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D5263-23 – Standard Test Method Technical Guide
ASTM D5263‑23 specifies a colorimetric procedure for evaluating the relative degree of oxidation in bituminous coal caused by weathering. By extracting humic acids with an alkali solution and measuring their absorbance at a specific wavelength, this test method provides a practical guide for selecting coals intended for metallurgical applications.
📜 Scope and Significance
This test method applies to coals ranging from high volatile A bituminous to low volatile bituminous in rank. It is specifically intended for coals oxidized through weathering and is explicitly not sensitive to thermally oxidized coal. The procedure yields a relative measure of oxidation rather than a quantitative percentage, functioning primarily as a guide for suppliers, buyers, and users in the metallurgical industry. Notably, lower rank bituminous coals are more easily extracted than higher rank coals.
| 🟦 Parameter | 📏 Specification |
|---|---|
| Applicable Coal Rank | High Volatile A Bituminous to Low Volatile Bituminous |
| Detected Oxidation Type | Weathering (not thermal oxidation) |
| Measurement Type | Relative degree (non‑quantitative) |
| Extracted Constituents | Humic acids |
| Primary Application | Guide for metallurgical coal selection |
⚙️ Apparatus and Reagents
The standard mandates precise laboratory equipment. The analysis requires a single‑beam, grating transmission spectrophotometer with a range of 340 nm to 900 nm, and measurements are taken at 520 nm. Sample cuvettes or test tubes must have a light path from 10 mm to 17 mm; an inside diameter of 17 mm ± 0.3 mm is typical. An analytical balance with a sensitivity of 0.001 g, a hot plate capable of boiling, and a thermometer with an accuracy of ± 0.5 °C up to 100 °C are required.
| 🛠️ Apparatus | ⚡ Required Specification |
|---|---|
| Transmission Spectrophotometer | Single‑beam, grating; 340 nm – 900 nm; measure at 520 nm |
| Test Tubes / Cuvettes | Light path 10 mm – 17 mm; common ID 17 mm ± 0.3 mm |
| Analytical Balance | Sensitivity to 0.001 g |
| Hot Plate | Capable of bringing aqueous solutions to a boil |
| Thermometer | Up to 100 °C, sensitivity ± 0.5 °C |
| Filter Paper | Type II, Class F and G |
| Timer | Capable of measuring 30 min to the nearest second |
| Graduated Cylinder | 100 mL capacity |
| Beaker | 400 mL capacity |
Key reagents include Sodium Hydroxide Solution (certified 1 N) for the alkali extraction and Octylphenoxypolyethoxyethanol Nonionic Surfactant as a wetting agent. Reagent water conforming to ASTM D1193 must be used, and laboratories should follow the competence guidelines of ASTM D7448.
⚠️ Important Limitation: This test method does not provide a quantitative measurement of the amount of oxidized coal present. It is strictly a relative guide intended for metallurgical coal characterization. Furthermore, it is not applicable to thermally oxidized coal.
🧪 Test Summary and Procedure
The core procedure involves extracting humic acids from the coal sample using a sodium hydroxide solution. The resulting alkali extract is then measured colorimetrically. The intensity of the color produced by the humic acids, quantified as the transmittance of the solution at 520 nm, is a direct function of the degree of oxidation. The laboratory conducting the test should adhere to the practices established in ASTM D7448 for sampling and analysis competence.
💡 Key Measurement Insight: The color intensity of the humic acids extracted is a function of the oxidation degree. Lower rank bituminous coals are more easily extracted than higher rank coals, which should be accounted for when interpreting results across different rank categories (see ASTM D5263, Note 1).
❓ Frequently Asked Questions
🔍 What is the primary purpose of ASTM D5263‑23?
The primary purpose is to determine the relative degree of oxidation in bituminous coal caused by weathering. It serves as a guide for evaluating coals intended for metallurgical use, helping suppliers and buyers compare oxidation levels.
💡 Can this test method be used for thermally oxidized coal?
No, ASTM D5263‑23 explicitly states that it cannot be sensitive to thermally oxidized coal. It is specifically designed for coals that may be oxidized as a result of weathering.
⚡ What are the key instrumental requirements for this test?
The procedure requires a transmission spectrophotometer capable of measuring at 520 nm with a range of 340