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/~ <br />04i 16/92 <br />17:14 $ 17196'23365 <br />A TRF.AT~'1VT <br />agTTLE MT, GOLD {I P. 06 <br />FOR 1VII~~D CYANIDE <br />PRECII"ITATION OF COPPERAND NICKEL CYIA~NIDE~ <br />by <br />.T. J. Byerley, K Eons, G V. Trvng and V. T. Le <br />Aepartmeat of Chemical Engineering <br />University of Waterloo <br />Walerluu, Ottfario <br />Canada N2L 3G1 <br />(519) 885-1211 <br />/"~ <br /> <br /> <br />~sTRacT <br />The precipitation characteristics of copper and nickel <br />cyanides fiam solutions continuing capper anc and nickel <br />ryaao complexes arc ~-•*+»*+ed. Equilibrium pretdpitatioa <br />calculations are presented as well as comparative <br />experimental data. The practical significance of the <br />precipitation data is discussed is the context of an initial step <br />in an overall treatment strategy for mixed cyanide effiueats. <br />1NT1tOA1,]CTIQN <br />The environmental hazards and treatment problems <br />associated with cyanide effluents are well known. Many <br />industries such as metal recovery (primary and secondary) <br />metal finishing (plating and heat treating) electronic <br />component manufacturing and photographic bleaching <br />processesgenerstenqueous waste containing a broadrange of <br />inorganic compounds, principally heavy metals, cyanide, <br />thioryaaate and thiosalts- Gold or silver recovery operations <br />have long been identified as a major but not CxGusive source <br />of this type of effluent. These liquors usually fall into two <br />categories, those where the cyanide moiety is essentially in the <br />free state and thoscwhcre alargeportion ofthe ryatvde occurs <br />is the form of rather stable metal cyano complexes. This latter <br />class is often the result of cyaaidation being applied to ores, <br />wncen[rates and tailings of the sulfidic type which coo[aia <br />high levels of copper, nickel, iron, etc. 'I-hese metal sulfides <br />aze co-leached to varying de ces to form a series of anionic <br />complexes such as GU(CN)3~ Ni(CN)gz-and Fe(CN)6 ". In <br />addition, the sulfide sulfur~S~ is oxidized to various oxysulfur <br />compounds such as SaD3 -, SnD6~ and St74z- and in some <br />cases as much as 50% of [he CN' in the leaching circuit is lost <br />by conversion to SCN' through reaction with <br />R~-~~ t ~w ~.+~ <br />C~nt~~~ ~. ~ Rz~ ~o I <br />Table 1 shows a range of compo~[ion observed for barren <br />(each liquor produced under these conditions. <br />TARE F N <br />EFFLUENT COMPOSITION RANGE <br />Coacentratlon Range <br />Component mgll <br />CN- (total) 360-1200 <br />Ci~T (free) 200-700 <br />SCN' 50-1400 <br />52D3Z variable <br />SnO~ - variable <br />SOa up to 250 <br />Gu 25-700 <br />Fe OS-1S <br />Zn 2.60 <br />Co + Ni 0.160 <br />Ca 6-800 <br />pH 10.4-ll.ti <br />The effects of the contaminants and their build up in the <br />cyanidatioa circuit to levels describdd in Table 1 are two fold. <br />FusUy, as the leach liquor becomes increasingly fouled, the <br />kinetic of the leaching process itself is significantly decreased <br />which eventually leads to increased ryanide consumption if <br />satisfactoryleachiagtates arc to be ntainta'med. The efficiency <br />of precious metal precipitation from the pregnant but fouled <br />solution is also observed to be adveYSely affected. Secondly, <br />the effluent treatment rcquucments for any barren leach <br />liquor of this type which may be di9charged from IhC circuit, <br />wnstitute a major problem. <br />RANDOL GOLD FORUM 88 <br />thronate spedes. <br />~.~ ~ <br />r ~• -331 <br />