This Technical Specification specifies three methods of digestion for solid recovered fuels:
a) microwave assisted digestion with hydrofluoric, nitric and hydrochloric acid mixture;
b) hot water bath digestion of with hydrofluoric, nitric and hydrochloric acid mixture, after ashing of the SRFs sample;
c) oven digestion with nitric, perchloric and hydrofluoric acid mixture.
Instrumental determination of Si, Al, K, Na, Ca, Mg, Fe, P, and Ti is performed by Inductively Coupled Plasma Spectrometry with optical detection or other suitable spectroscopic techniques such as Flame Atomic Spectroscopy.
The effectiveness of the digestion can be verified by qualitative X-ray fluorescence (XRF) analysis on the remaining residue. If necessary an alternative digestion method (among those proposed) shall be used.
XRF can be used for the analysis of Si, Al, K, Na, Ca, Mg, Fe, P, Ti, after ashing (550 °C) of the sample: other elements can be analysed by XRF providing that the concentration levels are above the instrumental detection limits of the XRF instrumentation and after proper preliminary testing.
Method a) is recommended for general use, but the amount of the test portion can be very low in case of high concentration of organic matter. Method b) is recommended for SRFs with high organic matter concentration that can be difficult to digest with the other methods.
Method c) is recommended for SRFs samples for which the other methods leave a significant insoluble residue.
All the listed methods are suitable for the determination of Si, provided that closed containers are used for sample dissolution. XRF is highly recommended for Si, P and Ti analysis.