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Inco's cyanide removal
<br />technology working well
<br />E.A. Devuyst, G. Robbins, R. Vergunst, B. Tandi and P.F. lamarino
<br />A unique pmcess for removing cya-
<br />nide and base metal complexes from
<br />indusuial waste streams was patented
<br />by Borberly et al. (1984j. The process
<br />uses S0, (liquid or gas, or solutions of
<br />sulfite salts, or from burning elemental
<br />sulfur), plus air that is dispersed in the
<br />effluent using a well agitated vessel. .
<br />Acid produced in the oxidation reac-
<br />tions is neutralized with lime at a con-
<br />trolled pH generally in the range 7 to 10.
<br />The reaction requires the presence of
<br />soluble copper as a catalyst that can be
<br />supplemented by copper sulfate if nec-
<br />essary.
<br />The process can be applied to the
<br />detoxification of gold and silverminirtg
<br />waste streams, such as carbon-in-pulp
<br />(CIP) tailing pulps, barren solution
<br />bleeds, pond waters and hwp leach rinse
<br />solutions and also [o plan ng shops waste
<br />water.
<br />The SOJAir process has substantial
<br />advantages over two of the main alter-
<br />native methods of cyanide destruction,
<br />namely alkaline chlorination and hydro-
<br />gen peroxide.
<br />Alkaline chlorination is highly penal-
<br />ized in terms of reagent consumption.
<br />Chlorine is a strong oxidant reacting
<br />with species other than cyanide present
<br />in the effluent such as thiocyanate and
<br />sulfides. Funhertnore, alkaline chlori-
<br />nation is an incomplete detoxification
<br />process. Iron cyanide is not removed
<br />and the potential for harmful bypro-
<br />ducts species exist. Consequently, final
<br />effluents may be subject [o additional
<br />treatment in order to comply with regu-
<br />latory demands.
<br />Hydrogen peroxide is selective for
<br />cyanide in solutions but is an extremely
<br />expensive rcaeent that, in many cases,
<br />decomposes rapidly in the presence of
<br />solids. This may lead to high reagent
<br />consumption or incomplete cyanide
<br />deswction,
<br />The Inco SOJAir process is selective
<br />for total cyanide detoxification, includ-
<br />ing iron cyanide, which is removed as a
<br />precipitate, using safe.low-cost reagents.
<br />It is, therefore, the most costtffec[ive
<br />process for cyanide deswction today
<br />and is the only reliable process for slurry
<br />treatment. At the end of 1990, there
<br />were 32 licenses for t'te Into SOJAir
<br />cyanide destruction [ecr:nology in North
<br />America.
<br />Plant performance
<br />CIP, ClL or repu7ped railings
<br />The Inco SO,/Air process is suited for
<br />the removal of cyanide from carbon-in-
<br />pulp (CiP), carbon-in-las=h (CIL) or
<br />repulped leach tailings. This is because
<br />rteagen[ consumption is vinuaily unaf-
<br />fected by sulfide and oxide ores.
<br />Operations currently using the Inco
<br />process on tailings arc Lac Minerals'
<br />Colosseum (3 ktld or 3300 stpd),
<br />Canamax's Keva River (400 Ud or 440
<br />sr::,l, Equin Silver (9 kt/d or 9900
<br />stpol, Inco-Golden Knight's Casa Ber-
<br />ardi (1.2 kt/d or 1300 stpd 1, Wes[min's
<br />Premier Gold (2 kVd or 2200 stpd),
<br />Placer-Dome's Kiena (1.3 kUd or 1400
<br />stpd), Homestake-Chevron's Golden
<br />Bear (400 Ud or 440 stpd7, Echo Bay's
<br />Kettle River (2 kt/d or 2200 stpd) and
<br />McCoy-Cove (8 kt/d or 8800 stpd), Lac
<br />Mineral's Bousquet Two (1.5 kUd or
<br />1650 stpd) and the Hope Brook Gold
<br />Mine (3.5 kUd or 3850 stpd). Typical
<br />results are shown in Table 1.
<br />In [hest operations, c} snide deswc-
<br />tion isusually carried out insingle-stage
<br />reactors equipped with suitable agita•
<br />Lion mechanisms and aeration. With a
<br />few exceptions, liquid SO- is used as it is
<br />one of the most economical and avail-
<br />able S0, sources. For maximum process
<br />efficieric}•, the pH is controlled in :m
<br />optimum range that dep_nds on feed
<br />solution chemistry and type of ore n~: -
<br />ent in the feed pulp.
<br />The treatment of pulps befora ..
<br />charge has several advantages over a
<br />facility designed to reduce the cyanide
<br />concenva[ion by natural degradatitm.
<br />Removal of cyanide by natural degrada-
<br />tion requires collection ponds that must
<br />be lined (sometimes double-lined). Or,
<br />they must be large enough to mainutin
<br />acceptable cyanide levels rompatible
<br />with surrounding grn end water. The
<br />cost of liners or dam c, ~nswction is well
<br />documented. In Canada, and cen:tin
<br />areas of the US, where rain and snowfall
<br />arc high. discharge from tailings ponds
<br />is often required.
<br />In a natural degradation system, fur-
<br />ther veatmentwould berequired before
<br />EA. Devuyst is manager of technical Sales,
<br />Q. Robbins, member SME, L5 technical sales
<br />representative, R. Vergunst is process engi-
<br />neer, B. Tandi is process specialist and F'.F.
<br />lamarino is senior technologist with Inco Ex-
<br />pbrafionandTectutiralServices Inc. Devuyst,
<br />Vergunst, Tandi and lamarino are at 2160
<br />Flavelle Blvd., Sheridan Park Research Cen-
<br />ter, Mississauga, Onuno, Canada LSK 7Z9.
<br />Robbins is at 7 t 5 East Braemar Road, Nanh
<br />Vancouver, British Columbia. Canatla V7N
<br />4(i1.
<br />Heap leach solution untler treatment using the Into SO fAir process at Sunshine Mining's Smrw
<br />Caps gold mine in California.
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