Overview
ISO 2367:1972 specifies a gravimetric method using 8‑hydroxyquinoline (quinolinol‑8) for determining aluminium content in cryolite (natural and artificial). The procedure covers sample fusion, chemical separation, precipitation of aluminium as an aluminium–quinoline complex, and gravimetric weighing to obtain aluminium content expressed as percent Al.
Key topics and requirements
- Scope and limits
- Applicable to natural and artificial cryolite provided Fe2O3 ≤ 0.15%.
- Also applicable to products with a molar ratio NaF : AlF3 ≈ 3 to 1.7.
- Analytical principle
- Acid fusion of a weighed test portion with potassium pyrosulfate (K2S2O7).
- Recovery into hydrochloric acid, removal of interfering elements, and precipitation of aluminium with ammonium benzoate in an acetic reducing medium.
- Re‑dissolution and reprecipitation as aluminium tri(quinolin‑8‑oxide) (tri(quinolinolate‑8)), followed by filtration, washing, drying at 130 °C, and weighing.
- Reagents & apparatus (examples from the method)
- Reagents: hydroxy‑8‑quinoline (20 g/L in acetic acid), ammonium benzoate solutions, acetic buffer, sodium sulfite, HCl, sulfuric acid, tartric acid, ammonia.
- Apparatus: platinum crucible, electric furnace (750 ± 25 °C), glass‑fritted crucible (porosity 3–15 μm), drying oven at 130 °C.
- Calculation
- Aluminium content is calculated gravimetrically using the mass of the dried aluminium tri(quinolinolate‑8) precipitate and a conversion factor (method provides factor 0.0587).
Applications and users
- Who uses this standard
- Chemical and materials testing laboratories performing cryolite analysis.
- Quality control teams at producers or processors of cryolite and related mineral products.
- Metallurgical/industrial laboratories requiring a validated gravimetric aluminium determination for specification compliance or material certification.
- Practical uses
- Routine determination of aluminium content in cryolite batches.
- Verification of product conformity where low levels of iron and defined NaF:AlF3 ratios are present.
- Baseline method for comparison with other analytical techniques in mineral analysis.
Related standards
- ISO/R 1619 (preparation and conservation of samples for testing) is referenced in the method for sample handling and preparation.
Keywords: ISO 2367, cryolite analysis, aluminium determination, 8‑hydroxyquinoline gravimetric method, gravimetric analysis, aluminium content, cryolite standard, mineral testing.