Effect of pyrite removal by chromous chloride on organic matter structure in Huadian oil shale

Influence of pyrite removal by chromous chloride (CrCl₂) on structure of organic matter in Huadian oil shale was examined using ultimate analysis, ¹³C NMR, XPS and TG-MS technology. The results show that CrCl₂ treatment leads to 96.19% removal of pyrite from oil shale. The relative contents of aliphatic, aromatic, and carboxyl/carbonyl carbons of organic matter remain about the same level after pyrite removal by CrCl₂, so does the pyrolysis characteristic temperature, indicating the carbon skeleton of organic matter is less affected by CrCl₂. However, the CrCl₂ treatment can break C-O bond in organic matter and reduce content of C-O/C-OH and O=C-O, leading to about 0.98% and 12.54% loss for organic carbon and organic matter, respectively. In addition, carbon content of organic matter significantly increases, hydrogen content slightly increases, and oxygen content is markedly reduced after pyrite removal by CrCl₂, resulting in a slight decrease of H/C but a marked decrease of O/C in organic matter. The mass loss of organic matter treated by CrCl₂ increases during pyrolysis because aliphatic carbon content of unit mass of organic matter increases 5.28%. Besides, the residual chromium oxide may also promote decomposition of organic matter during pyrolysis.