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,~ <br />VISTA 'N' CHEMICALS <br />BEI after extensive study has decided to market chemicals for use as both CN - <br />kill agents in tailings ponds and as detoxification agents for leach-heaps. <br />' In this way BEI hopes to increase their involvement in the industry and assist <br />in lowering operation costs. <br />The chemicals, known as Vista 'N', closely resemble ferrous sulphate but contain <br />' a controlled amount of zinc to help in the formation of stable, insoluble end- <br />products of CN reaction. <br />' These solid solution chemicals are tailored to the site requirements and the <br />particular operation. For example, in a tailings pond we suggest the use of low- <br />zinc Vista. The shorter the pond-recycle time, the lower the zinc content that <br />' is suggested. In leach-pad detox we suggest high zinc which reacts more slowly <br />but forms insoluble Zn/Fe(CN) compounds that are stable across a wide range of <br />pH while contributing neither Fe nor Zn to the ground water. <br />' USE IN TAILINGS PONDS <br />The use of a high (Vista 11) and low (Vista 6) level zinc compound will be <br />' discussed to illustrate their differences. The "standard" used to compare Vista <br />'N' effectiveness is ferrous sulphate (FeSDy7H~0). <br />As with ferrous sulphate, Vista complexes CN and removes it from the pond by <br />producing an insoluble compound. Most other processes rely upon oxidizing CN , <br />but the associated costs are high and quite often the problems they produce are <br />severe. <br />' Ferrous sulphate has been found to be satisfactory as a CN -kill agent in ponds <br />not only because it can produce very low CN levels (10-20 ppm in practice) but <br />' also because it acts rapidly and does not produce other problems when the pond <br />water is recycled. <br />' Vista performs equally well, but does so at lower cost and can leave a lot less <br />Fe in solution than does ferrous sulphate. <br />To illustrate the effectiveness of Vista compounds, tables 1 and to are <br />presented, A deliberately high loading_ of NaCN was added to deionized water to <br />produce a concentration of 206 ppm CN To this solution were added ferrous <br />sulphate, Vista 6 and Vista 11 compounds in the amounts of 2 lbs per ton of ore <br />equivalent. Figure 1 shows that Vista 6 and ferrous sulphate are nearly <br />equivalent in their ability to kill CN whereas Vista 11, although effective, is <br />not quite as good. Figure to shows Fe in solution and clearly V11 is far <br />superior to the other two compounds. <br />Tests were also run in a gold producers laboratory using true tailings slurry. <br />They were run at separate times on different slurries and hence the difference <br />in starting CN levels. <br />Figure 2 shows the effectiveness of V6 compared to ferrous sulphate in a slurry <br />' containing 130 ppm CN-. After six hours the results are close enough to be <br />considered the same for CN kill (92% vs 94%) and at 20 hours the kill for V6 and <br /> <br />