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AUG- 9-95 WED 16:C5 CROWN TECHNOLOGY FAX N0, 3179159096 P 05 <br /> When feeding dry ferrous sulfate, various types of dry feeders can be used. Vibrating, <br /> belt or screw conveyor type feeders are satisfactory. The storage bin should be equipped <br /> with a vibrator to provide free flowing material. Feeder discharge can be fed directly Into <br /> the tailings pump sump box. <br /> Alternatively, ferrous sulfate can be made up as a solution (10-20% F9SO47H20) and <br /> fed via a metering pump to the addition point. A circulating loop system with drop off lines <br /> and timer operated solenoid valves or flowmeters can also be used. (See attached flow <br /> sheets.) <br /> One western state gold mine successfully uses ferrous sulfate to complex cyanide <br /> In a tailings stream and maintains cyanide concentrations in the pond at levels which are <br /> not toxic to birds. Untreated tailings slurry contains about 450 ppm free cyanide and sodium <br /> cyanide, the pond Is maintained at levels of between 8 and 15 ppm sodluM cyanide. Addl- <br /> tion rates of 2.2 lbs, of ferrous sulfate heptahydrate are used to complex 0.88 lb& of sodium <br /> cyanide. This equates to 1 part iron complexing 2.0 parts sodium cyanide compared to <br /> a stoichiometric 5.3 parts sodium cyanide. The ferrous sulfate is also complexing other <br /> metal cyanides. The pH of the tailings slurry at this plant Is about 10 and is not adjusted <br /> during treatment. Ferrous sulfate replaced the more expensive hydrogen peroxide for <br /> cyanide treatment at this facility. <br /> Cost comparisons for the treatment of cyanide using peroxide and ferrous sulfate were <br /> as follows. <br /> Ch� Consumption Price Cost <br /> lbs/ton S/Ib y'— <br /> Hydrogen Peroxide $/ton <br /> 2.5 0.70 1.75 <br /> Ferrous Sulfate 2.2 0.10 0.22 <br /> Cost Savings 1.53 <br /> Total cost savings amounted to 2 million dollars per year. <br /> Ferrous sulfate can also be used to complex cyanide in heap leach dumps which are <br /> to be abandoned or removed for placement in another location. Ferrous sulfate solution <br /> can be applied by using the existing heap leach sprinkling system. Dosage rates should <br /> first be determined by laboratory column testing. The ferrocyanide complex is stable even <br /> under acidic conditions that are created by the decomposition of sulfide that may be pre- <br /> sent in the ore. <br /> -� 3 -- <br />