Some standard content:
Coal Industry Standard of the People's Republic of China
Determination Method of Alkalinity of Coal Mine Water
1 Subject Content and Scope of Application
This standard specifies the determination of water alkalinity by acid titration. This standard is applicable to the determination of alkalinity of coal mine water. 2 Method Summary
MT/T204—1995
Replaces MT204---89
Various alkalinity components in water react with standard acid solution, and the reaction end point (pH=8.3 and pH=4.5) is determined by pH indicator or pH meter.
3 Reagents
3.1 Water: distilled water without carbon dioxide.
3.2 Sodium carbonate standard solution: c(1/2Na2CO)=0.0400mol/L, weigh 2.1198±0.0002g of high-grade pure anhydrous sodium carbonate (GB/T1255) that has been dried at 150~180℃F for about 3h, dissolve in 100mL water, transfer to a 1000mL volumetric flask, dilute to scale with water, and shake well.
3.3 Hydrochloric acid standard solution: c(HCI)=0.04mol/L, absorb 3.4mL hydrochloric acid (GB/T622), transfer to a ground glass bottle, dilute to 1000ml with water, and shake well.
Standardization of hydrochloric acid standard solution: Pipette 20 ml of sodium carbonate standard solution (3.2) into a 250 ml conical flask, dilute with water to about 80 ml, add 2 drops of methyl orange indicator solution (3.6), titrate with hydrochloric acid standard solution until close to the end point, boil and remove carbon dioxide, cool and continue titrating until the yellow color changes to orange-red, which is the end point, and record the amount used. Calibrate 3 portions, take the arithmetic mean of their dosage, and calculate the concentration of the hydrochloric acid standard solution according to formula (1):
0.0400×20
Wherein: (i—concentration of hydrochloric acid standard solution, mol/l; V—arithmetic mean of the dosage of hydrochloric acid standard solution, ml. (1
3.4 Phenolphthalein indicator solution: weigh 0.5g phenolphthalein (GB/T10729), dissolve it in 50mL, 95% ethanol (GB/T679), add 50ml water and mix well.
3.5 Bromocresol green-methyl red mixed indicator solution: weigh 0.04g methyl red (HG/T3-958) and 0.2g bromocresol green (HG/T 3-1220), dissolve it in 100mL, 95% Z ethanol (GB/T 679). 3.6 Use methyl orange indicator solution: weigh 0.1g methyl orange and dissolve it in 100ml water. 4 Instruments
4.1 pH meter: measuring range 0~14, minimum scale value 0.01pH unit. 4.2 Analytical balance: sensitivity 0.1mg.
4.3 Burette: 25ml, minimum scale value 0.1ml. 4.4 Pipette: 20ml, accuracy ±0.04ml.; Approved by the Ministry of Coal Industry of the People's Republic of China on November 6, 1995 570
1996-0 3-01 Implementation
MT/T204-1995
50mL, accuracy is ±0.08mL.
4.5 Graduated pipette: 5mL, minimum graduation value 0.05ml. 5 Determination steps
Phenolphthalein alkalinity titration: Use a pipette to draw 50mL of water sample, transfer it into a 250mL conical flask, add 5 drops of phenolphthalein indicator solution (3.4), if the solution is pink, titrate with hydrochloric acid standard solution (3.3) until the red color disappears, which is the end point (pH=8.3). Record the amount of hydrochloric acid used as V p.
Total alkalinity titration: Pipette 50mL of water sample into a 250mL conical flask, add 5-7 drops of mixed indicator solution (3.5) or 2 drops of methyl orange indicator solution (3.6), and titrate to the endpoint (pH-4.5) with hydrochloric acid standard solution (3.3). The mixed indicator changes from green to red, and the methyl orange indicator changes from yellow to orange-red. Then boil the solution for 2-3 minutes to drive out carbon dioxide, cool to room temperature, and titrate to the endpoint if the color changes. Record the amount of hydrochloric acid used as V. If the water sample contains phenolphthalein alkalinity , then add 2 drops of methyl orange indicator solution (3.6) to the water sample after titration of phenolic acid and alkalinity, and then titrate with hydrochloric acid standard solution (3.3) to orange-red (pH=4.5). The amount of this part of hydrochloric acid standard solution is Vm. Vm plus V. is V. Some water samples are colored, turbid or contain oxidants that decolorize the indicator. These water samples should be titrated in a 250mL beaker, and the titration end point (pH8.3 and pH=4.5) must be determined with a pH meter. 6 Expression of measurement results
The total alkalinity of the water sample is calculated according to formula (2):
TA 1 000V/ci× 50. 04
c: total alkalinity content in TA water sample (measured in CaCO3), mg/L; V--volume of hydrochloric acid standard solution consumed in titrating total alkalinity, mL; Ci--concentration of hydrochloric acid standard solution, mol/L; 50.04-molar mass of calcium carbonate (1/2CaCO3), g/mol; Vr
-volume of test water sample, mL.
If the basic components of the alkalinity of the water sample are bicarbonate, carbonate and hydroxide ions, their contents can be calculated based on the titration results V, and V. The volume of standard acid consumed by a certain component can be found in Table 1 and substituted into the following corresponding formula: Table 1 Relationship between OH-, CO and HCO; in water Titration results
V,s.1/2V.
OH- consumed
standard acid volume, ml
CO” consumed
standard acid volume.ml.
2(V,--V,)
1 000c,V2 × 61. 02
1 000c,V3 X 30. 01
HCO: consumed
standard acid volume, ml
·（3)
Where: HCO,-
MT/T 204---1995
1 000cV. × 17. 01
Content of bicarbonate ion in water, mg/L; Content of carbonate ion in water, mg/L; Content of hydroxide ion in OH water, mg/L; Cr
V2.V..V,--
Concentration of hydrochloric acid standard solution, mol/l;
Consumption volume of standard acid of corresponding component of alkalinity obtained from Table 1, mL Test water sample volume, mL;
Molar mass of bicarbonate ion (HCO:), g/mol; Molar mass of carbonate ion (1/2CO-), g /mol; molar mass of hydroxide ion (OH~), g/mol. The calculated result is rounded to three decimal places and rounded to two decimal places. 7 Precision
The allowable error of the same laboratory determination shall comply with the provisions of Table 2: Table 2
Total alkalinity content, mg(CaCO:)/L
Bicarbonate ion content, mg/L
Carbonate ion content, mg/L.
Hydroxide ion content, mg/L
Additional instructions:
Absolute allowable error, mg/L||tt| |This standard was 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 was drafted by the Sichuan Coalfield Geology Research Institute. The main drafters of this standard are Wu Fuxian, Zhou Chongji and Li Yufang. This standard is entrusted to the Sichuan Coalfield Geology Research Institute for interpretation. This standard was first issued in 1989.
Relative allowable difference, %
(5)
Determination method of alkalinity in coal mine water
(MT/T2041995)Revision Notes
(Sichuan Coalfield Institute of Geology) bzxz.net
The alkalinity of water refers to its ability to quantitatively react with strong acids to a certain H value. It is a measure of the comprehensive characteristics of water. Only when the chemical composition of the water sample is known can it be interpreted as a specific substance. The alkalinity of water is of great significance for the use and treatment of surface water and groundwater. Because in most surface water and groundwater, some minor components that constitute alkalinity, such as hydrogen sulfide (HS\), hydrogen silicate (HSiO,), phosphate oxygen (HF()\), and other weak inorganic acids and organic acids, even if they exist, their content is very small. Therefore, under the above premise, the content of bicarbonate, carbonate and hydroxide ions, the main components of alkalinity in water, can be determined by chemical calculation methods. In this revision, in order to improve the content of the standard, the title of the standard was changed to the determination method of alkalinity in coal mine water, and the alkalinity, bicarbonate, carbonate and hydroxide ion content were calculated by determination. The standard is in accordance with GB1.4-88, and with reference to similar foreign standards, the contents of some items of the original standard (MT204-89) were revised and supplemented. 1 Key points of standard revision
a) Supplemented the items of reagents and the accuracy of instruments. b) Supplemented the calculation of total alkalinity content and hydroxide ion content in water. ) The allowable difference of the same laboratory determination was revised. 2 Explanation of revised articles
2.1 In Chapter 3 of the standard, 3.2 sodium carbonate standard solution; 3.4 phenolic acid indicator solution; 3.6 methyl orange indicator solution were added. The original standard did not list reagent items, but only listed and used them during the operation process. In the instrument part of Chapter 4, the graduation value and accuracy requirements of burettes, pipettes and graduated pipettes were supplemented. 2.2 In the analysis steps of Chapter 5 of the standard, one section of the original standard was rewritten into two sections, indicating the pH value of the end point of the segmented titration. The first section is the titration of phenolphthalein alkalinity, which refers to the phenol alkalinity that only exists when the pH of the water sample is >8.3. The water sample is titrated with a standard acid solution to the endpoint (pH-8.3), at which time half of all the hydroxide ions and carbonate ions have reacted. The second section is the titration of total alkalinity, which refers to the water sample with a pH>4.5, which is titrated with a standard acid to the endpoint (pH-4.5), at which time all the hydroxide, carbonate and bicarbonate ions in the water sample have reacted with the acid. In essence, the determination of total alkalinity (when the content of other minor components that may constitute alkalinity is very small and can be ignored) is the determination of the total amount of the above three alkalinities. 2.3 In the description of the analysis results in Chapter 6 of the standard, the calculation formula for the total alkalinity content in water is supplemented. The total alkalinity is expressed in milligrams (calcium carbonate) per liter, which was previously expressed in milligram equivalents per liter. The current expression method is consistent with similar international standards. The standard supplements the relationship table of hydroxide, carbonate and bicarbonate ions in water to facilitate the calculation of the content of these ions. The original standard does not calculate hydroxide ions, but it was supplemented during this revision because some high-alkalinity coal mine groundwater may contain hydroxide ions, and its content needs to be calculated.
2.4 In Chapter 7 of the standard, the allowable error of the measurement was revised and supplemented. The allowable error of the original standard for parallel measurement in the same laboratory was changed to the allowable error of the measurement in two laboratories. And the allowable error is stipulated as follows: when the total alkalinity is ≤200mg/L, the absolute allowable error is 6mg/L; when it is >200mg/L, the relative allowable error is 3%. When the bicarbonate ion is ≤200mg/l, the absolute allowable error is 6mg/L; when it is >200mg/l, the relative allowable error is 3%. When the carbonate ion is ≤50mg/L, the absolute allowable error is 2mg/L; when it is >50mg/L, the relative allowable error is 4%. When the hydroxide ion is ≤30mg/l, the absolute allowable error is 1.5mg/l.; when it is >30mg/L, the relative allowable error is 5%. 660
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