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~^ ~ .. <br />THE RECOVERY OF CYANIDE FROM SLURRIES _ <br />r. .. , <br />'~ ~ by <br />T.I. Madder •nd A.J. Goldstone ' <br />INTRODUCTION . <br />The use of cyanide for extraction of precious metals has been practiced for nearly a century, since k was <br />first employed In New Zealand In 1898. Cyanldatlon Is an efFlclent process capable of extracting minute <br />amounts of gdd from complex chemical and mineral matrices. In theory, a sdution of 100 mg/I of free <br />cyanide can provide the maximum rate and extern of gdd dfssdution. in practice, concentrations of 200- <br />800 mg/I of total cyanide are open required for gdd and silver recovery. <br />The metal extraction process may Invdve ekher vat or heap leach, with recovery being accomplished <br />through zinc preclpkatbn or activated carbon adsorptbn. The milling, extraction, arxi recovery processes <br />produce waste streams Induding barren sdutlons, tailings slurries, and excess decant water. Oualkatively, <br />the chemistry of these waste streams are similar containing a variety of constkuents Incltding cyanide <br />complexes, metals, and In-organics (I.e. ammonia, thlocyanate, cyanate, sulfate, and nitrates). Ouantkatively, <br />the waste streams vary substantially exhlbking concentrations ranging over several orders of magnitude. <br />A summary of the chemical composition of various barren sdutions and slurries are present.;d In Table 1. <br />TABLE t <br />CHEMICAL COMPOSITION OF BARREN SOLUTIONS AND TAILINGS SLURRIES <br />~--, <br />~. <br /> <br />Paramete~'t <br />Arsenic <br />Cadmium <br />Chromium <br />Copper <br />Iron <br />Lead <br />Manganese <br />Mercury <br />Nickel <br />_ Selenium _ _ <br />.. S1ver ._. .. <br />Zinc -- c <br />_ Total Cyankie . _ <br />WAD Cyanide <br />Free Cyanide <br />Ammonia-N <br />Thlocyanate <br />Hardness (as CaCO~ <br />Sulfate <br />Temperature (ln °C) <br />Flow (In gpm) <br />Rance of Concentrations <br /><0.02 - 10.0 <br /><0.005 - 0.10 <br /><0.02 • 0.10 <br />0.10 •400.0 <br />0.50 -40.0 <br /><0.01 • 0.10 <br />0.10 - 20.0 <br /><0.0001 - 0.05 <br />0.02 - 10.0 <br />. <0.02 - 6:0 . <br />_. <0.005-2.0 <br />0.05 - 100.0 <br />_ 0.50 - 1000.0 <br />0.50 -650.0 <br /><0.01 • 200.0 <br /><0.10 - 50.0 <br />< 1.0 - 2000.0 <br />200 - 1500 <br />5 - 10000 <br />0 • 35 <br />1 •6000 <br /> <br />t'~ All values fn mgJt, unless otherwise stated. <br />