Overview
ISO 5975:1983 defines an EDTA titrimetric method for the determination of calcium (Ca) and magnesium (Mg) in chromium ores. The procedure covers sample decomposition, separation of interfering elements, standardization of EDTA solutions, volumetric titration using appropriate indicators, and calculation and expression of results. The method is intended for products with Ca > 0.1% (m/m) and Mg > 3.0% (m/m). The original text also cross‑references related ISO guidance (see ISO 4297 / ISO 6629 as noted in the source).
Key topics and technical requirements
- Analytical principle: Complexometric titration with ethylenediaminetetraacetic acid (EDTA) to quantify Ca and Ca+Mg; Mg is calculated by difference.
- Sample preparation / decomposition:
- Wet decomposition with nitric and perchloric acids; for refractory ores, additional HF treatment, fusion with sodium carbonate and combination of melts are described.
- Removal of bulk chromium by distillation of chromyl chloride (chromium separation) and reduction to trivalent chromium before further processing.
- Separation of interferences: Iron, titanium, aluminium and manganese are removed by precipitation with ammonia in the presence of ammonium persulfate.
- Reagents and standards:
- EDTA standard solutions at specified molarities (examples in the text: 0.005, 0.0125, 0.025 mol/L) and procedures for standardization against magnesium reference solutions.
- Buffer solution, indicators (fluorexon for Ca, Eriochrome Black T for Ca+Mg, malachite green), acids (HNO3, HClO4, HF), ammonium persulfate.
- Titration & indicators:
- Visual titration or photoelectric titrimeter recommended. Fluorexon used for Ca (pH ~2.2), Eriochrome Black T for Ca+Mg (pH ~10).
- Calculations & quality control:
- Formulas for converting EDTA volumes to Ca and Mg content, conversion factors between Mg and Ca equivalents, and expression on a dry basis.
- Permissible tolerances for duplicate determinations are provided for both Ca and Mg ranges.
Applications and users
ISO 5975 is directly applicable to:
- Mining and minerals laboratories performing chrome ore assay and compositional analysis.
- Metallurgical and smelting quality control teams needing reliable Ca/Mg data for process control.
- Third‑party testing labs, research organizations and regulatory bodies involved in chemical analysis of chromate minerals.
The method supports decisions in ore valuation, beneficiation, process adjustment and compliance testing.
Related standards
- ISO 6629 and ISO 4297 are cited in the original text for general instructions and complementary methods; users should consult these related ISO documents for broader sampling and analytical context.
Keywords: ISO 5975, chromium ores, EDTA titrimetric method, calcium determination, magnesium determination, volumetric titration, chemical analysis, ore assay, EDTA standardization.