Determination of major and minor ash-forming elements in solid biofuels

The development of reliable and appropriate methods for the accurate determination of major (Al, Ca, Fe, K, Mg, Na, P, Si, Ti) and minor (As, Ba, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Tl, V, Zn) ash-forming elements in solid biofuels was the major goal of Task III.2 of the EU project BioNorm. For this purpose, wood+bark, straw and olive residues were analysed using several digestion and determination methods. The digestion methods included wet decomposition in closed vessels with different acid mixtures as well as dry-ashing techniques. The determination systems included FAAS, GFAAS, CVAAS, ICP-OES, ICP-MS, XRF as well as direct Hg-determination. Tests were carried out to optimise the methods applied. To summarise the outcomes of these tests, different digestion procedures were developed for major and minor elements. Digestion with H2O2/HNO3/HF followed by neutralisation with H3BO3 was validated for major element analyses, while digestion with H2O2/HNO3/HF was validated for minor element analyses. The validation results show that the applied digestion methods can be recommended for solid biofuel analyses. For the determination of the elements investigated in solid biofuels, the following detection systems can be recommended: FAAS for Ca, Fe, K, Mg, Na, Si, Mn, Zn; ICP-OES for Al, Ca, Fe, K, Mg, Na, P, Si, Ti, Mn, Zn, Ba, Cr, Cu, Mn, Ni, V, Zn; GFAAS for Cd, Cr, Cu, Ni, Pb; ICP-MS: P, Ti, As, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sb, V, Zn and direct determination as well as CVAAS for Hg.