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~, <br />i , <br />1 <br />,i <br />i <br />~1 <br />L <br />1 <br />i <br />1 <br />1 <br />HEAP LEACH PADS <br />Th_e detoxifying of heaps, at the end of campaigns,is more complicated than simple <br />CN reduction in ponds because of the laws governing ground-water standards. <br />Levels of CN' below 0.2 ppm are mandated. In addition, the levels of all heavy <br />metals are equally mandated. Although the chemical processes described above for <br />ponds would no doubt work in heaps there are numerous problems,such as: <br />1. Water Flushing - Availability of water <br />(Dilution) Length of time needed <br />2. Hypochlorite and - Generally discouraged by the State <br />peroxide Expensive <br />3. <br />4 <br />SG, <br />Ferrous Sulphate - <br />In a number of sites heavy metal content is <br />increased due to oxidation of the help <br />- Expensive <br />Increase heavy metal content of water through <br />oxidation <br />Increases Fe level beyond standards <br />May reduce pH below 6 <br />Although cheap they take a long time to reduce CN <br />and cannot be guaranteed to succeed <br />5. Bacteria - <br />