Distribution and mineralogical residence of trace elements in the Israeli carbonate oil shales

Abstract

The abundance and mineralogical residence of 33 elements have been determined in the Israeli carbonate oil shales. The associations of the different elements with the main solid phases were established using a selective sequential extraction and inter-element correlations. The selective sequential extraction procedure was adapted to the carbonate oil shale to distinguish between five fractions: a. soluble and exchangeable elements were extracted by 1M NH4NO3 reagent at pH=7; b. carbonate minerals were extracted by 1M NaAc reagent at pH=4; c. phosphate minerals were extracted by 0.04M NH2OH·HCl+25% HAc reagent; d. the oxidizable material which contained organic matter and sulfides was extracted by 30% H2O2+0.01M HNO3; and e. the insoluble residue which contained mainly aluminosilicates was extracted by sinter with Na2O2. The results indicate that a major part of each element is bound to the main phase structures rather than situated on exchangeable sites or soluble salts and, therefore, is not leachable. The oxidizable materials, which include organic matter and sulfides, contain various trace elements. The elements S and Se were extracted almost completely in this fraction and high percentages of the trace elements As, B, Cd, Ce, Cr, Cu, La, Mo, Ni, Th, U, V and Zn were released. Numerous elements substantially remained in the insoluble residue. The insoluble residue fraction accounted for>85% of the total contents of Al, Si, K, Co, Cs, Rb and Ti, and for tens of percentages of the elements Fe, Mg, B, Ba, Ce, Cr, Cu, La, Li, Mn, Pb, Sb, Th and V. This kind of data is useful for predicting which elements and their quantities may be released into the products and into the surrounding environment as a result of oil shale processing.