ASTM E247 Silica Determination in Manganese & Iron Ores
The estimation of silica content in manganese ores, iron ores, and other such materials is done using the ASTM E247 standard test method. This method uses gravimetric analysis, which is a laboratory technique that uses the change in mass to calculate the amount or concentration of an analyte.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM E247 is a standardized analytical method used primarily in the mining and metallurgical industries to precisely quantify the amount of silica ($SiO_{2}$) in specific ores. Because silica levels directly impact the quality of the finished metal and the efficiency of the smelting process, this test is a cornerstone of quality control.
The method employs a gravimetric approach, a “referee” or classical wet-chemistry technique. It is highly valued for its accuracy when handling high-silica concentrations, where instrumental methods may require frequent calibration or encounter interference.
Scope, Applications, and Benefits
Scope
ASTM E247 evaluates:
- SiO₂ content (wt%) in iron and manganese ores
- Gravimetric method (acid dehydration and ignition)
- Photometric method (silicomolybdate blue colorimetry for lower SiO₂)
- Applicable to ores, concentrates, sinter, and pellets
Applications
- Quality assessment of manganese and iron ores
- Raw material inspection in mining and beneficiation plants
- Process control in iron and steelmaking operations
- Material characterization for trade and commercial transactions
- Research and development in mineral processing and metallurgy
Benefits
- Ensures accurate and reliable determination of silica content
- Supports quality control of ores and mineral raw materials
- Helps in evaluating ore suitability for metallurgical processing
- Reduces variability in analytical results through standardized procedures
- Aids in compliance with industry and regulatory specifications
Testing Process
Sample Preparation
Dry the ore sample, grind to the specified fineness, and homogenize thoroughly.
1Weighing
Accurately weigh a representative test portion of the prepared sample.
2Decomposition
Digest the sample using appropriate acids to dissolve the matrix and release silica.
3Calculation
Calculate % SiO₂ based on residue mass and original sample weight.
4Technical Specifications
| Parameter | Details |
|---|---|
| Analyte | Silica (SiO₂) |
| Sample Form | Dried and finely ground powder |
| Sample Weight | As specified by the standard (typically ~0.5–1 g) |
| Measurement Basis | Mass of ignited silica residue |
| Accuracy | High accuracy for routine chemical analysis |
| Standard Reference | ASTM E247 |
Instrumentation Used
- Analytical balance
- Drying oven or muffle furnace
- Beakers, crucibles, and digestion vessels
- Hot plate or heating mantle
- Filtration apparatus
- Desiccator
- Data recording and calculation tools
Results and Deliverables
- SiO₂ content (wt%) by gravimetric or photometric method
- Replicate data and precision statement
- HF correction data (gravimetric, if applied)
- Comparison to specification limits
- Certificate of analysis for commercial reporting
- Full ASTM E247 analytical report
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Frequently Asked Questions
Silica is the primary acidic gangue in iron ore. Each unit of SiO₂ requires approximately 1.5 units of basic flux (limestone/dolomite) in the blast furnace to form slag, increasing coke consumption and slag volume. Lower SiO₂ iron ore is more valuable as it reduces flux requirements, energy costs, and liquid slag volume per tonne of iron.
The gravimetric method measures SiO₂ by weight after chemical separation and ignition, suitable for higher SiO₂ concentrations (>0.5 wt%). The photometric (silicomolybdate blue) method measures SiO₂ in solution by UV-Vis absorbance and is more sensitive, preferred for trace SiO₂ (<0.5 wt%) in high-purity materials.
After ignition, a small amount of SiO₂ remains mixed with other insoluble impurities in the residue. Treatment with hydrofluoric acid volatilizes SiO₂ as SiF₄; the weight loss after HF treatment gives the true SiO₂ content and eliminates the contribution of co-precipitated impurities such as TiO₂ and Al₂O₃.
XRF (ASTM E322) is widely used for routine multi-element ore analysis including SiO₂, offering faster turnaround. However, ASTM E247 titrimetric/gravimetric methods are the referee methods for commercial arbitration and certification purposes due to their primary measurement traceability.
Ore samples must be dried (105–110 °C), crushed, and ground to −75 µm (200 mesh) for representative analysis. Homogeneous, fine-grained samples are essential for accurate silica determination by both gravimetric and photometric methods.
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