ISO 14388-2:2014

Overview - ISO 14388-2:2014 (Chromium reducible sulfur, CRS)

ISO 14388-2:2014 specifies a chromium reducible sulfur (CRS) methodology within the ISO 14388 acid‑base accounting suite for acid sulfate soils. The standard describes a laboratory procedure to measure inorganic sulfides (e.g. pyrite, marcasite, greigite, mackinawite) and elemental sulfur without interference from organic sulfur or sulfate. CRS is used to quantify the soil’s potential sulfidic acidity, a key input for calculating net acidity and informing land management, remediation and regulatory compliance.

Key technical topics and requirements

• CRS measurement principle: digestion of soil in an acidic chromous chloride solution to release H2S, trapping as zinc sulfide (ZnS), and quantification by iodimetric titration.
• pH measurement in 1 mol/l KCl: soils are tested as a 1:40 suspension; the pHKCl result determines subsequent analyses.
• Decision tree based on pHKCl:
  • If pHKCl < 6.5 → determine titratable actual acidity (TAA).
  • If pHKCl < 4.5 or jarosite is present → determine net acid‑soluble sulfur (SNS or NAS) as the difference between hydrochloric acid (4 mol/l HCl) extractable sulfur and potassium chloride extractable sulfur.
  • If pHKCl > 6.5 → assess acid neutralizing capacity (ANC) (e.g., inorganic carbon by combustion or ANC by back‑titration).
• Ancillary analyses: potassium chloride extractable S, Ca, Mg to help calculate retained acidity and neutralizing components.
• Quality and safety: analytical‑grade reagents, blank testing for sulfur/Ca/Mg, and awareness of chromium and H2S hazards are emphasized.
• Reporting and calculations: procedures and formulae are provided to convert titration results into sulfur and acidity units for acid‑base accounting.

Practical applications and who uses the standard

• Environmental and geotechnical laboratories performing acid‑base accounting for saltmarsh, coastal wetlands, mining waste or construction sites.
• Environmental consultants, mining companies, regulators and remediation teams assessing risk of acid generation, designing lime dosing or neutralization strategies, and preparing compliance documentation.
• Researchers studying sulfidic soil behavior, acid sulfate soil mapping, and long‑term management of reclaimed land.

Related standards

• ISO 14388-1: Introduction, sampling, definitions (companion guidance).
• ISO 14388-3: SPOCAS suite analysis (alternative acid‑sulfide methods).
• ISO 10694: Determination of organic and total carbon (used for ANC by inorganic carbon).
• Applicable ISO laboratory glassware and water quality standards cited within the document.

Keywords: ISO 14388-2, Chromium reducible sulfur, CRS, acid sulfate soils, acid-base accounting, net acidity, titratable actual acidity, pHKCl, acid neutralizing capacity.