Sequential Extraction Procedure for Elemental Speciation in Jordanian Oil Shale Ash

Abstract

This study investigates the mineralogical composition and elemental distribution of oil shale and its ash from Sultani deposits using X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses, respectively. The XRD analysis of the oil shale samples confirmed the presence of calcite and quartz as primary mineral phases. However, XRD analysis of the oil shale ash revealed the presence of gypsum in addition to calcite and quartz, suggesting thermal decomposition and mineral transformation during combustion. The Sequential solvent extraction procedure provides insights into the distribution of heavy metals within Sultani oil shale ash. Specifically, the water-soluble fraction (stage 1) exhibited the presence of readily mobile metals, notably sulfur and silicon. In the exchangeable fraction (stage 2), metals were identified as bound to particle surfaces and acid-soluble salts, with notable concentrations of calcium, iron, and other trace elements observed. Manganese oxide and organically bound metals emerged in the easily reduced fraction (stage 3), while metals associated with oxidizable minerals were predominant in the oxidizable fraction (stage 4). Additionally, the non-mobile fraction (stage 5) entrapped metals within mineral crystal lattices, indicating limited mobility.