It sounds as if this refers to the carbon that has been used in treatment plants and so contains other dangerous substances too. Example: The mercury laden activated carbon presents a disposal dilemma.[citation needed] If the activated carbon contains less than 260 ppm mercury, Federal regulations allow it to be stabilized (for example, trapped in concrete) for landfilling.[citation needed] However, waste containing greater than 260 ppm is considered to be in the high mercury subcategory and is banned from landfilling (Land-Ban Rule).[citation needed] It is this material which is now accumulating in warehouses and in deep abandoned mines at an estimated rate of 1000 tons per year.[citation needed]
The problem of disposal of mercury laden activated carbon is not unique to the U.S. In the Netherlands this mercury is largely recovered[16] and the activated carbon is disposed by complete burning.
http://en.wikipedia.org/wiki/Activated_carbon#Environmental_...

--------------------------------------------------
Note added at 43 mins (2010-11-20 22:06:35 GMT)
--------------------------------------------------

También hay carbón compactado que se usa para distintos fines, hasta briquetas para asado/barbacoa, pero es evidente que aquí no se trata de eso.