Overview
ISO 9035:1989 specifies a titrimetric method for determining the acid‑soluble iron(II) content in natural and processed iron ores. The method applies to ores containing 1 % to 25 % acid‑soluble Fe(II) and only traces of metallic iron. It is intended for use in conjunction with reducibility test methods (ISO 4695 / ISO 7215) and includes procedural details, precision data and three annexes (flowchart, derivation of precision and trial data).
Key topics and technical requirements
- Scope limits
- Applicable to ores with 1–25 % acid‑soluble Fe(II).
- Not applicable when sulfide sulfur > 0.3 % (m/m) or free carbon > 5 % (m/m).
- Principle
- Dissolution of the predried sample in hydrochloric acid under an inert atmosphere or with CO3/CO3– trapping of evolved gases.
- Addition of a sulfuric–phosphoric acid mixture, dilution and titration of Fe(II) with potassium dichromate (standard solution; c ≈ 0.01667 mol/L).
- Endpoint indicated by sodium diphenylaminesulfonate (indicator).
- Reagents and apparatus (selected)
- Hydrochloric, sulfuric, phosphoric acids; hydrofluoric acid optional for high‑silica ores.
- Sodium carbonate / sodium hydrogen carbonate for neutralization/trapping.
- Gockel safety trap or inert‑gas feed (nitrogen/argon), class B burette (ISO 385‑1), 500 ml conical flask.
- Standard dichromate solution preparation (e.g., dissolve 4.904 g K2Cr2O7 and dilute to 1 000 ml).
- Sample preparation
- Crush/pulverize to minus 100 µm (or minus 160 µm for ores with combined water/oxidizable compounds).
- Predry at 105 °C ± 2 °C (per ISO 7764).
- Typical decomposition at ~90 °C; decomposition time normally ~30 min (max 60 min).
- Quality control & precision
- Run analyses in duplicate; validate with a certified reference material analyzed in parallel.
- Temperature correction for dichromate titre: ~0.02 % relative per 1 °C difference.
- Precision quantified by repeatability and reproducibility regression equations; annexes provide trial data and statistical background.
Applications and users
This standard is relevant for:
- Metallurgical and analytical laboratories performing iron ores analysis.
- Mining companies and QA/QC teams monitoring ore chemistry for processing and reducibility testing.
- Research groups and process engineers linking Fe(II) content to reduction behavior and pellet/feedstock characterization.
Practical uses include routine chemical quality control, verification of reagent preparation, and validating reducibility test protocols.
Related standards
Keywords: ISO 9035, acid‑soluble iron(II), titrimetric method, potassium dichromate titration, iron ores analysis, reducibility tests, sampling, certified reference material.
