# 61.51 Definitions.
Terms used in this subpart are defined in the act, in subpart A of this part, or in this section as follows:
(a) *Mercury* means the element mercury, excluding any associated elements, and includes mercury in particulates, vapors, aerosols, and compounds.
(b) *Mercury ore* means a mineral mined specifically for its mercury content.
(c) *Mercury ore processing facility* means a facility processing mercury ore to obtain mercury.
(d) *Condenser stack gases* mean the gaseous effluent evolved from the stack of processes utilizing heat to extract mercury metal from mercury ore.
(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.
(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.
(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.
(h) *Hydrogen gas stream* means a hydrogen stream formed in the chlor-alkali cell denuder.
(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.
(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.
(k) *Cell room* means a structure(s) housing one or more mercury electrolytic chlor-alkali cells.
(l) *Sludge* means sludge produced by a treatment plant that processes municipal or industrial waste waters.
(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.
[38 FR 8826, Apr. 6, 1973, as amended at 40 FR 48302, Oct. 14, 1975]