Overview
ISO 22146:2018 specifies an automatic titration method with citric acid to determine the reactivity of carbonate liming materials - specifically calcium carbonate and calcium magnesium carbonate. The method measures the speed and effectiveness of a liming material’s neutralising potential by maintaining pH at 4.5 and recording citric acid consumption over a fixed time (15 minutes). It applies to materials with a maximum particle size of 6.3 mm (per ISO 20977). Note: marble dolomite with low BET surface area is covered by EN 14984.
Keywords: ISO 22146:2018, carbonate liming materials, reactivity, automatic titration, citric acid, neutralising value.
Key Topics and Requirements
- Principle: Limited acid decomposition of carbonates; citric acid consumption at pH 4.5 over 15 min is the reactivity metric.
- Scope: Applies to CaCO3 and Ca/Mg carbonate liming materials with particle size ≤ 6.3 mm.
- Critical steps:
- Accurate identification of liming material type (affects precision).
- Correct sample preparation and size distribution (ISO 14820-2 / ISO 20977).
- Calibration and performance of the pH electrode and pH-stat program in the titrator.
- Use of a suitable precipitated calcium carbonate (PCC) reference.
- Appropriate stirring (propeller or non-grinding magnetic stirrer) to ensure homogeneous dispersion.
- Apparatus & reagents:
- Automatic burette/titrator with pH-stat, pH meter, propeller or magnetic stirrer, beakers.
- Citric acid monohydrate solution (conventional concentration ρ = 457.17 g/L).
- PCC reference material, silicone defoamer, pH buffers (pH 4 and 7), water per ISO 3696.
- Testing practice: Samples are tested “as received” to align reactivity with neutralising value and MgO measurements; correction factors are applied later (additional uncertainty should be evaluated).
Applications and Users
- Quality control and batch testing for lime producers and fertilizer manufacturers.
- Independent analytical laboratories performing reactivity and neutralising value assessments.
- Agronomists, soil scientists and regulatory bodies verifying liming materials for agricultural use.
- Product certification, specification compliance, and R&D into liming product performance.
Benefits: faster, more representative automated testing closer to soil conditions; improved repeatability and suitability for routine QC.
Related Standards
- ISO 20977 - size distribution of liming materials
- ISO 20978 - determination of neutralising value (titrimetric methods)
- ISO 14820-2 - sample preparation for liming materials
- ISO 3696 - water for laboratory use
- EN 14984 - marble dolomite reactivity (low BET)
- EN 12048 - moisture determination for solid fertilizers and liming materials
For laboratories and manufacturers, ISO 22146:2018 provides a practical, automated procedure to quantify carbonate liming material reactivity for quality assurance and agronomic performance assessment.
Open preview (PDF)Carbonate liming materials — Determination of reactivity — Automatic titration method with citric acid
