Overview
ISO 4349:2024 - Solid recovered fuels - Determination of the recycling index for co-processing defines a standardized method to quantify the share of material recovery when solid recovered fuels (SRFs) are co-processed (e.g., in a cement kiln). The standard introduces the recycling index (R‑index): the mass fraction (in percent of dry matter) of SRF that can be considered recycled on a material level. The R‑index is calculated from the ash content and the ash composition of SRF.
Key technical topics and requirements
- Scope and definitions
- R‑index = share of SRF considered recycled (mass % of dry matter).
- Co‑processing = simultaneous energy and material recovery (typical example: cement clinker production).
- Sampling and sample preparation
- Sampling per ISO 21645; preparation per ISO 21646; final test fraction ≤ 1.0 mm and dried.
- Hard inert impurities are sorted and documented.
- Ash determination
- Ash content determined per ISO 21656:2021 (method B, ash at 815 °C on dry basis).
- If ash yields are low, procedures are given to increase ash mass (repeat ashing or larger inert bowls).
- Elemental analysis methods
- Method A: wet digestion (HCl, HNO3, HF) with microwave assistance; analysis by ICP‑MS or ICP‑OES (≈200 mg ash required).
- Method B: fused‑bead preparation with lithium metaborate, dissolution and ICP‑OES (≈100 mg ash required).
- Method C: pellet preparation with binder and XRF analysis (≈4.5–10 g ash required depending on pellet size).
- Alternative methods allowed if performance comparable.
- Calculation
- Element concentrations are converted to element oxides using conversion factors (e.g., Al → Al2O3, Ca → CaO, Si → SiO2, etc.).
- The R‑index calculation uses ash content and oxide composition to determine the material recovery share.
- Quality and reporting
- Specifies reagents, apparatus (muffle furnace, ICP, XRF), performance characteristics and required information for the test report.
Practical applications
- Quantifying how much SRF contributes to material recycling when co‑processed in cement kilns or other industrial processes.
- Supporting circular economy reporting, sustainability metrics, and substitution calculations for mineral raw materials and fossil fuels.
- Providing a reproducible laboratory method for compliance, environmental reporting, and procurement specifications for SRF suppliers and cement manufacturers.
Who should use ISO 4349:2024
- Cement and clinker manufacturers assessing SRF co‑processing.
- SRF producers and waste management companies demonstrating recycling performance.
- Accredited testing laboratories performing ash and elemental analyses.
- Regulators and sustainability auditors evaluating material recovery claims.
Related standards