Role of Natural Organic Matter as Sorption Suppressant in Soil

摘要

Black carbon (charcoal,char,soot,biochar) in its raw state can be a strong adsorbent of organic compounds.This paper reviews and presents new evidence that during weathering in soil the surface activity of black carbon becomes reduced by deposition of natural organic matter from the surrounding soil matrix on its surfaces.This can rapidly lead to as much as a two order-of-magnitude decline in the distribution coefficient of the contaminant,and a sharp decline in the N2 B.E.T.specific surface area of the black carbon in the mixture.Humic substances suppress sorption by competing for sorption sites and,at cryogenic temperatures,by blocking pore entrances.The competitive effect increases with adsorbate molecular size due to size exclusion (steric) constraints that allow smaller molecules greater access to interior surfaces.It may also increase to the extent adsorbate and humics undergo common interactions with the surface,such as H-bonding.Weathering of black carbon must be taken into accounted in contaminant fate models and in strategies involving the use of black carbon for crop enhancement or soil stabilization.