Mineral Processing and Extractive Metallurgy Review: An International Journal A Review on Recovery of Copper and Cyanide From Waste Cyanide Solutions

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A Review on Recovery of Copper and Cyanide From Waste Cyanide Solutions a

b

Feng Xie , David Dreisinger & Fiona Doyle

a

a

Department of Materials Science and Engineering, University of California, Berkeley, California, USA b

Department of Materials Engineering, University of British Columbia, Vancouver, British Columbia, Canada Accepted author version posted online: 07 Jun 2012.Version of record first published: 11 Feb 2013.

To cite this article: Feng Xie , David Dreisinger & Fiona Doyle (2013): A Review on Recovery of Copper and Cyanide From Waste Cyanide Solutions, Mineral Processing and Extractive Metallurgy Review: An International Journal, 34:6, 387-411 To link to this article: http://dx.doi.org/10.1080/08827508.2012.695303

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Mineral Processing & Extractive Metall. Rev., 34: 387–411, 2013 Copyright # Taylor & Francis Group, LLC ISSN: 0882-7508 print=1547-7401 online DOI: 10.1080/08827508.2012.695303

A REVIEW ON RECOVERY OF COPPER AND CYANIDE FROM WASTE CYANIDE SOLUTIONS Feng Xie1, David Dreisinger2, and Fiona Doyle1 Downloaded by [The University of British Columbia] at 14:23 18 February 2013

1

Department of Materials Science and Engineering, University of California, Berkeley, California, USA 2 Department of Materials Engineering, University of British Columbia, Vancouver, British Columbia, Canada The mainstream technology for leaching gold from gold ore is still leaching in aqueous alkaline cyanide solution. However, when copper minerals are present in the gold ore, high levels of free cyanide must be maintained during leaching because many common copper minerals react with cyanide, forming copper cyanide complexes that deplete the solution of free cyanide. This results in a significant economical penalty through excessive cyanide consumption and loss of valuable copper in tails. Environmental constraints controlling the discharge of cyanide from mining industry are being tightened by local governments worldwide. The solution chemistry of copper in cyanide solution and various technologies for the recovery of copper and cyanide from barren gold cyanide solutions were reviewed in the paper. Direct recovery methods are mainly based on the acidification–volatilization–reneutralization (AVR) process or its modifications. These processes are not very efficient for treating low cyanide solutions and high metal cyanide solutions due to their substantial operational cost. Indirect recovery technologies by activated carbon, ion-exchange resins (IX) and solvent extraction (SX) have been extensively studied. The basic principle of these technologies is to pre-concentrate copper (and part of cyanide) into a small volume of eluant or stripping solution. The copper and cyanide in the resulted solutions can be further recovered by AVR or similar processes or by the electrowinning process. Activated carbon is only suitable for use as a polishing process to remove cyanide to lower levels from those cyanide solutions where the cyanide content is already low. Compared to activated carbon, ion exchange resins are less easily poisoned by organic matter and can usually be eluted at room temperature, and selectivity for particular metals can be achieved by the choice of the functional group incorporated into the bead or by the selective elution process. Solvent extraction process developed base on guanidine and modified quaternary amines exhibit relative fast extraction kinetics and can be operated in a continuous manner. It will be necessary to thicken and wash the solids in order to produce a clarified feed solution while treating the slurry from operations using carbon-in-pulp (CIP) for the recovery of gold. Other copper and cyanide recovery technologies such as biosorption or direct electrowinning were also proposed, but they have still not found their way to practical application. Keywords: copper, cyanide, recovery

Feng Xie is currently affiliated with the University of British Columbia. Address correspondence to Feng Xie, Department of Materials Engineering, University of British Columbia, 309-6350 Stores Road, Vancouver, BC V6T 1Z4, Canada. E-mail: [email protected] 387

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INTRODUCTION The cyanidation process has been practiced for treating gold ores by most of the gold processing plants for more than 100 years. Elsner (1846) first established the important fact for gold dissolution in cyanide solution:

Downloaded by [The University of British Columbia] at 14:23 18 February 2013

4Au þ 8KCN þ O2 þ 2H2 O ¼ 4KAuðCNÞ2 þ 4KOH

ð1Þ

The modern cyanidation process was mainly attributed to the patent by McArthur and the Forrest brothers between 1887 and 1888, which was rapidly developed into a commercial process that widely spread in gold mining industry, especially with the invention of Merill-Crowe process (Marsden and House 1992). Conventionally, after solid=liquid separation, the precious metals (gold and silver) in the pregnant leaching solutions were recovered by zinc precipitation: 2 2AuðCNÞ 2 þ Zn ¼ ZnðCNÞ4 þ 2Au

ð2Þ

The carbon adsorption process (i.e., the well-known Carbon-In-Pulp=CarbonIn-Leach process, CIP=CIL) has been developed into the mainstream gold recovery technology after 1970s and has helped promote the cyanidation process considerably. The simplified flowsheet for CIP=CIL and conventional zinc-precipitation processes is shown in Figure 1. Though some alternative lixivants have been developed due to environmental pressure (Senanayake 2004; Aylmore and Muir 2001), none of them has yet found its way to practical application. A challenge for the cyanidation process is the treatment of the large amount of cyanide-contaminated effluents since most of the cyanide consumed in cyanidation process is actually wasted in the effluents; some occurring as free cyanide, with the balance forming metal cyanide complexes (Botz, Mudder, and Akcil 2005; Fleming 2005). For example, the initial reaction of pyrrhotite in the cyanide solution can be

Figure 1 Schematic flowsheets for CIP=CIL and Zn-precipitation processes.

RECOVERY OF COPPER AND CYANIDE FROM WASTE CYANIDE SOLUTIONS

389

expressed as: Fe7 S8 þ NaCN ¼ 7FeS þ NaSCN

ð3Þ

FeS and SCN can be further oxidized to form iron cyanides and various aqueous sulfur species such as sulfate:


2FeS þ 12NaCN þ 5O2 þ 2H2 O ¼ 2Na4 FeðCNÞ6 þ 2Na2 SO4 þ 4NaOH

ð4Þ

When copper minerals are present in the gold ore, high levels of free cyanide must be maintained during leaching because many common copper minerals react with cyanide, forming copper cyanide complexes that deplete the solution of free cyanide. It was reported that except for chalcopyrite (CuFeS2) and Chrysocilla (CuSiO3), the reactivity of most common copper minerals such as chalcocite (Cu2S), covellite (CuS), cuprite (Cu2O), and malachite (CuCO3 Cu(OH)2) with cyanide is substantial (Hedley and Tabachnik 1968; Sceresini 2005). Cu2 S þ 7NaCN þ 1=2O2 þ H2 O ¼ 2Na2 CuðCNÞ3 þ 2NaOH þ NaCNS

ð5Þ

CuS þ 4NaCN þ 1=4O2 þ 1=2H2 O ¼ Na2 CuðCNÞ3 þ NaOH þ NaCNS

ð6Þ

Cu2 O þ 6NaCN þ H2 O ¼ 2Na2 CuðCNÞ3 þ 2NaOH

ð7Þ

CuCO3 þ 8NaCN þ 2NaOH ¼ 2Na2 CuðCNÞ3 þ 2Na2 CO3 þ 2NaCNO þ H2 O ð8Þ A significant part of copper cyanide complexes remain in the solution after gold recovery by carbon adsorption (or zinc precipitation). It was known that less than 2% of the cyanide consumed accounts for the dissolution of gold and=or silver in many gold operations and the majority of the cyanide was actually consumed by those cyanide soluble minerals found commonly in gold bearing ores (Marsden and House 1992). The direct recycling of the barren cyanide solution back to the gold leaching process may result in heavy buildup of copper cyanide complexes, which may suppress gold recovery since a high concentration of copper cyanide complexes in leachate substantially compete with gold=silver for available carbon (or zinc). Depending on the copper concentration, a bleed or all the barren solution has to be removed and either be sent to the tailings or to a metal cyanide destruction process (Fleming 2005). The current available methods to detoxify cyanide-containing effluents include destruction by natural degradation, by biological process or by chemical oxidation (Palmer et al. 1988; Goode et al. 2001). Due to concerns for the environment, natural degradation process was seldom used as the sole detoxification unit in cyanide effluent treatment. Biological processes have not been extensively used in gold mining industry, probably because of their high cost and instability (Clark, Jordan, and Malloy 2001). As the oldest and most widely recognized process for cyanide destruction, alkaline-chlorination process is sometimes employed, primarily in the plating industry, though occasionally it is running in a few mining sites too. The destruction processes (INCO SO2=Air, Caro’s acid or

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hydrogen peroxide) can be very efficient in destroying free cyanide in the cyanide effluents: CN þ O2 þ SO2 þ H2 O ¼ CNO þ H2 SO4

ð9Þ

CN þ H2 O2 ¼ CNO þ H2 O

ð10Þ

CN þH2 S2 O5 ¼ CNO þ H2 SO4

ð11Þ


The cyanate hydrolyzes to form carbon dioxide or carbonate depending on the pH of the solution: In acidic conditions, CNO þ2Hþ þ H2 O ¼ CO2 þ NHþ 4

ð12Þ

In basic conditions, CNO þ OH þ H2 O ¼ CO2 3 þ NH3

ð13Þ

The destruction of effluents containing high cyanide concentration could severely decrease the profitability of the gold plant operations. If present, the valuable metals (such as copper) will report to the sludge. Sometimes this may even render the cyanidation process ineffective if the copper and complexed cyanide are not recovered after gold recovery (Griffiths et al. 1990; Robbins 1996; Goode et al. 2001; Jay 2001). On the other hand, the use of cyanide in the gold mining industry is attracting more public concerns, and environmental constraints controlling the discharge of cyanide from gold mining industry are being tightened by the local governments worldwide, especially after several cyanide spills happened (DeVries 2001). Nowadays, the concentration of free cyanide and the WAD (weak-acid-dissociable) cyanide species discharged into the tailing is usually required to be controlled below a strict limit (at many sites it is 50 mg=L to tails and 0.1 mg=L or less if there is any discharge to a receiving waterway). Subsequently, there has been growing interest in the recovery technologies of valuable copper and cyanide from cyanide effluents arising from gold mining industry. However, there are few cyanide recovery plants built on a commercial scale though a number of cyanide recovery technologies and several convincing case studies have been reported. Some practical considerations on the cyanide management in gold plants have been summarized by Ritcey (2005) and Fleming (2005). In this paper, the mainstream technologies for the recovery of copper and cyanide from barren gold cyanide solutions produced in the cyanide leaching of copper-gold ore and their recent development were reviewed. The solution chemistry of copper in cyanide solutions will be shortly introduced before heading to the discussion on recovery processes. SOLUTION CHEMISTRY OF COPPER CYANIDES The thermodynamics of copper in cyanide solutions has been well described (Sharpe 1976; Flynn and McGill 1995; Lu, Dreisinger, and Cooper 2002a). In the typical gold leaching solution, copper mainly exists in the 1 þ oxidation state and 2 3 may form cyanocuprate ions, CuðCNÞ 2 ; CuðCNÞ3 ; CuðCNÞ4 , depending on


391

cyanide and copper concentrations, pH, temperature, etc. The corresponding series of equilibrium between copper and cyanide can be represented as follows:


Cuþ þ CN ¼ CuCN

K1 ¼

½CuCN ½Cuþ ½CN

ð14Þ

CuCN þ CN ¼ CuðCNÞ 2

K2 ¼

½CuðCNÞ 2 ½CuCN½CN

ð15Þ

2 CuðCNÞ 2 þ CN ¼ CuðCNÞ3

K3 ¼

½CuðCNÞ2 3 ½CuðCNÞ ½CN 2

ð16Þ

3 CuðCNÞ2 3 þ CN ¼ CuðCNÞ4

K4 ¼

CuCN ¼ Cuþ þ CN HCN ¼ Hþ þ CN

½CuðCNÞ3 4 ½CuðCNÞ2 3 ½CN

Ksp ¼ ½Cuþ ½CN Ka ¼

ð17Þ ð18Þ

½Hþ ½CN ½HCN

ð19Þ

The values of 1020 for Ksp and 109.21 for Ka are generally accepted. However, different values of complex constants for copper cyanide species have been reported (Lu 1999). The differences among the reported values of K1, K3 and K4 are relatively small, but there is significant disagreement on the value of K2. Some reported values of the association constant of log b2 for CuðCNÞ 2 are listed in Table 1, where b2 is defined as: CuCN þ 2CN ¼ CuðCNÞ 2

b2 ¼

½CuðCNÞ 2

ð20Þ

½CuCN½CN 2

Using the data reported by Flynn and McGill (1995) (the log values of K1 to K4 are 10.5, 11.2, 5.3, 1.5, respectively), the copper speciation diagrams under different pH and molar ratios of cyanide to copper (CN=Cu) are shown in Figures 2 and 3, respectively (the formation of Cu2O, CuCN and CuðCNÞ 2 are negligible under the specified conditions and they are not shown in the Figures). The speciation diagrams Table 1 The reported association constants of log b2 for CuðCNÞ 2 Reference Vladimirova and Kakovsky 1950 Rothbaum 1957 Hancock, Finkelstein, and Evers 1972 Bek and Zhukov 1973 Helfter, May, and Sips, 1993

Temperature, C

log b2

25 20 22 25 25

23.71 21.7 1.0 21.7 0.2 24 0.23 23.97 0.01


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Figure 2 Plot of the calculated fraction of copper cyanide complexes vs pH ([Cu] ¼ 3.93 103 mol=L, CN=Cu ¼ 5; 25 C; after Xie and Dreisinger 2009a).

show that a low pH favors the formation of copper cyanide complexes with low coordination numbers. When CN=Cu is constant, the formation of CuðCNÞ 2 only occurs at low pH; the concentration of CuðCNÞ3 is negligible below pH 7 and 4 increases with an increase in pH. In alkaline cyanide solutions, copper mainly occurs 3 as CuðCNÞ2 3 and CuðCNÞ4 . Higher concentration of free cyanide favors the formation of the complexes with high coordination numbers. At pH 11, about 95% of

Figure 3 Plot of mole fraction of copper cyanide species vs Log [CN] (([Cu] ¼ 3.93 103 mol=L, pH ¼ 11, 25 C; after Xie and Dreisinger 2009a).


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Table 2 Some properties of copper(I) cyanide species

Species

Geometry

Cu-C bond, pm

C-N bond, pm

Frequency, cm1 (in aqueous)

Molar absorptivity cm2 M1 103 (aq)

CuCN(aq) CuðCNÞ 2

Linear Linear

190.6 193.2

116.8 117.1

– 2125

– 0.16

CuðCNÞ2 3

Triangular planar

206.8

117.6

2094

1.09

CuðCNÞ3 4

Tetrahedral

222.7

118.0

2076

1.66


Data of Cu–C and C–N bond length is from Kuznetsov et al. 2002 and other properties from Flynn and McGill (1995).

copper occurs as CuðCNÞ2 when CN=Cu ratio is three; when CN=Cu ratio 3 increases up to 10, about 47% of copper occurs as CuðCNÞ2 with 53% as 3 CuðCNÞ3 . The infrared and Raman spectra for the copper(I) complexes have been 4 studied and the information on their geometry has been confirmed. Some properties of three copper cyanide complexes are summarized in Table 2 (Sharpe 1976; Flynn and McGill 1995; Kuznetsov, Maslii, and Shapnik 2002). A magnetic resonance study on copper cyanide geometry indicates that CuðCNÞ2 3 has a distorted tetrahedral rather than a plane triangular (Sharpe 1976). Though different values of Cu-C and C-N bond length have been reported, the Cu-CN bond length increases with the number of cyanide ions in the complex, which is explained by the negative charge of the central atom increasing with the number of negatively charged ligands and by an increase in their electrostatic repulsion. An increase in the number of ligands also leads to an increase in the C-N bond length (Kuznetsov et al. 2002; Torre et al. 2006). Copper(II) cyanide complexes are unstable in the typical cyanide solutions with respect to the reduction of Cu(II) by cyanide: In acid solution, 2Cu2þ þ 4HCN ¼ 2CuCNðsÞ þ C2 N2 ðaqÞ þ 4Hþ

ð21Þ

In basic solution, 2Cu2þ þ 7CN þ 2OH ¼ 2CuðCNÞ2 3 þCNO þ H2 O

ð22Þ

The log K values of these two reactions are so large that there is no known complexing agent for Cu(II) that will prevent the reduction of Cu(II) by CN (Flynn and McGill 1995). The rapid decomposition of cupric cyanide results in the oxidation of cyanide which has led to the use of cupric ions as a catalyst to destroy cyanide in wastewaters (Tessier 1989; Chen, You, and Ying 1992; Robbins 1996). RECOVERY PROCESSES The technologies for cyanide recovery from cyanide slurry or solutions can be roughly classified into two categories: direct and indirect recovery processes. As the simplest direct recovery method, directly recycling the barren cyanide solution (after gold recovery) back to the cyanidation process is a common cyanide management


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technology in gold plants if this can satisfy an overall water balance in the operating circuit. In addition, the buildup of species due to the recycling should not deteriorate the gold recovery process. While these requirements can be usually met in a heap leach operation, they may be difficult to be satisfied in most milling operations and a cyanide destruction circuit is usually adopted to dispose of cyanide contaminated slurry=solutions. Other direct recovery technologies include the AVR (Acidification-Volatilization-Regeneration) process and its modifications, such as sulfide-precipitation based processes. The basic principle of indirect recovery technologies is to pre-concentrate valuable metal (mostly subject to copper) cyanide complexes into carbon=resin=solvent from which the loaded copper and cyanide can be further recovered by AVR or similar processes after eluting or stripping. Therefore there is no discrete boundary between these two technology categories. AVR/MNR/SART The AVR (Acidification-Volatilization-Regeneration) process was first developed in the early part of the 20th century (Riveros, Molnar, and McNamara 1993; Stevenson et al. 1998; Fleming 2001). The process concept is relatively simple: the waste cyanide solution is first acidified to weak acidic pH (usually below 4–5 by addition of sulfuric acid) and then brought into contact with high-pressure air. Most of the cyanide is converted to HCN which is volatilized by air and then adsorbed in alkaline solutions to produce aqueous NaCN or Ca(CN)2. The main reactions involved in this process are as follows: 2CN þ H2 SO4 ¼ 2 HCNðaqÞ þ 2 SO2 4

ð23Þ

HCNðaqÞ þ air ¼ HCNðgÞ

ð24Þ

HCNðgÞ þ NaOH ¼ NaCN þ H2 O

ð25Þ

The cyanide-free solution then passes through a neutralization step to precipitate the heavy metals (Riveros et al. 1993). The CyanosorbTM process is a variation of the AVR process which uses the same principle to treat waste cyanide pulps instead of the clear solutions (Stevenson et al. 1998). In these processes, copper is precipitated as copper cyanide (CuCN) during the acidification stage. 2 CuðCNÞ2 3 þ H2 SO4 ¼ CuðCNÞðsÞ þ 2HCN þ SO4

ð26Þ

The precipitate CuCN is an unsaleable product which also contains valuable cyanide. Furthermore, in the presence of iron cyanides, the precipitation of Prussian-blue type compounds (with the general formulae as Me2Fe(CN)6 H2O, where Me may be Cu, Ni, Zn, or Fe (II)) may also take place. These results in a significant loss of copper reported to the effluent (Flynn and McGill 1995). The AVR process was undertaken for cyanide recycle at Flin Flon (Canada) since 1930s and was abandoned after 1975, probably due to the high operation cost, especially substantial reagent (acid and base) consumption and energy required by air sparging. It was believed that the process may be applied economically to effluent solutions



395

containing a total of >150 mg=L of cyanide, but in case of low cyanide concentration in the tailings, it was generally considered to be unsuitable for producing a final solution for discharge because of the high cost of reducing the cyanide concentration down to the required control levels (Marsden and House 1992). In order to recover valuable copper from waste cyanide solutions, some modified AVR processes have been developed. The MNR process developed by Metallgesellschaft Natural Resources involves a solid=liquid separation process to obtain a clarified cyanide solution, to which water-soluble sulfide compounds (NaSH or Na2S) are added to precipitate base metals, mainly subject to copper (Potter, Bergmann, and Haidlen 1986). The solution is then acidified to pH < 5 by the addition of sulfuric acid. The copper sulfide precipitate is recovered by filtration. The acidification and sulfidization reaction of copper cyanides is presented below: 2Na3 CuðCNÞ4 þ 3:5 H2 SO4 þ NaSH ¼ Cu2 S þ 3:5 Na2 SO4 þ 8HCN ðaqÞ

ð27Þ

The precipitation of cuprous sulfide (synthetic chalcocite) is favored due to its extremely low solubility. This reaction is irreversible at pH < 5 and takes place quantitatively with stoichiometric additions of sulfide ions and acid. Other base metals present in the solution will also co-precipitate (Dreisinger, Ji, and Wassink 1995; Barter et al. 2001). The neutralization step may be performed directly on the acidified solutions (after filtration of copper sulfide) or may be linked to a volatilization step. The hydrogen cyanide gas generated in the acidification process is volatilized and reabsorbed in an alkaline solution. The SART (Sulfidization=Acidification— Recycling—Thickening) process is based on the same theory as that of MNR (Figure 4). The feed solution is first acidified by the addition of sulfuric acid (typically pH 4–5) and metals are precipitated with the addition of sulfide ions. Rather than by direct filtration in the MNR process, a combination of thickening and filtration is adopted by the SART process to recover copper sulfide precipitate. The process has been successfully practiced at Telfer Gold Mine in Australia, but it only operated in full-scale for a few months (MacPhail, Fleming, and Sarbutt 1998; Dreisinger et al. 2001; Barter et al. 2001). In the BioteQ process, biogenic H2S

Figure 4 Simplified flowsheet of the SART process.

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F. XIE ET AL.


gas, rather than soluble sulfide salts, is employed to precipitate copper from cyanide solutions. It was reported that several commercial plants, implementing BioteQ’s BioSulfide and ChemSulfide processes for treating acid mine drainage, have been developed (Adams, Lawrence, and Bratty 2008). The concerns involved in sulfide-precipitation based process include: the species buildup in the re-circulating solution phase (same to that in the direct recycling of the barren solution to cyanidation) since iron cyanides and thiocyante are not precipitated; the co-precipitation of other metals (such as ZnS) may potentially decrease the grade and quality of Cu2S precipitate which is supposed to be sold as the feed to a copper smelter. Activated Carbon Activated carbon is a generic term for a broad range of amorphous, carbon-based materials, prepared so as to exhibit a high degree of porosity and a large associated surface area. Due to the particular affinity of gold and silver cyanide to adsorption, activated carbon has been extensively used in the gold recovery process in the past decades. Since activated carbon can act both as an adsorbent and a catalyst for the oxidation of cyanide, it has also been suggested for recovery of cyanide and metal-cyanide species from waste cyanide solution. An early technology was the Calgon process which employed columns packed with granular activated carbon to recover cyanide and metals from waste cyanide solution (Bernardin 1976; Hoffman 1973). In order to increase the kinetics of cyanide oxidation on the carbon, cupric ions and oxygen were added to the cyanide wastewaters before feeding them into the treatment system. The use of activated carbon as a modification for the AVR process, to remove metal and cyanide, has also been proposed (Adams 1994; Batzias and Sidiras 2001; Adams et al. 2008). Since plain carbon adsorption is not efficient at removing free cyanide from the effluents, modification and impregnation technologies, such as Al, Cu, Ag and Ni, impregnated activated carbons have been developed (Manktelow, Paterson, and Meech 1984; Adams 1994; Williams 1997; Adhoum and Monster 2002; Deveci et al. 2006). It was suggested that the following reactions might occur on the surface of the impregnated activated carbon when the metal ion such as Agþ or Niþ was added: Agþ þ COOH ¼ COOAg þ Hþ

ð28Þ

Niþ þ COOH ¼ COONi þ Hþ

ð29Þ

where, -COOH represents the acidic carboxyl functional group present on the carbon surface. It was reported that the adsorption capacity and the feasible removal rates of cyanides were substantially boosted since they were not only removed by adsorption on the surface of the plain carbon, but could also be removed by those 2 added chemicals (for example, by forming AgðCNÞ 2 and NiðCNÞ4 on the surface). While conducting the column studies, Adhoum and Monster (2002) found that the maximum cyanide removal capacity of the plain and silver-impregnated activated carbons was 7.1 mg=g and 26.5 mg=g, respectively. Activated carbon has been also proposed for copper and cyanide recovery from gold mill effluents (Breuer, Jeffrey, and Dai 2005; Dai and Breuer 2009, Dai,


397


Jeffrey, and Breuer 2010a, 2010b). Though activated carbons usually exhibit good affinity for gold and silver cyanide complexes (AuðCNÞ 2 and AgðCNÞ2 ), they have a much lower capability on adsorption of copper from cyanide solutions since cop3 per mainly occurs as CuðCNÞ2 3 or CuðCNÞ4 in alkaline cyanide solution (if cyanide 2 3 is not depleted). CuðCNÞ3 or CuðCNÞ4 has a much weaker affinity for carbons, probably due to their strong hydrophilic characteristics. Thus, the metallic copper is used to first complex the free cyanide in the solution and concurrently convert CuðCNÞ3 and the majority of CuðCNÞ2 to CuðCNÞ 4 3 2 which can be readily absorbed by the carbon (Dai et al. 2010a, 2010b). The copper cyanide can then be recovered by a carbon elution process. Ion Exchange Resin The commercial scale application of ion exchange resins in the gold mining industry was well established in the former Soviet Union in the 1970s and more research and investigations on the fundamental and practical aspects of ion exchange resin technologies on gold cyanidation have been conducted since then (Fleming and Cromberge 1984a, 1984b; Bolinski and Shirley 1996; Seymore and Fleming 1989). Ion exchange resins also present a possible alternative for the treatment of waste cyanide effluents. As early as the 1950s, Walker and Zabban (1953) developed a bench scale ion exchange resin process to concentrate cyanide from the aqueous waste streams, produced in electroplating operations. Goldblatt (1956, 1959) first developed an ion exchange resin process to recover cyanide and copper from the waste cyanide effluents arising from the Stilfontein Gold Mine’s cyanidation operations. The strong base ion exchange resin, Amberlite IRA-400 (Rohm & Haas), was applied to remove cyanide and metals from the recycled water containing CN, SCN, Zn, Ni, Co, and Cu. The system comprised of two adsorption columns. The metal cyanide complexes were removed in the first column. The effluent was then forwarded to the second column containing ‘‘CuCN-conditioned’’ resins where the remaining free cyanide was removed as copper cyanide. The treated effluent was returned to the leaching tanks. Both columns were then eluted with 1% H2SO4 solution. CN was converted to HCN and recovered as NaCN. The acid solution was then contacted with a strong acid resin, IR-120 (Rohm & Haas), to remove dissolved metals. After several adsorption=elution cycles, copper cyanide (CuCN) was found to accumulate in the resin, causing a reduction in its exchange capacity. This solid was further removed as a soluble complex by elution with a ferric sulfate solution. Two typical resin technologies for recovery of copper from cyanide solutions are the AuGMENT process and the Vitrokele process, in both of which strong base resins were used to recover metals and cyanide from cyanide solutions. The use of guanidine-based resin to extract metals from gold leachate was also reported (Kordosky et al. 1993; Jermakowicz and Kolarz 2002). AuGMENT process. The AuGMENT process was developed by SGS Lakefield Research and the DuPont Corporation in which strong base resin (quaternary amine functionality) was used to recover and pre-concentrate copper cyanide from gold-plant tailings (Le Vier et al. 1997; Fleming 1998; Fleming, Grot, and Thorpe 1998; Fleming 2005). The chemistry involved in the various unit operations was

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based on the formation of different copper cyanide complexes as the cyanide to copper molar ratio was varied. CuCN precipitated resin was used as the adsorbent for the adsorption of free cyanide and soluble copper cyanide. The adsorption step was carried out with a barren solution containing a cyanide to copper molar ratio (CN=Cu) of at least four. It was believed that during adsorption, CuðCNÞ2 3 or a higher complex reacted with CuCN producing CuðCNÞ which allowed the 2 maximum copper loading (60–80 g=L resin) to be achieved. The loading mechanism can be described by the following equation: 2 2 2R SO2 4 ðCuCNðsÞ Þ þ CuðCNÞ3 þ 2CN ¼ 3R CuðCNÞ2 þ R CN þ SO4

ð30Þ where, R represents the resin matrix and functional group. Once loaded, the copper cyanide species were eluted from the resin using a concentrated copper cyanide solution having a cyanide to copper molar ratio of approximately four, which converted 2 CuðCNÞ 2 to CuðCNÞ3 . The elution process can be described as: 2 2 2R CuðCNÞ2 þ CuðCNÞ2 3 þ 2CN ¼ R CuðCNÞ3 þ CuðCNÞ3

ð31Þ

Finally the resin was regenerated via conversion to the CuCN form with sulfuric acid. The eluate was submitted to electrowinning to produce copper cathodes. Gold has to be recovered prior to copper electrowinning and cyanide recovery. Cyanide can also be recovered via AVR circuit where the copper cyanide is precipitated and re-dissolved in the loaded catholyte ahead of the electrowinning circuit. One potential disadvantage of the processes is that the precipitated CuCN may block the resin pores, decreasing the opportunity for additional metal cyanide complexes to be adsorbed into the resin. If cobalt is present in the effluent, the possible polymerization of adsorbed cobalt cyanide complexes under strongly acidic conditions will poison the resins (Goldblatt 1959; Leaõ, Ciminelli, and Costa 1998; Jay 2001). Vitrokele process. The resin used in the Vitrokele process is based on a highly cross-linked polystyrene structure (VitrokeleTM 911 and 912, which probably have the quaternary amine functionality) (Jay 2001). The loaded resins were eluted with the strong cyanide eluant to recover copper cyanide species. Precious metals and other strong bound metal cyanide complexes (if present) were ‘‘crowded’’ from the resins with tetracyanozincate (ZnðCNÞ2 4 ). Sulfuric acid was used in the last elution cycle to destroy most of the cyanide complexes to regenerate the resins (Whittle 1992). The chemistry involved in the process can be described as follows: Loading: ðR NCH3 Þ2 SO4 þ 2 ½AuðCNÞ2 ¼ 2 R NCH3 AuðCNÞ2 þ SO2 4

ð32Þ


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Stripping: 2R NCH3 AuðCNÞ2 þ ZnðCNÞ2 4 ¼ ðR NCH3 Þ2 ZnðCNÞ4 þ 2 AuðCNÞ2 ð33Þ

Regeneration:


ðR NCH3 Þ2 ZnðCNÞ4 þ H2 SO4 ¼ ðR NCH3 Þ2 SO4 þ ZnSO4 þ 4HCNðgÞ ð34Þ This process has been successfully applied for treating the heap leachate at the Connemara Mine in Zimbabwe (Satalic, Spenser, and Paterson 1996). It was also tested at May Day Mines (Cobar, Australia) from July 1997 to June 1998 (DeVries 2001). However, some technical problems developed during the operation of the process resulted in the abandonment of the Vitrokele process at the Mines. One of the major problems was that the elution of copper from the resin was not effective. Similar to the AuGMENT process, the reaction between the residual copper cyanide in the resin with the eluant (H2SO4) led to the formation of CuCN, which passivated the active sites on the resin surface. Cognis AuRIX resin. The AuRIX resin is a weak base ion exchange resin developed by Cognis for the recovery of precious metals (gold and silver) from gold cyanide leachate (Kordosky et al. 1993). It is a typical styrene-divinylbenzene resin bead functionalized with a guanidine functional group. Guanidines are very strong organic bases having an intermediate basicity between that of primary amines and quaternary amines. Each of them exhibits a pKa of approximately 12 and is capable of being protonated to form a guanidinium cation at the operating pH of the gold leachate (usually 10–11). This guanidinium cation can form an ion-pair with aurocyanide, resulting in gold extraction from the cyanide solution. By increasing the basicity of the aqueous phase, the guanidinium cation is converted to the neutral guanidine functionality. The neutral guanidine functionality no longer forms an ion-pair with aurocyanide, resulting in gold stripping from the resin. Ideally, the extraction of Au(I) from cyanide solution by the resin can be described by the following equations: R G þ H2 O ¼ R GHþ OH

ð35Þ

R GHþ þ AuðCNÞ2 ¼ R GHþ AuðCNÞ 2

ð36Þ

Overall reaction: þ R G þ H2 O þ AuðCNÞ 2 ¼ RGH AuðCNÞ2 þ OH

ð37Þ

where, R-G represents the function group of the resin and R-GHþ represents its protonated form (Virnig and Wolfe 1996). Selectivity. The selectivity of resins for different metal cyanide complexes is dependent on the chemical features of both, the resins and the complexes, including the charge of complex, hydrophobic=hydrophilic characters of the resin, type of matrix, and also, the steric effects, such as the alkyl chain length of the functional


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group (Riveros 1993; Leaõ et al. 2001a, 2001b). Generally, a low degree of hydrophilicity and a low ionic density increase the affinity of a resin for lower charged metal cyanide complexes, such as AuðCNÞ 2 and AgðCNÞ2 , and a high degree of hydrophilicity and a high ionic density increase the resin selectivity for multivalent hydrated 4 ions, such as CuðCNÞ3 4 and FeðCNÞ6 . For example, polystyrene weak-base resins such as Dowex MWA-1 and Amberlite IRA-93 present an attractive environment for AuðCNÞ 2 since they have a relatively hydrophobic character on account of their polystyrene matrix, and the tertiary amine groups are not ionized in an alkaline medium. Thus, a selectivity order of Au > Zn > Ni > Cu > Fe for these resins was observed when they were used for adsorption of metal cyanides from alkaline cyanide solutions. On the contrary, the affinity of a strong base resin, Amberlite IRA-458, for metallocyanide complexes is Zn > Fe > > Cu, Ni > Au. This is probably because the polyacrylamide structure of Amberlite IRA-458 has a strong hydrophilic character due to the presence of carbonyl and secondary amine groups, which can interact strongly with the water molecules, resulting in a significant low adsorption of AuðCNÞ 2 . It was observed that both the strong base resins, the Imac HP555s, which have a polystyrene–divinylbenzene matrix containing triehylammounium group, load predominantly the CuðCNÞ2 3 complex. In contrast, Amberlite IRA958, the polyacrylic resin containing the trimethylammounium functionality, sorbed signifi3 cant amounts of both CuðCNÞ2 ˜ o et al. 1998; Leaõ, Costa, 3 and CuðCNÞ4 (Lea and Ciminelli 2000; Lucky et al. 2000a; Lu, Dreisinger, and Cooper 2000b; Leaõ et al. 2001a, 2001b). The impurities in the aqueous phase may significantly affect the adsorption capability and selectivity of ion exchange resins. It was reported that in highly saline solutions, only CuðCNÞ2 3 forms predominately when the molar ratio 2 of cyanide to copper is 2.2–2.5, where both CuðCNÞ 2 and CuðCNÞ3 will occur in non-saline solutions according to the speciation calculation (Luckey et al. 1999a, 1999b). In the presence of an excess of cyanide in highly saline solutions, copper only 2 occurs as CuðCNÞ3 4 and the formation of CuðCNÞ3 has not been observed. Thus, the selectivity of ion exchange resins for copper and other metal cyanide complexes in highly saline solutions may be significantly different from that in non-saline solutions (Luckey et al. 1999a; Luckey, Van Deventer, and Shallcross 2000). Solvent Extraction Solvent extraction has been successfully practiced in the recovery processes of many metals, such as uranium, copper and nickel. The use of solvents for purification and concentration of gold from cyanide solutions has been long of interest, but has never been practiced commercially. More technical papers emerged after the findings that the selective extraction of cyano-anions could be accomplished by addition of modifiers, for example, organophosphorous compounds, to weak base extractants such as primary, secondary and tertiary amines, which make it possible to effectively extract gold cyanide in alkaline conditions (Miller and Mooiman 1984; Mooiman and Miller 1986). Villaverde and Martin (1995) examined the feasibility of solvent extraction of gold and silver from the Gossan barren dam waters originated from gold cyanidation process. Different extraction solvents including Primene (ATP, a primary commercial amine), TBP (Tributylphosphate), and Cyanex (general formula C24H51OP), and their combinations were investigated. They



401

suggested that it was possible to separate and concentrate gold, and to a lesser extent silver and copper, by means of solvent extraction with the synergistic extractant, Cyanex þ ATP. The waste dam water could be treated directly at pH 9 and overall, 90% gold recovery could be achieved under optimum conditions. Solvent extraction of zinc and cadmium from alkaline cyanide solutions by quaternary amines (Aliquat 336 and Adogen 464) was examined by Moore (1975) and Moore and Groenier (1976). Riveros et al. (1990) have even run a small pilot plant to demonstrate the potential application of quaternary amines (Aliquat 336 dissolved in Solvesso 150) for recovery of gold from cyanide leachate. However, the big challenge for using quaternary amines to recover metal cyanides is the stripping of the loaded metal cyanide complexes. Since the extraction of metal cyanide complexes is still very high at a high pH, it will be difficult to remove the loaded metals by simply varying solution pH (Alonso-Gonzalez et al. 2010; Moore 1975; Moore and Groenier 1976). It was reported that sodium hypochlorite (NaClO) and formaldehyde (HCNO) can strip the loaded zinc and cadmium cyanide complexes efficiently. Alternatively, the strong NaOH solution (as high as 12 mol=L) has to be used to strip the loaded cadmium from the solvent loaded with 0.025 mol=L of Aliquat 336 (Moore 1975; Moore and Groenier 1976). Later, LIX 7800 series extractants (the mixture of quaternary amine Aliquat 336 and nonylphenol with different molar ratios) were developed by Cognis and were proposed for extraction of metals from cyanide solutions (Mattison and Virnig 2001). It was believed that the presence of nonylphenol in the solvent mixture could render the extraction capability of Aliquat 336 pH-dependent. The extraction and stripping of copper cyanide complexes by the solvent mixture of quaternary amine and nonylphenol can be expressed as follows (Davis et al. 1998): ðQþ X Þorg þ ðHPÞorg þ OH ¼ ðQþ P Þorg þ X þ H2 O

ð38Þ

where, Qþ denotes the quaternary ammonium cation; HP denotes the protonated form of the nonylphenol; and X, the extracted anion (Mattison and Virnig 2001). Under low pH conditions, nonylphenol is protonated and the quaternary ammonium compounds extract an anion from the aqueous phase. Under more highly alkaline conditions, nonylphenol starts to be significantly converted to the highly hydrocarbon-soluble phenoxide anion (P) and forms an ion pair with the quaternary ammonium cation (QþP). Consequently the extracted anion will be gradually expelled to the aqueous phase with increasing equilibrium pH. After the introduction of AURIXTM 100 ion exchange resin by Cognis, the solvent product with the similar functionality, LIX 79, a tri-alkylguanidine extractant was also developed (Kordosky et al. 1992; Virnig and Wolfe 1996). Guanadine extractants were also proposed for recovery of copper from alkaline copper cyanide solutions (Dreisinger et al. 1995; Dreisinger et al. 1996; Dreisinger et al. 2001; Dreisinger et al. 2002). The use of the guanadine extractant, LIX 7950, which is also based on formulation of an alkylguanidine but has a higher concentration of guanidine and shows a higher basicity, for recovery of copper from copper cyanide solutions, has been studied extensively (Xie and Dreisinger 2008; Xie and Dreisinger 2009a; Xie and Dreisinger 2010). Following the same principle as AURIX resins,

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the guanidine functional group undergoes protonation to form guanidinium cation, when in contact with an aqueous solution. The guanidinium cation can form an organic soluble ion pair with the anions in the aqueous phase, resulting in their extraction. RGorg þ H2 O ¼ RGHþ OH org

ð39Þ

2 2 þ 2RGHþ OH org þ CuðCNÞ3 ¼ ðRGH Þ2 CuðCNÞ3org þ 2OH

ð40Þ


Overall reaction: 2 þ 2RGorg þ H2 O þ CuðCNÞ2 3 ¼ ðRGH Þ2 CuðCNÞ3org þ 2OH

ð41Þ

where, RGorg represents the extractant molecule in the organic phase and RGHþ org , its prononated form (Virnig and Wolfe 1996; Xie and Dreisinger 2009a). The extractant allows the extraction of copper at a lower pH (e.g., pH < 10) and the loaded copper can be stripped off with strong basic solutions. Some information of two typical extractants, LIX 79 and Aliquat 336 is summarized in Table 3 (Kordosky et al. 1992; Mattison and Virnig 2001). It was reported that for both extractants, LIX 7950 and LIX 7820, low equilibrium pH favors the extraction of copper and cyanide and a high CN=Cu molar ratio depresses the loading of copper and cyanide (Figures 5 and 6) (Xie and Dreisinger 2009a; Xie and Dreisinger 2009b; Xie and Dreisinger 2009c; Xie and Dreisinger 2010). Their research also confirmed that CuðCNÞ2 ion is preferentially 3 extracted over CuðCNÞ3 4 and CN by both extractants. Solvent extraction of the mixture of metal cyano complexes exhibits a selectivity order, which is as follows: Zn > Ni > Cu > Fe. Cyanide is only extracted as complexed cyanide and virtually all the free cyanide remains in the aqueous phase which allows for the potential recycling of the barren solution to the cyanidation process. The schematic flowsheet of solvent extraction of copper from cyanide solutions is shown in Figure 7. The selectivity sequence of metal cyanide complexes in the organic solvent has been explained Table 3 Some information on LIX1 79 and Aliquat1 336

Molecular formula Molecular weight, g=mol Specific gravity (25 C) Schematic structure

N: No information available.

LIX1 79

Aliquat1 336

N N 0.80–0.85

C25H54ClN 404.16 0.884



403

Figure 5 The effect of CN=Cu ratios on copper extraction with LIX 7950 (Org: 10% v=v LIX 7950 and 50 g=L 1-dodecanol in n-dodecane, aq: [Cu] ¼ 3.93 103 mol=L; A=O ¼ 1; 25 C; after Xie and Dreisinger 2009a) (color figure available online).

qualitatively in terms of the degree of hydration of the anions, charge and size effect (or charge density), and geometric factors (Irving and Damodaran 1971; Miller and Mooiman 1984; Mooiman and Miller 1986; Yin et al. 2011). Generally, due to charge density effect, for the same central bonding metal, e.g., Cu, the lower charged metal cyano complexes, CuðCNÞ2 are extracted preferentially over the higher 3 charged complexes, CuðCNÞ3 ; for same charged complexes, those complexes with 4 lower coordination numbers are extracted preferentially over those with higher coor2 dination numbers (e.g., ZnðCNÞ2 3 > CuðCNÞ3 (Riveros et al. 1990). The SCN ions present may potentially compete for the available extractant with copper

Figure 6 The effect of CN=Cu ratio on copper extraction with LIX 7820 (Org: 2% LIX 7820 in n-octane, aq: [Cu] ¼ 3.93 103 mol=L; A=O ¼ 1; 20 C; after Xie and Dreisinger 2009b).


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Figure 7 Schematic flowsheet of solvent extraction of copper from cyanide solutions.

cyanide species during the extraction, and copper extraction decreases significantly with an increase of the SCN content in the solution (Xie and Dreisinger 2009a). According to reaction (1) and (2), the formation of thiocyante is inevitable during cyanide leaching if copper sulfide minerals are present in the gold ore. Additional extraction=stripping processes may have to be adopted to remove the thiocyanate from the organic solvent before they are recycled to the extraction stage.

Miscellaneous Soto, Nava, and Jara (1997) developed a method by adjusting solution pH to recover cyanide and copper from cyanide solutions containing copper and thiocyanate. Copper was first precipitated as copper thiocyanate (CuSCN) or as copper cyanide (CuCN) depending on pH and the concentration of thiocyanate and cyanide in the effluent. The precipitates then could be separated from the effluent by filtration after settling. Further, recovery process was needed to extract copper from the precipitate. The decant solution and the filtrate containing the bulk of the cyanide were then oxidized with ozone to transform the remaining thiocyanate into cyanide. Cyanide was not oxidized by ozone under the adopted conditions. The regenerated solution, rich in free cyanide, was recycled to the cyanidation process. Recovery of over 96% copper and cyanide were reported in their laboratory tests. The biosorption process of metal-cyanide complexes, tetracyanocuprate (II), CuðCNÞ2 4 , and tetracyanonickellate (II), NiðCNÞ2 , from waste cyanide solutions by using different 4 fungal cultures, was studied (Patil and Paknikar 1998; Natarajan, Subramanian, and Modak 1999). It was found that the biomaterials tested in the study showed high value of metal uptake from cyanide effluent, particularly for gold and zinc. The fungi (C. Cladorporioides) showed maximum loading capacity of 40 mmol=g CuðCNÞ2 4 or 34 mmol=g NiðCNÞ2 and 1 mol=L sodium hydroxide was effective to remove the 4 bound metal-cyanide species. HW Process Technologies Inc. (HWPT) developed a membrane-based ion fractionation system, which specifically separated copper from gold and silver species in a cyanide matrix (Lombardi and Bernard 2001). It was reported that this Engineered Membrane Separation technology combined pore-size



405

specific, electrostatically charged membranes with engineered materials of construction and application-specific operational design that rejected multivalent ionically 3 charged species (such as CuðCNÞ2 3 and CuðCNÞ4 ) to the concentrate and trans mitted monovalent species (such as AuðCNÞ2 and AgðCNÞ 2 ) through the membrane to the permeate. Lu, Dreisinger, and Cooper (1999, 2002a, 2002b) developed a membrane-electrolysis cell with graphite felt to recover copper and recycle the cyanides. Copper recoveries up to 60% were achieved with an energy consumption of 1–2 kWh=kg, which is quite close to those encountered in electrowinning copper from sulfate solutions. When using sulfite as the alternate anodic species in the non-membrane cell, copper was electrowon from a cyanide electrolyte containing 70 g=L Cu (CN=Cu ¼ 3) and 0.5 mol=L Na2SO3 at a cathode current efficiency of 95%, with an energy consumption of about 0.8 kWh=kg Cu. The process has been suggested as a subsequent process for treating eluants or stripping solutions from copper pre-concentration step by ion exchange resin or solvent extraction. SUMMARY The mainstream technology for leaching gold from gold ore is still leaching in aqueous alkaline cyanide solution. The presence of copper minerals in the gold ore may result in a significant economical penalty in excessive cyanide consumption and loss of valuable copper in the tails. Several technologies are now available for the recovery of copper and cyanide from gold-plant solutions or slurry, but none of them has yet found its way to practical application. The main drawback associated with the AVR=MNR=SART process appears to be the high operational cost—the reagents (acid and base) and the energy required to strip HCN by air sparging. Indirect recovery technologies through activated carbon, ion-exchange resins, and solvent extraction have been studied extensively. The basic principle of these technologies is to pre-concentrate valuable metal (copper) cyanide complexes into a small volume of eluant or stripping solution. The copper and cyanide in the resulted solutions can be further recovered by AVR, SART, or electrowinning process. For those gold cyandiation plants where activated carbon is already used for extraction process (CIP=CIL, carbon-in-pulp=carbon-in-leaching), the use of activated carbon for treating cyanide effluent would be simple since it is convenient for installation on-site. However, the adsorption capability of activated carbons for copper cyanides is much lower than those for gold=silver cyanides. Their adsorption capacity for free cyanide is also poor (even for those pre-impregnated carbons). Therefore, they are more suitable for use in a polishing process to remove cyanide to low levels when initial cyanide concentration is already low (for example, 1–5 mg=L) (Botz and Mudder 1997; Fleming 2005). Ion exchange resins offer certain advantages over activated carbon. They are less easily poisoned by organic matter and can usually be eluted at room temperature, and selectivity for particular metals can be achieved by the choice of the functional group incorporated into the bead or by the selective elution process. The main drawback associated with resin technologies is their high operational cost which has severely hampered their widespread application. While carbon and ion exchange resin processes can be operated with both slurry and solution feeds, solvent extraction technologies need a clarified feed solution. The process can operate through continuous stages if the extraction and stripping of

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copper cyanides can be realized by simply adjusting pH. For operations using carbon-in-pulp (CIP) for the recovery of gold, it will be necessary to thicken and wash the solids in order to produce a clarified feed solution for SX circuit. For treating heap leaching solutions, overflow stream or dam return water from tailings, this probably will not be a limitation. Other recovery technologies, such as biosorption and direct electrowinning, have also been proposed; however they are yet to find their way to practical application.


REFERENCES Adams, M. D., 1994, ‘‘Removal of cyanide from solution using activated carbon.’’ Minerals Engineering, 7, pp. 1165–1177. Adams, M. D., Lawrence, R., and Bratty, M., 2008, ‘‘Biogenic sulfide for cyanide recycle and copper recovery in gold-copper ore processing.’’ Minerals Engineering, 21, pp. 509–517. Adhoum, N. and Monster, L., 2002, ‘‘Removal of cyanide from aqueous solutions using impregnated activated carbon.’’ Chemical Engineering and Processing, 41, pp. 17–21. Alonso-Gonzalez, O., Nava-Alonso, F., Uribe-Salas, A., and Dreisinger, D., 2010, ‘‘Use of quaternary ammonium salts to remove copper-cyanide complexes by solvent extraction.’’ Minerals Engineering, 23, pp. 765–770. Aylmore, M. G. and Muir, D. M., 2001, ‘‘Thiosulfate leaching of gold-A review.’’ Minerals Engineering, 14, pp. 135–174. Barter, J., Lane, G., Mitchell, D., Kelson, R., Dunne, R., Trang, C., and Dreisinger, D., 2001, ‘‘Cyanide management by SART.’’ In Cyanide: Social, Industrial and Economic Aspects, pp. 549–562, Warrendale, PA: TMS. Batzias, F. A. and Sidiras, D. K., 2001, ‘‘Wastewaters treatment with gold recovery through adsorption by activated carbon.’’ Water Pollution VI, International Series on Progress in Water Resources, 3, pp. 143–152. Bek, R. Y. and Zhukov, B. D., 1973, ‘‘Electrodeposition of copper from cyanide electrolytes, Part II: Formation constants for copper cyanide complexes.’’ IZV. Sib. Otd. Akad. Nauk USSR, Ser. Kim. Nauk, 4, pp. 52–56. Bernardin, F. E., 1976, ‘‘Selecting and specifying activated-carbon-adsorption system.’’ Chemical Engineering, 83, pp. 77–82. Bolinski, L. and Shirley, J., 1996, ‘‘Russian resin-in-pulp technology, current status and recent developments.’’ In Proceedings of the Randol Gold Forum ‘96, Squaw Creek, CA, USA, April 21–24, Randol International, pp. 419–423. Botz, M. and Mudder, T., 1997, ‘‘Mine water treatment with activated carbon.’’ In Randol Gold Forum’97, Monterey, CA, USA, May 18–21, pp. 18–21. Botz, M. M., Mudder, T. I., and Akcil, A. U., 2005, ‘‘Cyanide treatment: Physical, chemical and biological process.’’ In Advances in Gold Ore Processing, pp. 672–702, Amsterdam: Elsevier. Breuer, P. L., Jeffrey, M. I., and Dai, X., 2005, ‘‘Leaching and recovery of copper during the cyanidation of copper containing gold ores.’’ In Treatment of Gold Ores, Quebec, Canada: CIM, pp. 279–293. Chen, Y., You, C., and Ying, W., 1992, ‘‘Cyanide destruction by catalytic oxidation.’’ In 46th Purdue Industrial Waste Conference Proceedings, Chelsea, MI, USA, May 14–16, Lewis Publishers Inc., pp. 539–545. Clark, P., Jordan, D. M., and Malloy, T. M., 2001, ‘‘Cyanide Heap Biological Detoxification.’’ In Cyanide: Social, Industrial and Economic Aspects, Proceedings of a Symposium held at Annual Meeting of TMS, February 11–15, Warrendale, PA, USA: TMS, pp. 237–251.



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Dai, X. and Breuer, P. L., 2009, ‘‘Cyanide and copper cyanide recovery by activated carbon.’’ Minerals Engineering, 22, pp. 469–476. Dai, X., Jeffrey, M. I., and Breuer, P. L., 2010a, ‘‘Comparison of activated carbon and ion-exchange resins in recovering copper from cyanide leach solutions.’’ Hydrometallurgy, 101, pp. 48–57. Dai, X., Jeffrey, M. I., and Breuer, P. L., 2010b, ‘‘A mechanistic model of the equilibrium adsorption of copper cyanide species onto activated carbon.’’ Hydrometallurgy, 101, pp. 99–107. Davis, M. R., MacKenzie, M. W., Sole, K. C., and Virnig, M. J., 1998, ‘‘A proposed solvent extraction route for the treatment of copper cyanide solutions produced in leaching of gold ores.’’ In Alta Copper Hydrometallurgy Forum, Brisbane, Australia. Deveci, H., Yazici, E. Y., Alp, I., and Uslu, T., 2006, ‘‘Removal of cyanide from aqueous solutions by plain and metal-impregnated granular activated carbons.’’ International Journal of Mineral Processing, 79, pp. 198–208. DeVries, F., 2001, ‘‘Brief overview of the Baia Mare Dam Breach.’’ In Cyanide: Social, Industrial and Economic Aspects, Warrendale, PA: TMS, pp. 11–14. Dreisinger, D. B., Wassink, B., De Kock, F. P., and West-Sells, P., 1996, ‘‘Solvent extraction and electrowinning recovery of copper and cyanide—Recent developments.’’ In Randol Gold Forum ’96, Squaw Creek, CA, USA, April 21–24, pp. 315–319. Dreisinger, D., Ji, J., and Wassink, B., 1995, ‘‘The solvent extraction and electrowinning recovery of copper and cyanide using XI7950 extractant and membrane cell electrolysis.’’ In Randol Gold Forum ’95, Perth, Australia, pp. 239–244. Dreisinger, D., Wassink, B., Lu, J., De Kock, F., Ji, J., West-Sells, P., and Dunne, R., 2001, ‘‘Solvent extraction recovery of copper cyanide from spent gold mill effluents.’’ In Cyanide: Social, Industrial and Economic Aspects, Proceedings of a Symposium held at Annual Meeting of TMS, February 11–15, Warrendale, PA, USA: TMS, pp. 347–360. Dreisinger, D., Wassink, B., Ship, K., King, J., Hames, M., and Hackl, R., 2002, ‘‘Cyanide recovery by solvent extraction.’’ In International Solvent Extraction Conference, Cape Town, South Africa: South African Institute of Mining and Metallurgy, pp. 798–803. Elsner, L., 1846, ‘‘Observation on the behavior of pure metals in an aqueous solution of cyanide.’’ German Journal Fu¨r Praktische Chemie, 37, pp. 441–446. Fleming, C. A., 1998, ‘‘The potential role of anion exchange resins in the gold industry.’’ In EPD Congress, San Antonio, TX, USA, February 16–19, TMS Annual Meeting, pp. 95–118. Fleming, C. A., 2001, ‘‘The case for cyanide recovery from gold plant tailings – positive economics plus environmental stewardship.’’ In Cyanide: Social, Industrial and Economic Aspects, Proceedings of a Symposium held at Annual Meeting of TMS, February 11–15, Warrendale, PA, USA, pp. 271–288. Fleming, C. A., 2005, Cyanide Recovery: Advances in Gold Ore Processing, pp. 703–727, Amsterdam: Elsevier. Fleming, C. A., Grot, W. G., and Thorpe, J. A., 1998, ‘‘Hydrometallurgy extraction process.’’ US Patent 5,807,421. Fleming, C. and Cromberge, G., 1984a, ‘‘The elution of auro-cyanide from strong and weak base resins.’’ Journal of the South African Institute of Mining and Metallurgy, 84, pp. 269–280. Fleming, C. and Cromberge, G., 1984b, ‘‘Small scale pilot-plant tests on the resin-in-pulp extraction of gold from cyanide media.’’ Journal of the South African Institute of Mining and Metallurgy, 84, pp. 369–378. Flynn, C. M. and McGill, L. M., 1995, ‘‘Cyanide Chemistry – Precious Metals Processing and Waste Treatment: Bureau of Mines.’’ US Patent (9429).


408

F. XIE ET AL.

Goldblatt, E., 1956, ‘‘Recovery of cyanide from waste cyanide solution by ion exchange.’’ Industrial and Engineering Chemistry, 48, pp. 2107–2114. Goldblatt, E., 1959, ‘‘Recovery of cyanide from waste cyanide solution by ion exchange.’’ Industrial and Engineering Chemistry, 51, pp. 241–246. Goode, J. R., McMullen, J., Wells, J. A., and Thomas, K. G., 2001, ‘‘Cyanide and the Environment: Barrick Gold Corporation’s Perspective.’’ In Cyanide: Social, Industrial and Economic Aspects, (C. Young, L. Tidwell, and C. Anderson, Eds.), pp. 12–15, Warrendale, PA: TMS. Griffiths, A., Ahsan, M. Q., Norcross, R., Knorre, H., and Merz, F. W., 1990, ‘‘Process for generating an oxidizing reagent for the treatment of polluted water.’’ US Patent 4,915,849. Hancock, R. D., Finkelstein, N. P., and Evers, A., 1972, ‘‘Stabilities of the cyanide complexes of the monovalent group IB metal ions in the aqueous solutions.’’ Journal of Inorganic and Nuclear Chemistry, 34, pp. 3747–3751. Hedley, N. and Tabachnik, H., 1968, Chemistry of Cyanidation (Mineral Dressing Notes), No. 23, New York: American Cyanamid Company. Helfter, G., May, P. M., and Sips, P., 1993, ‘‘A general method for the determination of copper(I) equilibria in aqueous solution.’’ Journal of the Chemical Society, Chemical Communications, pp. 1704–1706. Hoffman, D. C., 1973, ‘‘Oxidation of cyanides adsorbed on granular activated carbon.’’ Plating, 60, pp. 157–161. Irving, H. M. N. H. and Damodaran, A. D., 1971, ‘‘The extraction of complex cyanides by liquid ion exchangers.’’ Analytica Chima Acta, 53, pp. 267–275. Jay, W. H., 2001, ‘‘Copper cyanide recovery system.’’ In Cyanide: Social, Industrial and Economic Aspects, (C. Young, L. Tidwell, and C. Anderson, Eds.), pp. 317–340, Warrendale, PA, USA: TMS. Jermakowicz-Bartkowiak, D. and Kolarz, B. N., 2002, ‘‘Gold recovery from guanidine resins.’’ Separation Science and Technology, 37(15), pp. 3513–3524. Kordosky, G. A., Sierokoski, J. M., Virnig, M. J., and Mattison, P. L., 1992, ‘‘Gold solvent extraction from typical cyanide leach solutions.’’ Hydrometallurgy, 30(1–3), pp. 291–305. Kordosky, G. A., Kotze, M. H., Mackenzie, J. M. W., and Virnig, M. J., 1993, ‘‘New solid and liquid ion exchange extractants for gold.’’ In Proceedings of XVIII International Minerals Processing Congress, Sydney, Australia: AusIMM, pp. 1195–1203. Kuznetsov, A. M., Maslii, A. N., and Shapnik, M. S., 2002, ‘‘Quantum-chemical study of electroreduction mechanism of copper(I) cyanide complexes.’’ Russian Journal of Electrochemistry, 38, pp. 123–131. Le Vier, K. M., Fitzpatrick, T. A., Brunk, K. A., and Ellett, W. N., 1997, ‘‘AuGMENT Technologies: An update.’’ In Randol Gold Forum, March 18–21, 1997, Monterey, CA, USA, pp. 135–137. Leaõ, V. A., Ciminelli, V. S. T., and Costa, R. S., 1998, ‘‘Cyanide recycling using strong-base ion exchange resins.’’ JOM, 50(10), pp. 66–69. Leaõ, V. A., Costa, R. S., and Ciminelli, V. S. T., 2000, ‘‘Cyanide recycling using ion exchange resins—Application to the treatment of gold-copper ores.’’ In Proceedings of the XXI International Mineral Processing Congress, Rome, Italy: Elsevier, A6, pp. 1–9. Leaõ, V. A., Luckey, G. C., Deventer, J. S. J., and Ciminelli, V. S. T., 2001a, ‘‘The dependence of sorbed copper and nickel cyanide speciation on ion exchange resin type.’’ Hydrometallurgy, 61, pp. 105–119. Leaõ, V. A., Luckey, G. C., Deventer, J. S. J., and Ciminelli, V. S. T., 2001b, ‘‘The effect of resin structure on the loading of copper and iron cyano complexes.’’ Solvent Extraction and Ion Exchange, 19, pp. 507–530. Lombardi, J. A. and Bernard, R., 2001, ‘‘HW Process Technologies Inc’s engineered membrane separation (EMSTM) of copper and gold in cyanide solutions.’’ In Cyanide: Social,



409

Industrial and Economic Aspects, Proceedings of a Symposium held at Annual Meeting of TMS, February 11–15, 2001, Warrendale, PA, USA: TMS, pp. 341–346. Lu, J., 1999, Copper electrowinning from cyanide solutions, Ph.D Thesis, The University of British Columbia. Lu, J., Dreisinger, D. B., and Cooper, W. C., 1999, ‘‘Anodic oxidation of copper cyanide on graphite anodes in alkaline solution.’’ Journal of Applied Electrochemistry, 29, pp. 1161–1170. Lu, J., Dreisinger, D. B., and Cooper, W. C., 2002a, ‘‘Thermodynamics of the aqueous copper-cyanide system.’’ Hydrometallurgy, 66, pp. 23–36. Lu, J., Dreisinger, D. B., and Cooper, W. C., 2002b, ‘‘Copper electrowinning from dilute cyanide solution in a membrane cell using graphite felt.’’ Hydrometallurgy, 64, pp. 1–11. Luckey, G. C., Van Deventer, J. S. J., Chowdhury, R. L., and Shallcross, D. C., 1999a, ‘‘The effect of salinity on the capacity and selectivity of ion exchange resins.’’ Mineral Engineering, 12, pp. 769–785. Luckey, G. C., Van Deventer, J. S. J., Chowdhury, R. L., and Shallcross, D. C., 1999b, ‘‘Raman study on the speciation of copper cyanide complexes in highly saline solutions.’’ Hydrometallurgy, 53, pp. 233–244. Luckey, G. C., Van Deventer, J. S. J., and Shallcross, D. C., 2000, ‘‘Equilibrium model for the sorption of gold cyanide and copper cyanide on trimethylamine ion exchange resin in saline solutions.’’ Hydrometallurgy, 59, pp. 101–113. MacPhail, P. K., Fleming, C. A., and Sarbutt, K. W., 1998, ‘‘Cyanide recovery by the SART process for the Lobo-Marte Project—Chile.’’ In Proceedings—Randol Gold Forum’98, Denver, CO, USA: Randol International, pp. 319–324. Manktelow, S. A., Paterson, J. G., and Meech, J. A., 1984, ‘‘Removal of copper and cyanide from solution using activated carbon.’’ Minerals and the Environment, 6, pp. 5–9. Marsden, J. and House, I., 1992, The Chemistry of Gold Extraction, London: Ellis Horwood Ltd. Mattison, P. and Virnig, M., 2001, ‘‘LIX-7800 series: A new reagent family for reversibly extracting anions from alkaline solutions.’’ In Solvent Extraction for the 21st century. Proceedings of ISEC’99, v.1, Barcelona, Spain, July 11–16, 1999, (M. Cox, M. Hidalgo, and M. Valiente, Eds.), pp. 375–379. Miller, J. D. and Mooiman, M. B., 1984, ‘‘A review of new development in amine solvent extraction systems for hydrometallurgy.’’ Separation Science and Technology, 19, pp. 895–909. Mooiman, M. B. and Miller, J. D., 1986, ‘‘The chemistry of gold solvent extraction from cyanide solution using modified amines.’’ Hydrometallurgy, 16, pp. 245–260. Moore, F. L., 1975, ‘‘Solvent extraction of cadmium from alkaline cyanide solutions with quaternary amines.’’ Environmental Letters, 10(1), pp. 37–46. Moore, F. L. and Groenier, W. S., 1976, ‘‘Removal and recovery of cyanide and zinc from electroplating wastes by solvent extraction.’’ Plating and Surface Finishing, 63(8), pp. 26–29. Natarajan, K. A., Subramanian, S., and Modak, J. M., 1999, ‘‘Biosorption of heavy metal ions from aqueous and cyanide solutions using fungal biomass.’’ In Biohydrometallurgy and the Environment Toward the Mining of the 21st Century, International Biohydrometallurgy Symposium, IBS’99, Process Metallurgy 9B, June 20–23, 1999, Madrid, Spain. Amsterdam: Elsevier, pp. 351–361. Palmer, S. A. K., Breton, M. A., Nunno, T. J., and Sullivan, D. M., 1988, Metal Cyanide Containing Wastes Treatment Technologies, Park Ridge, NJ: Noyes Data Corporation. Potter, G. M., Bergmann, A., and Haidlen, U., 1986, ‘‘Process of recovering copper and of optionally recovering silver and gold by leaching of oxide and sulfide-containing materials with water-soluble cyanides.’’ US Patent 4,587,110. Riveros, P. A., Molnar, R. E., and McNamara, V. M., 1993, ‘‘Alternative technology to decrease the environmental impact of gold milling.’’ CIM Bulletin, pp. 167–171.


410

F. XIE ET AL.

Ritcey, G. R., 2005, ‘‘Tailings management in gold plants.’’ Hydrometallurgy, 78, pp. 3–20. Riveros, P. A., 1993, ‘‘Selectivity aspects of the extraction of gold from cyanide solutions with ion exchange resins.’’ Hydrometallurgy, 33, pp. 43–58. Riveros, P. A., 1990, ‘‘Studies on the solvent extraction of gold from cyanide media.’’ Hydrometallurgy, 24, pp. 135–156. Robbins, G. H., 1996, ‘‘Historical development of the INCO SO2=AIR cyanide destruction process.’’ CIM Bulletin, 89, pp. 63–69. Rothbaum, H. P., 1957, ‘‘The composition of copper complexes in cuprocyanide solutions.’’ Journal of Electrochemical Society, 104, pp. 862–866. Satalic, D., Spenser, P., and Paterson, M., 1996, ‘‘Vitrokele: Commercial application in the gold industry.’’ In Proceedings from AusIMM Conference, Diversity: The Key to Prosperity, March 24–28, 1996, Melbourne, Australia: The Australasian Institute of Mining and Metallurgy, pp. 167–171. Sceresini, B., 2005, ‘‘Gold-copper ores.’’ In Advances in Gold Ore Processing, (M. Adams, Ed.), Amsterdam: Elsevier, pp. 789–824. Senanayake, G., 2004, ‘‘Gold leaching in non-cyanide lixiviant systems: Critical issues on fundamentals and applications.’’ Minerals Engineering, 17, pp. 785–801. Seymore, D. and Fleming, C. A., 1989, ‘‘Golden Jubilee resin-in-pulp plant for gold recovery.’’ In Proceedings of the Randol Gold Forum, 1989, Sacramento, CA, USA, November 10–11, 1989, Randol International, pp. 243–252. Sharpe, A. G., 1976, The Chemistry of Cyano Complexes of the Transition Metals, London: Academic Press. Soto, H., Nava, F., and Jara, J., 1997, ‘‘Cyanide regeneration and copper recovery from cyanide solutions.’’ In Global Exploitation of Heap Leachable Gold Deposits, February 9–13, 1997, TMS Annual Meeting, Orlando, FL, USA: The Mineral, Metal & Materials Society, pp. 151–160. Stevenson, J., Botz, M., Mudder, T., Wilder, A., and Richins, R., 1998, ‘‘Recovery of cyanide from mill tailings.’’ In The Cyanide Monograph, 1st ed., (T. Mudder, M. Botz, and A. Smith, Eds.), London: Mining Journal Books, pp. 241–264. Tessier, R. R., 1989, ‘‘Cyanide removal from waste waters by catalytic oxidation with hydrogen peroxide and copper sulfate catalyst.’’ Canadian Patent CA 1,257,019. Torre, M., Bachiller, D., Mendueles, M., Menendez, C. O., and Diaz, M., 2006, ‘‘Cyanide recovery from gold extraction process waste effluents by ion exchange I. equilibrium and kinetics.’’ Solvent Extraction and Ion Exchange, 24, pp. 99–117. Villaverde, J. A. T. and Martin, P. R., 1995, ‘‘Metals recovery from liquid effluent of Gossan waste.’’ In Proceedings of the International Symposium on Waste Processing and Recycling in Mineral and Metallurgical Industries II, August 20–24, Vancouver, BC, Canada: CIM, pp. 35–46. Virnig, M. J. and Wolfe, G. A., 1996, ‘‘LIX 79: A new liquid ion exchange reagent for gold(I) and silver.’’ In ISEC’96 Proceedings, Value Added through Solvent Extraction, 1, Melbourne, Australia, March 19–23, pp. 311–316. Vladimirova, M. G. and Kakovsky, I. A., 1950, ‘‘The physicochemical constants characteristic of formation and composition of the lowest cuprous cyanide complex.’’ Journal of Applied Chemistry of the USSR, 23, pp. 615–632. Walker, C. A. and Zabban, W., 1953, ‘‘Disposal of plating-room wastes, V, Treatment of cyanide waste solutions by ion exchange.’’ Plating, 40, pp. 269–278. Whittle, L., 1992, ‘‘The piloting of VitrokeleTM for cyanide recovery and waste management at two Canadian gold mines.’’ In Randol Gold Forum, March 25–27, Vancouver, CA, USA: Randol International, pp. 379–384. Williams, N. C. and Petersen, F. W., 1997, ‘‘The optimization of an impregnated carbon system to selectively recover cyanide from dilute solutions.’’ Minerals Engineering, 10, pp. 483–490.



411

Xie, F. and Dreisinger, D., 2008, ‘‘Copper solvent extraction from waste cyanide solution by a solvent mixture of a quaternary amine and nonylphenol.’’ In Proceedings of ISEC 2008, September 15–19, Arizona, USA: CIM, pp. 107–112. Xie, F. and Dreisinger, D., 2009a, ‘‘Recovery of copper and cyanide from waste cyanide solution by LIX 7950.’’ Minerals Engineering, 22, pp. 190–195. Xie, F. and Dreisinger, D., 2009b, ‘‘Recovery of copper and cyanide from waste cyanide solution by LIX 7820.’’ Solvent Extraction and Ion Exchange, 27, pp. 459–473. Xie, F. and Dreisinger, D., 2009c, ‘‘Study on solvent extraction of copper and cyanide from water cyanide solution.’’ Journal of Hazardous Materials, 169, pp. 333–338. Xie, F. and Dreisinger, D., 2010, ‘‘Copper solvent extraction from waste cyanide solution by LIX 7950.’’ Transaction of Nonferrous Metals Society of China, 20, pp. 1136–1140. Yin, X., Opara, A., Du, H., and Miller, J., 2011, ‘‘Molecular dynamics simulations of metal-cyanide complexes: Fundamental considerations in gold hydrometallurgy.’’ Hydrometallurgy, 106, pp. 64–70.

Mineral Processing and Extractive Metallurgy Review: An International Journal A Review on Recovery of Copper and Cyanide From Waste Cyanide Solutions

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