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

Abstract

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.     

Selective recovery of gold from spent gold sulphite solutions by electrodeposition on graphite cloth electrodes

A flow-through cell, employing an array of twin graphite cloth electrodes and connected to a charge injector potentiostat was employed for the electroseparation of gold from gold sulphite, Au(SO₃) ₂ ^3– , solution containing cadmium, copper and chloride ions. The high overvoltage for the reduction of gold ions in this medium prevents its selective deposition (copper codeposits and hydrogen gas evolves at the same time). Hydrogen peroxide, added judiciously, oxidizes sulphite to sulphate; the gold Au(I) ions complex with chloride, establishing a system similar in its electrochemical behaviour to one previously discussed. Gold chloride, [AuCl₂]^–, solutions disproportionate readily; to minimize this process, a double flow-through system was built, in which the sulphite and hydrogen peroxide solutions enter a small mixing chamber as separate streams, are mixed in the appropriate ratio and allowed to react only a few minutes before reaching the electrodes. Gold deposits on the first graphite screen, and cadmium and copper deposit partially on the next screen, providing an economical approach to the continuous recovery and/or separation of gold from gold sulphite effluents containing base metal admixtures.     

Electroless recovery of gold chloride using inherently conducting polymers

Conducting polymers deposited onto reticulated vitreous carbon (RVC) were shown to remove gold from aqueous solutions in a facile and highly efficient fashion. For acidic solutions with initial [AuCl₄]^? concentrations between 0.1 and 1000 ppm, gold recoveries >90% were obtained. Experiments, conducted using solutions containing 0.1 ppm [AuCl₄]^?, also demonstrated that the composite materials were significantly more effective at recovering gold than activated carbon. Gold removal from solutions containing [AuCl₄]^? and much higher concentrations of iron was highly selective. Copyright © 2004 Society of Chemical Industry     

Stripping of Au(I) from a Loaded Cetyltrimethylammonium Bromide/Tributyl Phosphate Organic Solution: Conversion and Reduction

The recovery of Au(I) from cyanide leaching solutions by solvent extraction techniques has attracted wide interest in the past decades. However, no substantial progress in industries has been reported yet, because of the difficulties concerning gold stripping from loaded organic phases, such as the quaternary amines extraction systems. In this work, a new technique for the recovery of Au(CN)₂ ^? from the loaded cetyltrimethylammonium bromide / tributyl phosphate organic solution by a two‐step stripping procedure is suggested first by Au(CN)₂ ^? conversion by HCl into corresponding chloride complex ions, and then by chemical reduction of auro‐chloride complex ions in TBP organic phases to give metal gold powder. The influences of HCl concentrations, reaction time, and various reducing agents used on the percent gold conversion and reduction were investigated. About 33% of Au(CN)₂ ^? in the initial TBP organic phase could be precipitated as metal gold powder in the conversion step, while 67% was converted into AuCl₂ ^? or AuCl₄ ^? and held in the organic phase. Subsequently, the loaded organic phase after conversion was contacted with reducing agents such as sodium sulfite, ammonium oxalate, or hydrazine hydrate. Most (>98%) of the auro‐chloride complex ions could be effectively reduced as metal gold. As a result, the total gold recovery from the initial TBP organic phases after the two stripping procedures achieved more than 98%. The ¹⁹⁸Au radioactive tracer was employed to determine the concentration and distribution behavior of gold in both organic and aqueous solutions. In addition, the experiment on the reuse of the organic phase after gold stripping showed that there was no obvious loss in percent gold(I) recovery after one cycle of the extraction‐ stripping‐ regeneration process no matter what reducing agent was used.     

Kinetic modelling of gold cyanide multi-cycle adsorption and elution using activated carbon in the presence of foulants

A novel procedure was used to study the kinetics of multiple exposure of a granular activated carbon in a laboratory-scale packed bed to solutions containing gold and sodium cyanide, or in addition one of several organic reagents commonly used in mineral processing. The repeated use of a carbon sample simulated the practice in industrial gold recovery operations. A batch, unsteady state adsorption model which assumed constant intraparticle diffusivity of Au(CN)₂^- was used to model the kinetics of gold uptake. Upon repeated exposure of a carbon sample, up to a 3- to 4-fold decrease in the intraparticle diffusivity of Au(CN)₂^- was observed, combined with a much smaller loss of adsorption capacity.     

Uptake and recovery of gold by immobilized persimmon tannin

Some attempts were made to recover gold from aqueous systems using immobilized persimmon tannin. This adsorbent adsorbed gold from solutions containing hydrogen tetrachloroaurate(III) with high efficiency, whereas there was minimal adsorption from solutions containing gold(I) sodium thiomalate and sodium dicyanoaurate(I). The adsorption of gold was rapid, and was affected by the pH of the solution, temperature, external gold concentration and amount of adsorbent. Adsorbed gold was easily desorbed with 1 mol dm^?3 thiourea solution, indicating that immobilized persimmon tannin can be repeatedly re-used for the recovery of gold using adsorption-desorption cycles.     

Gold Recovery from HCl Solutions using Cyphos IL‐101 (a Quaternary Phosphonium Ionic Liquid) Immobilized in Biopolymer Capsules

Tetraalkyl phosphonium chloride (Cyphos IL‐101), an ionic liquid (IL), was tested for gold recovery from HCl solutions: first in liquid/liquid extraction systems (using toluene and hexane as solvent) and in a second step, after being immobilized in a biopolymer composite matrix. SEM‐EDAX analysis was used for the characterization of the resins. The sorption capacity reached up to 140 mg Au(III) g^?1 in 1 M HCl solutions. Base metals that do not form anionic chlorocomplexes and nitrate or chloride ions (at 5 g L^?1) did not interfere with Au(III) binding. Gold binding probably occurs through the interaction of R₃R'P⁺ with AuCl₄ ^?. The kinetics of sorption was carried out varying agitation speed, metal concentration, IL content, and resin drying. Intraparticle diffusion played an important role on the control of sorption kinetics. Gold could be desorbed from the loaded IL‐impregnated resin using thiourea (in HCl solutions). The resin could be re‐used for at least 4 cycles. The resins are specially adapted for the recovery of gold from low metal concentrations.     

Gold‐cyanide biosorption with L‐cysteine

L ‐Cysteine increased gold‐cyanide biosorption by protonated Bacillus subtilis, Penicillium chrysogenum and Sargassum fluitans biomass. At pH 2, the maximum Au uptakes were 20.5 µmol g⁻¹, 14.2 µmol g⁻¹ and 4.7 µmol g⁻¹ of Au, respectively, approximately 148–250% of the biosorption performance in the absence of cysteine. Au biosorption mainly involved anionic AuCN₂⁻ species adsorbed by ionizable functional groups on cysteine‐loaded biomass carrying a positive charge when protonated [(biomass–cysteine–H⁺)–(AuCN₂⁻)]. Deposited gold could be eluted from Au‐loaded biomass at pH 3–5. The elution efficiencies were higher than 92% at pH 5.0 with the Solid‐to‐Liquid ratio, S/L, = 4. Increasing solution ionic strength (NaNO)₃ decreased Au uptake. FTIR analyses indicated that the main functional groups involved in gold biosorption in the presence of L ‐cysteine are probably N‐, S‐ and O‐containing groups. The present results confirm that certain waste microbial biomaterials are capable of effectively removing and concentrating gold from solutions containing residual cyanide if applied under appropriate conditions. © 2000 Society of Chemical Industry     

GOLD EXTRACTION FROM THIOSULFATE SOLUTIONS USING MIXED AMINES

ABSTRACT

The extraction of gold from thiosulfate solutions with amine oxide and its mixture with amines has been studied, the results show that the amine oxide (TRAO) has a higher extraction ability for gold compared with tertiary amine. It can extract gold from neutral and weakly alkaline thiosulfate solutions, similar to the primary amine as extractant. The addition of TRAO enhances the extent of gold extraction with primary, secondary, and tertiary alkyl amines, respectively. The stoichiometry for the extraction of gold from thiosulfate solutions using the mixed solvent containing the primary amine N₁₉₂₃ and the amine oxide TRAO was investigated using slope analysis. The compositions of the gold extraction species with mixed organic solvents are proposed.     

Extraction of gold from cyanide or chloride media by Cyanex 923

A new phosphine oxide extractant, commercially known as Cyanex 923, has been studied in order to be applied in the recovery of gold from either cyanide or chloride aqueous media. Au(CN)₂⁻ is extracted by this reagent throughout the whole pH range. The presence of lithium salts in the media improves the extraction. The extraction mechanism proposed can be explained in terms of a solvating reaction, the species formed in the organic phase being the following: Li⁺Au(CN)₂⁻3(R₃PO). The stripping can be performed by low ionic strength solutions such as dilute KCN solutions, and the reaction is enhanced by an increase in temperature. In chloride media, the extractant is able to extract gold (III) in the entire range of acid concentrations. The amount of extraction agent required, to achieve the same level of extraction, in this medium is much lower than in the cyanide media. The temperature has a negative effect on the extraction. Another difference observed between the two media, is that the presence of ionic salts in chloride media has no influence on the extraction, which may be attributed to the fact that the extracted species, HAuCl₄, is a protonated instead of an ionic species. © 1998 SCI     

Ion Exchange Resins for Gold Cyanide Extraction Containing a Piperazine Functionality, 2. Study of the Gold Extraction Reaction

Ion exchange technology is offered as an alternative to activated carbon for gold cyanide recovery. A new type of ion‐exchange resin (PS‐PIP) incorporating a piperazine group, linked to a styrene‐divinylbenzene macroporous network, is described. The extraction of Au(CN)₂^– and other metal cyanides with the PS‐PIP resin involves three modes of metal extraction: the protonated secondary amine groups of the resin (at acidic pH conditions), the free amine groups of the resin (at neutral and basic pH values) and the small portion of the quaternary ammonium groups participate in the gold extraction mechanism. The gold cyanide extraction reaction on the polymeric piperazine was studied by a combination of metal extraction data, from batch experiments, and IR and XPS spectroscopic analysis of the metal loaded polymers. Extraction isotherms of gold cyanide show that gold binding is possible from 40–60 mg Au/g of resin in alkaline solutions, up to 150 mg Au/g of resin in acidic solutions. Efficient stripping of gold from the resin was achieved using ethanol/water solutions of sodium hydroxide, or 0.5 mol/l thiourea in sulfuric acid solutions.     

The dissolution of palladium in various electrolytes

The electrochemical dissolution of palladium in a number of aqueous solutions containing ClO₄, Cl^?, I^?, has been investigated using current-potential and impedance-potential measurements. It is concluded that during active dissolution, from Cl^? containing solution, the reaction to form a soluble complex PdCl₂ is inhibited by a PdOH layer and passivated by PdO. Dissolution in I^? containing solutions proceeds by a different mechanism.     

Electrochemical recovery of silver from cyanide leaching solutions

In the hydrometallurgy industry cyanide solutions are the most common leaching baths used during the extraction of metals such as silver and gold. After extraction, the solution containing various cyanide species, and usually copper cyanide, has a higher concentration than the gold and silver complexes. Higher concentration of copper species may interfere during the selective recovery of precious metals. This work presents a study of the selective recovery of silver from leaching solutions mimicking those used in industry. Chemical speciation and cyclic voltammetry studies showed that copper reduction occurs at more negative potentials than silver in the cyanide leaching solutions. The cyclic voltammetry of cyanide solutions on a vitreous carbon electrode showed that copper cyanide ions modify the interface properties, lowering the overpotential required for silver reduction. A macroelectrolysis study of a simulated leaching solution (10^–4 M Ag(I), 0.1 M Cu(I) in 0.5 M CN^– at pH 10), was carried out in a filter press electrochemical reactor (ElectroCell AB) with a reticulated vitreous carbon electrode (RVC), nominally having 45 pores per inch and a flow rate of 5 cm³ s^–1 at 25 °C. The study showed that the high copper concentration does not interfere in the selective deposition of silver.     

Solvent Extraction of Au(III) by the Chloride Salt of the Amine Alamine 304 and Its Application to a Solid Supported Liquid Membrane System

Abstract

The extraction of Au(III) by the chloride salt of the amine Alamine 304 (R₃NH⁺Cl^?) in xylene from hydrochloric acid solutions has been investigated. The analysis of metal distribution data by numerical calculations suggested the formation of the species R₃NH⁺AuCl₄ ^? in the organic phase with formation constant log K _ext = 5.44. The results obtained on Au(III) distribution have been implemented in a solid‐supported liquid membrane system, where in NaSCN solutions were found to be the most effective to strip the metal from the organic solution. Influence of membrane composition, metal concentration on gold transport, and the selectivity of the system have also been studied.     

Characteristics of gold biosorption from cyanide solution

Gold adsorption from cyanide solution by bacterial (Bacillus subtilis), fungal (Penicillium chrysogenum) and seaweed (Sargassum fluitans) biomass was examined. At pH 2.0, these biomass types were capable of sequestering up to 8.0 µmol g⁻¹, 7.2 µmol g⁻¹ and 3.2 µmol g⁻¹, respectively. An adverse effect of increasing solution ionic strength (NaNO₃) on gold biosorption was observed. Gold‐loaded biomass could be eluted with 0.1 mol dm⁻³ NaOH with efficiencies higher than 90% at pH 5.0 at the Solid‐to‐Liquid ratio, S/L, = 4 (g dm⁻³). Cyanide mass balances for the adsorption, desorption as well as for the AVR process indicated the stability of the gold‐cyanide which did not dissociate either upon acidification or upon binding by biomass functional groups. Gold biosorption mainly involved anionic AuCN₂⁻ species bound by ionizable biomass functional groups carrying a positive charge when protonated. FTIR analyses indicated that the main biomass functional groups involved in gold biosorption are most probably nitrogen‐containing weak base groups. The present results confirmed that waste microbial biomaterials have some potential for removing and concentrating gold from solutions where it occurs as a gold‐cyanide complex. © 1999 Society of Chemical Industry     

SOLVENT EXTRACTION OF GOLD IN THIOSULFATE SOLUTIONS WITH AMINES

ABSTRACT

The solvent extraction of gold from thiosulfate solutions with alkyl amines was studied. The experimental results showed that with both aliphatic and aromatic hydrocarbons as diluent, the power of amines for extraction of gold decreased in the order: primary > secondary > tertiary amine. Further study indicated that the initial gold concentration and ionic strength in aqueous phase had no significant influence on the extraction of gold with primary amine N₁₉₂₃. The extraction of gold at high pH values increased with an increase of the extractant concentration. The enthalpy change for the extraction with N₁₉₂₃ was calculated ?120.8 kJ mol^?1. From these experimental results, the equations of extraction of gold with N₁₉₂₃ from thiosulfate solution with and without the presence of ammonia have been derived respectively.     

A Potential Alternative for Precious Metal Recovery from E-waste: Iodine Leaching

Printed circuit board (PCB) is the essential part of electronic devices and has an important source of base and precious metals with high economic potential. In this study, selective leaching of gold from PCB was performed in an iodine-hydrogen peroxide (I₂-H₂O₂) solution system. The effects of different parameters such as iodine concentrations, H₂O₂ concentrations and solids-% on the gold leaching dynamics were investigated. The results show that increasing solids-% has a negative influence on the gold leaching. However, gold recovery from the e-wastes in a solution containing 3% iodine, 1% H₂O₂ with solids-% of 15% resulted with 100% recovery among all leaching tests.     

Electrochemical studies on gold electrodes in acidic solutions of thiourea containing gold (I) thiourea complex ions

Electrochemical studies were made of the behaviour of gold electrodes in degassed acidic solutions containing between 0.00l to 0.03 M thiourea and between 10^–5 to 10^–3 M gold(I)thiourea. At anodic overpotentials of up to 0.3 V the dissolution of gold was rapid, and nearly reached the maximum diffusioncontrolled rate. The exchange current density was greater than 10^–6 A cm^–2, and dissolution proceeded at 100% efficiency. At higher anodic potentials, thiourea was oxidized to formamidine disulphide and other sulphur-containing compounds and the dissolution of gold became partly inhibited, while the current efficiency decreased markedly.The reduction of gold(I)thiourea was diffusion-controlled at cathodic overpotentials between –0.15 to –0.35 V, after which slight inhibition was observed. Thiourea itself did not contribute to the cathodic reaction, but formamidine disulphide could be reduced on a freshly deposited gold surface; in the absence of gold(I)thiourea in the solution, the reduction of formamidine disulphide caused rapid passivation of the gold surface. In 0.01 M thiourea and 0.1 M sulphuric or perchloric acid, the diffusion coefficient of the Au(CS(NH₂)₂) ₂ ⁺ ion was 1·1 x 10^–5 cm² s^–1 at 30°C.The standard reduction potential at 30° C of the redox couple Au(CS(NH₂)₂) ₂ ⁺ ¦Au on a fresh gold surface wasE ₀=0.352 V, but on a passivated gold surface this value increased to as much asE ₀=041V.     

THE EXTRACTION OF CESIUM AND STRONTIUM FROM ACIDIC HIGH ACTIVITY NUCLEAR WASTE USING A PUREX PROCESS COMPATIBLE ORGANIC EXTRACTANT

Purex process compatible organic systems which selectively and reversibly extract cesium and strontium from synthetic mixed fission product solutions containing3M HNO₃, have been developed. This advance makes the development of continuous solvent extraction processes for their recovery more likely.

The matrix solution from the Purex process consists of tributyl phosphate (TBP) and kerosene. For cesium and strontium recovery a macrocyclic polyether (crown compound) has been developed for each element. When used in conjunction with a liquid cation exchanger in the matrix solution, the crown compounds will extract either alkali metals or alkaline earths from the synthetic mixed fission product solution. The organic cation exchangers used in this research were didodecylnaphthalene sulfonic acid (DNS) and dinonylnaphthalene sulfonic acid (NNS). As was expected both zirconium and ruthenium also tend to be extracted due to the TBP in the matrix solution and to their complex chemistry.

The most favorable cesium and strontium complexing solutions have been tested for radiation stability to 10⁷ rad using a 0.4 × 10⁷ rad/hr ⁶⁰ Co source. The distribution coefficients dropped somewhat but remained above unity.

For cesium the comp1exing organic solution is 5vol% (0.10M) NNS, 27vol% TBP and 68vol% kerosene containing 0.05M bis 4,4′,(5′) [l-hydroxy 2-ethylhexyl]benzo 18-crown-6 (Crown XVII). with an aqueous phase containing 0.006M Cs^+l in contact with an equal volume of extractant, the Dorg/aq = 1.6 at a temperature of 25?35°C.

For strontium the complexing organic solution is 5vol% (0.10M) NNS, 27vol% TBP and 68vol% kerosene containing 0.02M bis 4,4′(5′) (l-hydroxyheptyl)cyclohexo 18-crown-6 (Crown XVI). with an aqueous phase containing 0.003M Sr⁺² in contact with an equal volume of extractant, the Dorg/aq 1.98 at a temperature of 25?35°C.     

Preparation of Self-Assembled Monolayers from Micellar Solutions

The self-assembly of alkanethiols on gold surfaces from micellar aqueous solutions was investigated using Triton X-100, sodium dodecylsulfate, and cetyltrimethylammonium bromide as representative nonionic, anionic, and cationic surfactants, respectively. The surfactant solutions solubilized the otherwise water-insoluble alkanethiols, which self-assembled on gold to form organized assemblies very similar to those prepared using the conventional procedures, i.e., exposure of the gold surface to a nonaqueous solution of the alkanethiol. The resulting derivatized gold electrodes exhibited typical electrochemical properties, such as low capacitance values and substantial blocking of the voltammetric reduction of Ru(NH₃)₆³⁺. The concentration of surfactant was found to have a profound effect on the rate of alkanethiol chemisorption.