ISO 9035:1989 PDF

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

• ISO 4695, ISO 7215 - reducibility test methods (use in conjunction).
• ISO 7764 - sample preparation for chemical analysis.
• ISO 385‑1, ISO 4791‑1 - laboratory apparatus vocabulary/requirements.
• ISO 5725 - statistical treatment of precision data.

Keywords: ISO 9035, acid‑soluble iron(II), titrimetric method, potassium dichromate titration, iron ores analysis, reducibility tests, sampling, certified reference material.