20 Ambient Temperature Oxidation Technologies for Treatment of Cyanide Rajat S. Ghosh, Thomas L. Theis, John R. Smith, and George M. Wong-Chong CONTENTS 20.1 Alkaline Chlorination Technologies 394 20.1.1 Process Description and Implementation 394 20.1.2 Achievable Treatment Levels 395 20.1.3 Design Considerations 396 20.1.4 Cost of the Technology 398 20.1.5 Technology Status 398 20.2 Oxidation Technologies with Ozone and Hydrogen Peroxide 398 20.2.1 Process Description and Implementation 398 20.2.2 Achievable Treatment Levels 403 20.2.3 Design Considerations 403 20.2.4 Cost of the Technology 403 20.2.5 Technology Status 404 20.3 Photocatalytic Oxidation Technology 404 20.3.1 Process Description 404 20.3.2 Achievable Treatment Levels 404 20.3.3 Design Considerations 405 20.3.4 Cost of the Technology 405 20.3.5 Technology Status 405 20.4 INCO’s Air/SO 2 Process 406 20.4.1 Process Description 406 20.4.2 Achievable Treatment Levels 407 20.4.3 Design Considerations 408 20.4.4 Cost of the Technology 408 20.4.5 Technology Status 408 20.5 Technology Screening Matrix and Additional Technologies 408 20.6 Summary and Conclusions 408 References 411 Chemical oxidation at ambient temperatures is perhaps the most common treatment technology for cyanide in contaminated waters. Oxidation technologies, such as alkaline chlorination and ozonation perform well for free and weak metal–cyanide complexes (weak acid dissociable cyanide [WAD]) in water, soil slurries, and sludges [1–5]. However, energy-intensive oxidation technologies, such as 393 © 2006 by Taylor & Francis Group, LLC 394 Cyanide in Water and Soil ambient temperature photocatalytic oxidation are necessary to treat strong metal– cyanide complexes in water, soil slurries, and sludges [5]. The following ambient temperature oxidation technologies are described in detail in this chapter: • Ambient temperature alkaline chlorination • Ambient temperature oxidation with ozone and hydrogen peroxide • Photocatalytic oxidation technologies • INCO’s Air/SO 2 process These technologies have been applied for the treatment of water, soil slurries, and sludges containing free cyanide, weak metal–cyanide complexes, or strong metal–cyanide complexes. Descriptions for the technologies follow, and include the following main features: • Process description and implementation • Achievable treatment levels • Design considerations • Critical design conditions • Residuals generated • Technology complexity • Cost information • Status of technology implementation temperature oxidation technologies. 20.1 ALKALINE CHLORINATION TECHNOLOGIES 20.1.1 P ROCESS DESCRIPTION AND IMPLEMENTATION The most widely used technology for the destruction of free cyanide and certain weak metal–cyanide complexes is chlorineoxidation under alkalineconditions, commonlyknownas alkalinechlorination. Here, free cyanide and certain weakly complexed metal cyanides (i.e., WAD cyanides), such as copper, cadmium, and nickel cyanide, are oxidized to cyanate (CNO − ) and subsequently to carbon dioxide and nitrogen gas. Chlorine gas or hypochlorite (ClO − ) is used as the oxidant, and an alkali (e.g., sodium hydroxide or lime) is used to produce the pH conditions above 9.5 needed to sustain the oxidation reaction. When chlorine gas is used as the oxidizing agent, the process chemistry is given by the following reaction [1,6,7]: CN − +2NaOH +Cl 2 → CNO − +2Na + +2Cl − +H 2 O (20.1) The above reaction proceeds at significant rates under alkaline conditions (pH 10 and higher) [8]. Addition of alkali is essential to maintain the proper reaction pH and to prevent the generation of any toxic cyanogen chloride (CNCl) or HCN gas, which forms at pH < 10 [6]. The oxidation of cyanide to cyanate is rapid, requiring about 15 to 30 min of contact time and Cl/CN dose of about 3 (on a mass basis). The complete destruction of cyanide can be accomplished by lowering the pH of the solution after cyanate formation to 9 and addition of excess chlorine. This second reaction proceeds as follows [7]: 3Cl 2 +2CNO − +4NaOH → 2CO 2 +N 2 +2Cl − +4Na + +4Cl − +2H 2 O (20.2) © 2006 by Taylor & Francis Group, LLC The chapter concludes with a technology summary matrix (Table 20.7) for all the available ambient Ambient Temperature Oxidation Technologies 395 TABLE 20.1 Typical Operating Conditions for a Two-Stage Alkaline Chlorination Process Chlorine dose NaOH dose Redox Retention Stage pH (g Cl/g CN) (g NaOH/g CN) potential (mV) time (min) 1 9.5–11 2.7–3.0 3.1–3.4 350–400 30–60 2 8.0–8.5 4.1–4.5 4.2–4.6 600 30–60 Source: Data from Palmer, S.A.K., Breton, M.A., Nunno, T.J., Sullivan, D.M., and Surprenant, N.F., Metal/Cyanide Containing Wastes: Treatment Technologies, Corp, N.D., Ed., Noyes Data Corp., Park Ridge, NJ, 1998. In cases where a metal–cyanide species is oxidized, the liberated metal generally forms a hydroxide precipitate under the alkaline conditions of the reaction. Treatment of thiocyanate (SCN − ) by alkaline chlorination occurs in the pH range of 10 to 11.5 according to the following reaction: 2SCN − +8Cl 2 +20OH − → 2CNO − +2SO −2 4 +16Cl − +10H 2 O (20.3) The alkaline chlorination process for free and WAD cyanide can be operated as a one-or two-step process in either batch or continuous flow. In the two-step process, the first step is used for oxidation of cyanide to cyanate; in thesecond step, cyanate is oxidized to carbon dioxide and nitrogen. Cyanate, however, can also be hydrolyzed to CO 2 and NH 3 by adjusting pH to the 7 to 8 range, which reduces the chlorine demand. There is extensive full-scale application of this technology in electroplating and gold mining operations. Table 20.1 gives typical operating conditions for a two-stage, full-scale continuous flow alkaline chlorination unit for treating free and WAD cyanide. treatment of cyanide in tailings pond decant water [9]. Although the figure shows chlorine gas being used, this can be replaced by hypochlorite solution, which would eliminate the recirculation pump and chlorine eductor; however, a hypochlorite solution feed pump would still be required. The hypo- chlorite feed pump or chlorine gas feed would be oxidation–reduction potential (ORP) controlled and effluentquality producedby alkalinechlorination systems atfour goldmining operations. It should be noted thatresidual chlorineis toxic to many speciesin theenvironment and discharge of effluents with high residual chlorine concentrations can be problematic and, in some instances, will be prohibited. For the treatment of certain weak metal–cyanide and strong metal–cyanide complexes, modifica- tions to this process are implemented, including increasing the temperature and retention times in the reaction vessel [6,10,11]. Details of high temperature alkaline chlorination technology are provided 20.1.2 ACHIEVABLE TREATMENT LEVELS Weakly complexed metal cyanides are typically reduced to a concentration less than 1 mg/l, while free cyanide concentrations following alkaline chlorination are usually less than 0.2 mg/l. These performance levels will depend on chlorine dosage, reaction pH, reaction time, and the general chlorine demand of the waste. This technology is not applicable for strongly complexed metal cyanides like iron– or cobalt–cyanide complexes. © 2006 by Taylor & Francis Group, LLC Figure 20.1 presents a schematic flow diagram of a typical alkaline chlorination system for the the lime/alkaline feed would be pH controlled. Tables 20.2 and 20.3 present operating parameters and under thermal technologies in Chapter 22. 396 Cyanide in Water and Soil pH ORP Reactor tank(s) 0.5–1.5 h pH 10–11.5 Tailings sump To tailings pond Recirculating pump Eductor Chlorine gas or hypochlorite Mixing Solid tails Lime slurry Barren solution or tailing pond water FIGURE 20.1 Schematic flow diagram of a typical alkaline chlorination system. (Source: Smith, A. and Mudder, T., The Chemistry and Treatment of Cyanidation Wastes, Mining Journal Books, Ltd., London, 1991. With permission.) TABLE 20.2 Operating Parameters for Full-Scale Alkaline Chlorination Operations Giant Mosquito Baker Carolin Yellowknife Parameter Creek mine mine mine mine Mill capacity (Tpd) a 100 100 1250 1200 Solids cyanided Ore Ore Concentrate Roaster calcine Solid feed rate (Tpd) a 100 100 75 140 Treatment mode Batch Cont. Cont. Cont. Solution treated Barren Barren Barren Tailings pond overflow Solution rate 3 to 5.5 m 3 14.4 m 3 /day 216 m 3 /day 6545 m 3 /day batches/day Form of chlorine Gaseous Calcium Gaseous Gaseous hypochlorite No. reactor tanks 1 2 1 1 Retention time (h) 6 14 8 0.5 pH 11 11.5 11 11.5 pH control Manual Manual Auto Auto Chlorine control Manual Manual Manual Manual a Tpd = metric tons (tonnes) per day. Source: Smith, A. and Mudder, T., The Chemistry and Treatment of Cyanidation Wastes, Mining Journal Books, Ltd., London, 1991. With permission. 20.1.3 DESIGN CONSIDERATIONS The critical design parameters for alkaline chlorination include chlorine/cyanide (Cl/CN) ratio, reaction pH, and reaction time. The technology is well suited for treatment up to 5000 mg/l of © 2006 by Taylor & Francis Group, LLC Ambient Temperature Oxidation Technologies 397 TABLE 20.3 Performance Data for Full-Scale Alkaline Chlorination of Gold Mill Effluents Constituents, mg/l Mine CN a T CN b W CNS Cu Fe Ni Zn As NH 3 TRC d Baker Influent 2000 1900 1100 c 290 2.4 — 740 — — — Effluent 8.3 0.7 — 5.0 2.8 — 3.9 — — 2800 e % removal 99.6 99.9 — 98.3 — — 99.5 — — — Carolin Influent 1000 710 1900 c 97 150 — 110 — — — Effluent 170 0.95 — 0.38 53 — 5.8 — — 190 % removal 83 99.9 — 99.6 64.7 — 94.7 — — — Mosquito Creek Influent 310 226 330 c 10.0 9.4 — 93 — — — Effluent 25 0.49 — 0.33 8.0 — 1.4 — — 320 % removal 91.9 98.8 — 96.7 14.9 — 98.5 — — — Giant Yellowknife Influent 7.5 7.1 6.3 6.7 <0.1 1.2 0.1 12.1 — — Effluent 1.3 1.2 1.0 0.09 <0.1 0.7 0.1 — — — % removal 82.7 85.1 84.1 98.7 — 41.7 — — — — Polishing pond O/F 0.15 0.09 — 0.03 <0.1 — <0.1 0.14 9.4 1.1 % removal 98 98.7 — 99.6 — — — 99.7 — — All samples unfiltered. a CN T = total cyanide by distillation. b CN W = weak acid dissociable cyanide by ASTM Method C. c Analysis not available due to analytical difficulties. d TRC = total residual chlorine. e Additional chlorine added with a view to destroying cyanide contained in solid tailings slurry. Source: Smith, A. and Mudder, T., The Chemistry and Treatment of Cyanidation Wastes, Mining Journal Books, Ltd., London, 1991. With permission. free cyanide using batch systems, while continuous processes with flow rates up to 5 gpm can treat up to 1000 mg/l, with optimal treatment efficiency usually achievable for concentrations below 100 mg/l and influent flow rates up to 100 gpm [6,7,12]. Waste chlorine demand greatly influences Cl/CN ratio; chlorine demand does not depend only on cyanide content. The technology is not suitable for waste streams containing strong metal–cyanide complexes, such as ferro- or ferricyanide and high concentrations of thiocyanates (SCN − ). Moreover, optimal efficiency is achieved for influents containing less than 100 mg/l of total suspended solids (TSS), less than 1000 mg/l of total dissolved solids (TDS), pH levels between 9 and 13, and ORP greater than 200 mV. As far as residuals are concerned, metal hydroxide sludges can be generated if the influent stream contains appreciable amounts of weak metal–cyanide complexes, or metals in other forms. Weaker complexes that dissociate during the process of oxidation will liberate metal cations, leading to the formation of metal hydroxides under alkaline pH conditions. Residual chlorine and chloramines are also generated, which, because of their toxic nature, should be removed by dechlorination prior to discharge. At pH < 9, generation of CNCl, a toxic gas, as an intermediate during the oxidation of © 2006 by Taylor & Francis Group, LLC 398 Cyanide in Water and Soil cyanide to cyanate is a concern. Careful control of pH and ORP should be in place to prevent any evolution of CNCl gas. The technologyis relatively easy toimplement andoperate. It requires basicwastewater treatment unit operations and continuous monitoring of pH to prevent production of CNCl and HCN. Chlorine gas handlingand leakage pose possible health hazards. If metal hydroxide sludgesare generated, they may require additional treatment for stabilization prior to disposal. Moreover, the heat of reaction from chlorine and cyanide decomposition may require some form of temperature control before the final effluent can be discharged to the sewer. 20.1.4 COST OF THE TECHNOLOGY Capital costs for a typical 500 gpm system for treating waste streams that contain free and WAD complexes hasbeen reportedas approximately$300,000 (1990cost basis), withtypical operationand maintenance (O&M) costsvarying between $5 and $7 per kilogram of cyanide destroyed [6,9,12,13]. 20.1.5 TECHNOLOGY STATUS Alkaline chlorination is a well-established, commerciallypracticed technology with many successful full-scale applications in place in electroplating and gold mining industries [6,9,12,13]. Prefabricated chemical feedand monitoringequipment suitablefor implementing thistechnology arecommercially available. However, some bench-scale testing for a particular application usually is desirable for determination of optimal Cl/CN dose, pH conditions, and reaction time. 20.2 OXIDATION TECHNOLOGIES WITH OZONE AND HYDROGEN PEROXIDE 20.2.1 P ROCESS DESCRIPTION AND IMPLEMENTATION These processes involve the oxidative destruction of free and WAD forms of cyanide by either ozone or hydrogen peroxide under alkaline pH (9–11) conditions. Oxidation of cyanide (CN − )to cyanate (CNO − ) occurs in 10–15 min in the presence of excess ozone under alkaline conditions (9 < pH < 10) according to the following reaction [14]: CN − +O 3 → CNO − +O 2 (20.4) Gurol and Bremen [3] reported a first-order reaction rate coefficient (2600 ± 700 M −1 sec −1 ) for constant for ozone decay as a function of total cyanide concentration. As shown in this figure, the cyanide oxidation rate increases with increase in pH. Rate expressions for ozone oxidation of cyanide at three different pH values are as follows [3]: −d[O 3 ]/dt = (2600 ±700)[CN T ] 0.55±0.06 [O 3 ] at pH = 11.2 (20.5) −d[O 3 ]/dt = (2700 ±850)[CN T ] 0.83±0.14 [O 3 ] at pH = 9.5 (20.6) −d[O 3 ]/dt = (550 ±200)[CN T ] 1.06±0.1 [O 3 ] at pH = 7.0 (20.7) The presence ofcopper wasfoundto catalyze thecyanide oxidation processaccording tothe following reaction [15]: 2Cu + +11CN − +3O 3 → 2Cu(CN) 3− 4 +3CNO − +3O 2 (20.8) © 2006 by Taylor & Francis Group, LLC ozonation of free cyanide at pH 11.2. Figure 20.2 presents the observed pseudo-first-order rate Ambient Temperature Oxidation Technologies 399 3.0 Phosphate solutions pH 11.2 1 2.5 2.0 Log k obs (sec – 1 ) 1.5 1.0 0.5 0 – 4.0 – 3.0 – 2.0 Log [CN T ], M – 1.0 0 pH 9.5 2 pH 7.0 3 1 2 3 FIGURE 20.2 Observed pseudo-first-order rate constant for ozone decay vs. total cyanide concentration on log scales. (Source: Reprinted with permission from Gurol, M.D. and Bremen, W.H., Environ. Sci. Technol., 19, 804, 1985. Copyright 1985. American Chemical Society.) In the presence of excess ozone, cyanate is hydrolyzed to bicarbonate and nitrogen according to the following reaction [14]: 2CNO − +3O 3 +H 2 O → 2HCO − 3 +N 2 +3O 2 (20.9) This second stage reaction is much slower than the cyanate formation reaction and is usually carried out in the pH range of 10 to 12 where the reaction rate is relatively constant. Temperature variation within the ambient range does not have a significant effect on the reaction rates. However, the use of ultraviolet (UV) light to enhance radical formation [6] and the presence of copper catalyst [12] have each been shown to increase the rate of the second stage reaction. The metal–cyanide complexes of cadmium, copper, nickel, silver, and zinc are readily oxidized by ozone. For treatment of strong metal–cyanide complexes, such as iron– and cobalt–cyanide, modifications to the existing process are implemented, including prolonged UV light exposure to promote photodissociation [4,5]. However, Guroland Holden[15] reportedoxidationof iron–cyanide complexes in the presence of excess ozone (ozone to iron cyanide ratio of 30:1 on a molar basis) under laboratory conditions. Thiocyanate/SCN − is readily oxidized by ozone [16]. Layne et al. [16] determined that for pH > 11, SCN − reacts with ozone to form CN − and SO 2− 4 , and the free CN − is subsequently oxidized to CNO − as shown in reaction (20.4). © 2006 by Taylor & Francis Group, LLC Additional discussion of this reaction and the catalytic effect of the copper is provided in Chapter 5. 400 Cyanide in Water and Soil Hydrogen peroxide provides another alternative in treating free and weakly complexed metal cyanides in waters and wastewaters. Although H 2 O 2 is a weaker oxidizing agent than ozone (standard electrode potential of 0.878 V in alkaline solution compared to 1.24 V for ozone under same solution conditions), cyanide can be fully converted by hydrogen peroxide to ammonia and carbonate under alkaline conditions, according to the following reactions: CN − +H 2 O 2 → CNO − +H 2 O (20.10) CNO − +H 2 O + OH − → NH 3 +CO 2− 3 (20.11) The first reaction is optimal in the pH range of 9.5 to 10.5 [8]. The second reaction, however, is very slow under alkaline condition and increases as pH decreases [17]. The cyanide oxidation rate also depends onthe excesshydrogen peroxide concentration, cyanide concentration, and temperature. The reaction rates can also be enhanced by the presence of a metal catalyst, such as copper, which ultimately reacts with ammonia to form a tetraamino copper complex that is largely nonreactive [8]. Copper-catalyzedhydrogen peroxide oxidationofWADcyanidecomplexes in wastewateris prac- ticed commonly in the gold mining industry [9]. The destruction of weak metal–cyanide complexes occurs according to the following reactions: M(CN) −2 4 +4H 2 O 2 +2OH − Cu catalyst −→ 4CNO − +4H 2 O + M(OH) 2 (s) (20.12) CNO − +2H 2 O −→ NH + 4 +CO 2− 3 (20.13) where M is a metal cation, such as Cu or Zn. The copper, which is added as a catalyst or present in the waste as Cu(CN) − 2 , can react with strongly complexed Fe(CN) 4− 6 to form an insoluble bimetallic complex according to the following reaction: Fe(CN) 4− 6 +2Cu +2 −→ Cu 2 [Fe(CN) 6 ](s) (20.14) It is customary to add copper sulfate pentahydrate as the catalyst to produce a copper concentration of about 10 to 20% of the WAD cyanide concentration. The peroxide dose needed for successful oxidation of cyanide species may be 200 to 450% of the required amount indicated by stoichiometry [9]. The high peroxide dosage rate is reflective of the presence of other oxidizable materials in the wastewater that can compete for the peroxide, as well as the inherent loss of oxidation capacity as some of the peroxide may decompose to oxygen and water: 2H 2 O 2 −→ O 2 +2H 2 O (20.15) To reduce these decomposition losses, peroxide stabilizers such as silicate (employed in Degussa’s SILOX process) and sulfuric acid, which forms peroxymonosulphuric acid (Caro’s acid), have been developed and deployed with substantial savings over the conventional peroxide process [18]. for cyanide [18]. As shown in this figure, hydrogen peroxide is added to the first reaction tank along with the influent solution. In the second mixingtank, copper isadded as copper sulfate to catalytically promote the cyanide oxidation reaction. The supernatant from the second mixing tank then goes to the third tank, where enough settling of solid sludges (copper–iron–cyanide solids; iron hydroxides) and increased residence time causes complete removal of cyanide, and cyanide-free supernatant is discharged into the tailings pond. tinuous tailings slurry treatment system using hydrogen peroxide at the OK Tedi Mine in Papua, © 2006 by Taylor & Francis Group, LLC Figure 20.3 presents a schematic flow diagram of a typical hydrogen peroxide treatment system Figure 20.4 and Table 20.4 present a schematic flow diagram and performance data for a con- Ambient Temperature Oxidation Technologies 401 H 2 O 2 storage Feed pump To tailings pond Reaction tanks CuSO 4 catalysts (if required) Tailings pulp or Barren solution FIGURE 20.3 Schematic flow diagram of a typical hydrogen peroxide treatment system for cyanide. (Source: Botz, M. et al., Cyanide Monograph, Mining Journal Books, Ltd., London, 1998. With permission.) Measuring cell Control unit Multiplier Reaction tank H O pumps 22 Main tailings stream Control stream Redox pH H 2 O 2 Control valve Flow meter Sample for analysis 1– 10 mg/l CN T <0.3 mg/l WAD CN Control system Tailings slurry 1100 m /h 110– 300 mg /l CN 3 T Activator CN Caroate NaOH H 2 SO 4 FIGURE 20.4 Schematic flow diagram for the Degussa hydrogen peroxide process at the OK Tedi Mine. (Source: Smith, A. and Mudder, T., The Chemistry and Treatment of Cyanidation Wastes, Mining Journal Books, Ltd., London, 1991. With permission.) New Guinea. Because of the lack of suitable means to determine the necessary dosage of H 2 O 2 quickly and accuratelyenoughto allow efficientuseof thereagent fortreatment oflarge effluent flows, a continuous automatic titration is implemented in a small sidestream as depicted in Figure 20.4. The pH of the sidestream is adjusted automatically to a particular value, and a fast-acting strong oxidizing agent is dosed. The rate of dosage is controlled by a redox measurement carried out in the presence of a special catalyst (“Activator CN”). Simultaneous to the addition of the strong oxidizing agent (an aqueous solution of “caroate,” potassium monopersulfate) to the sidestream, H 2 O 2 ,ata concentration of 70% by weight, is added to the main tailings stream via a control valve. The opening © 2006 by Taylor & Francis Group, LLC 402 Cyanide in Water and Soil TABLE 20.4 Tailings Slurry Characteristics after Degussa Hydrogen Peroxide Treatment at OK Tedi Mine Before H 2 O 2 After H 2 O 2 Parameter Treatment Treatment Tailings flow 1100 m 3 /h 1100 m 3 /h Solids content 45% 45% pH 10.5–11.0 10.2–10.8 Free cyanide 50–100 mg/l Undetectable WAD cyanide 90–200 mg/l <0.5 mg/l Total cyanide 110–300 mg/l 1–10 mg/l Dissolved Cu 50–100 mg/l <0.5 mg/l Dissolved Zn 10–30 mg/l <0.1 mg/l Dissolved Fe 1–3 mg/l 1–3 mg/l Source: Smith, A. and Mudder, T., The Chemistry and Treatment of Cyanidation Wastes, Mining Journal Books, Ltd., London, 1991. With permission. TABLE 20.5 Treatment Performance for Three Hydrogen Peroxide Treatment Plants Before Treatment (mg/l) After Treatment (mg/l) CN WAD CN Cu Fe CN WAD CN Cu Fe Case study #1 19 19 20 <0.1 0.7 0.7 0.4 <0.1 Pond overflow a Case study #2 1350 850 478 178 <5 <1 <5 <2 Barren bleed b Case study #3 353 322 102 11 0.36 0.36 0.4 d <0.1 Heap leach solution c a Preliminary plant results from pre-operational test runs. b Typical results during first six months of operation. c Average of 25 measurements made over 10 days of plant operation. d Value dropped from 1.0 to 0.4 over 4 days due to coagulation and settling. Source: Smith, A. and Mudder, T., The Chemistry and Treatment of Cyanidation Wastes, Mining Journal Books, Ltd., London, 1991. With permission. of this valve is controlled by a signal obtained by multiplying the signal from the control unit by a second signal obtained from a tailings flow meter. Table 20.5 presents performance data from three other hydrogen peroxide treatment facilities at gold mining sites. While the data in Tables 20.4 and 20.5 show excellent removal of cyanide by oxidation and precipitation of metals, it must be recognized that these facilities are only used for treatment of primary constituents of concern, like cyanide. Hydrogen peroxide treatment does not affect ammonia, nitrate, or thiocyanate; treatment of these constituents will require additional treatment units. Hydrogen peroxide oxidation for free cyanide can also be effective under alkaline conditions, and in the presence of a metal catalyst (Fe, Al, Ni) or formaldehyde. The patented Kastone © 2006 by Taylor & Francis Group, LLC [...]... conventional alkaline chlorination processes © 200 6 by Taylor & Francis Group, LLC Cyanide in Water and Soil 404 20. 2.5 TECHNOLOGY STATUS Ozonation and hydrogen peroxide application are well-established technologies with limited fullscale applications in place [6], mainly in the mining and electroplating industries Prefabricated chemical feed and monitoring equipment suitable for implementing this technology... Proceedings of 23rd Annual Aerospace/Airline Plating and Metal Finishing Forum and Exposition, Jacksonville, FL, 1987 15 Gurol, M.D and Holden, T.E., The effect of copper and iron complexation on removal of cyanide by ozone, Ind Eng Chem Res., 27, 1157, 1988 © 200 6 by Taylor & Francis Group, LLC 412 Cyanide in Water and Soil 16 Layne, M.E., Singer, P.C., and Lidwin, M.I., Ozonation of thiocyanate, in Proceedings... Sullivan, D.M., and Surprenant, N.F., Metal /Cyanide Containing Wastes: Treatment Technologies, Corp, N.D., Ed., Noyes Data Corp., Park Ridge, NJ, 1988 7 Shelton, S.P., Examination of treatment methods for cyanide wastes, Report No NADC-7819 8-6 0, Naval Material Command, Washington, DC, 1979 8 Hartinger, L., Handbook of Effluent Treatment and Recycling for the Metal Finishing Industry, 2nd ed., Finishing Publications,... available 20. 3 PHOTOCATALYTIC OXIDATION TECHNOLOGY 20. 3.1 PROCESS DESCRIPTION This three-step process involves UV-light-aided photodissociation of metal cyanide complexes, including the strong iron– and cobalt cyanide complexes, to free cyanide The liberated free cyanide is further oxidized to CO2 and NO− , using either ozone or H2 O2 in the presence of a TiO2 catalyst 3 Photodissociation of ferri- and ferrocyanide... treatment and analysis of cyanide wastewater, prepared for Air Force Engineering Center, Report No AFCEC-TR-7 4-5 , Thiokol Corporation, Tyndall AFB, FL, 1975 3 Gurol, M.D and Bremen, W.H., Kinetics and mechanism of ozonation of free cyanide species in water, Environ Sci Technol., 19, 804, 1985 4 Streeben, L.L., Schornick, H.M., and Wachinski, A.M., Ozone oxidation of concentrated cyanide wastewater from... Robbins, G., Vergunst, R., Tandi, B., and Iamarino, P.F., INCO’s cyanide removal technology working well, Mining Eng., Feb., 205 , 1991 27 Devuyst, E.A., Tandi, B., and Conard, B.R Treatment of cyanide ferrocyanide effluents, U.S Patent No 4,615,873, 1986 28 Scott, J and Ingles, J., State of the art processes for the treatment of gold mill effluents, Mining, Mineral and Metallurgical Processes Division,... (ii) on-site generation resulting in reduced transportation, storage, and handling costs, and (iii) elimination of potential formation of chlorinated organics However, on-site generation facilities and power requirements may incur significant capital and operating costs [19] 20. 2.4 COST OF THE TECHNOLOGY The capital cost of ozone oxidation technology is significantly higher than the alkaline chlorination... SO2 /Air oxidation results in limited thiocyanate treatment (10 to 20% ) and no treatment of ammonia and nitrate TABLE 20. 6 INCO’s Air/SO2 Destruction of Cyanide in CIP Tailings, CIL Tailings, Repulped Tailings, Barren Solution, and Pond Water Cyanide concentration, mg/l Mine Colosseum Ketza River Equity Casa Berardi Weatmin Premiere Golden Bear McBean (barren) Lynngold (pond) Mineral Hill (barren) Lac... The Chemistry and Treatment of Cyanidation Wastes, Mining Journal Books, Ltd., London, 1991 © 200 6 by Taylor & Francis Group, LLC Cyanide in Water and Soil 408 20. 4.3 DESIGN CONSIDERATIONS The optimum operating conditions for free cyanide and weak metal cyanide complexes are pH of approximately 9, cyanide to cupric ion mass ratio of 5:1, and cyanide to sulfur dioxide mass ratio between 1:3 and 1:7 [9]... in Proceedings of Conference on Cyanide and the Environment, Tucson, AZ, 1984, p 433 17 USEPA, Managing cyanide in metal finishing, Capsule Report, EPA 625/R-99/009, U.S Environmental Protection Agency, Office of Research and Development, Cincinnati, OH, 200 0 18 Botz, M., Devuyst, E.A., Mudder, T., Norcross, R., Ou, B., Richins, R., Robbins, G., Smith, A., Steiner, N., Stevenson, J., Waterland, R., Wilder, . chlorine demand. There is extensive full-scale application of this technology in electroplating and gold mining operations. Table 20. 1 gives typical operating conditions for a two-stage, full-scale. full-scale continuous flow alkaline chlorination unit for treating free and WAD cyanide. treatment of cyanide in tailings pond decant water [9]. Although the figure shows chlorine gas being used, this. Tables 20. 2 and 20. 3 present operating parameters and under thermal technologies in Chapter 22. 396 Cyanide in Water and Soil pH ORP Reactor tank(s) 0.5–1.5 h pH 10–11.5 Tailings sump To tailings pond Recirculating pump Eductor Chlorine