Distribution analysis and speciation of arsenic and selenium in soils containing framboidal pyrite

Soils and rocks containing framboidal pyrite are prone to be oxidized and cause problems of the elution of sulfuric acid, heavy metals, and semimetals even when their contents are small because of a large specific surface area. Therefore, obtaining the knowledge regarding the speciation of heavy and semimetals in soils and rocks containing framboidal pyrite is very important. In this study, regarding framboidal pyritecontaining soils that release arsenic and selenium, we performed: (1) the analyses of elemental distribution via laser ablation-inductively coupled plasma mass spectrometry and microregion X-ray fluorescence spectrometry and (2) the analyses of the morphology of arsenic and selenium (bulk and local regions) via As and Se-K-edge X-ray absorption near edge structure. Results indicated that pyrite was involved in the immobilization of both arsenic and selenium in soils containing framboidal pyrite, but it is highly possible that the distribution of arsenic and selenium in the soil was different. Arsenic was fixed as FeAsS on the surface of framboidal pyrite. Selenium existed as Se(0) and Se(IV) inside the framboidal pyrite, i.e., on the surface of pyrite microcrystals constituting the framboidal pyrite.