Gold Cyanide Complex Research Articles

Electrochemistry of Molybdenum Single Crystals and Thin Wires in Cyanide and Gold Cyanide Electrolytes

Thin wires of molybdenum coated with gold are used for space applications and the adhesion of the gold layer is decisive for their use. The surface morphology of the wires is determined by the manufacturing process and preferential orientation of single crystal surfaces is expected. In this work three different single crystal surfaces were studied together with a 20 μm molybdenum wire to elucidate the importance of surface morphology on the electrodeposition process for gold. Electrochemical impedance spectroscopy was used to study the molybdenum samples in the absence and presence of gold cyanide complexes. The results show large pseudocapacitance prior to gold deposition, indicating the presence of a thin molybdenum oxide film on the surface. Thus, the electrodeposition takes place on the surface oxide and is afflicted with a nucleation overpotential. The overpotential is only slightly dependent on the single crystal orientation, while it is more negative for the wire. The adhesion of gold on the flat single crystal surfaces is weak but marginally better on the wire. This clearly shows that strong chemical binding to the surface is absent and that other processes, such as physical interlocking of the gold layer is necessary for good adhesion.

Experimental and molecular modeling investigation on adsorption of gold cyanide complex onto the iron oxide and hydroxide minerals

Complex and refractory gold ores contain high amount of iron oxide and hydroxide minerals, potential adsorbents of gold through preg-robbing phenomenon. In this study, density functional theory (DFT) approach was used to investigate the adsorption of Au(CN)2- complex on hematite, magnetite, and goethite surfaces. The most stable adsorption occurred for goethite when the Au(CN)2- complex was adsorbed from the Au atom along the y axis on the Fe site and the interaction energy was the highest. The following trend was obtained for the preg-robbing potential, which is in good agreement with experiments carried out on synthetic minerals: Goethite > Hematite > Magnetite.

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-).

New gold (III) cyanide complex TGS 121 induces ER stress, proteasome inhibition and death of Ras-hyperactivated cells

Metal-based agents in cancer therapy, like cisplatin and its derivates, have established clinical applications but also can induce serious side effects. Thus, metallotherapeutic alternatives for platinum derivatives are developed and intensively studied. Platinum is replaced by several transition metals including gold. Especially gold (III) complexes can have the same square-planar structure and are isoelectric with platinum (II). Hence, they are developed as potential anti-cancer drugs. Thus, our group projected and developed a group of novel cyanide-based gold (III) complexes.Within this work, we aimed to characterize the safety and effectivity of one of them, TGS 121. TGS 121 in our preliminary work was selective for Ras-hyperactivated cells. Here we studied the effects of the novel complex in cancerous Ras-3 T3 and non-cancerous NIH-3 T3 cells. The complex TGS 121 turned out to be non-toxic for NIH-3 T3 cells and to induce death and alternations in Ras-hyperactivated cells. We found induction of ER stress, mitochondria swelling, proteasome inhibition, and cell cycle block. Moreover, TGS 121 inhibited cell migration and induced the accumulation of perinuclear organelles that was secondary to proteasome inhibition.Results presented in this report suggest that stable gold-cyanide TGS 121 complex is non-toxic, with a targeted mechanism of action and it is promising in anticancer drug discovery.

Modelling of the kinetics adsorption of gold (I) cyanide complex ion by active carbons prepared from Parinari macrophylla shells

Nowadays, one of the sectors to valorization of waste is their transformation in nobler materials rather than in energy. This study is about the valorization of agricultural waste (Parinari Macrophylla shells) for the development of active carbons, the characterization of porous materials gotten and the kinetic study for adsorption of gold (I) cyanide complex ion. The development is made by impregnation in KOH followed of a pyrolysis under flux of N2 or CO2. The characteristics determined for adsorption are iodine index, methylene blue index, pH to point of zero charge (pHPZC) as well as the textures characteristics gotten by adsorption of nitrogen at 77 K. For adsorption of gold (I) cyanide complex ion , the kinetics model’s pseudo-order 1, pseudo-order 2, the model of Elovich and those diffusions of Boyd and Weber-Morris are studied. The results of the characterization showed that samples are basic (pHPZC > 7), present the specific surfaces of 1008 m2/g and 1063 m2/g with percentages in microporous surface more than 78% and for microporous volume more than 71%. The kinetics of adsorption of gold (I) cyanide complex ion (Au(CN)2-) obeys more to pseudo-order 2 model and a multi-linearity of the models of Elovich and diffusions during adsorption.

Modelling of the kinetics adsorption of gold (I) cyanide complex ion by active carbons prepared from Parinari macrophylla shells

Modelling of the kinetics adsorption of gold (I) cyanide complex ion by active carbons prepared from Parinari macrophylla shells

Destabilisation of gold cyanide complex by sulphur species: A computational perspective

The interaction of gold cyanide complex with elemental sulphur and all metastable sulphur species has been studied using Density Functional Theory (DFT). The elemental sulphur and sulphide species formed during pre-treatment of refractory gold ores or dissolution of sulphide minerals form a series of metastable species including hydrosulphide, polysulphide, thionates, sulphite and finally sulphates which are known to have a detrimental effect on gold cyanidation. Previous researchers have attributed this effect mainly to passivation of the gold surface. However, interaction of dissolved aurocyanide with sulphur species has received almost no attention. Here, DFT molecular modelling has been used for the first time to describe the interaction of dissolved gold cyanide and sulphur species, and to explain the reduction and destabilisation potential of sulphur species in gold cyanidation.Computational modelling shows that sulphur species can have a significant negative effect on the stability of gold cyanide complex. Elemental sulphur and sulphide ion with −446.6 and − 198.4 kJ.mol−1 interaction energies have the most negative effect. S0 and S2− contribute to the destabilisation of gold cyanide via two different mechanisms of precipitation of AuCN and thiocyanate formation as well as reduction of gold by formation of sulphite and sulphates respectively. The effect of elemental sulphur can be neutralised by excess free cyanide in solution, while sulphide ion can still stay reactive toward gold cyanide in the presence of free cyanide. Addition of lead salt can decrease the inhibiting effect of sulphide ions by formation of lead sulphide. However, lead cannot eliminate the negative effect of elemental sulphur. It is concluded that oxidation of sulphur species can significantly overcome the adverse impact of sulphur species on the stability of gold cyanide complex. The destabilisation of gold cyanide complex by sulphur metastable species is introduced as one of the main mechanisms for loss of gold in sulphide gold ores.

Mechanistic Insights into C(sp2)−C(sp)N Reductive Elimination from Gold(III) Cyanide Complexes

AbstractA new family of phosphine‐ligated dicyanoarylgold(III) complexes has been prepared and their reactivity towards reductive elimination has been studied in detail. Both, a highly positive entropy of activation and a primary 12/13C KIE suggest a late concerted transition state while Hammett analysis and DFT calculations indicate that the process is asynchronous. As a result, a distinct mechanism involving an asynchronous concerted reductive elimination for the overall C(sp2)−C(sp)N bond forming reaction is characterized herein, for the first time, complementing previous studies reported for C(sp3)−C(sp3), C(sp2)−C(sp2), and C(sp3)−C(sp2) bond formation processes taking place on gold(III) species.

Mechanistic Insights into C(sp2 )-C(sp)N Reductive Elimination from Gold(III) Cyanide Complexes.

A new family of phosphine-ligated dicyanoarylgold(III) complexes has been prepared and their reactivity towards reductive elimination has been studied in detail. Both, a highly positive entropy of activation and a primary 12/13 C KIE suggest a late concerted transition state while Hammett analysis and DFT calculations indicate that the process is asynchronous. As a result, a distinct mechanism involving an asynchronous concerted reductive elimination for the overall C(sp2 )-C(sp)N bond forming reaction is characterized herein, for the first time, complementing previous studies reported for C(sp3 )-C(sp3 ), C(sp2 )-C(sp2 ), and C(sp3 )-C(sp2 ) bond formation processes taking place on gold(III) species.

Bioleaching of gold from waste printed circuit boards by alkali-tolerant Pseudomonas fluorescens

This paper evaluated the ability of Pseudomonas fluorescens to leach gold from waste printed circuit boards (WPCBs). Gold was recovered as gold-cyanide complex and cyanide was produced by Pseudomonas fluorescens. In this paper, the effect of pH on gold leaching efficiency was studied, the P.fluorescens was domesticated to grow at higher pH (pH 8 and 9), and the concentration of cyanide ions (CN−) available for bioleaching was increased in alkaline pH. The results showed that at 0.67% w/v pulp density of pretreated waste printed circuit boards powder, mutated bacteria attained gold biorecovery of 27% at pH 9, while the unadapted bacteria only 23% of bioleaching efficiency was achieved. Results revealed that bioleaching efficiency of gold from waste printed circuit boards decreased with the increase of pulp density, and 0.33% w/v pulp density had the maxnium influence to bioleaching efficiency of gold, which could reach 42%. In the two-step bioleaching process, the initial amounts of bacteria had a certain impact on the leaching efficiency, and 3.33% v/v of the initial bacterial liquid was a suitable addition. The type of substrate also affected the leaching bioleaching efficiency. The leaching efficiency in the later stage of gold leaching will be greatly improved to 54%, when glycine and methionine were added to the medium for cyanide production. This may be due to positive effect by the methionine, which could regulate the glycine pool of the cells.

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.

Reduction of preg-robbing activity of carbonaceous gold ores with the utilization of surface blinding additives

The carbonaceous matter present in some gold ores adsorbs the gold cyanide complexes from the leached solution and transport them to tailings, resulting in loses and preventing the recovery of the metal – a phenomenon known as preg-robbing. The present work aims at evaluating the capacity of 8blinding additives to deactivate/passivate the carbonaceous matter present in mineral coals and in gold ores. Initially, adsorption experiments with 3 mineral coals at different levels of maturation (anthracite, bituminous and lignite) were carried out to simulate the complex carbonaceous matrix of the gold ores. The coal presenting the best adsorptive capacity was selected for the experiments with the blinding additives. Different concentrations of additives (562–28,125 g/tcoal) and conditioning times (5, 30 and 120 min) were investigated. The blinding additives presenting satisfactory results were used in the deactivation/passivation carbonaceous gold ore experiments. Adsorption experiments showed that the anthracite coal adsorbed gold cyanide while bituminous and lignite coal failed to do so. It is believed that the difference in the adsorptive capacity presented by the mineral coals owes to the structure of the carbonaceous material, and also that the anthracite coal structure is similar to what is found in the carbonaceous gold ores presenting preg-robbing activity. The deactivation/passivation experiments indicated that the additives A1, A2, A3, A4 and A5 suppressed the adsorptive capacity of the anthracite by 60–85% in concentrations varying from 562 to 28,125 g/tcoal respectively. The additive presenting the best performance was A2. Experiments with a carbonaceous gold ore indicated that the use of 350 and 1000 g/tgold ore of additive A1 presented the best recoveries, 90.12 and 90.69%, resulting in the lowest presence of gold contents in the tailings, 1.17 and 1.25 g/t respectively. These values are very close to what was reported for CIL leaching (89.89% and 1.30 g/t) and considerably higher than values observed in the conventional leaching (83.79% and 2.10 g/t). Despite presenting the best deactivation/passivation performance when used with the anthracite coal, additive A2 did not reduce the preg-robbing activity of the carbonaceous matter of the ore, resulting in an increase in gold content in the tailing. The use of additives in the industrial process will demand a simpler and less expensive operational facility and the performance will be similar to the CIL technique.

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.

Efficient extraction of gold(I) from alkaline aurocyanide solution using green ionic liquid-based aqueous biphasic systems

Abstract Ionic liquid-based aqueous biphasic extraction is an environmentally benign technology for separation of various substances. In this study, aqueous biphasic systems (ABSs) consisting of 1-alkyl-3-methylimidazolium bromide ionic liquids (ILs) (alkyl = butyl, hexyl, and octyl) and phosphate-based salts were studied for extraction of gold(I) from alkaline aurocyanide solutions for the first time. The results indicated that gold(I) preferentially migrated into the IL-rich phase, achieving remarkable extraction efficiency up to 99.9%. The extraction mechanism of gold(I) was evaluated based on characterization by FT-IR spectroscopy, X-ray photoelectron spectroscopy. The results revealed the electrostatic interaction between gold(I) cyanide complex and IL was the main driving force for gold(I) partition. The migration of gold(I) into IL-rich phase was associated with an extraction mechanism by ion pair formation of [Cnmim+]•[Au(CN)2−]. Furthermore, the microscopic structure of the IL-rich solution was also determined by transmission electron microscopy. It was found that the presence of [Au(CN)2−] anion induced the aggregation of ionic liquids. Finally, the gold present in IL-rich phase was successfully recovered by direct electrodeposition on a copper cathode. The proposed extraction strategy using IL-based ABSs is envisaged as potential platform for the green partition of gold(I) from alkaline aurocyanide solution.

Recovery of Au(CN)2− with magnetic reduced graphene oxide hydrogel in aqueous leach solution

Magnetic reduced graphene oxide hydrogel as an adsorbent could be easily separated from water or solid suspensions. In this work, reduced graphene oxide/magnetite/ascorbic acid hydrogel (rGO/Fe3O4/AAH) was fabricated through one-step hydrothermal method as the adsorbent for gold-cyanide complex ions (Au(CN)2−) in aqueous solution. The study was performed through the measurement of adsorption capacity and characterization via XRD, FT-IR, Raman, SEM, TEM and XPS. The results indicated that nano-scale magnetite particles were successfully anchored on rGO sheets and three-dimensional rGO/Fe3O4/AAH was generated during the hydrothermal process. The adsorption results suggested that rGO/Fe3O4/AAH was an effective adsorbent for recovering Au(CN)2− from aqueous solution with the maximum adsorption capacity of 309 mg/g, while the spent rGO/Fe3O4/AAH could be easily collected using a magnetic separator. The adsorption of Au(CN)2− on rGO/Fe3O4/AAH was found to be spontaneous, endothermic process. These results could be of great significant guidance for efficiently recovering Au(CN)2− from ore slurry in the future.

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.

Recovery of [Au(CN) 2 ] − from gold cyanidation with graphene oxide as adsorbent

Abstract The recovery of gold cyanide complex Au(CN) 2 − from gold cyanidation with graphene oxide (GO) and GO hydrogel have been studied to explore the possibility of the application of GO or GO hydrogel in gold cyanidation process for extracting gold. The study was performed on the adsorption of artificial Au(CN) 2 − aqueous solution on GO and GO hydrogel. The adsorption results, as well as the SEM-EDS, AFM and XPS, demonstrated that GO was a better adsorbent for the recovery of Au(CN) 2 − from aqueous solution than conventional activated carbon because of its higher adsorption capacity and adsorption rate. It has been also found that the adsorption of Au(CN) 2 − on GO followed the Langmuir isotherm and fitted well with both the pseudo-first-order and pseudo-second-order kinetics models. The recovery of Au(CN) 2 − with GO might be attributed to the interaction between Au(CN) 2 − and oxygenous function groups on GO surface. GO hydrogel exhibited excellent Au(CN) 2 − adsorption property and easy separation, which enabled it a potential adsorbent in gold cyanidation.

Efficient adsorption of Au(CN)2− from gold cyanidation with graphene oxide-polyethylenimine hydrogel as adsorbent

Abstract The adsorption of gold cyanide complex ion (Au(CN)2−) on graphene oxide-polyethylenimine hydrogel (GO/PEI hydrogel) from gold cyanidation has been studied to explore the possibility of the application of GO/PEI hydrogel in gold cyanidation process for extracting gold from ores. The adsorption was carried out in artificial Au(CN)2− aqueous solution with GO/PEI hydrogel as adsorbent. The experimental results, as well as IR, XPS and SEM−EDS, have shown that GO/PEI hydrogel exhibited a high adsorption capacity and a fast adsorption rate of Au(CN)2−, suggesting that GO/PEI hydrogel might be a good adsorbent for the recovery of Au(CN)2−. The adsorption of Au(CN)2− on GO/PEI hydrogel obeyed the Langmuir isotherm model and fitted well with the pseudo second order model. The good recovery of Au(CN)2− was largely related to the porous structure, large specific surface area, as well as the oxygenous functional groups on the surface of GO/PEI hydrogel.

Statistical Optimization, Kinetic and Isotherm Studies on Selective Adsorption of Silver and Gold Cyanocomplexes Using Aminoguanidyl- Chitosan Imprinted Polymers

Aminoguanidyl-chitosan imprinted polymers (AGCIPs) were synthesized and applied to the selective extraction of silver and gold cyanocomplexes from aqueous solutions. Batch adsorption parameters for the recovery of silver and gold cyanocomplexes from aqueous solutions by the AGCIPs viz., contact time, solution pH, initial metal concentrations and temperature, were optimized by a two-level fractional factorial design and the Box-Behnken matrix. The equilibrium data correlated well with Langmuir isotherm model; and the maximum adsorption capacities for silver cyanide calculated from the Langmuir equation were 429.2 mg Ag g-1 and 319.5 mg Ag g-1 at pH 6.9 and 10, respectively; whereas they were 319.5 mg Au g-1 and 312.5 mg Au g-1 for gold cyanide in the same order. Adsorption kinetics suggested that these materials predominantly display a pseudo-second-order kinetic mechanism, while thermodynamic parameters revealed that the adsorption process was spontaneous and of exothermic nature. Investigation on the adsorption selectivity showed that the selectivity coefficients of AGCSIP (gold cyanide) with respect to Ag(CN)2 -, Fe(CN)6 -, and Hg(CN)2 - were 8.675, 26.005 and 5694.667 respectively whereas for AGCIP (Silver cyanide) they were 3.017, 75.478 and ∞ for Au(CN)2 -, Fe(CN)6 -, and Hg(CN)2 - respectively. This indicates that AGCSIPs have excellent selectivity for silver and gold cyanide complexes. Regeneration and reusability studies also revealed that 2M solution of KNO3 at pH 10.5 could be used to regenerate the AGCIPs; and these materials could be recycled up to five times without significantly diminishing their adsorption capacity.

Meeting the challenge of Penjom Gold Mine’s geology in the recovery of fine gold in carbonaceous ores

Ore bodies that were previously deemed unfeasible to mine have now become economically feasible due to the increase of gold price in recent years. In addition to the increase in gold price, some processes that have been under development have now been proven viable. Also, the geology of a mine would influence the recovery strategy of the gold from the ores. Evidence of this is seen at Penjom Gold Mine (PGM) in Malaysia, where carbonaceous gold ores are mined and processed. PGM produces one of the world's worst preg-robbing gold ores, yielding very low recoveries from traditional carbon-in-leach methods. Preg-robbing is preferential absorption of gold-cyanide complex ions (Au(CN) 2 - ) by organic carbon in the carbonaceous gold ores. The gold processing facilities in PGM are designed to address the challenges of fine gold recovery from carbonaceous and sulphide ores. Since employing the resin-in-leach process in mid-1999, gold recovery rates consistently run close to 90% which is a remarkable 30% improvement over recovery rates using activated carbon. The resin-in-leach process is not as common and appears as a result of thorough development work conducted since late 1940s. The objective of this paper is to analyse how preg-robbing carbonaceous gold ores can be processed economically. This objective will be achieved through literature research and using the most recent practical work findings from PGM. Optimization of process parameters in order to achieve acceptable gold recovery under low operating costs will be emphasized. The most important finding from this paper is the success of the resin-in-leach process in recovering gold from carbonaceous gold ores and the most up-to-date process parameters of cyanide concentration, temperature, and pH used in the hydrometallurgical circuit.