As used in this subpart, all terms not defined herein shall have the meaning given them in the Act and in subpart A of this part.

(a) Primary zinc smelter means any installation engaged in the production, or any intermediate process in the production, of zinc or zinc oxide from zinc sulfide ore concentrates through the use of pyrometallurgical techniques.

(b) Roaster means any facility in which a zinc sulfide ore concentrate charge is heated in the presence of air to eliminate a significant portion (more than 10 percent) of the sulfur contained in the charge.

(c) Sintering machine means any furnace in which calcines are heated in the presence of air to agglomerate the calcines into a hard porous mass called sinter.

(d) Sulfuric acid plant means any facility producing sulfuric acid by the contact process.