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POLYCHLORINATED BIPHENYLS <br />• Polychlorinated biphenyls or PCBs are in use in <br />mill. Inventory, use, control, and disposal of <br />under the auspices of the PCB management <br />reference in Appendix C. <br />SODIUM CYANIDE (NaCN) <br />electrical equipment at the <br />PCBs are strictly managed <br />plan, which is included for <br />In the event of a spill, sodium cyanide (NaCN) should be isolated from water <br />and acid. Water reacts with NaCN to slowly release cyanide gas (HC:N) and <br />acid reacts with it to quickly release HCN. <br />To lessen the impact of NaCN when it is spilled into water, caustic and <br />hypochlorite can be added to convert cyanide to less toxic cyanate, but care <br />must be taken not to overdose. <br />NaCN arrives by truck in 200 pound drums and is stored in one of two 8 foot <br />by 8 foot by 20 foot cargo containers located south of the mill building and <br />west of the warehouse (Figure 21. The capacity of these cargo containers is <br />approximately 340 drums or 68,000 pounds. Sodium cyanide (solid) and <br />sodium hydroxide (liquid) are mixed in a five to ten percent solution and used <br />in the grinding and flotation phases of the milling process. The solution is <br />• mixed, stored, and circulated from a 4,700 gallon tank. The tank is fully <br />contained in a walled enclosure designed to hold 110% of tank volume. The <br />containment is equipped with a pump that returns any spillage back to the <br />tank. Henderson plans to install an additional 12,000 gallon storage tank in <br />the summer of 1999 for the storage of cyanide solutions. Plans are fix this <br />new tank to be constructed of dual walled steel, complete with an electrically <br />operated leak detection system. <br />SODIUM CARBONATE (SODA ASH) <br />Sodium carbonate (aka soda ash) is used as a water modifier to raise the pH <br />in the flotation circuit in the milling operation. Granular soda ash is stored in <br />a large orange guppy tank (110 ton capacity) located adjacent to and north <br />of the Mill building. The portable soda ash guppy tank rests on a large;, flat <br />asphalt paved area. Spillage from the tank would fall out on the asphalt, <br />where it could easily be scooped up with a shovel for re-use. Soda ash is a <br />valuable acid neutralizer and can also be used in acid spill clean-up work. <br />• <br />Page 9 <br />