Chemical and mineral composition of bottom ash from agri-food biomass produced under low combustion conditions

Abstract

The study aimed at conducting a detailed analysis of apple pomace (AP), walnut shells (WS), and sunflower husks (SH) ashes as potential raw materials for combustion at a temperature of 400 ± 15 °C (individual home furnace). Research methods such as ICP-OES/MS (atomic emission spectrometry with excitation in induced plasma and mass spectrometry), XRD (X-ray diffraction), and SEM–EDS (scanning electron microscopy with quantitative X-ray microanalysis) were utilized. Elemental CHNSO FlashSmart series analyser (Thermo Scientific) was employed for the analysis of oxygen (O). An automatic IR analyser was used to determine the carbon (C), total sulphur (S), and hydrogen (H) content. Total sulphur (S) and chlorine (Cl) were measured by the PN-EN ISO 16994:2016 standard. The nitrogen (N) content was determined by the catharometric method of chlorine by ion chromatography (IC). Higher concentrations of potentially toxic elements (PTE) such as As, Cr, Zn, Cd, Cu, Ni, Pb, Tl, U, and Th were detected in apple pomace ashes. The mineral composition of biomass ashes was found to be highly diverse, with sunflower husk ashes containing the highest amount of minerals, including quartz, dolomite, calcite, magnesite, sylvite, arcanite, fairchildite, and archerite. Quartz was identified in apple pomace ash, while in sunflower husk ash, it was determined to be present only as an amorphous substance. The estimated total dust emission to the atmosphere from biomass combustion was found to be at a similar value (1.23 to 1.35 kg/Mg).