Overview
ISO 4689-3:2017 specifies a combustion/infrared method for the determination of sulfur content in iron ores. The procedure uses a high-frequency induction furnace to combust a prepared sample in oxygen and measures evolved SO2 with an infrared detector. It applies to natural iron ores, iron ore concentrates and agglomerates (including sinter) with sulfur contents from 0.002 % to 0.25 % (mass fraction). The method has limitations for samples with high combined water content (see Key Topics).
Key topics and technical requirements
- Scope and limits
- Applicable sulfur range: 0.002 % – 0.25 %.
- Not applicable to ores with > 1.0 % combined water. With a heated metal filter, apparatus can treat ores with < 3.0 % combined water.
- Principle
- Sample mixed with a flux (containing iron, tin, tungsten) and combusted in a high-frequency induction furnace using oxygen.
- Evolved SO2 is carried to an infrared absorption detector for quantification.
- Reagents and calibration
- Reagents specified (examples): metallic iron, tin, tungsten (very low S content), magnesium perchlorate drying agent, NaOH absorption media.
- Calibration via standard sulfur solutions prepared from dried potassium sulfate; recommended calibration series provided.
- Apparatus
- High-frequency induction furnace (heating coil, 1 200 °C capacity).
- Quartz combustion tube, refractory crucible, tin capsules, metal filter with heating device, dust trap, IR detector and measuring cell.
- Sampling and sample preparation
- Laboratory sample typically −100 µm (use −160 µm where combined water/oxidizable compounds are significant).
- Prepare predried test samples by drying at 105 °C ± 2 °C (ISO 7764).
- Typical test portion: ~0.5 g (use 0.2 g when sulfur > 0.1 %).
- Quality control
- Minimum duplicate determinations; include blank test and certified reference material (CRM) in each run.
- Procedures for calibration graph, calculation, repeatability and between-laboratory precision are included.
- Safety
- Method involves hazardous materials and high temperatures; users must apply appropriate health and safety practices.
Applications and users
- Routine sulfur analysis in mining and mineral processing labs.
- Quality control for iron ore concentrates, sinter products and raw ore prior to smelting or trading.
- Analytical and contract laboratories performing chemical characterization for production control, specification compliance and shipment certification.
- Useful for metallurgical engineers, QA/QC managers, assay labs and regulatory bodies monitoring sulfur content.
Related standards
- ISO 4689 series (other parts for sulfur/iron ore analysis)
- ISO 3082 - Sampling and sample preparation procedures
- ISO 7764 - Preparation of predried test samples
- ISO 2596 - Determination of hygroscopic moisture
- ISO 648 / ISO 1042 - Laboratory glassware specifications
- ISO Guide 35 - Reference material certification
Keywords: ISO 4689-3:2017, sulfur determination, iron ores, combustion/infrared method, high-frequency induction furnace, sulfur analysis, iron ore concentrates, sinter products, laboratory procedures.