Overview
ISO 8658:1997 specifies a laboratory method for the determination of trace elements in green and calcined coke intended for aluminium production. The method uses sample ashing, fusion, dissolution and measurement by flame atomic absorption spectrometry (FAAS). It is written for coke with ash ≤ 1% (m/m) and defines procedural steps, required reagents and apparatus to obtain reliable trace-element results relevant to aluminium smelting feedstocks.
Key topics and technical requirements
- Scope and target elements: applicable to green and calcined coke with individual element concentrations up to the following limits:
- Calcium 0.025% | Chromium 0.005% | Copper 0.025%
- Iron 0.030% | Lead 0.010% | Magnesium 0.010%
- Manganese 0.001% | Nickel 0.050% | Silicon 0.100%
- Vanadium 0.100% | Zinc 0.004%
- Sample preparation: representative sampling per ISO 6375; grind and reduce sample; test portion typically 5 g.
- Ashing: heat in a muffle furnace at 700 °C ± 10 °C for ~10 h, repeating heating/cooling cycles until constant mass.
- Fusion and dissolution: ash fused with anhydrous sodium carbonate and orthoboric acid, then dissolved in dilute hydrochloric acid for analysis.
- Analytical technique: FAAS with appropriate hollow-cathode lamps, flame type and slit/wavelength settings (Table 4 of the standard). Examples in the document: Ca (422.7 nm), Cr (357.9 nm), Cu (324.8 nm).
- Calibration and modifiers: preparation of multi-level calibration solutions and use of lanthanum chloride as chemical modifier for some determinations; reagent and glassware cleanliness requirements (acid-wash).
- Apparatus and reagents: specifies platinum crucibles, Meker burner, spectrometer, analytical-grade reagents and water complying with ISO 3696 (grade 2).
Applications and users
- Laboratories performing quality control of carbonaceous materials for the aluminium industry.
- Producers and purchasers of green coke and calcined coke who need verified trace-element data to control raw material quality and compliance.
- Analytical chemists and QA/QC personnel in metallurgy, smelting operations and material testing labs that require standardized FAAS procedures for routine monitoring of trace metals.
Related standards
This standard ensures consistent, reproducible trace-element measurement in coke feedstocks, supporting material selection and process control in aluminium production.