Binding of heavy metals by oxidised kerogen in (palaeo)weathered black shales

摘要: Abstract Sub-aerial weathering of black shales drives the gradual leaching sulphur- and organic-bound heavy metal elements, which are usually abundant in these rocks due to depositional conditions. The formation oxygen functional groups kerogen, however, can lead an opposing mechanism - adsorption binding, similar a process common soils. An increase cation exchange capacity (CEC) measured previously using complexes on oxidised under laboratory conditions implies that same phenomenon may occur naturally shale. This idea was tested unique, well-developed -preserved Permian palaeoweathering profile containing two neighbouring but diverse from Devonian/Carboniferous boundary Holy Cross Mountains (Poland). In studied shale beds, formed kerogen partially-weathered zone were found be responsible for significant changes properties hexamminecobalt(III) Cu(II)‑triethylenetetramine cations, probes CEC. Compared pristine part shales, partially weathered depleted total organic carbon (TOC), sulphur, metals, highly enriched Cu, is generally present low levels nascent shales. zone, where TOC content reduced, apparent CEC values surpass CECs predicted contents structures clay minerals, correlate linearly with developed during weathering. carboxyl suggested as being syn- or post-weathering enrichment Cu caused by remobilisation older Cu-sulphide ores area. As opposed natural weathering, aggressive oxidation, e.g. produces high proportion cross-linked do not participate adsorption. artificially samples reached limit corresponding those