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.     

Selective Removal of Carbon Dioxide from Wet CO2/H2 Mixtures via Facilitated Transport Membranes containing Amine Blends as Carriers

The selective separation of carbon dioxide (CO₂) from a wet gaseous mixture of CO₂/H₂ through facilitated transport membranes containing immobilized aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), ethylenediamine (EDA) and monoprotonated ethylenediamine (EDAH⁺) and their blends was experimentally investigated. The effect of CO₂ partial pressure, amine concentration, feed side pressure and amine species on the CO₂ and H₂ permeances were studied. The CO₂ permeability through amine solution membranes decreased with increasing CO₂ feed partial pressure but the H₂ permeance was almost independent of the H₂ partial pressure. A comparison of experimental results showed that single or blended amines with low viscosity and a moderate equilibrium constant, i.e., large forward and reverse reaction rate of CO₂‐amine, are suitable for effective separation of CO₂. The permeability of CO₂ generally increased with an increase in amine concentration, although this increase may be compromised by the salting out effect and decrease in diffusivities of species. The results obtained indicated that CO₂ permeance across a variety of amines are in the order of DEA (2 M) > MD (2 M) > MD (1 M) > MEA (2 M) > MEA (4 M) > MD (4 M) > DEA (1 M) > DEA (4 M) > MEA (1 M) for various concentrations of MEA + DEA blend and are in the order of EDAH⁺ (2 M) > DEA (2 M) > MH (2 M) > DH (2 M) > ED (2 M) > EDA (2 M) > MEA (2 M) for various blends of amine.     

The development of kinetics model for CO2 absorption into tertiary amines containing carbonic anhydrase

CO₂ absorption into aqueous solutions of two tertiary alkanolamines, namely, MDEA and DMEA with and without carbonic anhydrase (CA) was investigated with the use of the stopped‐flow technique at temperatures in the range of 293–313 K, CA concentration varying from 0 to 100 g/m³ in aqueous MDEA solution with the amine concentration ranging from 0.1 to 0.5 kmol/m³, and CA concentration varying from 0 to 40 g/m³ in aqueous DMEA solution with the amine concentration ranging from 0.05 to 0.25 kmol/m³. The results show that the pseudofirst‐order reaction rate (k_{0, amine}; s^?1) is significantly enhanced in the presence of CA as compared with that without CA. The enhanced values of the kinetic constant in the presence of CA has been calculated and a new kinetics model for reaction of CO₂ absorption into aqueous tertiary alkanolamine solutions catalyzed by CA has been established and used to make comparisons of experimental and calculated pseudo first‐order reaction rate constant (k_{0, with CA}) in CO₂‐MDEA‐H₂O and CO₂‐DMEA‐H₂O solutions. The AADs were 15.21 and 15.17%, respectively. The effect of pKa on the CA activities has also been studied by comparison of CA activities in different tertiary amine solutions, namely, TEA, MDEA, DMEA, and DEEA. The pKa trend for amines were: DEEA > DMEA > MDEA > TEA. In contrast, the catalyst enhancement in amines was in the order: TEA> MDEA> DMEA> DEEA. Therefore, it can be seen that the catalyst enhancement in the amines decreased with their increasing pKa values. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Extraction kinetics of cerium(IV) from sulfuric acid medium by the primary amine N1923 using a constant interfacial area cell with laminar flow

BACKGROUND: Thermodynamic studies on Ce(IV) extraction with primary amine N1923 demonstrate that primary amine N1923 is an excellent extractant for separation of Ce(IV) from Re(III). In order to clarify the mechanism of extraction and to optimize the parameters in practical extraction systems used in the rare earth industry, the extraction kinetics was investigated using a constant interfacial area cell with laminar flow in the present work. RESULTS: The data indicate that the rate constant (k_ao) becomes constant when stirring speed exceeds 250 rpm. The apparent forward extraction rate is calculated to be 10^?1.70. The activation energy (E_a) was calculated to be 20.5 kJ/mol from the slope of log k_ao against 1000/T. The minimum bulk concentration of the extractant necessary to saturate the interface (C_min) is lower than 10^?5 mol L^?1. CONCLUSION: Studies of interfacial tension and the effects of stirring rate and specific interfacial area on the extraction rate show that the extraction rate is kinetically controlled, and a mass transfer model has been proposed. The rate equation has been obtained as: ? d[Ce(IV)]/dt = 10^?1.70[Ce(IV)] [(RNH₃)₂SO₄]^1.376. The rate‐controlling step has been evaluated from analysis of the experimental results. Copyright © 2007 Society of Chemical Industry     

Adsorption of zinc (II), cadmium (II), and copper (II) with PTFE Selective Resin containing primary amine N1923 and Cyanex925

In the present study, a synergistic extraction mixture, primary amine N1923 (RNH₂) and Cyanex925 (B), was loaded on PTFE powder to prepare PTFE Selective Resin and was employed for the adsorption of zinc, cadmium, and copper from chloride medium. The effects of shaking time, resin amounts, concentration of metal ions, and experimental temperature on the distribution coefficients were determined. The stoichiometry of the adsorbed complexes was determined to be MCl₂·(1/2)RNH₂·B with the Selective Resin. The equilibrium constants and thermodynamic quantities (ΔH, ΔG, and ΔS) were calculated. Furthermore, the Freundlich isotherm proved to be more suitable than the Langmuir isotherm to indicate the effect of concentration of M²⁺ on the adsorption with PTFE Selective Resin.     

Michael addition polymerizations of trifunctional amines with diacrylamides

With the aim to get a clear understanding of this category of polymerizations, the Michael addition polymerizations of trifunctional amines, i.e. 4-aminomethyl piperidine (AMPD), N-methyl ethylenediamine (MEDA), and 1-(2-aminoethyl) piperazine (AEPZ), with an equimolar diacrylamide, N,N′-methylene diacrylamide (MDA), were investigated. Similar to the polymerizations of these amines with an equimolar diacrylate, novel linear poly(amido amine)s containing secondary and tertiary amines in the backbones are obtained from these polymerizations as reflected by ¹³C NMR (INVGATE). In situ monitoring the polymerization processes using NMR shows that the reactivity sequence of three types amines in the trifunctional amines is 2° amine (original)>1° amine?2° amine (formed), and the 2° amine (formed) is kept out of the reaction. But these results are different from those reported for the polymerizations of the similar amines with an equimolar divinyl sulfone and some diacrylates. The molecular weights and properties of poly(amindo amine)s obtained were characterized by GPC, DSC and TGA, respectively.     

Bulk Gold-Catalyzed Oxidations of Amines and Benzyl Alcohol Using Amine N-Oxides as Oxidants

Abstract  

Bulk gold powder (~50 μm) catalyzes the oxidative dehydrogenation of amines to give imines using amine N-oxides (R₃N-O) as the oxidant. The reaction of dibenzylamine (PhCH₂–NH–CH₂Ph) with N-methylmorpholine N-oxide (NMMO) in the presence of gold powder at 60 °C produced N-benzylidenebenzylamine (PhCH=N–CH₂Ph) in 96% yield within 24 h. Benzyl alcohol was oxidized by NMMO to benzaldehyde in >60% yield in the presence of gold powder. Although O₂ was previously shown to oxidize amines in the presence of bulk gold, it is surprising that gold is also capable of catalyzing the oxidation of amines using amine oxides, which are chemically so different from O₂.     

Kinetics of hydrogen peroxide oxidation of alkyl dimethyl amines

We measured the absolute rate constants for the hydrogen peroxide oxidation of two different octyl dimethyl amines in isopropanol/water mixtures at 23°C. The amines were 1-octyl dimethyl amine (1) and 2-ethylhexyl dimethyl amine (2); their structures were analogous to those most often encountered in commercial alkyl dimethyl amine oxide production. The observed first-order rate constants for the disappearance of amine across a range of H₂O₂ concentrations (0.5–8 M) indicated that the overall rate was first-order in amine and 3/2-order in H₂O₂. Calculations showed k ₁=0.16 M⁻¹h⁻¹, k ₂=0.046 M⁻¹h⁻¹, and k ₁/k ₂=3.5. The rates appeared to decrease with increasing steric hindrance around the nitrogen atom. We also investigated the effect of water on the reaction rates. When [H₂O]<∼4.5 M in isopropanol, the rates increased with increasing [H₂O]; for [H₂O]>∼4.5 M, the rates were insensitive to [H₂O].     

Study of the kinetics of oxidation of amines by potassium ferricyanide in the presence of <Emphasis Type="Italic">N,N</Emphasis>-dimethyldodecylamine <Emphasis Type="Italic">N</Emphasis>-oxide

This research reports on the oxidation of different amines such as dibutylamine, diethylamine, dipropylamine, ethylamine, ethylmethylamine, propylamine, triethylamine, and trimethylamine by 0.001 M potassium ferricyanide in the presence of 0.03 M NaOH at 25°C in aqueous medium and/or in 0.03 M N,N-dimethyldodecylamine N-oxide (DDAO). Oxidation rates were studied with a spectrophotometer at 420 nm. The experimental data showed that the reaction was first-order with respect to [amine] _T and [Fe(CN)₆]³⁻. Also, the rate constant (k _obs) had values within the concentration range of 0.015–0.05 M of NaOH and increased above the critical micelle concentration values of DDAO. The dependence of the reaction rate on the nature of the salt was also investigated, and the thermodynamic parameters ΔG ^*, ΔH ^*, and ΔS ^* were calculated. A pseudo-phase model was applied to the system, and the binding constant of the amine to DDAO micelles was calculated.     

SYNERGISTIC EXTRACTION OF ZINC(II) BY MIXTURES OF PRIMARY AMINE N1923 AND CYANEX272

ABSTRACT

The extraction of zinc(II) and cadmium(II) from chloride solution by mixtures of primary amine N1923 and Cyanex272 (HA) was studied. The synergistic effect was observed for the extraction of zinc(II) while no synergistic effect for cadmium(II), which makes it possible to separate zinc(II) and cadmium(II) with the mixtures. The results showed that zinc(II) was extracted as (RNH₃Cl)₃·ZnClA instead of ZnA₂·2HA which was extracted by Cyanex272 alone. The extraction mechanism was discussed and the formation constants and thermodynamic functions were determined. The separation factors between zinc(II) and cadmium(II) were calculated.     

SOLVENT EXTRACTION OF PHENOL WITH MINERAL ACID SALTS OF HIGH-MOLECULAR-WEIGHT AMINES

Distribution equilibria in the solvent extractions of phenol with various mineral acid salts of high-molecular-amines were measured at 30°C to examine the effects of types of amines and mineral acids on the distribution equilibria.

It was found that the extraction is greatly enhanced by converting the free base amines into their hydrochloric acid salts in the cases of secondary and tertiary amines while it is decreased in the case of a primary amine. On the effect of types of mineral acids, sulfuric acid and hydrochloric acid salts of trioctylamine can much more effectively extract phenol than the free base amine and the order of the efficiency for phenol extraction was found to be as follows: Aliquat 336 > sulfuric acid salt of trioctylamine i its hydrochloric acid salt ≥ its nitric acid salt > its perchloric acid salt ? free base amine.     

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.     

STRIPPING OF GOLD FROM QUATERNARY AMINE EXTRACTION SYSTEMS

ABSTRACT

A new procedure based on the use of sodium perchlorate (NaC1O₄) and saturated potassium chloride (KCl) solutions for gold stripping from quaternary amine extraction systems is proposed for the first time. In this procedure, the stripping of Au(CN)₂ ^? is accomplished by the ClO₄ ^? ions in the first step, and the regeneration of quaternary amine is achieved by Cl^? ions in the second step.     

Extraction of Fatty Acids from Noncatalytically Cracked Triacylglycerides Using Aqueous Amines

It has been reported that a basic aqueous solution was effective in extracting short chain C₂–C₆ fatty acids from noncatalytically cracked triacylglyceride oils. However, the extraction efficiency was not optimal over the entire range (C₂–C₁₂) of acids present in the cracking reactor organic liquid product (OLP). Therefore, an additional study was performed to explore the efficiency of solvent extraction using aqueous amines for this application. Based on the screening of several amines, two tertiary amines, trimethyl amine (TMA), and dimethyl ethanolamine (DMEA), were selected and evaluated. The extraction conditions were optimized with respect to several factors: temperature, amine concentration, and the amine-to-OLPratio (amine/OLP). Under optimal conditions, both TMA and DMEA were effective in extracting a wide range of organic acids, with TMA removing 93% of total acids and DMEA removing 100% of total acids. The amine/OLP was found to be a significant factor, as was the concentration of the amine solution. Temperature was not found to be a significant factor over the range studied. These results provide a basis for the development of a scalable, continuous process to produce a variety of C₂–C₁₂ fatty acids from biological sources.     

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.     

Carbamate Chemistry at Interfaces: Practical Considerations and Challenges of Studying Amine Surfactants

It is well known that CO₂ reacts with primary and secondary amines in aqueous solutions and forms carbamates. This reaction can have consequences when studying the self-assembly of amines. In this article, we discuss the practical challenges when working with an alkyl Y-shaped amine (Y12-amine) and demonstrate how the formation of carbamate species influences the physicochemistry of the amine-based surfactant. A drift in dynamic surface tension was observed for Y12-amine at pH above pKa due to the reaction with the naturally occurring CO₂ from the atmosphere. The drift in dynamic surface tension was more pronounced at pH above pKa, than at and below pKa. Furthermore, the drift in dynamic surface tension of Y12-amine at pH 12 also affected the surfactant's critical micelle concentration (CMC). CMC of Y12-amine determined by the pendant drop at the air/water interface was almost five times higher than at the N₂/water interface. The latter result was in agreement with the one determined by monitoring the change in chemical shift of ¹H NMR in a N₂ atmosphere. Moreover, it was also shown that the adsorption of the amine at different interfaces influences carbamate formation.     

Highly Efficient Extraction of Rhodium(III) from Hydrochloric Acid Solution with Amide-Containing Tertiary Amine Compounds

Extraction of Rh(III) from a HCl solution with N,N-disubstituted amide–containing tertiary amine (ACTA) compounds (N,N-di-n-hexyl(N-methyl-N-n-octyl-ethylamide)amine (MonoAA), N-n-hexyl-bis(N-methyl-N-n-octyl-ethylamide)amine (BisAA), and tris(N-methyl-N-n-octyl-ethylamide)amine (TrisAA)) was investigated. The ACTAs extract Rh(III) more efficiently than tri-n-octylamine (TOA), and the extraction efficiency increases with increasing number of amide groups: TrisAA > BisAA > MonoAA ? TOA. For all ACTAs, the predominant Rh(III) complex extracted from 2 M HCl is probably {[RhCl₅(H₂O)]·(ACTA·H)₂}. The apparent basicity of the ACTAs and TOA varies in the opposite order from that observed for the Rh(III) extraction efficiency. Rh(III) can be readily back-extracted using 10 M HCl solution possessing a high selectivity over similarly loaded Pd(II) and Pt(IV).     

Role of chiral amine cocatalysts in the helix-sense-selective polymerization of a phenylacetylene using a catalytic system

We have examined the role of the chiral amine cocatalyst in the recently discovered helix-sense-selective polymerization of a phenylacetylene using a catalytic system consisting of an achiral rhodium complex ([Rh(norbornadiene)Cl]₂) as the catalyst and a chiral amine as the cocatalyst. Several chiral amines were effective for the polymerization reaction and their effectiveness depended on their bulkiness and coordination ability to rhodium. The sense selectivity of the polymerization increased with the concentration of the chiral amines. To discuss the structure of the true active species in the catalytic system, we have synthesized a new chiral rhodium complex having two chiral amines as ligands ([Rh(norbornadiene)(chiral amine)₂]⁺BF₄⁻). The isolated chiral complex also catalyzed the helix-sense-selective polymerization. These findings suggest that a chiral rhodium complex having two chiral amines may be the true active species when using the catalytic system consisting of [Rh(norbornadiene)Cl]₂ and a chiral amine.     

Study of some parameters responsible for the efficiency of hindered amine light stabilizers

The photooxidation of a styrene-butadiene-styrene block copolymer previously hydroperoxidized by reaction with singlet oxygen has been studied by measuring the increase of the carbonyl absorbance at 1720 cm^?1. Five different hindered amine light stabilizers (HALS) have been introduced into the polymer by diffusion from methanolic solutions, and their efficiencies as inhibitors of the photooxidation have been compared. The sequence of efficiency observed is: tert. amine > sec. amine > amino ether Under the experimental conditions used HALS are localized preferentially in oxidized regions of the polymer, and their efficiency can be correlated with their ability to catalyze the decomposition of clustered hydroperoxides. As a consequence, HALS are oxidized to nitroxy radicals that are the actual inhibitors of the photooxidation. A high local concentration of HALS in oxidized regions of the polymer also contributes to their efficiency, and this effect justifies the observation that some tertiary amines are more efficient than others.     

Solvent extraction of gold(I) from alkaline cyanide solution by dibutylcarbitol (DBC) with n‐octanol

BACKGROUND: Currently, cyanidisation is preferred for the extraction of gold because it has a number of advantages over other methods. Gold(I) can be extracted with various extractants, but there are no reports on the extraction of gold(I) from cyanide solution by dibutylcarbitol (DBC). In this work the extraction of gold(I) from alkaline cyanide solution using DBC with n‐octanol was studied. Several factors affecting the percentage extraction of gold(I), including DBC concentration, diluent concentration, equilibrium time, phase ratio, pH and gold concentration in aqueous phase, were investigated. RESULTS: The results showed that 96.2% of gold(I) could be extracted using an organic phase composed of 40% (v/v) DBC, 50% (v/v) n‐octanol and 10% (v/v) odourless kerosene. The extraction was quite fast and equilibrium could be established within 2 min. Stripping of the gold‐laden organic phase was carried out using sodium sulfite (Na₂SO₃) and sodium thiosulfate (Na₂S₂O₃) solutions, with Na₂S₂O₃ proving better than Na₂SO₃. The percentage stripping of gold(I) was 96.5% when the Na₂S₂O₃ concentration was 4% (w/w), and the stripping capacity of gold(I) exceeded 311.3 mg L^?1 when the phase ratio (A/O) was equal to 0.2. CONCLUSION: Gold(I) can be extracted from aqueous cyanide solution by DBC in the presence of n‐octanol and efficiently stripped by aqueous Na₂S₂O₃ solution. This method has the potential for practical application in the extraction and separation of gold. Copyright © 2008 Society of Chemical Industry