Desorption Of Gold Research Articles

Investigation into the influence of hydroxyl ions on the mechanism of interaction between cyanic compounds of gold and an active surface of carbon sorbents

In the framework of methods of quantum-chemical simulation, the possible participation of hydroxyl groups in the sorption and desorption of aurocyanides on active surfaces of aromatic characters is investigated. It is shown that the saturation of an active surface with hydroxyl groups leads to a considerable lowering of the barriers of sorption and desorption. This effect can be used to intensify the desorption of gold and silver from active carbons.

A paradigm for predicting selective oxidation on noble metals: oxidative catalytic coupling of amines and aldehydes on metallic gold

We demonstrate in the present work that relatively straightforward acid/base principles of surface reactivity predict oxygen-assisted amine-aldehyde coupling on metallic gold. Formed via the oxygen-assisted (Brønsted acid) N-H bond activation of dimethylamine, (CH3)2N(a) acts as a nucleophile to couple with various aldehydes, forming the corresponding amides. At low initial coverages of oxygen on the surface very high selectivities are achieved. The reaction proceeds via the surface-bound hemiaminal intermediate, which beta-hydride eliminates well below room temperature to form the amide product. On metallic gold desorption of the amide appears to be the rate-limiting step. Under the transient conditions employed in this work oxygen-assisted coupling of the amine with alcohols is limited, suggesting that such reactions must be conducted in the steady state in order to have both the aldehyde and adsorbed (CH3)2N(a) present simultaneously.

Synthesis of MPTS-modified cobalt ferrite nanoparticles and their adsorption properties in relation to Au(III)

Cobalt ferrite magnetic nanoparticles (Co-MNP) were prepared by a co-precipitation method and subsequently coated with (3-mercaptopropyl)trimethoxysilane (MPTS) for the extraction and recovery of Au(III) from aqueous chloride solutions. Physical characterization of the MPTS-modified particles (Co-MPTS) was performed using FT-IR, TGA, and SEM. Results from FT-IR confirmed that MPTS was present on the surface of the magnetic nanoparticles. The amount of MPTS was 0.36 mmol g −1 of Co-MPTS, obtained by elemental analysis. SEM images revealed aggregates composed of nanocrystalline Co-MPTS particles. The extraction efficiency as a function of the pH, contact time, and initial Au(III) concentration was evaluated. The modified particles showed maximum adsorption in the pH range from 1.0 to 4.0. The adsorption behavior of Co-MPTS toward Au(III) followed a Langmuir isotherm and the maximum adsorption capacity was found to be 120.5 mg g −1. The stability of the modified materials was improved as compared to that of bare Co-MNP. The subsequent desorption of gold could be achieved by using acidified thiourea solution; the highest gold recovery reached 85%.

The Uptake of Gold(I) from Ammonia Leaching Solution by Imidazole Containing Polymeric Resins

The polymeric resins containing guanylthiourea, 1-methylimidazole, 2-mercapto-1-methylimidazole ligands have been synthesized from vinylbenzyl chloride-divinylbenzene copolymers and used in the removal of Au(I) from ammonium buffer and ammoniacal thiosulphate solutions. The best gold sorption from ammonium buffer that contains 100 g/dm3 NH3 · H2O and 5 g/dm3 (NH4)2SO4, is reached in the case of 1-methylimidazole resin (2) (27.9 mg/g) and all three resins do not have a measurable sorption of copper(II) ammine complexes. The resins display a higher affinity towards gold(I) from ammoniacal thiosulphate solutions than from the ammonium buffer solution. The XPS analysis of gold loaded resins suggests the presence of gold at Au(I) oxidation state, most likely in the form of ionic pair Au(NH3)2 +OH− or neutral complex AuNH3OH and as highly-dispersed metallic gold. The degree of gold desorption is about 50% using 1% potassium cyanide solution in 0.3% hydrogen peroxide solution. Resins retain their capacity towards gold in five consecutive sorption/desorption cycles.

Adsorption of gold ions from industrial wastewater using activated carbon derived from hard shell of apricot stones – An agricultural waste

In this study, hard shell of apricot stones was selected from agricultural solid wastes to prepare effective and low cost adsorbent for the gold separation from gold-plating wastewater. Different adsorption parameters like adsorbent dose, particle size of activated carbon, pH and agitation speed of mixing on the gold adsorption were studied. The results showed that under the optimum operating conditions, more than 98% of gold was adsorbed onto activated carbon after only 3 h. The equilibrium adsorption data were well described by the Freundlich and Langmuir isotherms. Isotherms have been used to obtain thermodynamic parameters. Gold desorption studies were performed with aqueous solution mixture of sodium hydroxide and organic solvents at ambient temperatures. Quantitative recovery of gold ions is possible by this method. As hard shell of apricot stones is a discarded as waste from agricultural and food industries, the prepared activated carbon is expected to be an economical product for gold ion recovery from wastewater.

Sorptive Recovery of Gold(I) from Cyanide-containing Aqueous Alkali with Resins Containing Guanidinium Sorption Sites

A technique was developed for desorption of gold(I) from a strongly basic resin containing guanidinium sorption sites with aqueous-organic alkalis.

Thiocyanate solutions in gold technology

The scope for using KSCN solutions in the field of gold leaching from chemical preparation products of hard arsenopyrite concentrates is shown. More than 95% gold is recovered in weak acidic solutions (pH=2–5) at KSCN concentration 0.4 mol/L. The thiocyanate complexes are recovered on carbon adsorbents (BAU, UC, LKAU-4) as well as on ion exchangers (AV-17-10P, AP-100). The gold recovery degree is 99.2–99.8%. The desorption of gold from ion exchangers can be done by thiocarbamide solutions in H 2SO 4 at room temperature, and from carbon adsorbents by basic thiocarbamide solutions at ∼150 °C.

Adsorption of aurocyanide complexes onto carbonaceous matter from preg-robbing Goldstrike ore

Aurocyanide complex adsorption by naturally occurring carbon in Goldstrike ore has been implicated in a form of gold refractoriness known as “preg-robbing”. The aim of this work was to establish a relationship between the aurocyanide uptake capacity of Goldstrike ore carbonaceous matter and the preg-robbing behavior of the parent ore. The effect of varying contact time between the aqueous gold–cyanide and the carbonaceous matter on the uptake of aurocyanide complexes was also investigated. In column adsorption experiments, the adsorbed gold concentration from 100 mL of a gold–cyanide solution depended on the flow rate of the solution. The concentration of adsorbed gold increased with solution flow rate, reaching a maximum concentration at a flow rate of approximately 0.05 mL/min. As solution flow rate increased to more than 0.05 mL/min, the concentration of gold adsorbed on the carbon decreased. Desorption of adsorbed gold into 75-mL sodium cyanide solution also depended on solution flow rate. Maximum desorption of gold occurred at a flow rate of approximately 0.14 mL/min. The gold adsorbed at the lowest and highest flow rates was more slowly desorbed than the additional gold adsorbed at the intermediate flow rates. The concentration of gold remaining on the carbon after desorption at 0.14 mL/min correlated to the amount of gold adsorbed at the highest and lowest flow rates in the adsorption experiments. This amount of slowly desorbed gold correlated to the preg-robbing behavior of the ore, whereas the amount of additional adsorbed gold (i.e., gold adsorbed at intermediate flow rates) was similar for all of the ores. For all of the carbonaceous matters studied, the concentration of gold sorbed in both batch and column experiments increased after autoclaving.

Controlling atomizer surfaces by varying ascorbic acid pyrolysis conditions to modify activation energies for gold desorption in electrothermal atomic absorption spectrometry

As a chemical modifier on kinetic parameters for atomic absorption signals for gold, the effect of the temperature and hold time of the ascorbic acid pyrolysis step has been investigated. The signal for gold, dispersed individually into micro-sized pores, was analysed using Arrhenius plots based on solid-phase kinetics. The first kinetic order, corresponding to desorption of individually dispersed atoms, was chosen as best possible fit for all plots. Using mass dependency of the absorbance–time profile characteristics and activation energy supported the first kinetic order. Increasing the temperature of pyrolysis of ascorbic acid above 1676 K decreased the activation energy (Ea) for desorption of the gold atoms from 325 ± 11 kJ mol−1 to 108 ± 10 kJ mol−1. Below a pyrolysis temperature of 1676 K, the Ea value was nearly constant. The high Ea value corresponded to desorption of the adatoms dispersed at active sites on a rough surface with a surface fractal dimension (D) of 2.80 ± 0.16, evaluating quantitatively the degree of surface roughness. The low Ea value corresponded to D = 2.04 ± 0.16. If D is 2, the surface is completely flat. The closer the D value is to 3, the rougher the surface. At pyrolysis temperatures of 1003 and 1470 K, the Ea decreased from 309 ± 13 and 317 ± 11 kJ mol−1 and reached an average value of 283 ± 8 and 260 ± 18 kJ mol−1, respectively, by increasing the hold time of pyrolysis of ascorbic acid. At 1720 K, Ea decreased from 258 ± 6 kJ mol−1 and reached an average value of 159 ± 8 kJ mol−1 with increasing hold time of pyrolysis. The change in Ea, corresponding to pyrolysis temperature, is discussed from the viewpoint of a change in the degree of interaction with the pore wall surface relating to a change in degree of the surface roughness.

Evaluating a Dynamic Model for the Competitive Elution of Gold and Base Metals from Activated Carbon

During the past fifteen years significant progress has been made on carbon-in-pulp (CIP) technology for the extraction of gold. Most research on the mechanisms and kinetics of CIP subprocesses has focused on the adsorption step only; auxiliary unit operations such as elution have received less attention. Mathematical models have been developed for the elution of gold and can be used for design and process optimization. The adverse effect of high loadings of a base metal such as copper on carbon during the desorption of gold is known, but not yet fully understood. A multicomponent Freundlich equilibrium model was used for the simulation and evaluation of the elution of gold and base metals from activated carbon. This model was incorporated in a material balance for a series of well-mixed reactors simulating the effects of an elution column, and was related to the elution of spectator cations such as potassium via an empirical expression. The model successfully simulated the elution profiles, but it was found that base metals, and especially copper(I), complicate the modeling of the base metals due to the consumption of cyanide and the possible formation of polymeric gold-copper species on the carbon surface. The competition coefficients are parameters which indicate the extent to which the base metals affect the elution of gold. At high copper loadings the desorption behavior of copper and gold changed, and an increased adsorptivity was detected. It was postulated that this was mainly due to the formation of copper-gold polymeric chains.

Elution of Gold from Activated Carbon Using Supercritical Carbon Dioxide

A novel method for the desorption of gold from activated charcoal is reported. Ion pair solvation of sodium dicyanoaurate (I) (Na+ … Au(CN)2 − by tributyl-phosphate facilitates the charge neutralization necessary for the elution of the ionic Au(CN)2 − by the non-polar supercritical carbon dioxide. The method is sensitive to pressure and temperature, and the static (no CO2 flow) period is more significant than the dynamic (CO2 flow) period. The presence of water is necessary to effect extraction.

Gold recovery from cyanide solutions with a new fibrous polymer adsorbent

In a resin-in-pulp process for the recovery of gold cyanide from a very dilute solution it is desirable that the resin should exhibit the ability to load gold at the natural pH of the leach liquor and be stripped by an aqueous alkali. The present work describes the results of gold cyanide adsorption by new ion-exchange hollow fibers prepared by the amination of sulfochlorinated polyethylene. The fibers, chopped into suitably sized pieces, showed very fast adsorption and desorption of gold from mixed cyanide solutions.

A Reactor Model for Gold Elution From Activated Carbon with Caustic Cyanide Solution

A model for the Zadra elution process was developed based on pore diffusion inside the carbon particles, the dispersed plug flow in the elution column, and the gold desorption from carbon as a first order reaction. A set of process description equations was obtained. Numerical solutions for the system equations are given using the finite difference method, and the stability for the method was also analyzed. Fitting of experimental elution concentration profiles using this model was presented. The model can fit both the concentration profile and the recovery curve, and can simulate the elution process up to the final stage. It was found that the elution process is controlled by a first order rate constant and the effective intraparticle diffusivity in the carbon particle. The parameter analysis showed that the rate constant was dependent on the elution temperature and the chemical composition of the eluant. The effective intraparticle diffusivity was relatively constant under the experimental conditions.

A Reactor Model for Gold Elution From Activated Carbon with Caustic Cyanide Solution

A model for the Zadra elution process was developed based on pore diffusion inside the carbon particles, the dispersed plug flow in the elution column, and the gold desorption from carbon as a first order reaction. A set of process description equations was obtained. Numerical solutions for the system equations are given using the finite difference method, and the stability for the method was also analyzed. Fitting of experimental elution concentration profiles using this model was presented. The model can fit both the concentration profile and the recovery curve, and can simulate the elution process up to the final stage. It was found that the elution process is controlled by a first order rate constant and the effective intraparticle diffusivity in the carbon particle. The parameter analysis showed that the rate constant was dependent on the elution temperature and the chemical composition of the eluant. The effective intraparticle diffusivity was relatively constant under the experimental conditions.

A reactor model for gold elution from activated carbon with caustic cyanide solution

A model for the Zadra elution process was developed based on pore diffusion inside the carbon particles, the dispersed plug flow in the elution column, and the gold desorption from carbon as a first order reaction. A set of process description equations was obtained. Numerical solutions for the system equations are given using the finite difference method, and the stability for the method was also analyzed. Fitting of experimental elution concentration profiles using this model was presented. The model can fit both the concentration profile and the recovery curve, and can simulate the elution process up to the final stage. It was found that the elution process is controlled by a first order rate constant and the effective intraparticle diffusivity in the carbon particle. The parameter analysis showed that the rate constant was dependent on the elution temperature and the chemical composition of the eluant. The effective intraparticle diffusivity was relatively constant under the experimental conditions.

The mechanism of elution of gold cyanide from activated carbon

Numerous articles have appeared on the mechanism of the adsorption of gold cyanide onto activated carbon. In contrast, little information is available on the mechanism of elution of the adsorbed gold. It is the objective of this article to formulate such a mechanism on the basis of batch and column elution tests without analyzing adsorbed species on the carbon directly. The presence of spectator cations (Mn+) enhances the formation of Mn+{Au(CN)2−}n ion pairs on the carbon, which in turn suppress the elution of gold cyanide. The dynamics of removal of these cations determine the horizontal position of the gold peak in an elution profile. When the concentration of cations in the eluant is high and no cyanide is present in the solution or on the carbon, very little desorption of gold is observed. The quantitative effect of the concentration of spectator cations on the equilibrium for desorption of aurocyanide can be estimated from the elution profiles for gold and cations. Free cyanide in the eluant, which causes some competitive adsorption of cyanide with aurocyanide, therefore plays a minor role at the elevated temperatures used in industry. A more important effect of cyanide is its reaction with functional groups on the carbon, the products of which passivate the surface for adsorption of aurocyanide, and thereby cyanide promotes the elution of aurocyanide. The degree of passivation, which is determined to a large extent by the temperature of pretreatment, also affects the elution of cations and the degradation/adsorption of cyanide itself. Reactivation of the carbon surface occurs when the adsorbed/decomposed cyanide is removed by the eluant. At high temperatures of pretreatment, such as used in practice, it is not necessary to include a reactivation term in the mathematical model for elution.

The effect of temperature on the desorption of gold cyanide from activated carbon

Activated carbon is used worldwide for the extraction of gold cyanide from leached pulps. The elution of gold cyanide is usually conducted by soaking the loaded carbon in an alkaline solution of cyanide in a column, followed by a rinse with water at temperatures higher than 100° C. Because the effects of temperature, cyanide addition and ionic strength are confounded to an extent, little has been published with which to model the dynamic behaviour of this complex process. An attempt is made in this paper to isolate and quantify the effect of temperature on the desorption of gold from activated carbon. A mathematical model for the desorption process is presented in a summarized form, and is shown to predict experimental data satisfactorily. An increase in temperature results in a decrease in the adsorption and in an increase in the decomposition of cyanide. An activation energy of 87.1kJ mol −1 was determined for the decomposition of cyanide, which occurs mainly by hydrolysis at elevated temperatures. The isosteric heat of adsorption of gold cyanide decreased from 18.2 to 8.8kJmol −1 when a pre-treatment of cyanide was used prior to desorption. Therefore, the gold equilibrium becomes less sensitive to temperature after pre-treatment with cyanide. The desorption of gold cyanide seems to be more sensitive to the cation concentration at high temperatures. An increased temperature increases the maximum of the elution profile, and therefore enhances significantly the dynamics of desorption.

Effect of Ascorbic Acid on the Desorption of Gold in Graphite Furnace Atomic Absorption Spectrometry

Abstract In the graphite furnace atomic absorption spectrometry of gold, signals with a single peak were observed with a pyrolytic graphite (PG) furnace, while signals with a shoulder on the tailing edge were observed with a nonpyrolytic graphite (NPG) furnace. A thermal shift of the atomic absorption signals for gold occurs in response to changes in the concentration of ascorbic acid without any loss for each furnace. When the pre-pyrolysis of a 5% (m/V) ascorbic acid solution was carried out at 1270 K, although the background signal due to the release of amorphous carbon was not observed, a thermal shift of the gold signal was confirmed. At a pre-pyrolysis temperature over 1460 K, the peak absorbance was reduced by increasing the pre-pyrolysis temperature, while absorbance at the position of the signal for gold only was increased. The values of the Arrhenius activation energy for the desorption of gold were obtained to be 60 ± 2 kcal mol−1 for gold only, 93 ± 3 kcal mol−1 for gold with 5% (m/V) ascorbic acid and 99 ± 2 kcal mol−1 after a pre-pyrolysis of ascorbic acid at 1270 K.

Coadsorption‐induced effects at surfaces: Thermal desorption spectroscopy and x‐ray photoelectron spectroscopy study of oxygen compression by Au on Ru(001)

Coadsorption of gold on an oxygen saturated ruthenium surface causes dramatic changes in the energetics and kinetics of oxygen desorption and the selectivity of surface processes. The activation energy for desorption of oxygen (EA) is lowered, it is coverage independent, and the process is governed by first‐order kinetics. The lower EA prevents oxygen bulk diffusion, which otherwise competes with desorption from a pure oxygen layer, thus leading to a twofold increase in the amount of desorbing oxygen. A complete analysis of desorption data yields EA=81±4 kcal/mol, prefactor ν(1)=(4±2)×1014 s−1, and reaction order n=0.94. There is no direct interaction between Au and O, as inferred from gold desorption and x‐ray photoelectron spectroscopy data. We propose that changes in EA, ν, and n arise as three‐dimensional gold islands compress the oxygen overlayer causing a local increase in oxygen coverage. Desorption of oxygen occurs before the onset of Au desorption and as oxygen leaves the Ru surface, gold adatoms spread over Ru keeping the local oxygen coverage constant.

Gold desorption from activated carbon with dilute NaOH/organic solvent mixtures

This paper presents a study of the desorption of gold adsorbed onto activated carbon using mixtures of dilute NaOH and different organic solvents. The effect of the solvent components on the desorption rate was studied and a comparative study was made of gold desorption in the presence of cyanide and thiourea. The highest gold desorption rates were obtained with water/acetone/OH − solvents in the absence of cyanide. The isopropyl alcohol/water/thiourea/OH − system also appears to be highly effective at ambient temperature. The apparent activation energy for the isopropyl alcohol/water/OH − system is 36.4 kJ/mol and for the isopropyl alcohol/water/thiourea/OH − and acetone/water/OH − systems it is 28.0 kJ/mol. In all cases, the presence of NaOH in the solvent mixture is necessary to obtain high desorption rates and good extents of desorption.