Overview
ISO 13658:2000 specifies a standardized analytical method for the determination of zinc content in zinc sulfide concentrates (10% to 60% Zn, m/m). The method combines hydroxide precipitation to remove interfering Fe/Al/Mn and an EDTA complexometric (titrimetric) determination of zinc (with xylenol orange indicator) and includes procedures to account for cadmium interference and insoluble residues. The standard is intended for routine laboratory assay, quality control and commercial trading of zinc concentrates.
Key topics and technical requirements
- Scope: Applicable to zinc sulfide ores and concentrates containing 10–60% zinc (m/m).
- Principle: Sample dissolution (bromine + nitric acid; HF/H2SO4 for residue), precipitation of Al/Fe/Mn as hydroxides (ammonia, ammonium chloride, ammonium persulfate), masking of copper and separation of lead as sulfate; zinc and cadmium titrated together at pH 5.5–5.7 using EDTA and xylenol orange; cadmium determined separately for correction.
- Reagents & indicators: EDTA standard (0.1 mol/L), bromine, nitric/sulfuric/hydrochloric acids, ammonia, ammonium chloride, ammonium persulfate, hexamethylenetetramine buffer, maskingsolution (ammonium fluoride + sodium thiosulfate), xylenol orange and bromothymol blue.
- Apparatus & sample: Class A volumetric glassware, analytical balance (0.1 mg), hotplate, pH meter. Test portions typically 0.5 g from an air-equilibrated sample (or predried portions per Annex B).
- Quality control: Duplicate determinations under repeatability conditions, reagent blanks, standardization of EDTA against zinc metal under the same operating conditions.
- Interferences & residues: Annex A discusses interfering elements; Annex C covers determination of zinc in acid‑insoluble and hydroxide residues by FAAS; Annex D covers cadmium by AAS.
- Precision & accuracy: Repeatability standard deviation sr = 0.041% and reproducibility sR = 0.12% (percent). Procedures for expression of results and trading‑relevant decision limits are provided.
Practical applications - who uses it
- Analytical laboratories in mining companies and smelters for routine zinc assay of concentrates.
- Quality control and QA teams verifying concentrate composition before shipping or processing.
- Commercial traders and contract negotiators using standardized assay results for trade and settlement of zinc concentrates.
- Accreditation bodies and reference material producers validating trueness using CRMs.
Related standards
Safety note: The standard warns of hazardous materials and operations (bromine, acids, HF); laboratories must follow appropriate health & safety regulations.