Some standard content:
Coal Industry Standard of the People's Republic of China
Method for determination of hardness of coal mine water
1 Subject content and scope of application
MT/T206-1995
Replaces MT206--89
This standard specifies the determination of total hardness of calcium and magnesium in water by complexometric titration with disodium ethylenediaminetetraacetic acid (EDTA). This standard is applicable to the determination of total hardness of calcium and magnesium in coal mine water. 2 Method Summary
In an ammonia solution with a pH value of 10, use chrome black T as an indicator and EDTA standard solution for complexometric titration of the total amount of calcium and magnesium ions to calculate the total hardness composed of calcium and magnesium ions. 3 Reagents
3.1 Water: distilled water.
3.2 Hydrochloric acid solution: prepare a (1+2) solution with hydrochloric acid (GB/T622). 3.3 Ammonia solution: prepare a (1+4) solution with ammonia water (GB/T631). 3.4 Sodium sulfide solution: weigh 5g sodium sulfide (Na2S·9H,O) and dissolve it in 100mL water, store it in a glass bottle with a tight rubber stopper and isolate it from the air.
3.5 Ammonia buffer solution: weigh 67.50g ammonium chloride (GB/T658) and dissolve it in 570mL ammonia water (GB/T631), then add 5.0g EDTA disodium magnesium salt (C1oH12N,O.Na2Mg), dilute it with water to 1000mL, mix it well, and store it in a polyethylene bottle. 3.6 EDTA standard solution: c(1/2EDTA)=0.0200mo1/L, weigh 3.725g EDTA (GB/T1401) and dissolve it in water, dilute it to 1000ml, mix it well, and store it in a polyethylene bottle. Its concentration should be checked regularly. Standardization of EDTA standard solution: Use a pipette to draw 20mL of calcium standard solution (3.7) into a 250mL conical flask, dilute with water to about 50ml, and standardize three times according to the steps in Section 5.2. Take the arithmetic mean of the amount used, and calculate the concentration of EDTA standard solution according to formula (1): 0.020 0X20
Where: c1——concentration of EDTA standard solution, mol/LV-arithmetic mean of the amount of EDTA standard solution used, mL. (1)
3.7 Calcium standard solution: c(1/2CaCO,)=0.0200mol/L, weigh 1.0010±0.0002g of high-grade pure calcium carbonate that has been dried at about 150℃ for 2h and cooled to room temperature in a desiccator, place it in a 500mL conical flask, and moisten it with a small amount of water. Add hydrochloric acid solution (3.2) dropwise until calcium carbonate is completely dissolved (do not add excessive acid), add 200 mL of water, and boil for 3 to 5 minutes to drive out carbon dioxide. After cooling to room temperature, add 3 to 5 drops of methyl red indicator solution (3.9), neutralize with ammonia solution (3.3) until orange, quantitatively transfer the solution to a 1000 mL volumetric flask, dilute to scale with water, and shake well.
3.8 Magnesium standard solution: c(1/2MgO)=0.0200mol/L, weigh 0.4032±0.0002g of spectrally pure magnesium oxide that has been burned at about 820℃ for 1h and cooled to room temperature in a desiccator, place it in a 250mL conical flask, moisten it with a small amount of water, add hydrochloric acid solution (3.2) dropwise until the magnesium oxide is completely dissolved (do not add excessive acid), add 50mL of water, and then quantitatively transfer the solution to a 1000mL volumetric flask, dilute it with water to the scale, and shake.
MT/T 206--1995
3.9 Methyl red indicator solution: weigh 0.1g methyl red (HG/T3958), dissolve in 60ml, 95% ethanol (GB/T679), add 40ml water, mix well.
3.10 Eriochrome black T indicator: weigh 0.5g eochrome black T and 25g potassium chloride (GB/T646), mix and grind, store in a glass bottle with a ground stopper.
3.11 Congo red test paper.
4 Instruments
4.1 Analytical instrument: sensitivity 0.1mg.
4.2 Burette: 25ml. minimum graduation value 0.1ml. 4.3 Pipette: 20ml., accuracy ±0.04ml; 50mL, accuracy is ±0.08ml.
4.4 Graduated pipette: 5mL, minimum graduation value 0.05mlL. 5 Determination steps
5.1 Use a pipette to take 50ml of the water sample filtered with a glass fiber filter to remove suspended matter, transfer it into a 250ml conical flask, put in a small piece of Congo red test paper, and add hydrochloric acid solution (3.2) until the test paper just turns blue-purple (for water samples with alkalinity greater than 300mg (CaCO,)/L, boil for 1 to 2 minutes and cool to room temperature). 5.2 Add 4mL of buffer solution (3.5) and about 0.05g of chrome black T indicator (3.10), and titrate with EDTA standard solution (3.6) until the solution changes from purple-red to blue, which is the end point. Write down the amount used. If the buffer solution is not prepared with disodium magnesium EDTA, the endpoint is not obvious when calibrating the EDTA standard solution (see 3.6) and titrating the water sample without magnesium ions. A 5mL graduated pipette should be used to add 2.00mL of magnesium standard solution (3.8) to the titrated solution, and 50mL of water to which 2.00mL of magnesium standard solution has been added is used as a blank. The amount of titrant consumed by the titrated solution is deducted from the blank and then calculated.
5.3 If the water contains interfering ions and the titration endpoint is not obvious, 1.0mL of sodium sulfide solution (3.4) should be added. 5.4 When the amount of titrant used is less than 4.5mL, more test water sample should be used for titration, and the volume of buffer solution (3.5) should be increased proportionally; when the amount used is greater than 20mL, less test water sample should be used for titration, and water should be added to make the initial titration volume 50mL. 6 Expression of determination results
The total hardness of calcium and magnesium in water is calculated according to formula (2): TH = 1 000c,VX 50. 04
Formula: TH-total hardness of calcium and magnesium in water (calculated as CaCO,), mg/L; concentration of Cr-EDTA standard solution, mol/L; V,·---volume of EDTA standard solution consumed in titration of test water sample, mL; V.--volume of test water sample, mL
50.04--molar mass of calcium carbonate (1/2CaCO,), g/mol. If the calcium ion content in water is measured, the magnesium ion content can be calculated according to formula (3): Mg*000VX12.152-.6064Ca**576
·(3)
MT/T 206--1995
wherein: Mg2+
the content of magnesium ions in water, mg/L;
the molar mass of magnesium ions (1/2Mg2+), g/mol;——the content of calcium ions in water, mg/L, Ca2t-
0.6064——the conversion coefficient of calcium ions to magnesium ions. The calculation result is rounded to three decimal places and rounded to two decimal places. Precision
The tolerance of the same laboratory shall comply with the following table:Total hardness, mgCaCO:/l.
Magnesium ion content, mg/L
Absolute tolerance, mg/L
Relative tolerance, %
MT/T206—1995
Appendix A
Concept of water hardness
(reference)
Water hardness is an old concept used to describe the calcium and magnesium content in water. There are different expressions (total hardness, carbonate hardness, etc.). Different countries have different concepts and definitions, some of which are listed in Table A1. A1 Concepts and definitions
A1.1 Total hardness: In general water, the hardness of water is mainly determined by the content of calcium and magnesium ions. Total hardness is defined as the total concentration of calcium and magnesium.
A1.2 In addition to calcium and magnesium ions, some water also contains a considerable amount of multivalent metal ions such as iron and aluminum, which should also be included in the calculation of total hardness: 1 mmol/L of divalent metal ions is converted to 1 mmol/L of calcium carbonate; 1 mmol/L of trivalent metal ions is converted to 1.5mmol/L of calcium carbonate, and it should be noted in the analysis report. A1.3 Carbonate hardness and non-carbonate hardness: When the total hardness is numerically greater than the sum of the carbonate and bicarbonate alkalinity, the part of the hardness equivalent to the alkalinity is called "carbonate hardness" and the remaining part of the hardness is called "non-carbonate hardness". When the total hardness is numerically equal to or less than the sum of the carbonate and bicarbonate alkalinity, all hardness is carbonate hardness, and non-carbonate hardness does not exist. A2 Hardness scale
German hardness scale: 1 The German hardness scale (1°DH) indicates the hardness of water when it contains 10mg/L of calcium oxide or c (CaO) = 0.178mmol/L.
A2.2 British Hardness Scale: 1 British Hardness Scale (1 Ciark) indicates the hardness of water when it contains 1 grain/UK gallon, that is, 14.3 mg/L of calcium carbonate or c(CaCO,) = 0.143 mmol/L. A2.3 French Hardness Scale: 1 French Hardness Scale indicates the hardness of water when it contains 10 mg/L of calcium carbonate or c(CaCO,) = 0.1 mmol/1.
A2.4 American Hardness Scale: In the United States, hardness is expressed in parts per million (ppm) of calcium carbonate in water or in milligrams of calcium carbonate per liter of water. 1 mg/L of calcium carbonate is equivalent to the hardness of water when c(CaCO,) = 0.01 mmol/L. A3 Conversion Table
The various hardness units can be converted to each other using the following table. Table A1
mmol/L
mmoi/L
French degree
eClark
French degree
Additional notes:
MT/T206-1995
This standard is proposed by the National Coal Standardization Technical Committee. This standard is under the jurisdiction of the Mine Water Quality Branch of the National Coal Standardization Technical Committee. This standard is drafted by the Sichuan Coalfield Geology Research Institute. The main drafters of this standard are Wu Fuxian, Zhou Chongji and Li Yufang. This standard was first issued in 1989.
Method for Determination of Hardness in Coal Mine Water
(MT/T206—1995) Revision Notes
(Sichuan Coalfield Geology Research Institute)
Water hardness is the main item of water analysis and the main indicator of water quality evaluation. The hardness of water is mainly caused by calcium and magnesium salts contained in water. Other multivalent metal ions such as iron, manganese, aluminum, strontium, zinc, etc. also contribute to the hardness of water, but because their content is usually very small, they have little effect on the hardness of water. Under normal circumstances, the hardness of water mainly depends on the total content of calcium and magnesium ions in water. In this revision, the complexometric titration method selected and determined in the original standard (MT206-89) will not be replaced. Although the atomic absorption spectrophotometry method has been developed to determine calcium and magnesium ions, which can be converted into total hardness, the complexometric titration method is simple and easy to use. It is necessary to use these two methods in parallel to determine calcium, magnesium ions and hardness, which is consistent with international standards and relevant foreign standards. This revision was written in accordance with the requirements of the national standard (GB1.4-88), and with reference to international standards and relevant foreign national standards, the contents of some items of the original standard were revised and supplemented.
1 Key points of standard revision
Replaced and supplemented some reagent items, and supplemented the accuracy of the instrument part. a)
b) Supplemented the analysis steps in Chapter 5. Supplemented the description of the analysis results in Chapter 6. c)
d) Revised the allowable difference of the measurement results. 2 Explanation of some revised articles
2.1 The zinc standard solution in the original standard reagent part was replaced with the calcium ion standard solution; the preparation of the nitrogen buffer solution was changed to improve the buffering capacity; only chrome black T was used as the indicator, and other indicators were no longer listed in parallel. These reagent changes are to make the calibration of the complexing agent completely consistent with the measurement conditions of the water sample, and on the other hand, to be consistent with the reagents, measurement steps and operating conditions used in international standards and similar standards of advanced countries.
2.2 The reagent part is supplemented with magnesium ion standard solution, methyl red indicator solution, sodium sulfide solution, (1+2) hydrochloric acid solution, and (1+4) ammonia solution. These reagents are used when preparing other reagents, adjusting the acidity of the test water sample, or to make the calibration standard solution consistent with the measurement conditions of the water sample, and as inhibitors to eliminate the interference of other metal ions. In addition, the requirements for graduation value and accuracy of the burette, pipette and graduated pipette in the instrument part of Chapter 4 are supplemented and marked. 2.3 In the analysis steps of Chapter 5, the general of the original standard is rewritten into four items. Item 5.3 is added, and the interference is suppressed by sodium sulfide solution: if 25mL of the test water sample is diluted to 50mL and then measured, the interference of 20mg/L aluminum, cadmium, copper, lead; 5mg/L iron, 200mg/L zinc, and 10mg/L polyphosphate can be eliminated respectively. The amount of sodium sulfide solution can only be added to 1.0mL. Item 5.4 is added: If the amount of EDTA standard solution is less than 4.5mL, more test water samples should be taken for measurement. When the amount of EDTA standard solution is greater than 20mL, less test water samples should be taken and diluted to 50mlL for measurement. This can reduce the measurement error of low-content water samples. For water samples with high total calcium and magnesium content, the pH value of the test water sample can be kept in the range of 10.0±0.1 during titration to ensure the accuracy of the measurement results. 2.4 In the description of the analysis results in Chapter 6, the formula for calculating the magnesium ion content in water based on the amount of standard solution titrated and the measured calcium ion content in water is added.
2.5 The allowable difference of the measurement results in Chapter 7 has been revised. The original standard was the allowable difference for parallel measurements in the same laboratory, which has now been changed to the allowable difference for measurements in the same laboratory. After testing, the allowable difference has been revised to: when the total hardness is ≤200mg (CaCO:)/L, the absolute allowable difference is 4mg (CaCOs)/I; when it is >200mg (CaCO,)/L, the relative allowable difference is 2%. When the magnesium ion is ≤25mg/L, the absolute allowable difference is 1mg/L; when it is >25mg/L, the relative allowable difference is 4%.
(6) The appendix also revised and supplemented the concept of water hardness, the relationship between different types of hardness and their conversion.2 The reagent section is supplemented with magnesium ion standard solution, methyl red indicator solution, sodium sulfide solution, (1+2) hydrochloric acid solution, and (1+4) ammonia solution. These reagents are used to prepare other reagents, adjust the acidity of test water samples, or to make the calibration standard solution consistent with the conditions of the test water sample, and as inhibitors to eliminate the interference of other metal ions. In addition, the burette, pipette, and graduated pipette in the instrument section of Chapter 4 are supplemented and the requirements for graduation value and accuracy are indicated. 2.3 In the analysis steps of Chapter 5, the general of the original standard is rewritten into four items. Item 5.3 is supplemented, and the interference is suppressed by sodium sulfide solution: if 25mL of the test water sample is diluted to 50mL for determination, the interference of 20mg/L aluminum, cadmium, copper, and lead; 5mg/L iron, 200mg/L zinc, and 10mg/L polyphosphate can be eliminated respectively. The amount of sodium sulfide solution can only be added to 1.0mL. Added 5.4: If the amount of EDTA standard solution is less than 4.5mL, more test water samples should be taken for determination. When the amount of EDTA standard solution is greater than 20mL, less test water samples should be taken and diluted to 50mlL for determination. This can reduce the determination error of low-content water samples. For water samples with high total calcium and magnesium, the pH value of the test water sample can be kept in the range of 10.0±0.1 during titration to ensure the accuracy of the determination results. 2.4 In the description of the analysis results in Chapter 6, the formula for calculating the magnesium ion content in water based on the amount of standard solution titrated and the measured calcium ion content in water is added. wwW.bzxz.Net
2.5 The allowable difference of the determination results in Chapter 7 has been revised. The original standard was the allowable difference for parallel determinations in the same laboratory, which has now been changed to the allowable difference for determinations in the same laboratory. After testing, the allowable difference is revised to: when the total hardness is ≤200mg (CaCO:)/L, the absolute allowable difference is 4mg (CaCOs)/I; when it is >200mg (CaCO,)/L, the relative allowable difference is 2%. When the magnesium ion is ≤25mg/L, the absolute allowable difference is 1mg/L; when it is >25mg/L, the relative allowable difference is 4%.
(6) The concept of water hardness, the relationship between different types of hardness and their conversion have also been revised and supplemented in the appendix. 6632 The reagent section is supplemented with magnesium ion standard solution, methyl red indicator solution, sodium sulfide solution, (1+2) hydrochloric acid solution, and (1+4) ammonia solution. These reagents are used to prepare other reagents, adjust the acidity of test water samples, or to make the calibration standard solution consistent with the conditions of the test water sample, and as inhibitors to eliminate the interference of other metal ions. In addition, the burette, pipette, and graduated pipette in the instrument section of Chapter 4 are supplemented and the requirements for graduation value and accuracy are indicated. 2.3 In the analysis steps of Chapter 5, the general of the original standard is rewritten into four items. Item 5.3 is supplemented, and the interference is suppressed by sodium sulfide solution: if 25mL of the test water sample is diluted to 50mL for determination, the interference of 20mg/L aluminum, cadmium, copper, and lead; 5mg/L iron, 200mg/L zinc, and 10mg/L polyphosphate can be eliminated respectively. The amount of sodium sulfide solution can only be added to 1.0mL. Added 5.4: If the amount of EDTA standard solution is less than 4.5mL, more test water samples should be taken for determination. When the amount of EDTA standard solution is greater than 20mL, less test water samples should be taken and diluted to 50mlL for determination. This can reduce the determination error of low-content water samples. For water samples with high total calcium and magnesium, the pH value of the test water sample can be kept in the range of 10.0±0.1 during titration to ensure the accuracy of the determination results. 2.4 In the description of the analysis results in Chapter 6, the formula for calculating the magnesium ion content in water based on the amount of standard solution titrated and the measured calcium ion content in water is added.
2.5 The allowable difference of the determination results in Chapter 7 has been revised. The original standard was the allowable difference for parallel determinations in the same laboratory, which has now been changed to the allowable difference for determinations in the same laboratory. After testing, the allowable difference is revised to: when the total hardness is ≤200mg (CaCO:)/L, the absolute allowable difference is 4mg (CaCOs)/I; when it is >200mg (CaCO,)/L, the relative allowable difference is 2%. When the magnesium ion is ≤25mg/L, the absolute allowable difference is 1mg/L; when it is >25mg/L, the relative allowable difference is 4%.
(6) The concept of water hardness, the relationship between different types of hardness and their conversion have also been revised and supplemented in the appendix. 663
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