Copper Cyanide Complexes Research Articles

A new strategy for extraction of copper cyanide complex ions from cyanide leach solutions by ionic liquids

Copper cyanide complexes in cyanide leach solutions deteriorate the recoveries of gold. Herein, five phosphonate-based [P204]− ionic liquids were synthesized, which were pioneered to apply to extraction of copper cyanide complex ions in cyanide leach solutions. In the extraction process, macroscopic layered solids rich in copper cyanide complex ions were formed at the aqueous-organic phase interface, which was driven by self-assembly of ionic liquids. Notably, the layered solids can be obtained by simple filtration. The extraction behaviors were systematically studied in the present work. The results show that the extraction efficiency in excess of 90 % can be achieved at higher pH (13.16) and enriched as self-assembly solids in the process of one-step extraction and solidification, based on the self-assembly extraction systems of [P4444][P204] IL. It is worthy of note that no self-assembly sample was observed when the extraction systems is applied to extraction zinc and iron cyanide complex ions. It indicates that the present self-assembly extraction systems could be applied in separation copper and zinc/iron cyanide complex ions. Meanwhile, the coordination mechanism was investigated detaily, and the covalent nature played a leading role in the binding interaction. Remarkably, [P4444][P204] can be repeatedly used without obvious loss in extraction capacity of copper cyanide complex ions after two cycles, indicating that the IL has a good recycling ability. In conclusion, it is possible to employ the self-assembly extraction systems to separate and recover various valuable metals from aqueous solutions by designing and developing ILs extractants in the future.

Study on electrosorption behavior of weak metal cyanide complex ions based on coal-based electrode

Using the electrosorption technology treatment the cyanide wastewater has a good treatment effect, but the mechanism is not completely clear. In this paper, we conducted electrosorption experiments using simulated cyanide solutions to study the adsorption kinetics, thermodynamics, adsorption isotherms and analyze the reaction mechanism of zinc-cyanide and copper–cyanide complex ions. The results show that the electrosorption process of weak metals cyanide complexes treated by coal-based (CB) electrode conforms to the second-order kinetic model and follow the Langmuir model, affected by the dipole force and exchange of coordination groups. The equilibrium adsorption amounts of the two species at 2 V were 1.53 and 1.74 times higher than those at open circuit, respectively. During the electrosorption process, affected by the pseudo-capacitance, pore structure of CB electrodes and the charges of complex ions, the zinc-cyanide complex is bound in the double electric layer on the anode surface by the electric field, but partly decomposed to produce zinc ions and forms Zn(OH)2 in alkaline solution then generates ZnO precipitates, a small amount of Zn2+ were electrostatically adsorbed on the cathode surface for reduction deposition. However, the majority of the copper–cyanide complexes were purified by electrostatic adsorption to the double layer near the anode, while a small amount of decomposition occurred to produce Cu(OH)2 in the alkaline system, and almost no copper was deposited by reduction. This research results can enable us to better understand the removal characteristics of the weak metal cyanide complex ions in the process of electrosorption by CB electrode, and have great significance for the application of electrosorption technology to the treatment of cyanide wastewater.

Capture of copper cyanide complex ions based on self-assembly of ionic liquids actuation and application to cyanide wastewater

The tetrabutylammonium bis (2-ethylhexyl) phosphate [N4444][P204] ionic liquid (IL) was synthesized, which was applied to extract copper cyanide complex ions in cyanide tailing liquid stream pressure filtration. In the extraction process, macroscopic layered solids rich in copper cyanide complex ions were formed at the phase interface, which was based on self-assembly of ionic liquids actuation. The solid samples can be obtained by simple filtration. Meanwhile, the extraction behaviors were investigated in detail. The [N4444][P204] ionic liquid exhibited excellent extraction efficiency for copper cyanide complex ions. More than 90% of copper cyanide complex ions were extracted at pH 13.4 and enriched as self-assembly solids in the process of one-step extraction and solidification. Notably, the extraction efficiency of copper cyanide complex ions can still reach more than 75% after three cycles of organic phase with fresh aqueous phase. Furthermore, the analyses of the SEM, EDS, XPS, FTIR, and ESI-MS for self-assembly sample implied that the potential mechanism of extraction for copper cyanide complex ions is coordination reaction. It is worthy of note that the extraction system of [N4444][P204] IL has no extraction effect on iron cyanide complex ions. In the end, the proposed strategy may be further expanded to the separation of other metal cyanide complex ions by designing the ionic liquids.

Study on Removal Mechanism for Copper Cyanide Complex Ions in Water: Ion Species Differences and Evolution Process.

A large amount of cyanide-containing wastewater is discharged during electrode material synthesis. Among them, cyanides will form metal-cyanide complex ions which possess high stability, making it challenging to separate them from these wastewaters. Therefore, it is imperative to understand the complexation mechanism of cyanide ions and heavy metal ions from wastewater in order to obtain a deep insight into the process of cyanide removal. This study employs Density Functional Theory (DFT) calculations to reveal the complexation mechanism of metal-cyanide complex ions formed by the interaction of Cu+ and CN- in copper cyanide systems and its transformation patterns. Quantum chemical calculations show that the precipitation properties of Cu(CN)43- can assist in the removal of CN-. Therefore, transferring other metal-cyanide complex ions to Cu(CN)43- can achieve deep removal. OLI studio 11.0 analyzed the optimal process parameters of Cu(CN)43- under different conditions and determined the optimal process parameters of the removal depth of CN-. This work has the potential to contribute to the future preparation of related materials such as CN- removal adsorbents and catalysts and provide theoretical foundations for the development of more efficient, stable, and environmentally friendly next-generation energy storage electrode materials.

Recovery of Au and Ag from the roasted calcine of a copper-rich pyritic refractory gold ore using ion exchange resins

The recovery of Au and Ag from a roasted copper-rich pyritic refractory gold ore (78 g/t Au, 6.8 g/t Ag, 1.38 % Cu and 3.09 % Fe was investigated. Cyanide leaching and adsorption tests were performed at different concentrations of cyanide (1.5 g/L and 5 g/L NaCN) and the adsorbent dosages ranged from 2 g/L to 10 g/L. In the cyanide leaching tests, those performed at a high cyanide level (i.e., 5 g/L) produced high gold and silver extractions from the roasted ore apparently due to the increased availability of cyanide for gold leaching. Adsorption tests (CIL/CIP, RIL/RIP) were performed to investigate the selective recovery of gold and silver from copper-laden pregnant leach solutions obtained from cyanide leaching of the roasted ore. Activated carbon (NORIT GAC 1240), strong base resin (Purogold A194) and weak base resin (Purogold S992) were tested as adsorbents in these tests. The practical importance of increasing cyanide concentration on the selectivity (gold/silver vs copper) of resins as well as activated carbon was demonstrated. Each adsorbent offered good selectivity for gold over copper, particularly at a high concentration of cyanide (5 g/L NaCN). Purogold S992 appeared to be the most selective adsorbent with the highest gold and the lowest copper loadings. This distinctive trait makes the resin preferable for gold recovery from cyanide solutions containing significant levels of copper. Comparative pore size distribution analysis of the adsorbents has shown that Purogold S992 has the smallest pores with uniform size distribution among the adsorbents used. This was concomitant with its superior selectivity for gold at high cyanide concentration, which is linked with the small-size and linear gold-cyanide complexes c.f. large size and non-linear copper–cyanide complexes (Cu(CN)32– and Cu(CN)43-).

C(sp3)-H cyanation by a formal copper(iii) cyanide complex.

High-valent metal oxo complexes are prototypical intermediates for the activation and hydroxylation of alkyl C-H bonds. Substituting the oxo ligand with other functional groups offers the opportunity for additional C-H functionalization beyond C-O bond formation. However, few species aside from metal oxo complexes have been reported to both activate and functionalize alkyl C-H bonds. We herein report the first example of an isolated copper(iii) cyanide complex (LCuIIICN) and its C-H cyanation reactivity. We found that the redox potential (E ox) of substrates, instead of C-H bond dissociation energy, is a key determinant of the rate of PCET, suggesting an oxidative asynchronous CPET or ETPT mechanism. Among substrates with the same BDEs, those with low redox potentials transfer H atoms up to a million-fold faster. Capitalizing on this mechanistic insight, we found that LCuIIICN is highly selective for cyanation of amines, which is predisposed to oxidative asynchronous or stepwise transfer of H+/e-. Our study demonstrates that the asynchronous effect of PCET is an appealing tool for controlling the selectivity of C-H functionalization.

Removal of metal ions from cyanide gold extraction wastewater by alkaline ion-exchange fibers

The metal cyanide complex ions of gold extraction wastewater consume extra cyanide and compete with gold for adsorption on activated carbon during wastewater recycling. Therefore, the removal of metal cyanide complex ions from gold extraction wastewater is of great significance. In this study, polypropylene (PP) fibers were used to prepare strong acylated alkaline ion-exchange fibers (SAA-IEFs) using a polymer graft monomer method that achieved excellent adsorption of metal cyanide complex ions from gold extraction wastewater. The properties of the SAA-IEFs were characterized via scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). Adsorption experiments were conducted to study the adsorption performance and to verify the adsorption mechanism. The results show that the highest adsorption efficiencies of the SAA-IEFs for zinc and copper cyanide complex ions were 85.5% and 91.2%, respectively, and these performances were obtained when the SAA-IEF concentration was 50 g/L and pH was 10. The adsorption efficiency of the cyanide complexes in practical wastewater reached 92% at a concentration of 30 g/L. The desorption and regeneration results indicate that the adsorption capacity of the SAA-IEFs remained high after nine cycles. Moreover, an adsorption mechanism is proposed, and the adsorption process is best modeled using the Freundlich isotherm and pseudo-second-order kinetic model. These results indicate that chemisorption plays a dominant role in the adsorption process. Overall, SAA-IEFs are a promising, efficient, and cost-effective adsorbent for metal cyanide complex ion adsorption from gold extraction wastewater.

Purification of highly concentrated cyanide-containing wastewater via stepwise recovering of valuable components

This study develops an efficient technique to purify the highly concentrated cyanide-containing industrial wastewater by recovering the valuable components. Firstly, sodium sulfide, sodium polysulfide and ferrous sulfate were respectively used as the precipitating agents to retrieve zinc, copper and iron from wastewater stepwise. In the meantime, cyanide presented as free cyanide and copper–cyanide complexes were transformed into thiocyanate by polysulfide. Afterwards, the solvent extraction of thiocyanate was systematically conducted with trioctylamine (TOA) as the extraction agent and sodium hydroxide solution as the stripping agent. The results showed that the contents of zinc, copper and iron in the solution after precipitation were less than 1 mg·L−1. Focusing on the reaction between copper–cyanide complex and polysulfide, three stages were established for the first time. In the first stage, Cu(CN)32− was gradually converted to CuCN0 and thiocyanate was rapidly generated. In the second stage, in addition to the formation of thiocyanate, Cu(I) was oxidized by polysulfide and precipitated as CuS ultimately. With an apparent activation energy of 70.9 kJ∙mol−1, kinetic analysis of the second stage suggested a significant effect of temperature on the copper–cyanide complex conversion rate. The apparent reaction orders of zero-valent sulfur and cyanide was 1.34 and 2.33, respectively. After the extraction and stripping process, the extraction efficiency of thiocyanate was nearly 100 % and the concentration of it can be enriched to 125 g·L−1 in the stripping solution. TOA and thiocyanic acid formed an extraction complex in a 1:1 ratio. This approach achieves the simultaneous recovery of valuable metallic ions (zinc, copper and iron) and cyanide conversion under the alkaline condition, which provides a new idea for the treatment of highly concentrated cyanide-containing wastewater with a complicated composition.

Kinetic study on extraction of metal-cyanide complex ions by the N263-TBP system

In this study, the extraction of metal-cyanide complex ions in gold-leaching, cyanide-containing wastewater by a trioctylmethylammonium chloride (N263)-tributyl phosphate (TBP)-n-octanol-sulfonated kerosene system was investigated. The effects of N263 and TBP concentrations, the aqueous phase pH, and phase ratio (O/A) on the extraction were investigated by adopting the response surface methodology, and the operating parameters were optimized. The optimal solution was obtained by solving the model optimally. A Cu ion concentration of 3,000 mg/L, an N263 concentration of 0.459 mol/L, a TBP concentration of 0.214 mol/L, an initial pH of the aqueous phase of 10.064, and O/A of 0.900 were determined to be optimal for realizing an extraction yield of 99%. The effects of column height, oil droplet volume, metal ion concentration, N263 and TBP concentrations, and temperature on the mass transfer rate were investigated using the single droplet method. Kinetic studies showed that the kinetic equation for the extraction system was Rf (Mass transfer rate) = 1.57 × 10-4·CCu·CTBP·CN263. The apparent activation energy of Cu(I) was 15.186 kJ/mol. The extraction process was controlled by the diffusion process. Furthermore, the chemical reaction occurred at the two-phase interface, where the copper cyanide complex ions preferentially bound to TBP at the interface between the two phases, and the bound anion cluster then reacted with the N263 cation to form the extractive complex, which then entered the organic phase from the interface.

Hydrothermal Synthesis and Study of Compounds Based on Copper(I) Cyanide and Octahedral Rhenium CyanoHydroxo Cluster Complexes

Hydrothermal Synthesis and Study of Compounds Based on Copper(I) Cyanide and Octahedral Rhenium CyanoHydroxo Cluster Complexes

Precipitation of copper from cyanide leach solutions using sodium dimethyldithiocarbamate (SDDC)

Production of gold from copper-rich gold ores has received particular attention due to some technical and economic challenges associated with the ready dissolution of most copper minerals during cyanide leaching. This leads to excessive consumption of cyanide by forming copper cyanide complexes, which adversely affect downstream recovery and cyanide detoxification processes. In this study, a novel method is proposed to precipitate copper from cyanide solutions using sodium dimethyldithiocarbamate (C3H6NNaS2; SDDC). The influence of various parameters (i.e., reaction period (0–360 min.), concentration of SDDC (165–992 mM), [CN−]/[Cu] ratio (3–8), pH (10–12.5) and temperature (20–60 °C) on the precipitation of copper were investigated using synthetic copper-cyanide solutions. Increasing reaction time, concentration of SDDC and temperature were found to significantly improve the precipitation of copper. Increasing the ratio of [CN−]/[Cu] adversely affected the precipitation of copper with no precipitation being occurred at ratios of ≥6. Strong alkaline conditions appeared to have a slightly negative impact on the process. In the light of these findings, the response surface methodology (i.e., central composite design; CCD) was adopted to reveal the influence and interactions of [SDDC]/[Cu] ratio (21.0–126), initial concentration of copper (50–950 mg/L) and reaction period (15–360 min.) on the precipitation of copper. The analysis of the data confirmed that statistically significant parameters affecting the process were reaction time and [SDDC]/[Cu] ratio. It was also found that initial copper concentration did not significantly influence the process. Tests on real cyanide leach solutions derived from gold ores/concentrates demonstrated that the SDDC could selectively precipitate copper (as well as zinc and silver) from gold-bearing solutions. The activation energy (i.e., ≈67 kJ/mol) calculated by Arrhenius equation has indicated that the precipitation of copper is a chemically controlled reaction. Detailed characterisation of Cu-DDC precipitates was performed using SEM-EDS, FT-IR and particle size analysis. The precipitates (d80 = 16 μm) are thin, rod-like particles in brownish colour. The recovery of copper from Cu-DDC precipitates using acid solutions (HCl, H2SO4 and HNO3) was also investigated. Complete recovery of copper was achieved using HCl and HNO3 solutions at high concentrations. The findings have suggested that SDDC is an effective reagent for selective precipitation of copper from cyanide leach solutions.

Electrochemical sensor based on 1,8-dihydroxyanthraquinone adsorbed on a glassy carbon electrode for the detection of [Cu(CN)3](aq)2− in alkaline cyanide copper plating baths waste

This work reports the fabrication of a novel electrochemical sensor for the detection of the complex ion [ Cu ( CN ) 3 ] ( aq ) 2− , one of the main components of the effluents from cyanide alkaline copper plating baths. This sensor was prepared by using a surface modified glassy carbon (GC) electrode with 1,8-dihydroxyantroquinone (1,8-DHAQ). It was characterized by electrochemical impedance, Raman spectroscopy and UV–Visible spectroscopy. The electrochemical detection of [ Cu ( CN ) 3 ] ( aq ) 2− was performed by differential pulse voltammetry. The 1,8-DHAQ/GC electrochemical sensor exhibits good reproducibility and a linear range of 5.50 × 10 −7 –3.81 × 10 −6 mol L −1 , with a detection limit (LOD) of 1.20 × 10 −6 mol L −1 , quantification limit (LOQ) of 3.97 × 10 −6 mol L −1 , and robustness to interfering Cl − , NO 3 − , SO 4 2− y CO 3 2− ions. Finally, a DFT approach suggests an almost parallel orientation of the bis(1,8-dihydroxyanthraquinone) over a graphene domain of the glassy carbon surface, as well as the noncovalent nature of the interactions involved. Development of the 1,8-DHAQ/GC sensor for the electrochemical detection of the copper cyanide complex [Cu(CN) 3 ] 2− evaluated by RAMAN spectroscopy and Differential Pulse Voltammetry. • Copper cyanide complexes are pollutants, their control is of vital importance. • The GC surface was modified with 1,8-DHAQ by spontaneous adsorption. • Electrochemical determination of [Cu(CN) 3 ] (aq) 2− by Differential Pulse Voltammetry. • Decrease in the electrochemical signal of 1,8-DHAQ by [Cu(CN) 3 ] (aq) 2− interaction. • The 1,8-DHAQ/GC sensor allows [Cu(CN) 3 ] (aq) 2− detection at low concentrations.

Enhanced photocatalytic reaction and mechanism for treating cyanide-containing wastewater by silicon-based nano-titania

The treatment of cyanide-containing wastewater is very important for the sustainable development of gold industry. Treating wastewater by nano-titania (nano-TiO2) has the advantage of adsorbing heavy metals and catalyzing the decomposition of cyanogen simultaneously. Since the catalysis is limited by solid-liquid diphase system, the photocatalytic and adsorption efficiency is relatively low. This study aimed to enhance catalytic process based on silicon-based nano-TiO2 composite functional material to treat deeply cyanide-containing wastewater. The characteristics of the silicon-based nano-TiO2 material were studied by Brunner−Emmet−Teller (BET) and field emission scanning electron microscopy (FESEM)/ energy dispersive spectrometer (EDS), which indicated that the material has excellent dispersibility and large specific surface area(146.6±2.4 m2·g−1). Further, the comparison of the treatment effects of cyanide wastewater with pure nano-TiO2 and silicon-based nano-TiO2 material demonstrates that the latter is more effective on cyanide degradation. Almost 99.8% of cyanide degradation was achieved by silicon-based nano-TiO2 material under light irradiation within 135 min. The mechanism and X-ray photoelectron spectroscopy (XPS) analysis. It was found that the final decompositions of Copper cyanide complex and zinc cyanide complex are CO2, NO2, Cu2+ and Zn2+.

A novel uracil-based chemosensor for sequential detection of copper (II) and cyanide ions and its application in real samples

A simple uracil based chemosensor (UraCS) has been developed for sequential detection of Cu2+ and CN− in aqueous acetonitrile solution. The sensor UraCS showed a high selectivity, high sensitivity and quick response to copper ions in the presence of other competing cations including Cd2+, Fe2+, Hg2+, Al3+, Ni2+, Ba2+, Ca2+, Cr3+, Co2+, Zn2+, Cu2+, Pb2+, Ag+, Fe3+ and K+. In the presence of Cu2+, UraCS provided a distinct color change from colorless to dark yellow forming a complex with a 2:1 stoichiometry and reverse color change after addition of CN‾ to the probe containing UraCS-Cu2+ complex. More importantly, the results confirmed that the UraCS has widely linear detection range of 3.0 to 150 μM toward Cu2+ ions. The calculated limit of detection for Cu2+ ions was low as 0.28 μM. Moreover, interaction of UraCS with Cu2+ causes a significant fluorescence quenching at 378 nm. UraCS-Cu2+ complex could be successfully applied to detect cyanide ions via Cu2+ displacement approach. The free UraCS was recovered after adding the CN‾ ions in a few seconds due to the formation of the stable copper cyanide complex Cu(CN)x. The DFT calculation was also performed for better understanding of the Cu2+ sensing mechanism. Furthermore, chemosensor UraCS was successfully utilized in the preparation of test strips and supported silica gel for the detection of Cu2+ and CN− ions from aqueous environment and real water samples.

A simple pyrimidine based colorimetric and fluorescent chemosensor for sequential detection of copper (II) and cyanide ions and its application in real samples.

In this study, a new pyrimidine-based chemosensor (PyrCS) has been developed for sequential detection of copper (II) and cyanide ions. The PyrCS has revealed high sensitivity and selectivity toward copper ion over other metal ions in aqueous media. The PyrCS as an optical probe exhibited a distinct color change and a bathochromic shift in UV spectra in the presence of copper ion in a few seconds due to the formation of stable complex (PyrCS-Cu2+). The results confirmed that the PyrCS has a widely linear detection range of 0.3-30 μM toward Cu2+. The calculated limit of detection for Cu2+ ions was low as 0.116 μM. Moreover, the fluorescent intensity of PyrCS at 507 nm was significantly quenched in the presence of Cu2⁺ and Fe2⁺ ions. Additionally, complex PyrCS-Cu2+ was successfully used to detect cyanide ions via Cu2+ displacement approach. The free PyrCS was recovered after adding the CN‾ ions in a few seconds due to the formation of the stable copper cyanide complex Cu(CN)x. The calculated LOD for CN‾ ions was low as 0.320 μM. The data also clarified that the other competing anions did not create a clear color change in solutions. Since the proposed method could provide a vivid colorimetric response in the presence of detected analytes within the pH range of 3-9, we can claim that the developed chemosensor can be utilized in any physical and biological conditions.

Activated carbon adsorption of gold from cyanide-starved glycine solutions containing copper. Part 1: Isotherms

Cyanide-starved alkaline glycine solutions have been shown to have distinct advantages in terms of lower reagent consumption and detoxification needs, or leach rate and recovery, over cyanide- only and glycine-only leach systems respectively for gold ores with nuisance copper. Activated carbon has been shown to be suitable for gold adsorption from alkaline glycine systems, and is well established for cyanide based systems. Activated carbon being an effective substrate for the adsorption of gold thus offers a possible downstream carbon-in-pulp (CIP) recovery route for alkaline glycine leach systems and hybrid systems in the presence of cyanide. Given the frequent occurrence of gold deposits with high levels of nuisance copper, the equilibrium loading of gold and copper onto activated carbon from cyanide-starved alkaline glycine solutions containing copper and gold has been studied. Adsorption efficiency was studied in terms of equilibrium loading isotherms. Results showed that while copper adsorption is more sporadic based on goodness of fit, gold adsorption is more consistent and clearly follows the Freundlich isotherm model (good linear correlation of log Q vs log C values). The adsorption isotherms were obtained using a gold concentration of 2 ppm. In the presence of copper, the equilibrium gold loading increases with increasing glycine and calcium ion concentrations, decreases with increasing cyanide concentration and is not affected by initial gold concentration. The cuprous cyanide and cupric glycinate complexes lowered gold loading through a competitive adsorption with the copper (I) cyanide complexes adsorbing more rapidly on the carbon than their glycinate counterparts. The equilibrium gold loading capacity in cyanide-starved glycine solutions containing 2 ppm Au and 300 ppm Cu, at pH 11 was found to be 9.95 kgAu/toncarbon in 24 h, which is almost four times higher than the gold loading capacity in a pure cyanide system (2.7 kgAu/toncarbon) under similar conditions. The study revealed that activated carbon was an effective adsorbent for removal gold from cyanide-glycine aqueous solutions.

Enhanced Photoelectrocatalytic Oxidation of Cu(CN)32- and Synchronous Cathodic Deposition of Cu by Peroxydisulfate

Oxidation of Cu-cyanides by a photoelectrocatalytic method was enhanced by adding peroxydisulfate (PS). In the photoelectrocatalytic system (PEC), graphitic carbon nitride (g-C3N4) thin films prepared by a liquid-based reaction and graphitic carbon felt (GCF) were used as the photoanode and cathode, respectively. First, various processes, including PEC, PS oxidation, and PEC with PS addition (PEC/PS), were compared for Cu-cyanide removal. The addition of PS improved greatly the photoelectrocatalytic efficiency for the oxidation of CN- and the recovery of Cu on the cathode. The effect of the amount of K2S2O8 was investigated in detail. The removal efficiency of CN- and Cu recovery can reach up to 86.23% and 82.11%, respectively, with 1 mmol·L-1 K2S2O8 at 1.0 V bias potential. Combined with the SEM, EDS, and XPS analysis of the electrode surface, it was concluded that the free Cu+ was oxidized and existed in the precipitation and photoanode in the form of CuO. Conversely, the liberated Cu+/Cu2+ ions were electrochemically reduced to elemental Cu on the surface of the graphitic carbon felt cathode. As a result, metal Cu was recovered from the wastewater of the copper cyanide complexes. Electron spin resonance and radical quenching experiment analysis showed that the oxidation of CN- is assigned to sulfate radical oxidation and non-radical oxidation processes.

A DFT study on the speciation of aqueous gold and copper cyanide complexes

The speciation of copper and gold cyanide complexes was investigated using Density Functional Theory (DFT) in order to understand the behaviour of these complexes in aqueous solutions. To represent the local environment, two methods of implicit (COSMO) and explicit water molecules were utilized and the results were compared to evaluate their capability. The hydration state of the species, stability constants, cluster formation, interaction of different species and finally the gold leaching character of copper cyanide complexes were investigated in details.The solvation energy of Au(CN)2−, Cu(CN)2−, Cu(CN)3−2 and Cu(CN)4−3 were calculated as −41.1, −42.5, −98.1 and −168.7 kcal·mol−1 with 4, 4, 6 and 8 water molecules in the first shell of hydration, respectively. A high level of cluster formation was observed for both dicyano copper and gold complexes. Cu(CN)2− displayed the highest level of interaction with Au(CN)2− and mixed cluster formation of dicyano complexes was proposed as a mechanism of copper cyanide adsorption on the activated carbon. Other species including tri and tetracyano complexes were found to be well dispersed with minimal interaction with other species. The leaching potential of copper cyanide complexes was proved by computational modelling for the first time, here. Cyanide ions are released from all three different order copper cyanide complexes, while only released CN− from Cu(CN)3−2 and Cu(CN)4−3 dissolves gold and Cu(CN)2− passivates the gold surface by formation of Au(CN)-Cu(CN) layer. The results of this computational modelling study can be used in providing a more in depth understanding of the chemistry of gold hydrometallurgy in the presence of other metal ions.

Crystal structures of two mixed-valence copper cyanide complexes with N-methyl-ethylenedi-amine.

The crystal structures of two mixed-valence copper cyanide compounds involving N-methyl-ethylenedi-amine (meen), are described. In compound (I), poly[bis(μ3-cyanido-κ3C:C:N)tris(μ2-cyanido-κ2C:N)bis(N-methylethane-1,2-di-amine-κ2N,N')tricopper(I)copper(II)], [Cu4(CN)5(C3H10N2)2] or Cu4(CN)5meen2, cyanide groups link CuI atoms into a three-dimensional network containing open channels parallel to the b axis. In the network, two tetra-hedrally bound CuI atoms are bonded by the C atoms of two end-on bridging CN groups to form Cu2(CN)6 moieties with the Cu atoms in close contact at 2.560 (1) Å. Other trigonally bound CuI atoms link these units together to form the network. The CuII atoms, coordinated by two meen units, are covalently linked to the network via a cyanide bridge, and project into the open network channels. In the mol-ecular compound (II), [(N-methylethylenediamine-κ2N,N')copper(II)]-μ2-cyanido-κ2C:N-[bis(cyanido-κC)copper(I)] monohydrate, [Cu2(CN)3(C3H10N2)2]·H2O or Cu2(CN)3meen2·H2O, a CN group connects a CuII atom coordinated by two meen groups with a trigonal-planar CuI atom coordinated by CN groups. The mol-ecules are linked into centrosymmetric dimers via hydrogen bonds to two water mol-ecules. In both compounds, the bridging cyanide between the CuII and CuI atoms has the N atom bonded to CuII and the C atom bonded to CuI, and the CuII atoms are in a square-pyramidal coordination.

Enrichment of copper and recycling of cyanide from copper–cyanide waste by solvent extraction

The enrichment of copper from copper–cyanide wastewater by solvent extraction was investigated using a quaternary ammonium salt as an extractant. The influences of important parameters, e.g., organic-phase components, aqueous pH values, temperature, inorganic anion impurities, CN/Cu molar ratio, and stripping reagents, were examined systematically, and the optimal conditions were determined. The results indicated that copper was effectively concentrated from low-concentration solutions using Aliquat 336 and that the extraction efficiency increased linearly with increasing temperature. The aqueous pH value and concentrations of inorganic anion impurities only weakly affected the extraction process when varied in appropriate ranges. The CN/Cu molar ratio affected the extraction efficiency by changing the distribution of copper–cyanide complexes. The difference in gold leaching efficiency between using raffinate and fresh water was negligible.