Overview
ISO 7834:1987 specifies a molybdenum blue spectrophotometric method for the determination of arsenic in iron ores, iron ore concentrates and agglomerates (including sinter). The method covers sample preparation, reagents, apparatus, procedure (sintering, digestion, distillation of arsenic trichloride, colour development), calibration and result expression. It applies to arsenic concentrations from 0.0001 to 0.1 % (m/m) (1 to 1 000 µg/g).
Key points
- Analytical range: 1–1 000 µg As/kg (µg/g).
- Colourimetric measurement at about 840 nm (molybdenum blue complex).
- Toxicity warning: arsenic and many reagents used are hazardous - strict handling and disposal required.
Key topics and requirements
- Sample preparation and sampling: Laboratory sample of −100 µm (or −160 µm for ores with combined water/oxidizable compounds) prepared per ISO 3081/3082/3083 and ISO 7764 guidance for predried samples.
- Decomposition / digestion: Sintering with sodium peroxide followed by hydrochloric acid leach to convert arsenic to an analyzable form.
- Distillation: Conversion to arsenic trichloride and distillation into nitric acid receiver using a 250 ml distillation flask assembly (figure provided in standard).
- Colour development: Treatment of evaporated residue with ammonium molybdate–hydrazine reagent to form an arseno‑molybdenum blue complex.
- Spectrophotometry: Measure absorbance at ~840 nm against reagent blank; use 10 mm or 20 mm cells depending on sensitivity. Blank absorbance limits are specified (blank in 20 mm cell ≤ 0.025 ≈ 1 µg As).
- Calibration and calculation: Prepare calibration series from standard arsenic solutions; compute arsenic content using absorbance, slope factor and dilution/aliquot factors. Typical slope factor guidance (approx. 76 for a 10 mm cell) included.
- Quality control and precision: Run blank test(s) and certified reference materials in each batch; repeatability and between‑laboratory precision are given by regression equations and acceptance criteria.
Applications and who uses it
ISO 7834 is used by:
- Mining laboratory and metallurgical QC/assay labs for arsenic certification in iron ores and concentrates
- Environmental/industrial labs monitoring feedstock impurities that affect smelting, sintering and product quality
- Regulatory and inspection bodies requiring standardized arsenic measurement for product compliance
- Laboratories validating instrumentation and procedures for low‑level arsenic analysis in bulk minerals
Practical benefits include a standardized workflow for reproducible arsenic determinations, provision of calibration and precision checks, and explicit safety and cleaning procedures to minimise contamination and blank noise.
Related standards
Referenced standards include:
Keywords: ISO 7834, arsenic determination, molybdenum blue spectrophotometric method, iron ores, arsenic content, distillation, spectrophotometer, sampling, laboratory QC.