Alkaline Cyanide Solutions Research Articles

Separation of Palladium from Alkaline Cyanide Solutions through Microemulsion Extraction Using Imidazolium Ionic Liquids.

In this paper, three imidazolium-based ionic liquids, viz., 1-butyl-3-undecyl imidazolium bromide ([BUIm]Br), 1-butyl-3-octyl imidazolium bromide ([BOIm]Br), and 1-butyl-3-hexadecyl imidazolium bromide ([BCIm]Br), were synthesized. Three novel microemulsions systems were constructed and then were used to recover Pd (II) from cyanide media. Key extraction parameters such as the concentration of ionic liquids (ILs), equilibration time, phase ratio (RA/O), and pH were evaluated. The [BUIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion system exhibited a higher extraction percentage of Pd (II) than the [BOIm]Br/n-heptane/n-pentanol/sodium chloride and [BCIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion systems. Under the optimal conditions (equilibrium time of 10 min and pH 10), the extraction percentages of these metals were all higher than 98.5% when using the [BUIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion system. Pd(CN)42- was separated through a two-step stripping procedure, in which Fe (III) and Co (III) were first separated using KCl solution, then Pd(CN)42- was stripped using KSCN solution (separation factors of Pd from Fe and Co exceeded 103). After five extraction-recovery experiments, the recovery of Pd (II) through the microemulsion system remained over 90%. The Pd (II) extraction mechanism of the ionic liquid [BUIm]Br was determined to occur via anion exchange, as shown by spectral analysis (UV, FTIR), Job's method, and DFT calculations. The proposed process has potential applications for the comprehensive treatment of cyanide metallurgical wastewater.

Outstanding Performance of the Deep Eutectic Solvent-Based Aqueous Biphasic System Constructed with Sodium Citrate for a Green Gold Separation.

Aqueous biphasic systems (ABSs) that are based on deep eutectic solvents (DESs) are environmentally benign systems to use for metal ion separation. In this work, a series of DESs was synthesized for the first time with PEG 400 as hydrogen bond donors and tetrabutylphonium bromide (P4Br), tetrabutylammonium bromide (N4Br), or tetrabutylammonium chloride (N4Cl) as hydrogen bond acceptors, and then they were combined with citrate (Na3C6H5O7), which is eco-friendly, to construct an ABS for use in the separation of Au(I) from an aurocyanide solution. Phase diagrams of DESs + Na3C6H5O7 + H2O systems were constructed using the experimentally measured data. Multiple factors that affect the efficiency of the gold extraction were studied; these factors were the species of salt or DES and their content, the equilibrium pH, the oscillation time, and the initial gold concentration. Gold(I) is preferentially retained in the DES-rich phase, and the P4Br:PEG 1:2 + Na3C6H5O7 + H2O system has a high extraction efficiency of 100.0% under optimized conditions. FT-IR, NMR, and TEM characterizations and DFT calculations show that the migration of Au(I) from the salt-rich to the DES-rich phase follows an ion exchange mechanism. Specifically, Au(CN)2- replaces Br- in the original P4Br and generates a stable ion pair with the quaternary phosphonium salt cation, P+, and this replacement is driven by electrostatic attractions. A new strong hydrogen bond network simultaneously forms between the anionic Au(CN)2- and the -OH group in the PEG 400 component. Finally, the gold of Au(I)-loaded P4Br:PEG 1:2 can be successfully reduced by sodium borohydride with an efficiency of 100.0%. The strategy to extract gold(I) from alkaline cyanide solutions using an ABS based on DESs as proposed in this work provides a potential platform for developing green technology for recovering gold.

Comparative study of oxidants in gold cyanidation: A molecular picture

Oxygen plays a crucial role in the oxidation of gold in cyanidation. However, gold can be dissolved in oxygen free solutions by other oxidants. Here, the oxidizing potential of two other oxidants including peroxide (H2O2) and iron hydroxide (Fe(OH)4-) as the dominant Fe specie in alkaline cyanide solutions has been compared with oxygen. For this purpose, a computational modelling method using DFT has been used with BLYP functional. The interaction energy of O2,H2O2 and Fe(OH)4- with the 111 surface of Au is calculated and compared in absence and presence of cyanide ion. Oxygen adsorption energy was higher than the other species with energy values of −50. The H2O2 and the Fe(OH)4-, like oxygen, had a positive effect on the interaction of cyanide with 111 surface as well.

Hydrophobic phosphonium-based ionic liquids as novel extractants for palladium(II) recovery from alkaline cyanide solutions

Although phosphonium-based ionic liquids (ILs) have become popular green solvents for the separation of precious metals, these solvents have not been used thus far to recover Pd(II) from alkaline cyanide solutions. In this study, three novel phosphonium-based ILs, viz. tributyl(2-ethylhexyl) phosphonium bromide (TBEHPB), trioctyl (2-ethylhexyl) phosphonium bromide (TOEHPB), and trioctyl undecyl phosphonium bromide (TOUPB), were synthesized, respectively, and these ILs were used for the recovery of Pd(CN)42− for the first time. With the increase in the length of the alkyl chain in the phosphonium cation, the extraction percentage of Pd(II) increased. Under optimum conditions (i.e., contact time of 5 min, pH of 10.5, and temperature of 298 K), the TOUPB system exhibited a Pd(II) extraction percentage of greater than 99.0%. Furthermore, the TOUPB system exhibited excellent selectivity for Pd(II) in a mixed solution (separation factors of βPd/Fe and βPd/Co were greater than 2.0 × 103). The Pd(II) recovery percentage was still greater than 90.0% after five consecutive extraction-stripping cycles. The Job’s method, infrared spectroscopy, mass spectrometry, nuclear magnetic resonance spectroscopy, and UV–vis spectroscopy revealed that the extraction mechanism is ion exchange. The supramolecular structure of the extraction complex was established on the basis of density functional theory (DFT) calculations and Karl Fischer titration, and the extraction mechanism was further described at the molecular structure level. This study provides a new process for recovering Pd(II) from an alkaline cyanide medium.

Gold Cementation in Percolation Mode Using Dendritic Zinc Powders

Present article is devoted to study of electrolytic zinc powders usage features in gold mining industry. Electrolytic zinc powders characterized by dendritic shape and a high specific surface area. These features of electrolytic zinc powders provide a number of advantages for gold cementation from alkaline cyanide solutions. Dendritic form of electrolytic zinc powder makes it possible to reduce zinc layer hydraulic resistance on filtering surface, which is important when using cementation technologies based on filtration of gold-bearing solution through zinc powder layer. High specific surface area of electrolytic zinc powders favourably affects the rates of gold recovery from cyanide solutions, which is shown in cementation experiments from model and real (industrial) solutions.

Graphene aerogel/cellulose fibers/magnetite nanoparticles (GCM) composite as an effective Au adsorbent from cyanide solution with favorable electrochemical property

In the current work, the adsorption of Au, from an industrial alkaline cyanide solution, is reported by the use of a novel synthesized adsorbant, namely graphene aerogel/cellulose fibers/magnetite nanoparticles (GCM) composite. The GCM composite was successfully synthesized by a facile and cost effective mild chemical reduction route. The synthesized composite showed a high gold adsorption capacity (130 mg·g−1) with an appropriate hydrophilicity; in addition, it had the desired mechanical strength (7 kPa at 50% strain) that makes it suitable for the industrial exploitation. The effect of contact time and GCM concentration on the gold adsorption and also the kinetic aspects of the adsorption process were studied and it was found that a pseudo-second-order model can well described the experimental data. In addition, the synthesized composite can be easily collected and separated after the adsorption step by using a magnetic separator. The desorption efficiency of the Au loaded GCM composite was 60% after 20 adsorption-desorption cycles; interestingly, the remained Au in the GCM composite after these 20 cycles could provide the GCM composite decorated by Au nanoparticles (GCM/Au) that shows promising electrochemical characteristics. According to the Cyclic Voltammetry (CV) analysis, conducted in the [Fe(CN)6]3−/4− solution, the modification of glassy carbon electrode by the GCM/Au composite resulted in an increase in the electroactivity (more than two times increase in the redox peak separation); in addition, based on the results of Electrochemical Impedance Spectroscopy (EIS), there was a significant decrease in the charge transfer resistance (Rct) of the glassy carbon electrode modified by GCM/Au composite indicating a considerable improvement in the electrical conductivity and electron transfer.

Effect of PbO on cyanidation leaching behavior of bornite

During the cyanidation of gold‑copper ores or concentrates, the presence of cyanide-soluble copper significantly increases the cyanide consumption. However, the consumption of cyanide and dissolved oxygen, the concentration of sulfide ions in the leaching solution decreased with the increase of PbO amount. The SEM-EDS analyzed that there was no obvious corrosion on the surface of the bornite leaching residue in the presence of 1.5 g/L PbO, but the surface was getting very sleek. It was known from thermodynamic calculation that PbO would partially dissolve to form plumbite ions in the alkaline cyanide solution, and plumbite ions would react with sulfide ions to form PbS precipitate. The XPS analysis also proved that a large amount of undissolved PbO and PbS precipitation were adsorbed on the surface of bornite. The adhesion of PbO and PbS on the surface of bornite inhibited dissolution of bornite in the cyanide solution.

Thermodymanic Considerations on Gold Dissolution in Different Lixiviants (I)

The paper presents the main thermodynamic aspects related to gold dissolution in different lixiviants. We analyzedthe thermodynamic stability of the gold complexes with the most representative lixiviants with potential for use in the gold industry. Based on the stability constants we determined the electrode potentials of the gold dissolution reactions in variouslixiviants and we presented the electrochemical mechanism of gold dissolution is alkaline cyanide solutions.

Simultaneous extraction and recovery of gold(I) from alkaline solutions using an environmentally benign polymer inclusion membrane with ionic liquid as the carrier

In this study, a polymer inclusion membrane (PIM) was used for the extraction and recovery of gold(I) from alkaline cyanide solutions in a prompt, concise manner. Compared with traditional solvent extraction technology, PIM is especially suitable for the separation of low concentration gold(I). A PIM containing [A336][SCN] as the carrier, polyvinylidene difluoride as a polymer matrix, and 2-nitrophenyl n-octyl ether as the plasticizer was prepared using solvent volatilization and characterized by several techniques. In addition, effects of several experimental factors on the extraction and recovery efficiencies were studied; the experimental factors included the concentration of the extractant, the stirring rate, the species of the polymer matrix, the initial gold concentration in the feed solution, and the KSCN concentration in the strip solution. Results revealed that the membrane composition and in particular, the carrier concentration, significantly affect the extraction of gold(I). The extraction mechanism involved an anion exchange reaction between the carrier [A336][SCN] embedded in the matrix polymer and the gold cyanide complex in the feed phase, followed by diffusion through the PIM, and Au(CN)2− is eventually recovered in the stripping phase. More than 98.2% of gold in the feed phase was transported through the PIM into the stripping solution, which contains 3.0 mol/L KSCN with a permeability coefficient of 1.02 × 10−5 m/s under optimal conditions. Furthermore, the membrane lifetime was also evaluated using a continuous mode, and excellent stability was achieved for at least 9 days of continuous operation. These promising results demonstrate that the PIM technology has good prospects for the extraction and recovery of gold from alkaline solutions.

Gold sorption from cyanide media by ANS-3 anionite

Research results were presented for gold sorption from cyanide solutions by ANS-3 macroporous anionite based on styrene-divinyl benzene copolymer. Equilibrium data on gold sorption from a model cyanide solution agreed with the modified Langmuir-Freundlich equation within the studied gold concentrations. Gold stripping results with alkaline cyanide solution were given. Optimal structure of polymer matrix provides high mechanical and osmotic strength of ANS-3 anionite. The anionite is not subjected to an osmotic shock in alkaline solution allowing its application in hydrometallurgical processes including sorption from pulps.

Electrochemical study of silver telluride (Ag2Te): anodic and cathodic potential dependent-reactions in alkaline cyanide solutions

Although electrochemical characterization has been used to elucidate the species formed during hydrometallurgical processes, it has not been commonly applied to the cyanidation of precious metal tellurides. In this study, voltammetric characterization of the silver telluride (Ag2Te) reaction system in alkaline cyanide solutions (pH 10.9 and 1250 mg/L CN−) was carried out making use of carbon paste electrodes. For this purpose, the electrochemical reactions system of elemental silver and elemental tellurium were first studied by cyclic voltammetry in two aqueous media (i.e., aqueous solution at pH 10.9, and 1250 mg/L CN− at pH 10.9) and, by comparing the cyclic voltammograms obtained with those for Ag2Te, the electrochemical reaction system was elucidated. The results obtained showed that the anodic oxidation of Ag2Te in alkaline cyanide solutions occurred by at least two consecutive steps according to:Step 1 (fast reaction): Ag2Te + 4CN− ↔ Te + 2Ag(CN)2− + 2e−.Step 2 (slow reaction): Te + 3H2O ↔ TeO32− + 6H+ + 4e−while the cathodic reduction of Ag2Te in alkaline cyanide solutions occurred according to:Ag2Te+2e−↔2Ag+Te2−

Combined technology for gold desorption and ionite regeneration in the conical device

The principal technological scheme of desorption of gold and concomitant metal-impurities from the AM-2B resin phase used for the sorption processing of gold-bearing ores is considered. The proposed combined scheme, involving the use of two traditional, independent from each other methods (thiocyanate and acid-thiourea) for eluting gold, includes desorption of metal impurities from the resin with alkaline solutions of sodium thiocyanate, and gold with sulfuric acid solutions of thiourea. To shorten the duration of the process research of proposed technology was carried out the in a conical apparatus. The results of study of the elution of gold and impurity metals from anionite saturated with the following components, mg/g: Au – 2.6; Cu – 3.5; Zn – 1.3; Ni – 2.9; Co – 3.3, are given. It is shown that the main amount of impurity metals is desorbed from the resin upon its thiocyanate treatment, while the transition of gold into the eluate is negligible. The composition of the eluate in the thiocyanate treatment of saturated resin is, mg/l: Au – 1.7; Cu – 156.0; Zn – 53.0; Ni – 89.0; Co – 102.0. The subsequent treatment of the resin with sulfuric acid solutions of thiourea allows the conversion of 89.32 % of gold from the ion exchanger into the eluate. The resulting eluates containing ~113.0 mg/l gold and a small amount of impurities are target solutions for obtaining a valuable metal. The ion exchanger was regenerated by washing with water and treating with an alkaline solution of sodium to convert it to OH form, since gold sorption is carried out from alkaline cyanide solutions of heap leaching. Residual contents of components in the resin after regeneration were, mg/g: Au – 0.24; Cu – 0.23; Zn – 0.15; Ni – 0.07; Co – 1.29, which allows the successful use of the regenerated resin in the next stage of sorption.

A Novel Electrochemical Approach to Study the Interaction of Blinding Agents with Preg-Robbers in Carbonaceous Gold Systems

Preg-robbing usually refers to the adsorption of a gold cyanide complex, i.e. Au(CN)2 −, on the components of a gold ore including carbonaceous materials and other minerals during the gold leaching process (1-3). The adsorption of gold ions on carbonaceous materials is one of the most common phenomenon responsible for gold losses from the cyanide leaching process (1, 4). Depending on the carbon content of the ores, gold losses may reach 90 % of leachable gold due to preg-robbing during cyanidation (5). Chemical blinding agents have previously been investigated to passivate the surface of carbonaceous preg-robbers in the ores, thus reducing the extent of preg-robbing and allowing an increase in gold recovery (1, 3, 6, 7). However, the mechanism by which such agents suppress the ion-adsorption capability of the carbonaceous materials as well as their interactions with other components of the ore, including pyrite, and more importantly, gold, are yet to be fundamentally investigated. The latter process could severely affect final gold recovery if the surface of the gold becomes passivated. This study investigates the effect of various blinding agents on the main components of a gold-containing concentrate: carbon, gold and pyrite. A novel electrochemical approach is employed, i.e. double-layer capacitance measurements combined with electro-oxidation/reduction peaks obtained from cyclic voltammetry tests. Our group is the first to employ the electric double-layer theory to study the preg-robbing capacity of carbonaceous ores with total carbonaceous matter (TCM) contents as low as 0.3 % by weight. Figure 1 shows a comparison between the blinding activity, and durability, of various surfactants and chemical reagents, at different concentrations, on the surface of activated carbon particles over a 24-hour contact period. The capacitance is an indication of how well the chemical reagents have been adsorbed on the activated carbon particles with the lowest capacitance values showing the best surface adsorption. The study reveals that kerosene, Lecithin and Polymax 30 are among the best blinding agents for the activated carbon surfaces in terms of adsorption and durability. Further cyclic voltammetry studies on gold surfaces in alkaline cyanide solutions (with the added blinding agents) have shown that kerosene is the least detrimental to the gold cyanide leaching process, i.e. the electrochemical oxidation reaction for the formation of AuCN complex. Figure 1. A comparative study for the effect of various chemical reagents, i.e. Aristonate H and L, Lecithin, Sodium dodecyl sulfate (SDS), kerosene and Polymax 30, on the ion adsorption capability of the activated carbon particles over 24 hours.

Decomposition of hydrogen peroxide in alkaline cyanide solutions

Decomposition of hydrogen peroxide in alkaline cyanide solutions

Synergistic extraction of gold(I) from aurocyanide solution with the mixture of primary amine N1923 and bis(2-ethylhexyl) sulfoxide in supported liquid membrane

Utilization of supported liquid membrane (SLM) for the extraction of Au(I) from alkaline cyanide solution was investigated. The SLM consisted of a synergistic mixture of primary amine N1923 and bis(2-ethylhexyl) sulfoxide (BESO) in kerosene as carrier and a hydrophobic microporous polyvinylidene fluoride (PVDF) membrane as the solid support. The presence of both BESO and N1923 extractants in the liquid membrane induces an evident synergistic effect, allowing the latter to transfer Au(I) from the highly alkaline solution (pH>9.21). The fundamental parameters influencing the gold transport, such as stirring speed, composition of the liquid membrane, feed pH, NaOH concentration in stripping solution, and initial gold concentration in the feed solution were explored. The gold transport is almost quantitative after 7h under the optimum process conditions: a mixture of (0.50mol/L N1923 + 0.75mol/L BESO) in kerosene as membrane phase, stirring rate of 1000rpm in both phases, 5.0mg/L gold in 0.20mol/L NaCl solution with a pH of 9.60, and 0.10mol/L NaOH as stripping agent. The parameters defining the mass transfer model of Au(I) through the SLM are experimentally determined as: maximum permeability coefficient, P = 31.45 × 10−6m/s, the diffusion coefficient for [Au(CN)2−·RNH3+ ·2BESO] complex across the liquid membrane, Dorg = 1.42 × 10–12m2/s, and the thickness of the aqueous diffusion layer, daq = 2.07 × 10−5 m. Selectivity of this SLM system was evaluated by performing the permeation test of Au(CN)2- with other metal cyanide species in aqueous solution and it was found that the gold ions were preferred over other impurity ones. Finally, stability of this SLM system has also been examined on a continuous run mode and satisfactory stability was observed for five runs.

Recovery of copper and cyanide from waste cyanide solutions using emulsion liquid membrane with LIX 7950 as the carrier

ABSTRACTThe feasibility of using emulsion liquid membranes (ELMs) with the guanidine extractant LIX 7950 as the mobile carrier for detoxifying copper-containing waste cyanide solutions has been determined. Relatively stable ELMs can be maintained under suitable stirring speed during mixing ELMs and the external solution. Effective extraction of copper cyanides by ELMs only occurs at pH below 11. High copper concentration in the external phase and high volume ratio of the external phase to ELMs result in high transport rates of copper and cyanide. High molar ratio of cyanide to copper tends to suppress copper extraction. The presence of thiocyanate ion significantly depresses the transport of copper and cyanide through the membrane while the thiosulfate ion produces less impact on copper removal by ELMs. Zinc and nickel cyanides can also be effectively extracted by ELMs. More than 90% copper and cyanide can be effectively removed from alkaline cyanide solutions by ELMs under suitable experimental conditions, indicating the effectiveness of using the designed ELM for recovering copper and cyanide from waste cyanide solutions

SOLVENT EXTRACTION OF PALLADIUM(II) FROM ALKALINE CYANIDE SOLUTION BY THE DODECYL DIMETHYL-2-PHENOXYETHYL AMMONIUM BROMIDE

The direct extraction of Pd(CN) 4 2- from alkaline cyanide solutions with dodecyl dimethyl-2-phenoxyethyl ammonium bromide (DDPB) was investigated. Several factors affecting extraction efficiency, including DDPB concentration, modifier content, equilibrium time, phase ratio (O/A), pH and palladium concentration in aqueous phase, were studied. The results indicated that nearly all of the Pd(II) (>98%) was transferred from the aqueous phase into the organic phase. N-pentanol was the most appropriate modifier for the extraction of Pd(CN) 4 2- . Palladium can be separated efficiently by DDPB over base metals (Fe, Co, Ni and Cu) from alkaline cyanide medium. The extraction was quite fast and equilibrium could be established within 3 min. Most of Pd(II) (>96%) in the organic phase could be stripped with ammonium thiocyanate aqueous solutions, from which elemental palladium could potentially be recovered by the addition of hydrazine hydrate. The organic phase after stripping can be recycled for a continuous extraction-stripping operation. The extraction mechanism can be deduced based on FTIR spectrum and slope analysis while the mechanism of stripping can be explained by the principle of minimum charge density and Le Chatelier’s principle. The proposed method was applied to extract palladium from real cyanide leaching liquor of Pd flotation concentrate with satisfactory results. Fig. 1. Effect of different long-chain alcohols on the extraction percentage

Extraction of Au(I) from aurocyanide solution by using a synergistic system of primary amine N1923/bis(2-ethylhexyl) sulfoxide: A mechanism study

The synergistic effect of a mixture of bis(2-ethylhexyl) sulfoxide (BESO) and primary amine N1923 in kerosene on the extraction of Au(I) from alkaline cyanide solution was investigated. Experimental results demonstrate that addition of BESO into the organic phase can significantly enhance the basicity of amine N1923, in which the pH50 value can reach up to 11.91. Slope analysis suggested that the composition of the extracted complexes in the organic phase is [Au(CN)2−·RNH3+·2BESO]. The extracted complexes were characterized by FTIR spectroscopy, 1H NMR spectroscopy, mass spectrometry, and electrical conductivity analysis. FTIR and 1H NMR studies reveal strong interactions between BESO and N1923 molecules through hydrogen bonding between the O atoms in the SO groups and the H atoms in the –NH2 groups, forming SO…H–N. This hydrogen bonding enhances the basicity of N1923 and consequently the ability of N1923 to capture proton; Au(CN)2− serves as a counter anion against the protonated amine cation in the organic phase. Electrical conductivity measurements confirmed ionic character of the extracted complexes. The Au(I) extraction in the N1923/BESO system most probably involves the ion-association (ion pair) mechanism. A plausible microstructural model of the extracted complexes was proposed in the paper. Moreover, gold could be efficiently stripped from the loaded organic phase by using sodium hydroxide solution.

Cyanide leaching of gold catalysts

Gold catalysts remain of great interest, but a high gold price presents a concern. Gold can be leached from gold–titania catalysts using alkaline cyanide solutions. The specific activity of gold for CO oxidation can thereby be increased substantially, though the precise nature of the gold before and after treatment remains unclear. It seems unlikely that leaching proceeds in a simple manner by selective dissolution of metallic gold particles. Rather it is likely that cyanide ions interact with gold centers in several ways and, in addition, alkali metal ions may also modify activity.

Solvent Extraction of Palladium(II) from Alkaline Cyanide Solution by Benzyl Dimethyl-n-dodecylammonium Chloride

Asian Journal of Chemistry, a Multidisciplinary Chemistry Journal is an Peer Reviewed International Journal and publishes from India. The journal has been established since January 1989 on a firm foundation of International Quality Research. This Journal encompasses all branches of chemistry and its sub – disciplines like Pharmaceutical, Biological activities of Synthetic Drugs, Environmental Chemistry, Biochemistry, Polymer Chemistry, Petroleum Chemistry, and Agricultural Chemistry, etc.