Overview
ISO 12782-2:2012 - Soil quality: Parameters for geochemical modelling of leaching and speciation - Part 2 specifies a laboratory method for determining reactive crystalline iron oxides and hydroxides in soils and other materials (including waste) by dithionite extraction. The extracted “reactive” iron content is an operational parameter intended as input for geochemical modelling, supporting predictions of leaching, speciation, mobility and bioavailability of trace constituents in environmental risk assessments.
Key topics and technical requirements
- Scope and purpose
- Quantifies crystalline Fe(III) oxide/hydroxide phases using a dithionite-based extraction; results represent reactive crystalline iron for geochemical models.
- Principle
- Reduction of Fe(III) to soluble Fe(II) and complexation by reagents; crystalline iron is derived from the total dithionite-extractable iron minus amorphous iron (ascorbate extraction, ISO 12782-1).
- Sample preparation
- Guidance on laboratory sample size, particle size reduction and determination of water content (referencing ISO 11464 and ISO 11465).
- Apparatus and conditions
- Use of clean centrifuge tubes, centrifuge (preferably ~3 000 g), and a water-bath rotary shaker adjustable up to 60 °C (see Annex A for centrifugation conditions).
- Procedure
- Preparation of extraction solution, controlled extraction, analytical determination of Fe in extracts, calculation and expression of results.
- Quality and reporting
- Requirements for calculation, expression of results and the content of the test report to ensure data suitable for modelling input.
- Normative references
Applications
- Provides an input parameter for geochemical speciation and leaching models, improving extrapolation from laboratory leaching tests to field scenarios.
- Used in environmental risk assessment of contaminated soils, remediation projects, and characterization of materials such as:
- soils and amended soils
- municipal incinerator bottom ash, steel slag, bauxite residues
- recycled construction materials and various wastes
- Helps estimate adsorptive reactive surfaces (crystalline iron (hydr)oxides) that control trace metal binding, mobility and bioavailability.
Who should use this standard
- Environmental and geochemical laboratories
- Soil scientists, geochemists and environmental consultants
- Waste characterization specialists and remediation contractors
- Regulators and risk assessors requiring standardized geochemical input parameters
Related standards
- ISO 12782-1 (ascorbate extraction - amorphous Fe)
- ISO 12782-3 (ammonium oxalate/oxalic acid - Al oxides)
- ISO 12782 parts 4–5 (humic substances)
- Referenced sampling and laboratory standards listed in ISO 12782-2 for harmonized practice.
Keywords: ISO 12782-2:2012, soil quality, dithionite extraction, crystalline iron oxides, reactive iron, geochemical modelling, leaching, speciation, environmental risk assessment.
Open preview (PDF)Soil quality — Parameters for geochemical modelling of leaching and speciation of constituents in soils and materials — Part 2: Extraction of crystalline iron oxides and hydroxides with dithionite