Selective separation of gold from iron ore samples using ion exchange resin

Gold in iron ore samples is separated from iron (major matrix cation), antimony and vanadium using anion exchange resin in (0.2 M) HBr, potassium peroxodisulfate and acetone:water:nitric acid media. The exchangeable anion Cl⁻ of the ion exchanger Dowex 1X 4 is replaced by Br⁻ using (6 M) HBr solution. Certified reference material DGP-M1, spiked ferric magnetic oxide, gold radioactive tracer ¹⁹⁸Au and gold standard solutions are used to study the adsorption efficiency and the yield recovery of tetrabromoaurate AuBr₄⁻ from the resin. Ten eluents have been tried to elute gold from the column, and it has been found that a 10 ml potassium peroxodisulfate and 240 ml acetone:water:nitric acid [125:5:5] solution fulfills the objective. The set up of the separation procedure allows quantitative adsorption of gold by the resin, while the major matrix cation (Fe) and others (Cd, Ag, Cu, V, Sb, Ti) have been passed through the column with the feeding solution (0.2 M) HBr. The resin selectivity coefficient (K) of separating Au from Fe has been found to be K_Fe^Au≈6.4×10¹¹. The eluted Au is treated with K₂S₂O₈ and H₂O₂ for spectrophotometric determination as rhodamine-B complex at 555.6 nm. The linearity, detection limit, precision, and accuracy of the determination method have been found to be up to 2.0 μg g⁻¹, 0.018 μg g⁻¹, 0.009 μg g⁻¹ and 3%, respectively.     

Separation of trace amounts of indium, gallium and aluminium from each other by cation-exchange chromatography on AG50-X4 resin

Traces and minor amounts of indium, gallium and aluminium can be separated from gram amounts of thallium and from each other by cation-exchange chromatography on a column containing as little as 2 g of AG50W-X4, a cation-exchange resin with low cross-linking. An elution sequence of 0.1 M HBr in 40% acetone [for Tl(III)], 0.2M HBr in 80% acetone for In, 0.3M HCl in 90% acetone for Ga and 3M aqueous HCl for Al is used. The separations are very sharp and even 10-mug amounts of In, Ga and Al in synthetic mixtures are recovered quantitatively, with a standard deviation of 0.3 mug. The separation factors between neighbouring ions are extremely large (> 5000).     

A Green Protocol for Solvent-Free Conversion of Epoxides to Thiiranes with Dowex-50WX8–Supported Thiourea

Structurally different epoxides were efficiently converted to the corresponding thiiranes by Dowex-50WX8–supported thiourea under solvent-free conditions. The reactions were carried out either in an oil bath or under microwave irradiation to give the thiiranes in 75–98% yields within 30 sec–120 min.     

Ion exchange studies of U(VI) from aqueous Arsenazo-III solutions using AG-2X8, Dowex-50WX8 and Chelex-100 resins

The distribution of U(VI) between the anion exchanger AG-2X8, the cation exchanger Dowex-50WX8 and the chelating resin Chelex-100 and aqueous solutions of Arsenazo-III at different pH values was studied. The concentration of Arsenazo-III was in the range of 1.53·10^–4–1.23·10^–3M. Equilibrium pH was varied from 1.0 to 8.78 while U(VI) original concentration was held constant at 3.39·10^–4M. The effect of Arsenazo-III concentration and the variation of hydrogen ion concentration on U(VI) species formed in solution as well as the sorbed species was discussed. Use was made of IR spectroscopy to investigate the sorption behavior. The sorption of some interfering ions such as Th(IV), Zr(IV) and Ce(III) on the resins used at optimum conditions for the sorption of U(VI) was also investigated.     

Selective detection and recovery of gold at tannin-immobilized non-conducting electrode

A tannin-immobilized glassy carbon electrode (TIGC) was prepared via electrochemical oxidation of the naturally occurring polyphenolic mimosa tannin, which generated a non-conducting polymeric film (NCPF) on the electrode surface. The fouling of the electrode surface by the electropolymerized film was evaluated by monitoring the electrode response of ferricyanide ions as a redox marker. The NCPF was permselective to HAuCl₄, and the electrochemical reduction of HAuCl₄ to metallic gold at the TIGC electrode was evaluated by recording the reduction current during cyclic voltammetry measurement. In the mixed electrolyte containing HAuCl₄ along with FeCl₃ and/or CuCl₂, the NCPF remained selective toward the electrochemical reduction of HAuCl₄ into the metallic state. The chemical reduction of HAuCl₄ into metallic gold was also observed when the NCPF was inserted into an acidic gold solution overnight. The adsorption capacity of Au(III) on tannin-immobilized carbon fiber was 29 ± 1.45 mg g⁻¹ at 60 °C. In the presence of excess Cu(II) and Fe(III), tannin-immobilized NCPF proved to be an excellent candidate for the selective detection and recovery of gold through both electrochemical and chemical processes.     

Ion exchange studies of Arsenazo-III and thorium(IV) from aqueous solutions of Arsenazo-III with AG-2×8, Dowex-50 W×8 and Chelex-100

Iodine-125 from aqueous solutions were sorbed by several naturally occurring minerals such as kaolinite, ferrous oxide and hydrous aluminium oxides. Coagulation-flocculation and column experiments were conducted and compared to determine which method could more effectively and conveniently treat the effluent. At a pH value of 4.5, the mentioned minerals exhibited modest positive charges being able to attract the anions of¹²⁵I. For activities of effluents normally produced by different users, both treatments by coagulation-flocculation and column (mixture of kaolin and soil material) experiments were suitable. However, column methods were more effective, easy to handle, have low capital and maintenance costs for treating the wastes.     

Separation and determination of rare earth elements by Dowex 2-X8 resin using sodium trimetaphosphate as elution agent

The distribution coefficients of rare earth elements and thorium with Dowex 2-X8, 200-400 mesh, a strongly basic anion-exchange resin, have been determined regarding four different concentrations of sodium trimetaphosphate (3 x 10(-3), 5 x 10(-3), 7 x 10(-3) and 0.01 M). The separation of the rare earths and thorium obtained from an Australian monazite has been investigated by anion-exchange chromatography with sodium trimetaphosphate concentration gradient on a Dowex 2-X8 ion-exchange columns. The order of elution of the elements was the reverse of the order of elution of the same elements on Dowex 1 resin. The elution was investigated using 5 mg and 250 mg samples. In the separation of 5 mg samples, all elements were separated in 29 min. It has been seen that the elution peaks are narrow, tailing effects are very small, Dy and Y are well separated. Qualitative and quantitative determinations were realized by spectrofluorometry.     

Separation of the no-carrier-added 109Cd from Ag, Cu and 65Zn by use of a precipitation and AG1-X8 resin

The ¹⁰⁹Cd radionuclide was produced in the cyclotron via ^natAg(p,n)¹⁰⁹Cd reaction. The radiochemical separation of ¹⁰⁹Cd from silver and non-isotopic impurities comprised of two stages. The optimum conditions of the ¹⁰⁹Cd separation methods were: Ag precipitation with 0.015 M HCl and Cu and ⁶⁵Zn by use of 0.015 M HCl on AG1-X8 strong anion-exchange resin. Chemical and radionuclidic purity of ¹⁰⁹Cd were measured by ICP-AES and gamma-ray spectrometry respectively. Recovery yield and radionuclidic purity were obtained 99.7% and 99%, respectively.     

Selective recovery of polyhydroxyalkanoate inclusion bodies from fermentation broth by dissolved-air flotation

Selective dissolved-air flotation for the separation of medium-chain-length polyhydroxyalkanoate (PHA) inclusion bodies (IBs) from Pseudomonas putida cell debris is investigated. Measurements show that both P. putida cell debris and PHA IBs have an iso-electric point of approximately pH 3.5. Selective aggregation and as a result selective flotation of PHA IBs was observed near this pH. Qualitative prediction of the aggregation behaviour was possible on the basis of the Van der Waals, hydrophobic and electrostatic interactions. In some cases however, the stability of the suspension could not be explained with these forces alone. It was therefore suggested that additional interactions, such as steric/brush effects, play an important role in the aggregation process.     

Removal of Rhodamine-B from Aqueous Solution by Adsorption onto Crosslinked Alginate Beads

The biosorption of rhodamine-B from aqueous solution using crosslinked alginate beads was studied by contact method at fixed pH ?3 and room temperature (28 ± 0.2°C). Both the Freundlich and Langmuir isotherm models could describe the adsorption equilibrium of the rhodamine-B onto crosslinked alginate beads. The influence of various experimental parameters such as pH, temperature, effect of concentration and time were evaluated. It was observed that the adsorption capacity of rhodamine-B onto alginate beads decreased with increase in pH and temperature above room temperature.     

Kinetics of hydrogen peroxide decomposition with Fe(III) and Cr(III)-ethanolamines complexes sorbed on dowex-50W resin

The kinetics of the H₂O₂ decomposition in presence of Fe(III)- and Cr(III)-complexes of mono-, di-, and triethanolamine supported on Dowex-50W resin have been investigated. The decomposition process proceeded with first-order kinetics for the substrate concentration. The rate of reaction increased with increasing number of the coordinated ligands in the metal complex as well as with increasing ligand basicity. The decomposition reaction involved the formation of an intermediate active species, which converts into a peroxo-metal complex of brown, green, or gray color. A mechanism describing the decomposition process is proposed. © 1995 John Wiley & Sons, Inc.     

Preconcentration of total chromium on Dowex 50W-X8 resin loaded with 2-amino-benzenethiol

Application of Dowex 50W-X8 loaded with 2-amino-benzenethiol for preconcentration of total chromium (Cr(VI) and Cr(III)) in water samples and subsequent determination by inductively coupled plasma-atomic emission spectrometry was studied. The reagent 2-amino-benzenethiol loaded onto the resin effectively reduced Cr(VI) to Cr(III) and total chromium (both Cr(VI) and Cr(III)) formed chelate complex with the reagent in the Cr(III) valence state. Experimental parameters such as preconcentration time, solution flow rates, pH, and concentration of the eluent were optimized. The method has been applied for the determination of total chromium in seawater samples in the range of 0.1–200?µg?L^?1. A detection limit of 0.3?µg?L^?1 was achieved, and the relative standard deviation was about 5%.     

Selective recovery of gold(III) using cotton cellulose treated with concentrated sulfuric acid

Novel utilization of cotton cellulose was developed by chemically modifying with concentrated sulfuric acid to prepare a novel kind of adsorption gel for gold. The adsorption behaviors of the gel were investigated for various metals from acidic chloride media. The gel was found to be highly selective for Au(III) over other precious and base metals tested over the whole concentration range of hydrochloric acid. The maximum adsorption capacity for Au(III) was evaluated as 6.21 mmol/g at 303 K. The amount of adsorbed Au(III) was increased with increasing temperature. A kinetic study for the adsorption of Au(III) at various temperatures confirmed the endothermic adsorption process following pseudo-first order kinetics. The activation energy was evaluated as 78.8 kJ/mol. Interestingly, it was found that the adsorbed Au(III) was reduced to elemental form which was evidenced by the clearly visible elemental gold particles which was further confirmed by means of the X-ray diffraction spectrum and optical microscope image of the gel after the adsorption of Au(III). The mechanism of Au(III) adsorption on the cotton gel and its reduction to elemental gold was proved from the results of IR-spectra. The main mechanism could be explained in terms of the coordination of Au(III) to oxygen atom of C–O–C linkage of cross linked cotton gel and to the oxygen atoms of the hydroxyl groups at C₂ and C₃ atoms of pyranose ring of cotton cellulose followed by the reduction to metallic gold. The adsorbed gold in the cotton gel can easily be recovered by incineration.     

Selective cleavage of N-benzyl-protected secondary amines by triphosgene

A series of competition experiments has revealed that selective cleavage of N-benzyl-protected secondary amines can be achieved with triphosgene, thereby providing a useful range of carbamoyl chlorides.     

Selective shortening of single-crystalline gold nanorods by mild oxidation

Gold nanorods (NRs) have received much attention due to their size-dependent surface plasmon-related optical properties. A seed-mediated approach has recently been developed for the synthesis of Au NRs with varying length-to-diameter aspect ratios. With the introduction of silver ions in the growth solution, Au NRs of narrow size distributions can be produced in high yields. Herein we describe an approach for the continuous and selective shortening of Au NRs synthesized by the silver ion-assisted seed-mediated method through oxidation with environmentally benign oxygen at slightly elevated temperatures. UV-visible extinction measurements indicate that the longitudinal surface plasmon band of Au NRs decreases in intensity and blue-shifts as a function of the oxidation time. Transmission electron microscopy (TEM) imaging shows that the length of Au NRs decreases with oxidation and their diameter stays almost constant, which suggests that oxidation starts at the ends of Au NRs. The size distributions of shortened Au NRs are similar to those of starting NRs. Further oxidation transforms Au NRs into nanospheres, which become smaller in diameter and finally completely disappear. It has been found that the oxidation rate of Au NRs can be controlled by temperature and acid concentration. Furthermore, high-resolution TEM studies reveal that Au NRs synthesized by the silver ion-assisted seed-mediated method are single crystalline and they stay single crystalline during oxidation. It is expected that Au NRs of any aspect ratio with narrow size distributions within the limit of that possessed by starting NRs can be produced by this mild oxidation approach.     

Selective enhancement of nucleases by polyvalent DNA-functionalized gold nanoparticles

We demonstrate that polyvalent DNA-functionalized gold nanoparticles (DNA-Au NPs) selectively enhance ribonuclease H (RNase H) activity while inhibiting most biologically relevant nucleases. This combination of properties is particularly interesting in the context of gene regulation, since high RNase H activity results in rapid mRNA degradation and general nuclease inhibition results in high biological stability. We have investigated the mechanism of selective RNase H activation and found that the high DNA density of DNA-Au NPs is responsible for this unusual behavior. This work adds to our understanding of polyvalent DNA-Au NPs as gene regulation agents and suggests a new model for selectively controlling protein-nanoparticle interactions.     

Selective adsorption and separation of Cu(II) from Zn solution by CU resin

Journal of Radioanalytical and Nuclear Chemistry - The aim of present study was to determine the efficiency of CU selective resin for separation of radionuclides Cu from large excess of Zn....     

Selective enhancement of resonance light-scattering of gold nanoparticles by glycogen

Simple and sensitive methods for the determination of glycogen are desirable. This study was to establish the determination of glycogen based on the enhancement of the light-scattering intensity of gold nanoparticles (AuNPs) at nanogram per milliliter levels. Glycogen enhancement was independent of temperature and was highest at pH 7. The enhancement was linear from 10 to 800 ngmL(-1) with a 2 ngmL(-1) detection limit (3S/N). The standard deviation of the slope for 5 consecutive calibration runs was within 5%. Analysis of three artificial samples with varied glycogen concentrations had 98-102% recovery. Selected amino acids, glucose, lactose, BSA and trichloroacetic acid all showed minor effects on glycogen enhancement demonstrating the potential for glycogen determination in complex samples.