ISO 6331:2024

Overview

ISO 6331:2024 - "Chromium ores and concentrates - Determination of chromium content - Titrimetric method" - is the second edition international standard that specifies a laboratory titrimetric procedure for determining chromium in chromium ores and concentrates with a chromium mass fraction greater than 7.00%. The method covers sample decomposition by sodium peroxide fusion, oxidation of Cr(III) to chromate, and quantification of chromium(VI) by titration (visual or potentiometric).

Key technical topics and requirements

• Scope: Applicable to chromium ores and concentrates containing > 7.00% chromium.
• Principle: Fuse the test portion with sodium peroxide, leach and acidify the melt, oxidize Cr(III) to chromate using ammonium peroxodisulfate (with silver nitrate catalyst), then titrate chromium(VI) with ammonium iron(II) sulfate. End‑point determination may be by visual back‑titration with potassium permanganate or by potentiometric titration.
• Reagents: Specifies analytical grades and includes preparations for reagents such as sulfuric and orthophosphoric acids, manganese(II) sulfate, silver nitrate, ammonium peroxodisulfate, ammonium iron(II) sulfate (standard volumetric solution), and potassium permanganate.
• Apparatus: Ordinary lab glassware (Class A volumetrics per ISO 385/648/1042), porcelain/corundum crucibles, and potentiometric titration equipment: indicator and reference electrodes, burette, magnetic stirrer and millivoltmeter/pH‑meter.
• Sampling and sample prep: References ISO 6153 (increment sampling) and ISO 6154 (sample preparation) for representative analytical samples.
• Results and reporting: Includes procedures for calculation of chromium content, conversion to Cr2O3 when required, precision treatment, between‑laboratory precision, trueness checks and required test report content.

Note: ISO 6331:2024 contains technical updates from the 1983 edition, including revised potentiometric apparatus descriptions, crucible specifications, decomposition conditions, and added guidance on result acceptance and reporting.

Practical applications and who uses it

• Mining and concentrator laboratories for incoming ore characterization and batch quality control.
• Ferroalloy and metallurgical quality control labs to verify feedstock chromium content.
• Trading and inspection bodies for contract testing and material certification.
• Research and academic laboratories conducting geochemical or metallurgical studies on chromium ores.
• Regulatory agencies that require standardized test methods for material specification and compliance.

This standard ensures reproducible chromium assays for process control, product specification and trade settlement.

Related standards

• ISO 6153 - Chromium ores - Increment sampling
• ISO 6154 - Chromium ores - Preparation of samples
• ISO 385, ISO 648, ISO 1042 - Laboratory glassware specifications
• ISO 3696 - Water for analytical laboratory use
• ISO 6129 - Determination of hygroscopic moisture content
• ISO 80000‑1 - Quantities and units

For full procedural detail and official wording, obtain ISO 6331:2024 from ISO or your national standards body.

Keywords: ISO 6331:2024, chromium ores, titrimetric method, chromium determination, potentiometric titration, sodium peroxide fusion, ammonium iron(II) sulfate, potassium permanganate.