40 CFR §61.51

1. (a)Mercury means the element mercury, excluding any associated elements, and includes mercury in particulates, vapors, aerosols, and compounds.
2. (b)Mercury ore means a mineral mined specifically for its mercury content.
3. (c)Mercury ore processing facility means a facility processing mercury ore to obtain mercury.
4. (d)Condenser stack gases mean the gaseous effluent evolved from the stack of processes utilizing heat to extract mercury metal from mercury ore.
5. (e)Mercury chlor-alkali cell means a device which is basically composed of an electrolyzer section and a denuder (decomposer) section and utilizes mercury to produce chlorine gas, hydrogen gas, and alkali metal hydroxide.
6. (f)Mercury chlor-alkali electrolyzer means an electrolytic device which is part of a mercury chlor-alkali cell and utilizes a flowing mercury cathode to produce chlorine gas and alkali metal amalgam.
7. (g)Denuder means a horizontal or vertical container which is part of a mercury chlor-alkali cell and in which water and alkali metal amalgam are converted to alkali metal hydroxide, mercury, and hydrogen gas in a short-circuited, electrolytic reaction.
8. (h)Hydrogen gas stream means a hydrogen stream formed in the chlor-alkali cell denuder.
9. (i)End box means a container(s) located on one or both ends of a mercury chlor-alkali electrolyzer which serves as a connection between the electrolyzer and denuder for rich and stripped amalgam.
10. (j)End box ventilation system means a ventilation system which collects mercury emissions from the end-boxes, the mercury pump sumps, and their water collection systems.
11. (k)Cell room means a structure(s) housing one or more mercury electrolytic chlor-alkali cells.
12. (l)Sludge means sludge produced by a treatment plant that processes municipal or industrial waste waters.
13. (m)Sludge dryer means a device used to reduce the moisture content of sludge by heating to temperatures above 65 °C (ca. 150 °F) directly with combustion gases.