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===Mercury scrubbing===
Activated carbon, often infused with sulfur<ref>{{cite web | url = http://www.tigg.com/mercury-removal.html | title = Activated Carbon for Mercury Removal | accessdate = 2013-08-27 | last = Bourke | first = Marta | year = 1989 | deadurl = yes | archiveurl = https://web.archive.org/web/20130803024134/http://www.tigg.com/mercury-removal.html | archivedate = 2013-08-03 | df = }}</ref> or iodine, is widely used to trap mercury emissions from [[coal-fired power station]]s, medical [[Incineration|incinerators]], and from [[natural gas]] at the wellhead. This carbon is a special product costing more than US$4.00 per kg.{{citation needed|date=July 2017}}
Since it is often not recycled, the mercury-laden activated carbon presents a disposal dilemma.<ref>Tim Flannery, ''Here On Earth: A New Beginning'', Allen Lane (2011), p. 186.</ref> If the activated carbon contains less than 260 ppm mercury, United States federal regulations allow it to be stabilized (for example, trapped in concrete) for landfilling.{{Citation needed|date=May 2009}} 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|date=May 2009}} This material is now accumulating in warehouses and in deep abandoned mines at an estimated rate of 1000 tons per year.{{Citation needed|date=May 2009}}
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===Apparent density===
The solid or skeletal density of activated carbons will typically range between 2000 and 2100 kg/m<sup>3</sup> (125–130 lbs./cubic foot). However, a large part of an activated carbon sample will consist of air space between particles, and the actual or apparent density will therefore be lower, typically 400 to 500 kg/m<sup>3</sup> (25–31 lbs./cubic foot).<ref>TIGG Corporation. [http://www.tigg.com/granular-activated-carbon.html#Anchor-Apparen-32986 Granular activated carbon selection] {{webarchive|url=https://web.archive.org/web/20120912090347/http://www.tigg.com/granular-activated-carbon.html |date=2012-09-12 }}. Published 2012-05-8, retrieved 2012-09-21.</ref>
Higher density provides greater volume activity and normally indicates better-quality activated carbon.
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