Gold In Cyanide Solutions Research Articles

The role of oxidants in the intensive cyanidation of gold. 1. Gold dissolution

In the intensive cyanidation of gravity gold concentrates, sodium m-nitrobenzene sulfonate (NBS) is often used to supplement dissolved oxygen as the oxidant in the process. This paper presents the results of a largely electrochemical study of the behaviour of NBS during cyanidation. The results have confirmed that NBS acts as an oxidant in the cyanidation of gold and that the mixed potential model can be applied to describe the mechanism of its action.The mixed potential is a good initial indicator of the rate of gold dissolution and, as expected, the anodic dissolution of pure gold in cyanide solutions is characterized by passivation at potentials above about −0.35 V.The reduction of oxygen under the conditions of the present study occurs in two 2-electron steps with peroxide as an intermediate. Dissolution of gold occurs at potentials in the diffusion-controlled region for the first step. The cathodic reduction of NBS occurs in the same potential region as the reduction of oxygen. The reaction is first order in the concentration of NBS and is largely independent of the pH. The stoichiometry of the reaction involves six moles of gold per mole of NBS confirming that the amine is the final product of reduction of NBS.Rates of gold dissolution in various solutions have been measured using a calibrated linear polarisation method. The rate increases approximately linearly with increasing NBS concentration and is independent of pH. The rate in 0.5 g/L NBS is approximately the same as in oxygenated solutions.A relatively simple titration has been adapted for use in determining NBS concentrations.

Study of Preg-Robbing with Quicklime in Gold Cyanide Solutions Analyzed by Time-of-Flight Secondary Ion Mass Spectrometry

Preg-robbing is a phenomenon in which minerals retain gold, especially due to the presence of species like carbonaceous matter and silicates in the mineral. This study demonstrates the impact of quicklime, used to adjust the pH of a gold cyanidation solution, on the retention of gold contained in pregnant cyanidation solutions and sorption mechanisms. The retention capacity of four quicklime solutions was evaluated using proportions of 200 g of lime in 800 mL of solution and 10 g of lime in 500 mL of solution. The concentrations of the gold cyanide solutions were 10, 15, and 25 ppm. The insoluble lime residue in the acetic acid solution was separated and analyzed by XRD, FTIR, elemental carbon, and Raman spectroscopy techniques. SEM and TOF-SIMS were used to analyze the lime samples after exposure to the gold cyanide solution. The results show that retention was attributable to quicklime due to the effects of its carbon and silicate content, although chemisorption and physisorption mechanisms may also be responsible.

Oxidatively modified carbon as a promising material for gold extraction

In this work, we prepare a material termed oxidatively modified carbon (OMC), which significantly outperforms commercial activated carbon products available on the gold mining market. The intriguingly high sorption efficiency of OMC is explained by the graphene oxide (GO) like fine chemical structure of the particles' surface. At the same time, OMC can be easily prepared from readily available carbon sources by wet chemistry protocols with the cost of production ~10 lower than that for GO. The particulate structure of OMC allows simple separation from the used-up solutions. Addition of ammonia to the gold-cyanide solution, additionally boosts sorption capacity of OMC. The developed material can be used in gold mining industry as a sorbent, which can potentially increase the efficiency of the gold extraction process.

Study of the effect of high-temperature activation of quartz on the adsorption of gold cyanide

• Gold cyanide ions are chemically adsorbed onto the quartz surface after high-temperature activation. • After high-temperature activation, Au-Si is adsorbed together, and the valence state of Au is + 1. • The N-Si bonding is enhanced after high-temperature activation. • The Au-O interaction on the surface of Au(CN) 2 − and quartz is transformed into a Au-Si interaction. The leaching rates for gold in the roasting oxidation pretreatment-cyanidation gold leaching process are generally low. An adsorption experiment for quartz baking slag (roasting time of 3 h, roasting temperature of 650℃) and gold cyanide solution was carried out under different stirring time conditions. It is found that after high temperature activation of the quartz surface, gold cyanide can be adsorbed. When the stirring time reaches 50 min, the adsorption rate is 6.08%, and the unit adsorption amount is 0.05 mg·g −1 . The EDS spectrum clearly shows that the Au element is distributed among Si and O, and 0.02% Au is adsorbed on the surface of the quartz baking slag. To further prove the adsorption mechanism for the gold cyanide solution and quartz slag, infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface of quartz slags. Infrared spectroscopy analysis shows that new peaks emerge at 1429 cm −1 , 1878 cm −1 , and 1996 cm −1 after the elution experiment, and the characteristic peaks for inorganic cyanide are observed at 1878 cm −1 and 1996 cm −1 . This shows that after high-temperature activation of the quartz baking slag, chemical adsorption of gold cyanide occurs. The results obtained from X-ray photoelectron spectroscopy (XPS) show that during the adsorption process, Au-Si is adsorbed together, and Au shows a valence of + 1, which indicates that Au(CN) 2− ions are adsorbed onto the quartz activated at high temperature. Density functional theory (DFT) was used to determine the adsorption mechanism for Au(CN) 2− ions and different sites on the surface of quartz (1 0 1) before and after high-temperature activation (three Au-O, Au-Si, and N-Si adsorption sites). During the high-temperature activation process, the Au-O bonds and interactions on the surface of gold cyanide and quartz gradually transform into Au-Si bonds and interactions, and the N-Si bonds are also enhanced. This shows that the adsorption of gold cyanide onto quartz baking slag is enhanced after high-temperature activation. The simulation calculation result is consistent with the experimental results.

Dissolution of gold in chalcopyrite-containing cyanide solutions

The gold dissolution in anoxic cyanide solution in the presence of chalcopyrite was studied with a rotating disc electrode. It was found that the presence of chalcopyrite reduced and enhanced the dissolution activity of pure gold in the low and high potential regions, respectively. The dissolution of gold was diffusion-controlled at low potentials (≤177 mV) and low cyanide concentrations (≤980 mg/L); however, above the cyanide concentration of 980 mg/L, the current density of gold decreased and the dissolution of gold changed from diffusion-control to electrochemical reaction-control. At high potentials (>177 mV), gold dissolution was always controlled by diffusion. In cyanide solution containing chalcopyrite, appropriate increase of pH value and temperature could accelerate the dissolution of gold, but high pH value would promote the generation of passivation, which was harmful for the dissolution of gold in cyanide solution.

Gold recovery from very dilute solutions from a mine in closing process: Adsorption-desorption onto carbon materials

The aurocyanide complex recovery by precipitation with zinc decreases when gold concentration drops to <20μgL−1. Therefore, a technology capable of recovering gold from very diluted solution is necessary. Adsorption and desorption experiments were carried out with real solutions in batch and in continuous processes to determine the gold adsorption capacity and rate onto two activated carbons (AC). The results showed that AC F400 and CSC removed 86 and 81μgg−1, respectively, at pH11 and Ce of 10μgL−1 in about 4h. Whereas desorption test by NaOH and CN− showed a gold recovery of up to 86%. These experiments were correlated to the textural and chemical properties of adsorbents and to the chemical composition of samples from a heap leach process. AC is a highly efficient and selective adsorbent for gold cyanide solutions when gold is present in very low concentration (<12μgL−1).

Active and passive behaviors of gold in cyanide solutions

Active and passive behaviors of pure gold (Au) and roasted gold ore (RGO) electrodes were investigated at 25 °C in de-aerated agitated cyanide media. Cyclic voltammetry and potentiodynamic polarization with agitation at 100 r/min in 0.04 mol/L NaCN solution showed different peak positions and current densities. Potentiodynamic tests illustrate that the peak current densities increase greatly with increasing the cyanide concentration. Increasing the pH value from 10 to 11 resultes in a great decrease of current density, while it increases noticeably by decreasing the agitation from 100 to 60 r/min. In the presence of oxygen, Au and RGO electrodes show different characteristics of peak positions and corrosion rates. The potentiostatic studies show that increasing the potential from 1 to 1.4 V at pH value of 11 results in an 80% decrease of current density while decreasing the pH value from 11 to 10 at 1 V gives a 1.7 fold increase of current density, possibly due to more effective passive layer. Following polarization, electrochemical noise measurements (ENM) during decay periods show that Au results in more passive states at high potentials, showing pitting corrosion. The ENM results show that this technique can be a promising tool for a better understanding of gold leaching. The XPS studies prove the presence of passive oxides.

Effects of Under Bump Metallurgy (UBM) Materials on the Corrosion of Electroless Nickel Films

The “black pad” phenomenon, which refers to the blackening of electroless-plated nickel–phosphorus [Ni(P)] films during the immersion Au process, is reproduced using pure chemicals and its fundamental mechanisms are investigated. In the present analysis, under bump metallurgy (UBM) materials have profound effects on the black pad susceptibility, and the presence of abnormally large nodules (ALNs) is essential to the black pad occurrence. The Ni(P) films over Cu, Ag, and Au substrates all exhibit ALNs and are susceptible to black pads, while those over Ni and Co substrates do not have ALNs and therefore are not susceptible to black pad. In the former cases, submicron scale nodular variations of the surface curvature lead to variations in the P concentration in the Ni(P) films, which induces sufficiently large potential differences to drive galvanic corrosion when exposed to the electrolyte, which is a gold cyanide solution in this study. The UBM effect is ascribed to differences in the Ni(P) film growth mode, where the transition from a layer-by-layer growth mode to an island growth mode is easier over Cu, Ag, and Au UBMs.

Physico-chemical characteristics of activated carbons based on a copolymer of furfural and mineral raw materials of the Republic of Kazakhstan and their application in extracting gold from industrial solutions

Activated carbons are widely used in different industries for cleaning a variety of natural objects from of technogenic pollutants. In the article presents the results of physico-chemical investigations of activated carbons. The investigations on the sorption of gold in cyanide solutions activated sorbent based on furfural and sorbent based on shungit.

Recovery of Silver and Gold from Cyanide Solution by Magnetic Species Formed in the Electrocoagulation Process

Cyanidation is the predominant process by which gold and silver are recovered from their ores in metallurgical operations, and it is recognized that the Carbon in Pulp, the Merrill–Crowe, the Ion Exchange, and Solvent Extraction processes are used for concentration and purification of gold and silver from cyanide solutions. Among other available options for recovery of precious metals from cyanide solutions, Electrocoagulation (EC) is a very promising water and wastewater electrochemical technique that does not require high concentrations of silver and gold in cyanide solutions to yield excellent results. In this work, an introduction to the fundamentals of the EC process is given, followed by the conditions and results of the EC test run for removal of precious metals from cyanide solutions, and finally the characterization of the solid products formed during the EC process with X-ray Diffraction, SEM, and Transmission Mossbauer Spectroscopy. Results suggest that magnetite particles and amorphous iron oxyhydroxides are present (Lepidocrocite and Gohetite). With the EC process, the achieved removal efficiency of silver and gold from cyanide solutions, within 5 min, exceeded 99%.

Recovery of gold as a type of porous fiber by using biosorption followed by incineration

This study introduces a new process for the recovery of gold in porous fiber form by the incineration of Au-loaded biosorbent fiber from gold–cyanide solutions. For the recovery of gold from such aqueous solutions, polyethylenimine (PEI)-modified bacterial biosorbent fiber (PBBF) and PEI-modified chitosan fiber (PCSF) were developed and used. The maximum uptakes of Au(I) ions were estimated as 421.1 and 251.7mg/g at pH 5.5 for PBBF and PCSF, respectively. Au-loaded biosorbents were freeze-dried and then incinerated to oxidize their organic constituents while simultaneously obtaining reduced gold. As a result, porous metallic gold fibers were obtained with 60μm of diameter. Scanning electron microscopic (SEM) analysis and mercury porosimetry revealed the fibers to have 60μm of diameter and to be highly porous and hollow. The proposed process therefore offers the potential for the efficient recovery of metallic porous gold fibers using combined biosorption and incineration.

Fouling effect of different flotation and dewatering reagents on activated carbon and sorption kinetics of gold

In carbon-in-pulp and carbon-in-leach circuits, among different organic and inorganic compounds present in the gold cyanide solution, flotation reagents play the main role in the fouling of activated carbon. In this study the effects of different types and variable concentrations of flotation and dewatering reagents on the kinetics of gold sorption onto granular activated carbon (GAC) were evaluated on the basis of kinetic rate constant (i.e., k value) of an empirical rate equation. The lower the k value, the greater is the fouling effect. It was observed that the k value rapidly decreases by increasing the concentration of collectors including potassium isobutyl xanthate (PIBX) and potassium ethyl xanthate (PEX) up to 20 mg/L and at higher concentrations, the k value gradually leveled off to 53 h − 1 for PIBX, which is 46% lower than the 99 h − 1 for PEX. At low concentrations (i.e., up to 15 mg/L) of methyl isobutyl carbinol, the k value gradually reduced and at higher concentrations, the decrease is found to be more pronounced. The fouling effect of flocculant was negligible and it would be even insignificant at high concentrations. The combinational effect of flotation reagents on the kinetic activity of GAC towards gold sorption was synergistically better. The cumulative adsorption of flotation reagents onto GAC in a continuous circuit within 28 days resulted in 40% decrease of k value, although it was still above admissible limit of 80–100 h − 1 .

Co-intensification of cyanide leaching gold by mercury ions and oxidant

The effects of mercury ions on gold cyanidation were studied. The results show that under low cyanide concentration, gold cyanide process is controlled by CN − transfer, while at higher cyanide concentration, there forms passivation on gold surface. Therefore, chemical oxidation of gold in cyanide solution of higher concentration is controlled by surface reaction. Small quantity of additions of mercury ions bring about great increases in anodic gold dissolution rate, decreases the passivation and reduces the equilibrium activated energy. In addition, they also markedly change the effect pattern of cyanide concentration. Mercury ions show positive effects on cathodic reduction of oxygen and raise the rate of electrochemical step of the cathodic reduction of oxygen. Addition of a certain amount of hydrogen peroxide is confirmed to be an effective way for intensification of cathodic process on gold electrode. Active potential range and current peak on anodic dissolution are enlarged when being co-intensified with Hg 2+ and hydrogen peroxide. Co-intensifying effect may be obtained and gold leaching rate is considerably increased on cyanide leaching of gold from gold concentrates.

Recovery of zero-valent gold from cyanide solution by a combined method of biosorption and incineration

A new combined way of biosorption and incineration is presented for the recovery of gold from gold-cyanide solutions. Decarboxylated biosorbent (DCB) was prepared by removing interfering carboxyl groups from the surface of inactive Corynebacterium glutamicum. The recovery of gold from the exhausted biosorbents was performed using elution or incineration. The maximum gold(I) uptakes were obtained as 50.19 and 86.16mg/g for the raw biomass and DCB, respectively. The biosorption performance of DCB indicated that interfering carboxyl groups were successfully removed. The recovery efficiency of ionic gold through elution and purity of metallic gold by means of incineration were over 93% and as high as 61.89%, respectively. The result of XPS analysis indicated that the gold(I) was able to be reduced into zero-valent gold during incineration. It was noted that the combined method of biosorption and incineration could be effective for concentration and recovery of gold from the cyanide solutions.

A Study on the Mechanism of Black Pad Formation during Electroless Nickel Immersion Gold process

The “Black Pad” phenomenon referring to blackening of electrolessly plated nickel-phosphorous (Ni(P)) films after the immersion gold (IG) process was reproduced using pure chemicals for the first time. Chemical composition of the electrolyte most suitable for the black pad reproduction was proposed, and it was found that submicron scale nodular variation of the P content of the Ni(P) film induced potential differences large enough to drive galvanic corrosion when exposed to the electrolyte; gold cyanide solution in this case. Instead of conventional potential measurement techniques, corrosion couple experiments using Ni(P) films with different P content were performed to substantiate preferential corrosion, which occurred at the lower P side with the propensity of forming black pad getting more severe with the P content difference (ΔP) between films. Subsequent AFM analysis showed that variations of nodular shapes and curvatures among nodules led to submicron scale variations of the P content in the film, which could promote galvanic corrosion.

Comparison of catalytic activity of thallium and lead adatoms at the gold electrodeposition and dissolution in cyanide solutions

Catalytic activity of thallium and lead adatoms is compared in electrode processes involving gold in cyanide solutions. It is shown that in the presence of considered atoms on the interface, the gold dissolution is accelerated to the greater extent than its electrodeposition. Lead adatoms are shown to exert a substantially stronger effect on the anodic dissolution rate as compared with thallium adatoms, whereas the opposite trend is observed in the cathodic deposition. An explanation for the fact is proposed.

Electrochemical fabrication of single-crystalline and polycrystalline Au nanowires: theinfluence of deposition parameters

We report the electrochemical growth of gold nanowires with controlled dimensions andcrystallinity. By systematically varying the deposition conditions, both polycrystalline andsingle-crystalline wires with diameters between 20 and 100 nm are successfully synthesized inetched ion-track membranes. The nanowires are characterized using scanning electronmicroscopy, high resolution transmission electron microscopy, scanning tunnellingmicroscopy and x-ray diffraction. The influence of the deposition parameters, especiallythose of the electrolyte, on the nanowire structure is investigated. Gold sulfite electrolyteslead to polycrystalline structure at the temperatures and voltages employed. In contrast,gold cyanide solution favours the growth of single crystals at temperatures between 50 and65 °C under both direct current and reverse pulse current deposition conditions. Thesingle-crystalline wires possess a [110] preferred orientation.

Effects of sulfide and lead nitrate addition to a gold cyanidation circuit using potentiodynamic measurements

Corrosion potentiodynamic polarization experiments on a gold electrode in a cyanide solution with 0–30 ppm lead addition and 0–20 ppm sulfide were carried out. Solutions containing 300 ppm NaCN, adjusted to a pH 11.1 by NaOH and bubbled with air were used at atmospheric pressure and room temperature. If the concentration of lead ions was equal or larger than the sulfide ions a change of potential towards the more negative potential (a potential drop) was observed and this was accompanied by a significant increase in the corrosion rate (up to 10 mm y-1 in certain circumstances). If lead nitrate was added to a solution with a gold electrode that had been previously passivated by sulfides, the corrosion rate typically rose from about 0.3 to 0.95 mm y-1. The addition of lead nitrate to sulfides in cyanide solution can create a synergetic effect which results in an increase in dissolution rates of gold in cyanide solutions and this is accompanied by a drop in the corrosion potential of gold and a dramatic decline in thiocyanate and free sulfide concentrations.

Biological gold recovery from gold–cyanide solutions

This paper describes a process for recovering gold from aqueous cyanide solutions using naturally occurring soil microorganisms. In this research, microbes successfully liberated gold cations from aurocyanide complexes. The gold was subsequently captured on iron and zinc electron donors. Three sets of bench scale experiments were conducted using cyanide degrading biomass that had been enriched on cyanide as a sole nitrogen source. After cyanide degrading microorganisms populated microcosm reactors, the biomass was fed with a gold cyanide solution. Microorganisms consumed the CN − moiety of aurocyanide complexes, releasing gold cations. A portion of the gold was recovered on steel wool or zinc which served as cathodes. Although gold recovery rates were low, methods for improving efficiency were investigated.

Kinetics of enhanced gold dissolution: activation by dissolved silver

Coupled oxygen reduction and metal oxidation occur during leaching of gold in cyanide solutions. Both processes are altered by specific surface-active constituents in solution. Dissolved cyanide in solution depresses the rate of oxygen reduction while the presence of silver in solution enhances the rate of reduction. Similarly, the oxidation (dissolution) rate of gold is dramatically increased by dissolved silver in solution. For both cathodic and anodic processes, silver enhancement approaches a maximum near 1 ppm dissolved silver for low cyanide concentrations. High concentrations of cyanide diminish the effect of silver, indicating a competition between silver and cyanide for specific surface sites. These effects are demonstrated using cyclic voltammetry under a variety of conditions. Reaction rates, based upon potentiostatic, current-time data, are well correlated by a paralinear rate model. The model includes steady-state formation of a passivating film at the metal film interface, metal (gold ion) diffusion through the film, and dissolution at the film solution interface. Silver is found to enhance both the film diffusion process and film dissolution.