Overview
ISO 7335:1987 - "Iron ores - Determination of combined water content - Karl Fischer titrimetric method" specifies a laboratory titrimetric procedure to determine combined water in natural iron ores, concentrates and agglomerates (including sinter). The method covers a measurement range of 0.05 to 10 % (m/m) combined water and defines combined water as the fraction that can be removed only at temperatures substantially higher than 100–110 °C. The standard includes illustrated apparatus arrangements (heating tube, absorption cell, titration cell) and three annexes with additional guidance.
Key topics and requirements
- Scope and range: Applicable to iron ores, concentrates and sinter products with combined water from 0.05–10 % (m/m).
- Definition: Combined water = water removable only at temperatures well above 100–110 °C.
- Principle: Liberation of combined water by controlled heating (predrying at ~105 °C then progressive heating up to ~950 °C) in a dry nitrogen stream; collection of evolved water into an ethylene glycol–methanol absorber; titration by Karl Fischer titration with electrometric end-point detection.
- Apparatus: Heating tube, two furnaces (low and high temperature), drying towers, absorption cell, platinum electrodes, electrometric titrator, gas flowmeter and sample boats.
- Reagents: Dry nitrogen, desiccants (silica gel, Mg(ClO4)2), ethylene glycol–methanol absorber and Karl Fischer solution standardized on the day of use.
- Sampling & sample prep: Laboratory sample prepared per ISO 3081/3082/3083; predried test samples per ISO 7764; recommended particle sizes (e.g., −100 µm or −160 µm for ores with significant combined water/oxidizable compounds).
- Quality control: Blank tests, use of certified reference materials, replicate determinations, apparatus conditioning and calibration, and defined repeatability/precision criteria and calculation procedures for reporting results.
Applications and users
- Practical for metallurgical laboratories, mining QA/QC teams, iron ore concentrate producers, sinter plant quality control and accredited testing laboratories needing accurate combined water determination.
- Use cases: Moisture specification compliance, process control (drying, sintering), material characterization for shipping/sales contracts, and verification of product drying or calcination processes.
- Benefits: Provides a standardized, traceable method for combined water measurement that minimizes interference from free moisture and ensures comparable results across labs.
Related standards
- ISO 3081 - Iron ores: Increment sampling (manual)
- ISO 3082 / ISO 3083 - Sampling and sample preparation
- ISO 7764 - Preparation of predried test samples for chemical analysis
Keywords: ISO 7335:1987, combined water, Karl Fischer titrimetric method, iron ores, moisture determination, absorption cell, heating tube, laboratory standard.