GB/T 43349-2023 Liming material - Determination of neutralizing value - Titrimetric methods
1 Scope
This document specifies two methods for the determination of the neutralizing value (NV) of calcareous materials with a P2O5 content of less than 3%.
Method A is applicable to all liming materials except silicate liming materials.
Note 1: Examples of hard liming materials are limestone and dolomite. Examples of soft liming materials are chalk, marl and burnt lime.
Method B is applicable to all liming materials.
Neither method correctly takes into account the potential neutralizing value of material containing more than 3 % P2O5. For a more accurate agronomic assessment of products containing more than 3 % P2O5, EN 14984 is used to determine the liming efficiency.
Note 2: The methods described in ISO 6598 and ISO 7497 can be used for the determination of P2O5 content. Further information on P analyses is given in References [9] and [10].
Note 3: Carbonate consumes H+ and removes acidity in solution with subsequent dissociation to H2O and CO2. Forms of orthophosphate can consume H+ but are not dissociated to molecular forms that remove acidity. The acidity is back titrated with alkali causing an underestimation of NV.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3310-1 Test sieves - Technical requirements and testing - Part 1: Test sieves of metal wire cloth
Note: GB/T 6003.1-2022, Test sieves - Technical requirements and testing - Part 1: Test sieves of metal wire cloth (ISO 3310-1:2016, MOD)
ISO 3696 Water for analytical laboratory use - Specification and test methods
Note: GB/T 6682-2008, Water for analytical laboratory use - Specification and test methods (ISO 3696:1987, MOD)
ISO 8157 Fertilizers, soil conditioners and beneficial substances - Vocabulary
Note: GB/T 6274-2016, Fertilizers and soil conditioners - Vocabulary (ISO 8157:1984, NEQ)
ISO 14820-2 Fertilizers and liming materials - Sampling and sample preparation - Part 2: Sample preparation
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8157 apply.
4 Principle
Dissolution of the sample in a specified quantity of hydrochloric acid standard solution. Determination of the excess acid by back titration with a sodium hydroxide standard solution.
Note: For products containing iron, a preliminary oxidization is necessary in method B.
5 Reagents
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade.
Note: Commercially available solutions can be used.
5.1 Water
According to ISO 3696, grade 3.
5.2 Hydrochloric acid standard solution: c(HCl) = 0.5 mol/L.
This solution can be purchased from a chemical supply company certified to have a concentration within a 0.4 % variance (0.498 mol/L to 0.502 mol/L).
If preparing from concentrated HCl, determine the exact concentration of the solution by titration with sodium hydroxide standard solution (5.3) using phenolphthalein solution (5.4) as indicator.
Apply the appropriate correction factor in the calculation of the results (see Clause 9).
In case of any doubt about the concentration of the HCl solution, measuring the neutralizing value of a precipitated calcium carbonate (PCC, 5.6) is recommended.
5.3 Sodium hydroxide standard solution: c(NaOH) = 0.25 mol/L.
This solution can be purchased from a chemical supply company certified to have a concentration within a 0.2 % variance (0.2495 mol/L to 0.2505 mol/L).
If preparing from NaOH pellets, determine the exact concentration of the standard solution by titration against approximately 2 g of dried potassium hydrogen phthalate (KHC8H4O4), weighed to the nearest 0.001 g.
The solution shall be stored in a polyethylene bottle and absorption of carbon dioxide during storage should be avoided.
Note: 1 ml of 0.25 mol/L sodium hydroxide solution is equivalent to 51.055 mg of potassium hydrogen phthalate.
Apply the appropriate correction factor in the calculation of the results (see Clause 9).
In case of any doubt about the concentration of the NaOH solution, measuring the neutralizing value of a precipitated calcium carbonate (PCC, 5.6) is recommended.
5.4 Phenolphthalein indicator solution.
Dissolve 0.25 g of phenolphthalein in 150 ml of ethanol with a mass fraction of 93 % and dilute with water to 250 ml.
The phenolphthalein solution is a colour indicator to determine when the end point pH is reached and is only suitable in Method A with an end point pH of 7. The indicator is not required if a pH electrode is used to monitor end point pH.
Note: If there is a buffering capacity in the sample, a deviation can occur between phenolphthalein indicator solution (changes at pH 8.3) and pH end point with pH meter (7.0).
5.5 Hydrogen peroxide solution.
Dilute one volume of hydrogen peroxide [ρ(H2O2) = 30 g/100 ml] with four volumes of water.
Hydrogen peroxide is used in Method B to oxidize any reduced iron in slag liming materials.
5.6 Precipitated calcium carbonate.
Precipitated calcium carbonate of recognized analytical grade, minimum 99 % CaCO3.
Quality control check by using precipitated calcium carbonate and blank solution should be used in each series of measurements.
6 Apparatus
Usual laboratory apparatus and, in particular, the following.
6.1 Test sieve, conforming to the requirements of ISO 3310-1, of maximum aperture size 250 µm.
6.2 pH meter, minimum sensitivity 0.05 pH units, with a suitable glass electrode and a calomel or other reference electrode or a combined electrode, calibrated using two buffer solutions whose pH values cover the range pH 4 to pH 7.
A pH meter is not required if using phenolphthalein to determine end point pH of 7 in Method A.
6.3 Mechanical stirrer, e.g. magnetic stirrer.
6.4 Desiccator.
7 Sampling
Sampling is not part of the method specified in this document. Recommended sampling methods are described in ISO 14820-1 and ISO 14820-3.
Prepare the sample of the liming materials in accordance with ISO 14820-2.
8 Procedure
8.1 Preparation of the test sample
Dry the test sample at (105 ± 2) °C to constant mass. Record the as-received (mw) and dry (md) masses. Grind the sample so that it passes the 250 µm test sieve (6.1).
Note: A smaller sieve size depending on material type can be used such as 150 µm/Mesh 100 for slags.
Perform the following when titration is not processed immediately:
——In case of burnt lime, store the prepared test sample in a desiccator (6.4) until the effective measurement.
——Otherwise, store the prepared test sample in a waterproof plastic bag.
8.2 Determination
8.2.1 Method A
8.2.1.1 Test portion
Weigh about 0.5 g, to the nearest 0.001 g, of burnt or hydrated lime or 1 g of ground limestone or ground marl (prepared according to 8.1) into a 250 ml suitable flask.
8.2.1.2 Titration
Add 50 ml of the hydrochloric acid standard solution (5.2) with continuous shaking and boil gently for 5 min (10 min for hard materials) using boiling granules.
Cool down to 20 °C to 25 °C. Add a few drops of phenolphthalein solution (5.4) or insert pH and reference electrodes (6.2) into the solution. Stir (6.3) the solution.
Titrate with the sodium hydroxide standard solution (5.3) with moderate stirring (avoid splashing) until a pH of 7.0 or pink colour of phenolphthalein are stable for 1 min while stirring is maintained.
8.2.2 Method B
8.2.2.1 Test portion
Weigh about 0.5 g, to the nearest 0.001 g, of the prepared test sample (8.1) into a 250 ml suitable flask.
8.2.2.2 Titration
Rinse the inside walls of the flask with 10 ml of water.
Standard
GB/T 43349-2023 Liming material—Determination of neutralizing value—Titrimetric methods (English Version)
Standard No.
GB/T 43349-2023
Status
valid
Language
English
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PDF
Word Count
8500 words
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255.0
Implemented on
2024-6-1
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Detail of GB/T 43349-2023
Standard No.
GB/T 43349-2023
English Name
Liming material—Determination of neutralizing value—Titrimetric methods
GB/T 43349-2023 Liming material - Determination of neutralizing value - Titrimetric methods
1 Scope
This document specifies two methods for the determination of the neutralizing value (NV) of calcareous materials with a P2O5 content of less than 3%.
Method A is applicable to all liming materials except silicate liming materials.
Note 1: Examples of hard liming materials are limestone and dolomite. Examples of soft liming materials are chalk, marl and burnt lime.
Method B is applicable to all liming materials.
Neither method correctly takes into account the potential neutralizing value of material containing more than 3 % P2O5. For a more accurate agronomic assessment of products containing more than 3 % P2O5, EN 14984 is used to determine the liming efficiency.
Note 2: The methods described in ISO 6598 and ISO 7497 can be used for the determination of P2O5 content. Further information on P analyses is given in References [9] and [10].
Note 3: Carbonate consumes H+ and removes acidity in solution with subsequent dissociation to H2O and CO2. Forms of orthophosphate can consume H+ but are not dissociated to molecular forms that remove acidity. The acidity is back titrated with alkali causing an underestimation of NV.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3310-1 Test sieves - Technical requirements and testing - Part 1: Test sieves of metal wire cloth
Note: GB/T 6003.1-2022, Test sieves - Technical requirements and testing - Part 1: Test sieves of metal wire cloth (ISO 3310-1:2016, MOD)
ISO 3696 Water for analytical laboratory use - Specification and test methods
Note: GB/T 6682-2008, Water for analytical laboratory use - Specification and test methods (ISO 3696:1987, MOD)
ISO 8157 Fertilizers, soil conditioners and beneficial substances - Vocabulary
Note: GB/T 6274-2016, Fertilizers and soil conditioners - Vocabulary (ISO 8157:1984, NEQ)
ISO 14820-2 Fertilizers and liming materials - Sampling and sample preparation - Part 2: Sample preparation
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8157 apply.
4 Principle
Dissolution of the sample in a specified quantity of hydrochloric acid standard solution. Determination of the excess acid by back titration with a sodium hydroxide standard solution.
Note: For products containing iron, a preliminary oxidization is necessary in method B.
5 Reagents
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade.
Note: Commercially available solutions can be used.
5.1 Water
According to ISO 3696, grade 3.
5.2 Hydrochloric acid standard solution: c(HCl) = 0.5 mol/L.
This solution can be purchased from a chemical supply company certified to have a concentration within a 0.4 % variance (0.498 mol/L to 0.502 mol/L).
If preparing from concentrated HCl, determine the exact concentration of the solution by titration with sodium hydroxide standard solution (5.3) using phenolphthalein solution (5.4) as indicator.
Apply the appropriate correction factor in the calculation of the results (see Clause 9).
In case of any doubt about the concentration of the HCl solution, measuring the neutralizing value of a precipitated calcium carbonate (PCC, 5.6) is recommended.
5.3 Sodium hydroxide standard solution: c(NaOH) = 0.25 mol/L.
This solution can be purchased from a chemical supply company certified to have a concentration within a 0.2 % variance (0.2495 mol/L to 0.2505 mol/L).
If preparing from NaOH pellets, determine the exact concentration of the standard solution by titration against approximately 2 g of dried potassium hydrogen phthalate (KHC8H4O4), weighed to the nearest 0.001 g.
The solution shall be stored in a polyethylene bottle and absorption of carbon dioxide during storage should be avoided.
Note: 1 ml of 0.25 mol/L sodium hydroxide solution is equivalent to 51.055 mg of potassium hydrogen phthalate.
Apply the appropriate correction factor in the calculation of the results (see Clause 9).
In case of any doubt about the concentration of the NaOH solution, measuring the neutralizing value of a precipitated calcium carbonate (PCC, 5.6) is recommended.
5.4 Phenolphthalein indicator solution.
Dissolve 0.25 g of phenolphthalein in 150 ml of ethanol with a mass fraction of 93 % and dilute with water to 250 ml.
The phenolphthalein solution is a colour indicator to determine when the end point pH is reached and is only suitable in Method A with an end point pH of 7. The indicator is not required if a pH electrode is used to monitor end point pH.
Note: If there is a buffering capacity in the sample, a deviation can occur between phenolphthalein indicator solution (changes at pH 8.3) and pH end point with pH meter (7.0).
5.5 Hydrogen peroxide solution.
Dilute one volume of hydrogen peroxide [ρ(H2O2) = 30 g/100 ml] with four volumes of water.
Hydrogen peroxide is used in Method B to oxidize any reduced iron in slag liming materials.
5.6 Precipitated calcium carbonate.
Precipitated calcium carbonate of recognized analytical grade, minimum 99 % CaCO3.
Quality control check by using precipitated calcium carbonate and blank solution should be used in each series of measurements.
6 Apparatus
Usual laboratory apparatus and, in particular, the following.
6.1 Test sieve, conforming to the requirements of ISO 3310-1, of maximum aperture size 250 µm.
6.2 pH meter, minimum sensitivity 0.05 pH units, with a suitable glass electrode and a calomel or other reference electrode or a combined electrode, calibrated using two buffer solutions whose pH values cover the range pH 4 to pH 7.
A pH meter is not required if using phenolphthalein to determine end point pH of 7 in Method A.
6.3 Mechanical stirrer, e.g. magnetic stirrer.
6.4 Desiccator.
7 Sampling
Sampling is not part of the method specified in this document. Recommended sampling methods are described in ISO 14820-1 and ISO 14820-3.
Prepare the sample of the liming materials in accordance with ISO 14820-2.
8 Procedure
8.1 Preparation of the test sample
Dry the test sample at (105 ± 2) °C to constant mass. Record the as-received (mw) and dry (md) masses. Grind the sample so that it passes the 250 µm test sieve (6.1).
Note: A smaller sieve size depending on material type can be used such as 150 µm/Mesh 100 for slags.
Perform the following when titration is not processed immediately:
——In case of burnt lime, store the prepared test sample in a desiccator (6.4) until the effective measurement.
——Otherwise, store the prepared test sample in a waterproof plastic bag.
8.2 Determination
8.2.1 Method A
8.2.1.1 Test portion
Weigh about 0.5 g, to the nearest 0.001 g, of burnt or hydrated lime or 1 g of ground limestone or ground marl (prepared according to 8.1) into a 250 ml suitable flask.
8.2.1.2 Titration
Add 50 ml of the hydrochloric acid standard solution (5.2) with continuous shaking and boil gently for 5 min (10 min for hard materials) using boiling granules.
Cool down to 20 °C to 25 °C. Add a few drops of phenolphthalein solution (5.4) or insert pH and reference electrodes (6.2) into the solution. Stir (6.3) the solution.
Titrate with the sodium hydroxide standard solution (5.3) with moderate stirring (avoid splashing) until a pH of 7.0 or pink colour of phenolphthalein are stable for 1 min while stirring is maintained.
8.2.2 Method B
8.2.2.1 Test portion
Weigh about 0.5 g, to the nearest 0.001 g, of the prepared test sample (8.1) into a 250 ml suitable flask.
8.2.2.2 Titration
Rinse the inside walls of the flask with 10 ml of water.
