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

Abstract

Citation style: Derkowski Arkadiusz, Marynowski Leszek. (2018). Binding of heavy metals by oxidised kerogen in (palaeo)weathered black shales. A B S T R A C TSub-aerial weathering of black shales drives the gradual leaching of sulphur-and organic-bound heavy metal elements, which are usually abundant in these rocks due to depositional conditions. The formation of oxygen functional groups in kerogen, however, can lead to an opposing mechanism -metal adsorption and binding, similar to a process common in soils. An increase in cation exchange capacity (CEC) measured previously using metal complexes on black shales oxidised under laboratory conditions implies that the same phenomenon may occur in a naturally oxidised black shale. This idea was tested on a unique, well-developed and -preserved Permian palaeoweathering profile containing two neighbouring but diverse black shales from the Devonian/ Carboniferous boundary in the Holy Cross Mountains (Poland).In the studied black shale beds, the oxygen groups formed in kerogen in the partially-weathered zone were found to be responsible for significant changes in adsorption properties measured using hexamminecobalt(III) and Cu(II)-triethylenetetramine cations, which are common probes for CEC. Compared to a pristine part of black shales, the partially weathered zone was depleted of total organic carbon (TOC), sulphur, and sulphur-and organic-bound metals, and highly enriched in Cu, which is generally present in low levels in the nascent shales.In the partially weathered zone, where TOC content is reduced, apparent CEC values surpass the CECs predicted from the contents and structures of clay minerals, and correlate linearly with the content of oxygen groups developed during weathering. The adsorption properties of carboxyl groups in the oxidised kerogen are suggested as being responsible for the syn-or post-weathering enrichment in Cu caused by the remobilisation of older Cu-sulphide ores present in the area. As opposed to natural weathering, aggressive oxidation, e.g. under laboratory conditions produces a high proportion of cross-linked oxygen groups that do not participate in metal cation adsorption. The CEC values of artificially oxidised samples reached a limit corresponding to those of naturally oxidised shales.Editor: Michael E. Böttcher exchange capacity (CEC) of soils (Parfitt et al., 1995;Kaiser et al., 2008;Rengasamy and Churchman, 1999) and oxidised low-rank coals (Skodras et al., 2014). In extreme cases, it is the oxidised black carbon formed via incomplete combustion of vegetation or fossil fuels that is responsible for high CEC levels in soils (Liang et al., 2006;Cheng et al., https://doi.

Phosphorus-cycle disturbances during the Late Devonian anoxic events

“…Photic-zone euxinia was probably prevalent throughout the early and later parts of the Annulata Event, but with a re-oxygenation event taking place mid-event; however, bottom-water conditions were probably more variably oxic-dysoxic during the early stages of the Annulata crisis, before becoming persistently deoxygenated during the later stages (Racka et al, 2010). Photic-zone euxinia appears to have also prevailed in the Chęciny-Zbrza Basin throughout the Hangenberg Event (Marynowski et al, 2012), but it is less clear how bottom-water conditions developed during this crisis (Marynowski et al, 2012(Marynowski et al, , 2017Derkowski and Marynowski, 2018). (France,43° 27' 40.7" N,3° 2' 25.1" E) The Global Boundary Stratotype Section and Point (GSSP) for the base of the Famennian at Coumiac documents a well-oxygenated pelagic setting on the southern margin of the Rheic Ocean (Klapper et al, 1993).…”

Bioaccumulation and Health Risk Assessment of Heavy Metals in the Soil–Rice System in a Typical Seleniferous Area in Central China

“…This is of great concern because heavy metals cause adverse effects on human health and ecosystems (Fraga 2005;Zhuang et al 2009;Fang et al 2010;Gall et al 2015;Toth et al 2016;Liu et al 2017). Heavy metals are often enriched in sulfide minerals and shales (Coveney and Glascock 1989;Derkowski and Marynowski 2018;Pearce et al 2018). Mining and weathering of these source materials result in the release of heavy metals into the environment (Yu et al 2011;Anjum et al 2012), which is called multiple heavy metal pollution.…”

Bioavailability and Risk Variations of Heavy Metal(loid)s in Paddy Soils Developed from Eluvial and Alluvial Parent Materials in the Xitiaoxi Catchment, China

“…The enrichment degree and ecological risk of Cd were the most significant in the agricultural system of the studied watershed, which was attributed to the facile accumulation of Cd during black shale weathering and intense human activities in the Yangtze River Delta . Black shale is abundant in sulfide minerals; Cd, being a sulfophilic element, exhibits a high propensity for accumulation within black shale, and the adsorption of weathered kerogen induces secondary enrichment of Cd during black shale weathering. , Cd has been a prominent environmental problem in the soils of the Yangtze River Delta . Besides, Cd had a high biotoxicity coefficient, and it was easily activated in acidic soils .…”

“…14 Black shale is abundant in sulfide minerals; Cd, being a sulfophilic element, exhibits a high propensity for accumulation within black shale, and the adsorption of weathered kerogen induces secondary enrichment of Cd during black shale weathering. 68,69 Cd has been a prominent environmental problem in the soils of the Yangtze River Delta. 70 Besides, Cd had a high biotoxicity coefficient, and it was easily activated in acidic soils.…”