Overview
ISO 312:1986 specifies a titrimetric method for determining the active oxygen content of manganese ores, expressed conventionally as manganese dioxide (MnO2). This third edition (1986) is a minor revision that cancels and replaces the 1980 edition. The standard defines the principle, reagents, apparatus, sample requirements, analytical procedure and expression of results, and includes an illustrative figure of the apparatus.
Key topics and technical requirements
- Analytical principle: Reduction of MnO2 in the ore by an excess of ammonium iron(II) sulfate in sulfuric acid, followed by back-titration of the excess Fe(II) with standard potassium dichromate (K2Cr2O7) using sodium diphenylamine sulfonate as indicator.
- Reagents (as specified):
- Potassium dichromate standard solution (8.780 g/l)
- Ammonium iron(II) sulfate solution (60 g/l in sulfuric acid, 1+7)
- Phosphoric acid (specified concentration/density in the standard)
- Sodium diphenylamine sulfonate indicator (0.8 g/l)
- Apparatus: Ordinary laboratory glassware plus a specified conical flask fitted with two outflow pipes (figure provided). A source of carbon dioxide and a hotplate are used during dissolution.
- Sampling and sample preparation: Test sample crushed to ≤100 µm and air-dried; recommended test portion 0.25 g. Sampling and preparation reference ISO 4296 parts 1 and 2.
- Procedure essentials:
- Run three parallel determinations from the same sample; perform a blank test.
- Pass CO2 through the closed flask while heating with excess Fe(II) reagent to dissolve the ore.
- After cooling, add phosphoric acid and indicator, then titrate the excess Fe(II) with K2Cr2O7 until a persistent violet–blue end point.
- Standardize the dichromate titre against a standard manganese ore sample; use the average of three results.
- Expression of results: Active oxygen reported as % MnO2 on a dry basis using the measured titres and a conversion factor; permissible tolerances for three parallel determinations are given by ranges of active oxygen content.
Applications and who uses it
- Quality control and chemical assay laboratories in mining and mineral processing.
- Producers and traders of manganese ores and concentrates for grading and specification compliance.
- Regulatory bodies and inspection laboratories requiring standardized determination of active oxygen (MnO2 equivalent).
- Research and development groups working on manganese ore beneficiation or metallurgical feedstock characterization.
Related standards
- ISO 4296-1 - Manganese ores - Sampling - Increment sampling
- ISO 4296-2 - Manganese ores - Sampling - Preparation of samples
- ISO 4297 - Manganese ores and concentrates - General methods of chemical analysis
Keywords: ISO 312:1986, manganese ores, active oxygen determination, manganese dioxide, titrimetric method, ammonium iron(II) sulfate, potassium dichromate, sodium diphenylamine sulfonate.
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