problems mentioned in the background technology, the invention adopts the technical scheme that: the utility model provides a pretreatment methods before high chlorine water COD survey, the preprocessing device who uses includes the erlenmeyer flask, and the cooperation is placed flat separation absorption tube on the erlenmeyer flask, and the first half of flat separation absorption tube is located outside the erlenmeyer flask, and flat separation absorption tube top is equipped with the stopper, and the latter half of flat separation absorption tube is located the erlenmeyer flask, is equipped with the gas pocket on the lower half of flat separation absorption tube, all puts magnetic stirring magneton at the bottom of flat separation absorption tube bottom and the erlenmeyer flask. The conical flask is filled with seawater or water with a chlorinity of more than 0.5 to be measured. The flat-bottom separation absorption tube is filled with saturated alkaline solution. H2SO4+Cl-=HCl（g）+HSO4 -The sulfuric acid converts chloride ions in the solution into hydrogen chloride gas, the gas enters the flat-bottom separation absorption tube through the air holes, and the alkaline solution absorbs the hydrogen chloride gas. The reaction of sulfuric acid and chloride ion and the reaction of alkaline solution to absorb hydrogen chloride can be accelerated by magnetic stirring, and the reaction time can be greatly shortened.
The bottom of the lower half part of the flat-bottom separation absorption tube is flat. The diameter of the flat-bottom separation absorption tube is smaller, if the bottom is a curved surface, the stirring effect is not ideal, the bottom of the absorption tube is flat, the rotatable area of the magneton is the largest, the stirring effect of the alkaline solution is good, and the absorption speed of the hydrogen chloride gas is high.
The flat bottom separation absorption tube and the plug are both made of strong alkali corrosion resistant materials. The flat-bottom separation absorption tube is filled with strong alkali solution, has a corrosion and damage effect on glass materials, and is prepared from strong alkali corrosion resistant materials in order to prolong the service life of the device.
The ratio of the distance between the air holes and the bottom of the flat-bottom separation absorption tube to the distance between the air holes and the top of the lower half part of the flat-bottom separation absorption tube is 1: 0.5-1.5; the length ratio of the upper half part to the lower half part of the flat-bottom separation absorption tube is 1: 0.7-1.5. The proportion arrangement can ensure that the alkaline solution cannot overflow in the stirring process, and the hydrogen chloride gas can easily enter the flat-bottom separation absorption tube. The upper half part of the flat-bottom separation absorption tube plays a role in buffering gas, namely temporarily storing hydrogen chloride which enters the flat-bottom separation absorption tube but is not absorbed in time.
The pretreatment method comprises the steps of adding 96-98% sulfuric acid into seawater or water with the chlorinity of above 0.5 to be detected at the temperature of 0-45 ℃ and the stirring speed of 200-500 r/min, converting chloride ions in the water into hydrogen chloride gas, enabling the gas to enter a flat bottom separation absorption tube through air holes, and enabling an alkaline solution to absorb the hydrogen chloride gas. The method can rapidly remove chloride ions in water, has high removal rate, and remains HSO in water4 -The oxidability is weak, and the influence on COD measurement is small, so the effect of pretreating the high-chlorine water by adopting the method is good.
The saturated alkaline solution comprises sodium hydroxide or potassium hydroxide or lithium hydroxide or calcium hydroxide. The alkali liquor has strong alkalinity, fast absorption speed to hydrogen chloride gas and good absorption effect.
An application of a pretreatment method before high-chlorine water COD determination, which is used for removing chloride ions in water before the high-chlorine water COD determination.
Compared with the prior art, the invention has the advantages that: the device is simple, the preparation cost is low, and the operation is convenient; the method can quickly remove chloride ions in water, has high removal rate and remains HSO in water4 -The oxidability is weak, and the influence on COD measurement is small; the flat-bottom separation absorption tube filled with the alkaline solution is made of a strong alkali resistant material, and the strong alkali resistant material can be modified, so that the wear resistance of the flat-bottom separation absorption tube is enhanced, the abrasion of magnetons to a device in the magnetic stirring process is reduced, and the service life of the device is prolonged.
Drawings
FIG. 1 is a schematic view of a pretreatment device for COD determination of high-chlorine water according to the present invention.
Description of reference numerals: 1, a conical flask; 3, a flat bottom separation absorption tube; 4, magnetically stirring magnetons; 5, air holes; 6, plugging the plug.
Detailed Description
Example 1:
a pretreatment device: the separation absorption tube is a flat-bottom tube-dividing part which is made of a commercially available glass conical bottle with the volume of 250ml, the bottom outer diameter of 88mm, the height of 144mm and the caliber of 29mm, the inner tube diameter of 22mm, the height of 132mm (the upper end of the tube is 8mm higher than the bottle mouth), the upper end outer diameter of 29mm and the upper end inner diameter of 24mm of flat inner bottom are made of polytetrafluoroethylene, the inner tube diameter of 22mm, the height of 130mm, the lower end outer diameter of 24mm and the upper end inner diameter of 24mm are made of polytetrafluoroethylene, the slow-part tube part is arranged outside the cone, and the solid plug with the lower end outer diameter of 24mm is made of polytetrafluoroethylene.
Sample preparation:
preparing the artificial seawater with the chlorinity of 19.00 according to a Kester artificial seawater formula. High-quality pure potassium hydrogen phthalate is used as a standard substance, and the artificial seawater is used as a solvent to prepare standard samples with COD of 10.0mg/L, 40.0mg/L and 150.0mg/L respectively. And taking secondary redistilled water treated by potassium permanganate as a blank sample.
Sample pretreatment:
the pretreatment unit was immersed in 10% dilute nitric acid for over 24 hours prior to use. When the method is used for pretreatment, 20ml of sample and 20ml of distilled water blank are respectively transferred into two 300ml conical flasks, a magnetic stirrer is added and then placed in an ice bath, analytically pure sulfuric acid is slowly added under cooling and stirring under the condition that the temperature is controlled not to exceed 45 ℃, then a separation absorption tube filled with saturated NaOH solution is connected with the conical flasks and well installed, and the sample dechlorination pretreatment is completed after stirring at the room temperature of 250rpm for 1 h. During the pretreatment process, the saturated NaOH solution in the separation absorption tube is replaced by a new saturated NaOH solution when the saturated NaOH solution is out of service.
Evaluation of pretreatment effect:
the COD value of the sample and blank pretreated by the method is measured according to the dichromate determination method for water quality chemical oxygen demand (HJ 828-2017) of the national environmental protection standard of the people's republic of China, and a quite good experimental result is obtained and is shown as follows.
As can be seen from the table above, the pretreatment method before the COD measurement of the high-chlorine water has high removal rate of chloride ions in the water and accurate COD measurement result.
Example 2:
the utility model provides a pretreatment methods before high chlorine water COD survey, the preprocessing device who uses includes erlenmeyer flask 1, and the cooperation is placed flat separation absorption tube 3 on the erlenmeyer flask 1, and flat separation absorption tube 3 first half is located outside erlenmeyer flask 1, and flat separation absorption tube 3 top is equipped with stopper 6, and the latter half of flat separation absorption tube 3 is located erlenmeyer flask 1, is equipped with gas pocket 5 on the lower half of flat separation absorption tube 3, and magnetic stirring magneton 4 has all been put at the bottom of flat separation absorption tube 3 bottom and the erlenmeyer flask 1 bottle. The conical bottle 1 is filled with seawater or water with the chlorinity of more than 0.5 to be measured. The flat bottom separation absorption tube 3 is filled with a saturated alkaline solution. H2SO4+Cl-=HCl（g）+HSO4 -Sulfuric acid converts chloride ions in solution to hydrogen chloride gasThe gas enters the flat-bottom separation absorption tube 3 through the air hole 5, and the alkaline solution absorbs the hydrogen chloride gas. The reaction of sulfuric acid and chloride ion and the reaction of alkaline solution to absorb hydrogen chloride can be accelerated by magnetic stirring, and the reaction time can be greatly shortened.
The bottom of the lower half part of the flat-bottom separation absorption tube 3 is flat.
The flat bottom separation absorption tube 3 and the plug 6 are both made of a material resistant to strong alkaline corrosion. The strong base corrosion resistant material is modified Polytetrafluoroethylene (PTFE), and the preparation method comprises the following steps: mixing ethanol, water and a silane coupling agent KH550 according to a mass ratio of 18:2:5, and carrying out ultrasonic oscillation until the silane coupling agent is completely hydrolyzed. Then adding 100 times of serpentine powder in the mass of KH550 and 0.1 times of TMBA in the mass of KH550, putting the mixed solution into a high-energy ball mill for ball milling to fully react, and drying to obtain the nano-modified serpentine. Adding the nanoscale modified serpentine into absolute ethyl alcohol, stirring uniformly, and then adding PTFE powder and p-nitroanisole, wherein the mass ratio of the nanoscale modified serpentine to the PTFE powder to the p-nitroanisole is (3: 0.006): and 17, fully reacting and drying to obtain the modified PTFE material. Compared with a pure PTFE material, the prepared modified PTFE material has the advantages that the hardness is improved, the friction coefficient is reduced by 60 percent, the wear rate is reduced by at least one order of magnitude, and good tribological performance is shown. The silane coupling agent KH550 and TMBA generate a new strong chemical bond on the surface of the serpentine powder, and an isolating layer is formed on the surface of the serpentine powder, so that the bonding capability of the serpentine and the PTFE matrix is improved. The p-nitroanisole can obviously improve the dispersion effect of the serpentine in the PTFE, improve the agglomeration phenomenon of the serpentine in a polymer matrix and improve the conversion rate of the modified PTFE. However, the mechanism of the reaction is not clear, and further studies are required.
The ratio of the distance between the air holes 5 and the bottom of the flat-bottom separation absorption tube 3 to the distance between the air holes 5 and the top of the lower half part of the flat-bottom separation absorption tube 3 is 1: 1.5; the length ratio of the upper half part to the lower half part of the flat-bottom separation absorption tube 3 is 1: 1.2.
The pretreatment method comprises adding magnetic stirrer, placing in ice bath, controlling temperature not to exceed 45 deg.C, stirring at 300r/min, and measuring seawater or chlorine content of above 0.598 percent sulfuric acid is added into water, chloride ions in the water are converted into hydrogen chloride gas, the gas enters the flat-bottom separation absorption tube 3 through the air hole 5, and the hydrogen chloride gas is absorbed by alkaline solution. The method can rapidly remove chloride ions in water, has high removal rate, and remains HSO in water4 -The oxidability is weak, and the influence on COD measurement is small, so the effect of pretreating the high-chlorine water by adopting the method is good.
The saturated alkaline solution is sodium hydroxide.
An application of a pretreatment method before high-chlorine water COD determination, which is used for removing chloride ions in water before the high-chlorine water COD determination.
The ratio of the distance between the air holes 5 and the bottom of the flat bottom-separating absorption tube 3 to the distance between the air holes 5 and the top of the lower half of the flat bottom-separating absorption tube 3 includes, but is not limited to, 1:0.5 to 1.5, and further includes 1:0.52,1:0.54,1:0.56, … …,1: 1.46,1:1.48, and 1: 1.5.
The length ratio of the upper half part to the lower half part of the flat-bottom separation absorption tube 3 comprises, but is not limited to, 1: 0.7-1.5, and also comprises 1:0.72,1:0.74,1:0.76, … …,1: 1.46,1:1.48 and 1: 1.5.
Conventional operations in the operation steps of the present invention are well known to those skilled in the art and will not be described herein.
The embodiments described above are intended to illustrate the technical solutions of the present invention in detail, and it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention, and any modification, supplement or similar substitution made within the scope of the principles of the present invention should be included in the protection scope of the present invention.
Claims (3)
1. The pretreatment method before COD (chemical oxygen demand) determination of high-chlorine water is characterized in that a pretreatment device used in the pretreatment method comprises a conical flask (1), a flat-bottom separation and absorption tube (3) is arranged on the conical flask (1) in a matched mode, the upper half part of the flat-bottom separation and absorption tube (3) is positioned outside the conical flask (1), the top of the flat-bottom separation and absorption tube (3) is provided with a plug (6), the lower half part of the flat-bottom separation and absorption tube (3) is positioned in the conical flask (1), the lower half part of the flat-bottom separation and absorption tube (3) is provided with an air hole (5), and magnetic stirring magnets (4) are arranged at the bottom end of the flat-bottom separation and absorption tube (3) and the bottom of the conical flask (;
the ratio of the distance between the air holes (5) and the bottom of the flat-bottom separation absorption tube (3) to the distance between the air holes (5) and the top of the lower half part of the flat-bottom separation absorption tube (3) is 1: 1.5; the length ratio of the upper half part to the lower half part of the flat-bottom separation absorption tube (3) is 1: 1.2;
the flat-bottom separation absorption tube (3) and the plug (6) are both made of strong alkali corrosion resistant materials;
the bottom of the lower half part of the flat-bottom separation absorption tube (3) is flat;
the strong base corrosion resistant material is modified polytetrafluoroethylene, and the preparation method comprises the following steps: mixing ethanol, water and a silane coupling agent KH550 according to a mass ratio of 18:2:5, carrying out ultrasonic oscillation until the silane coupling agent is completely hydrolyzed, then adding 100 times of serpentine powder by mass of KH550 and 0.1 times of TMBA by mass of KH550, putting the mixed solution into a high-energy ball mill for ball milling to fully react, drying to obtain nano-modified serpentine, adding nano-modified serpentine into absolute ethanol, stirring uniformly, then adding PTFE powder and p-nitroanisole, wherein the mass ratio of the nano-modified serpentine to the PTFE powder to the p-nitroanisole is 3:0.006:17, and drying after full reaction to obtain a modified PTFE material;
the conical flask (1) is filled with seawater or water with the chlorinity of more than 0.5 to be measured;
the pretreatment method comprises the following steps: after a magnetic stirrer is added, the mixture is placed in an ice bath, 98 percent sulfuric acid is added into seawater or water with the chlorinity of more than 0.5 to be measured under the conditions that the temperature is controlled not to exceed 45 ℃ and the stirring speed is 300r/min, the chlorine ions in the water are converted into hydrogen chloride gas, the gas enters a flat-bottom separation absorption tube (3) through an air hole (5), and the hydrogen chloride gas is absorbed by alkaline solution;
the pretreatment method before the COD (chemical oxygen demand) determination of the high-chlorine water is used for removing chloride ions in the water before the COD determination of the high-chlorine water, and the RSD (remote sensing device) values of the determination results are 15.1%, 7.2% and 4.6% when the COD value of the high-chlorine water with the chlorinity of 19.00 is 10.0mg/L, 40.0mg/L and 150.0mg/L respectively.
2. The pretreatment method before COD measurement of high-chlorine water according to claim 1, characterized in that: the flat-bottom separation absorption tube (3) is filled with saturated alkaline solution.
3. The pretreatment method before COD measurement of high-chlorine water according to claim 2, characterized in that: the saturated alkaline solution is sodium hydroxide.
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| CN110850026B (en) * | 2019-11-12 | 2022-05-20 | 核工业北京化工冶金研究院 | Method for analyzing COD (chemical oxygen demand) of high-chloride acidic uranium solution |
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| CN105181688A (en) * | 2015-09-08 | 2015-12-23 | 新疆大学 | Method for measuring COD (Chemical Oxygen Demand) in water sample containing high-concentration Cl<-> by acidification chloride removal method |
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| DE2932444C3 (en) * | 1979-08-10 | 1982-03-18 | Schierjott, Günter, Dr.techn., 4630 Bochum | Method for separating interfering components from a liquid and device for carrying out the method |
| DE102009045529A1 (en) * | 2009-10-09 | 2011-04-21 | Endress + Hauser Conducta Gesellschaft für Mess- und Regeltechnik mbH + Co. KG | Method and apparatus for removing chloride from volatile organic carbon-containing samples |
| CN103616277A (en) * | 2013-10-23 | 2014-03-05 | 洛阳高新开发区双阳仪器有限公司 | Chemical oxygen demand determination method free from using mercury salts and silver salts |
| DE102014119547A1 (en) * | 2014-08-13 | 2016-02-18 | Endress + Hauser Conducta Gesellschaft für Mess- und Regeltechnik mbH + Co. KG | Apparatus and method for removing chloride from a liquid sample |
| CN106525832A (en) * | 2016-10-27 | 2017-03-22 | 新疆大学 | Manganese-chromium two-stage oxidation method for determining COD in high chlorine-containing wastewater |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN105181688A (en) * | 2015-09-08 | 2015-12-23 | 新疆大学 | Method for measuring COD (Chemical Oxygen Demand) in water sample containing high-concentration Cl<-> by acidification chloride removal method |
Non-Patent Citations (2)
| Title |
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| Reduction of chloride ion interference in chemical oxygen demand (COD) determinations using bismuth-based adsorbents;Bikas Vaidya et al;《Analytica Chimica Acta》;19971231;第357卷;第169-170页第2.5节 * |
| 纳米蛇纹石改性PTFE海水中摩擦学性能研究;陈许超;《中国优秀硕士学位论文全文数据库 工程科技Ⅱ辑》;20170115(第1期);第16、37页 * |
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