Highly efficient adsorbing noble metal ions by 3,4-dihydroxycinnamic acid-modified activated carbon

A method was established for the preconcentration of trace Au(III), Pd(II) and Pt(IV) by activated carbon modified with 3,4-dihydroxycinnamic acid. The separation and preconcentration conditions of analytes were investigated, such as effects of pH, the contacting time, the sample ?ow rate and volume, the elution condition and the interfering ions. At a pH of 1.0, the maximum static sorption capacity of the sorbent was found to be 374.8, 96.6 and 137.5 mg g^?1 for Au(III), Pd(II) and Pt(IV), respectively. The adsorbed metal ions were effectively eluted with 2.0 mL of 4% thiourea in 0.5 M HCl solution and determined by inductively coupled plasma optical emission spectrometry. The detection limit (3σ) of this method defined by IUPAC was found to be 0.12, 0.18 and 0.32 ?g L^?1 for Au(III), Pd(II) and Pt(IV), respectively. The relative standard deviation (RSD) was lower than 3.0% (n = 8) towards standard solutions. The method has been validated by analysing certified reference materials and successfully applied to the determination of trace Au(III), Pd(II) and Pt(IV) in road sediments samples.     

Synthesis and characterisation of morin-functionalised silica gel for the enrichment of some precious metal ions

Silica gel was firstly functionalised with aminopropyltrimethoxysilane obtaining the aminopropylsilica gel (APSG). The APSG was reacted subsequently with morin yielding morin-bonded silica gel (morin-APSG). The structure was investigated and confirmed by elemental and thermogravimetric analyses, IR and (13)C NMR spectral studies. Morin-APSG was found to be highly stable in common organic solvents, acidic medium (<2molL(-1) HCl, HNO(3)) or alkaline medium up to pH 8. The separation and preconcentration of Ag(I), Au(III), Pd(II), Pt(II) and Rh(III) from aqueous medium using morin-APSG was studied. The optimum pH values for the separation of Ag(I), Au(III), Pd(II), Pt(II) and Rh(III) on the sorbent are 5.7, 2.2, 3.7, 3.7 and 6.8, giving rise to separation efficiencies of 43.9, 85.9, 97.7, 60.9 and 91.0%, respectively, where the activity was found to be >90% in the presence of acetate ion. The ion sorption capacity of morin-APSG towards Cu(II) at pH 5.5 was found to be 0.249mmolg(-1) where the sorption capacities of Ag(I) and Pd(II) were 0.087 and 0.121mmolg(-1) and 0.222 and 0.241mmolg(-1) at pH 2.2 and 5.7, respectively. This indicates a 1:1 and 1:2 morin/metal ratios at pH 2.2 and 5.7, respectively. Complete elution of the sorbed metal ions was carried out using 10mL (0.5molL(-1) HCl+0.01molL(-1) thiourea) in case of Au(III), Pd(II), Pt(II) and Rh(III) and 10mL 0.5molL(-1) HNO(3) in case of Ag(I). Morin-APSG was successfully employed in the separation and preconcentration of the investigated precious metal ions from some spiking water samples yielding 100-folds concentration factor. The relative standard deviation (R.S.D.) and the T-test (|t|(1)) were calculated.     

Palladium and platinum sorption using chitosan-based hydrogels

Two chitosan hydrogels (prepared by NaOH neutralization and by polyphosphate ionotropic gelation) have been tested in the dry state for Pd(II) and Pt(IV) sorption at pH 2. Similar sorption isotherms with maximum sorption capacities close to 190 mg Pd g⁻¹ and 235 mg Pt g⁻¹ were achieved. The sorption mechanism involves electrostatic attraction of the chloro-anionic species onto protonated amine groups; the drastic decrease of sorption capacity with the addition of chloride ions supports this hypothesis. SEM-EDAX analysis suggests that sorption proceeds, in kinetic terms, through a shrinking core mechanism. Metal ions can diffuse throughout all the sorbent volume. The main differences between the sorbents are revealed by kinetics. The hydrogels prepared by ionotropic gelation in polyphosphate (C-PPh) allows reaching equilibrium much faster than the hydrogels prepared by the neutralization process (C-NaOH). While for C-PPh sorbent the chemical reaction rate seems to control sorption profiles, in the case of C-NaOH a combination of mechanisms including intraparticle diffusion resistance controls uptake kinetics. Metal desorption from loaded sorbents is possible using thiourea alone or in association with HCl solutions. The recycling of the sorbents is possible but for a limited number of cycles.     

Synthesis of N-Methyl-2-Thioimidazole Resin and Its Complex Behavior for Noble Metal Ions

The functional group capacity and the percentage of functional group conversion of crosslinked polystyrene resin bearing N-methyl-2-thioimidazole (MTIR) synthesized under optimum conditions are as high as 4.08 mmol/g resin and 96.0%, respectively. The apparent activation energies of sorption of MTIR for Au(III) and Pt(IV) are 13.1 and 13.4 kJ/mol, respectively. The sorption behavior of MTIR for Au(III), Pt(IV), and Pd(II) obeys the Freundlich and Langmuir isotherms. The sorption capacities of MTIR for Au(III), Pt(IV), and Pd(II) are as high as 4.33, 2.12, and 2.33 mmol/g resin, respectively. Au(III), Pt(IV), and Pd(II) adsorbed on MTIR can be eluted quantitatively by the eluant. The resin can be regenerated easily and reused without an obvious decrease in the sorption capacity for Au(III) and Pd(II). The resin has high sorption selectivity for noble metal ions. Au(III) can be separated quantitatively in the presence of high concentrations of Cu²⁺, Fe³⁺, Ni²⁺, and Mn²⁺. The recovery of platinum from the spent industrial catalysts is 98.6% by MTIR. The preconcentration and separation of palladium and platinum from the anode deposits of electrolysis of crude copper have been investigated. The resin may have potential industrial uses.     

<Emphasis Type="Italic">N</Emphasis>-(2-(2-Pyridyl)ethyl)chitosan (PEC) for Pd(II) and Pt(IV) sorption from HCl solutions

Chitosan was modified by grafting 2-pyridyl-ethyl moieties on the biopolymer backbone for the synthesis of a Platinum Group Metal (PGM) sorbent. The sorbent was tested for Pd(II) and Pt(IV) sorption from HCl solutions. Stable for HCl concentrations below 0.5 M, the sorbent reached sorption capacities as high as 3.2 and 2.6 mmol metal g⁻¹ for Pd(II) and Pt(IV), respectively. Metal sorption mainly proceeds by electrostatic attraction in acidic solutions, though a contribution of complexation mechanism cannot be totally rejected. The resistance to intraparticle diffusion is the main controlling mechanism for uptake kinetics. While agitation speed has a limited effect on kinetics, metal concentration and sorbent dosage have a greater effect on the kinetic profiles. The intraparticle diffusivity varies between 3 × 10⁻¹¹ and 4.5 × 10⁻¹⁰ m² min⁻¹. Thiourea (combined with HCl solution) is used for Pd(II) and Pt(IV) desorption. The resin could be desorbed and recycled for a minimum of five cycles maintaining high efficiencies of sorption and desorption.     

Sorption of noble-metal ions on silica with chemically bonded nitrogen-containing ligands

A study has been made of the sorption of Ir(IV), Rh(III), Pt(IV), Ru(IV), Os(VIII), Pd(II) and Au(III) from aqueous solutions by silica chemically modified with nitrogen-containing organic ligands, as a function of hydrochloric acid concentration, time of contact, concentration of the element and the ionic strength. Sorption of noble-metal ions at pH > 1 on a sorbent containing monoamine groups seems to be due to a complexation mechanism, and to an anion-exchange mechanism at pH < 1. With aminopropyl-silica 1000-fold concentration of Ir(IV) and Rh(III) from their 10(-8)-10(-7)M solutions was achieved and these metals were subsequently determined on the sorbent surface by X-ray fluorescence. Detection limits were 10-20 ng/ml. There was no interference from 1000-fold quantities of non-ferrous metal ions and Fe(III). With the sorbent containing bonded diethylenetriamine groups, 1000-fold concentration of Au(III) was achieved, and it was then determined on the sorbent surface by an atomic-emission method. Conditions for desorption of Au(III) with pyridine and potassium thiocyanate were developed.     

Column solid phase extraction and determination of ultra-trace Au,Pd and Pt in environmental and geological samples

A new sorbent based on cysteine modified silica gel (SiG-cys) was prepared and studied for preconcentration and separation of noble metals Au(III), Pd(II), Pt(II), Pt(IV). Its extraction efficiency was examined by batch and column solid phase extraction procedures. Laboratory experiments performed showed that sorbent is characterized with high selectivity, permiting quantitative sorption (93–97%) of noble metals Au, Pd and Pt from acidic media 0.1–2 mol L^? 1 HCl and unsignificant sorption (less than 2%) for common base metals like Cu, Fe, Mn and Zn. The analytes retained on the sorbent are effectively eluted with 0.1 mol L^? 1 thiourea in 0.1 mol L^? 1 HCl and measured by ETAAS or ICP OES under optimal instrumental parameters. The sorbent showed high mechanical and chemical stability and extraction efficiency was not changed after 500 cycles of sorption/desorption. The sorbent was successfully applied in analyticals procedures for preconcentration and determination of Au, Pd and Pt in geological and soil samples. Detection limits (3σ criteria) achieved, depending on the instrumental methods used are: ETAAS (0.005 μg L^? 1 for Au in river and sea water, 0.002 μg g^? 1 for Au in copper ore and copper concentrate); ICP OES (0.03 μg L^? 1 for Pd and 0.06 μg L^? 1 for Pt in river and sea water, 0.006 μg g^? 1 for Pd in copper ore and copper concentrate and 0.002 μg g^? 1 for soluble Pt in soil). The accuracy of the procedures developed was confirmed by added/found method for sea and river water; by the analysis of national certified materials (copper ore and copper concentrate for Au and Pd) and by determination of the sum of soluble Pt(II) + Pt(IV) in spiked soil samples.     

Pd(II) and198Au(III) sorption on 4(benzylcellulose)phenylthiocarbamoylamine

The mechanism of Pd(II) and¹⁹⁸Au(III) sorption on 4(benzylcellulose)phenylthiocarbamoylamine has been investigated. The data obtained from the sorption dependence on medium acidity and temperature, from isotherms, IR spectra and diffuse reflectance spectra led to the conclusion that the physical sorption of the two elements is accompanied by the formation of chelates. The sorbent might be employed for the concentration of Pd(II) and Au(III) from dilute solutions.     

Selective solid-phase extraction and separation of trace gold, palladium and platinum using activated carbon modified with ethyl-3-(2-aminoethylamino)-2-chlorobut-2-enoate

Activated carbon was chemically modified with ethyl-3-(2-aminoethylamino)-2-chlorobut-2-enoate to obtain a material for selective solid-phase extraction of trace Au(III), Pd(II) and Pt(IV) prior to their determination by inductively coupled plasma atomic emission spectrometry. Experimental conditions such as effects of pH, shaking time, sample flow rate and volume, elution and interfering ions were studied. The ions Au(III), Pd(II) and Pt(IV) can be quantitatively adsorbed on the new sorbent from solution of pH 1. The adsorbed ions were then eluted with 0.1 mol L^?1 hydrochloric acid and containing 4% thiourea. Many common ions do not interfere. The adsorption capacity of the material is 305, 92, and 126 mg g^?1 for Au(III), Pd(II) and Pt(IV), respectively, and the detection limits are 5, 11 and 9 ng mL^?1. The relative standard deviation is less than 3.0% (n?=?8) under optimum conditions. The method was validated by analyzing two certified reference materials and successfully applied to the preconcentration and determination of these ions in actual samples with satisfactory results.

Determination of gold,palladium and copper by flame atomic absorption spectrometry after preconcentration on silica gel modified with 3-(2-aminoethylamino)propyl group

A preconcentration method of gold, palladium and copper based on the sorption of Au (III), Pd (II) and Cu (II) ions on a column packed with 3-(2-aminoethylamino)propyl bonded silica gel is described. The modified silica gel was synthesized and characterized by FT-IR and C, H, N elemental analysis. At column preconcentration, the effects of parameters such as pH, volume, flow rate, matrix constituents of solutions and type of eluent on preconcentration of gold, palladium and copper were studied. The recoveries of Au (III), Pd (II) and Cu (II) were 98.93±0.51, 98.81±0.36 and 99.21±0.42 % at 95 % confidence level, respectively. The detection limits (δ) of the elements were 0.032, 0.016 and 0.012 μg ml⁻¹, respectively. The preconcentration method was applied for determination of gold and palladium in certified reference material SARM 7B and copper in river and synthetic seawater by FAAS. Gold, palladium and copper were determined with relative error lower than 10 %.     

Influence of the Degree of Chitosan Sulfoethylation on the Sorption of Palladium(II) Chloride Complexes from Multicomponent Solutions

The influence exerted by the degree of substitution of sulfoethylated chitosan cross-linked with glutaraldehyde on the sorption of Pd(II) chloride complexes from multicomponent solutions containing Pt(IV), Cu(II), Ni(II), Co(II), Cd(II), and Zn(II) was studied. The sorption of transition metal ions under the conditions of the experiment at pH 0.5–5.0 is virtually fully suppressed. The strongest interfering effect on the Pd(II) sorption is exerted by Pt(IV). Calculation of the selectivity coefficients K_Pd/Pt shows that the selectivity of the Pd(II) sorption relative to Pt(IV) increases with an increase in the degree of substitution of chitosan from 0.3 to 0.5. Integral kinetic curves of the Pd(II) sorption were obtained, and the dependences were subjected to mathematical processing using the models of diffusion and chemical kinetics. The equilibrium in the palladium(II) chloride solution–sorbent system is attained within 40 min. Pd and Pt are quantitatively desorbed from the sorbent surface under dynamic conditions with 3.5 M HCl solution.     

Sorption-luminescence determination of gold,silver, and platinum with the use of silica gel chemically modified with <Emphasis Type="Italic">N</Emphasis>-(1,3,4-thiodiazole-2-thiol)-<Emphasis Type="Italic">N</Emphasis>′-propylurea groups

Silica gel chemically modified with N-(1,3,4-thiodiazole-2-thiol)-N′-propylurea extracted gold(III) from solutions in the range of 6 M HCl-pH 8 and silver(I) from nitric acid solutions in the range of 6 M HNO₃-pH 8 and 1–2 M HCl at 20°C with 99.0–99.9% recovery and a sorption equilibration time of 5 min. Platinum(II) was quantitatively extracted at room temperature from solutions in the range of 4 M HCl-pH 8; the sorption equilibration time was 20 min. For the quantitative extraction of platinum(IV), it should be reduced to platinum(II). The intense yellowish orange luminescence (λ_max (Au) = 575 nm, λ_max (Ag) = 550 nm, and λ_max(Pt) = 620 nm) of surface complexes at 77 K under UV irradiation was used in the development of procedures for the low-temperature sorption-luminescence determination of gold, silver, and platinum. The detection limits were 0.15 (Au), 0.1 (Ag), and 0.05 μg (Pt) per 0.1 g sorbent. The calibration function was linear to 50 (Au, Ag) or 80 μg (Pt) per 0.1 g sorbent. The relative standard deviation in the determination of more than 5 μg of a metal was no higher than 6%. The sorption-luminescence determination procedures were tested in the determination of gold in gold-containing concentrates and their processing products and platinum in alumina-platinum catalysts.     

Selective solid-phase extraction of trace Au(III), Pd(II) and Pt(IV) using activated carbon modified with 2,6-diaminopyridine

A new sorbent was prepared by immobilization of 2,6-diaminopyridine on activated carbon and then used as a solid-phase extractant for trace Au(III), Pd(II) and Pt(IV) before their determination by ICP-AES. Effects of pH, the shaking time, the sample flow rate and volume, the elution condition and the potentially interfering ions were investigated. The optimum pH value is 1. The maximum static adsorption capacity for the three ions is 202.7, 38.5 and 30.1?mg?g^?1, respectively. The adsorbed metal ions can be completely eluted by 2?mL of the eluent solution that contains 0.05?mol?L^?1 HCl and 5% thiourea. Common other ions do not interfere. The detection limits (3??) are 0.16, 0.33 and 0.29?ng?mL^?1, respectively. The relative standard deviation (RSD) was lower than 3.0% (n?=?8). The new sorbent was applied to the preconcentration of the three ions in ore and rock samples with satisfactory results.

Ion chromatography of chloro complexes of the platinum group metals and gold using bonded phase silica substrates

The ion chromatography of chloro complexes of Au(III), Ir(IV), Ir(III), Os(IV), Pd(II), Pt(IV), Rh(III) and Ru(III) was investigated using anion-exchange and ion-interaction techniques involving silica-based phases. Chloride was either absent or at a very low level and the pH was high enough to enable steel-fabricated liquid chromatography equipment to be used. With anion exchange, Ir(IV), Ir(III), Os(IV) and Pt(IV) gave good stable chromatography and all produced linear calibration plots, except Ir(IV) owing to instability of the sample solution. The detection limits were Ir(III) 5, Os(IV) 10 and Pt(IV) 2 ng ml^?1. The ion-interaction technique was not so successful, only Au(III) and Pd(II) giving stable chromatography. The calibration plots were slightly curved, although acceptable, and the detection limits were 10 and 30 ng ml^?1 for Au (III) and Pd(II), respectively.     

Synthesis of Functional Resins Containing Heterocyclic Rings and Their Sorption Properties for Noble-Metal Ions

Five kinds of functional resins, 2-aminopyridine resin (2-APR), 3-APR, 4-APR, 2-hydroxypyridine resin (2-HPR), and 2-thiolbenzothiazole resin (2-TBTR), were synthesized. The functional group capacities of the resins were 3.0–4.2 mmol/g resin. The sorption capacities of 4-APR, 3-APR, and 2-APR for Au(III) and Pt(IV) were 3.12–3.22 mmol Au(III)/g APR and 1.27–1.60 mmol Pt(IV)/g APR. The molar complex ratios, Au(III)/NH-C₅H₄N and Pt(IV)/NH-Cs H₄N were 0.84–0.97 and 0.34–0.48, respectively. Selective sorption of 4-APR for various coexistent metal ions over a wide acidity range (1–5 N HCl) was in the following order: Pt(IV) > Au(III) > Cd²⁺ > Zn²⁺ > Pd(II) > Mn²⁺, Cu²⁺, Fe³⁺. The Au(III) adsorbed on APR can be quantitatively eluted with 2% aqueous thiourea. The regenerated APR can be reused without apparent decrease in the sorption capacity for Au(III). The separation of Au(III) and Cu²⁺ was studied preliminarily. The excellent properties show that APR may be used in the gold industry. The sorption capacities of 2-HPR for Au(III) is 0.99 mmol Au(III)/g 2-HPR. That of 2-TBTR for Au(III) is less than that of APR. 2-HPR is stable below 100°C, while 4-APR and 2-APR are stable below 80°C in air.     

Preconcentration of noble metals on a polymer support as complexes of organic reagents and their subsequent determination in the solid phase

Conditions of the sorption preconcentration of Pt, Pd, Au, Ag, and Hg as colored complexes of azorhodanines, tyrodine, and sulfonitrophenol M from acidic solutions (pH 0–2) on a polyamide membrane in the flow mode are determined. At a flow rate of 10–20 mL/min, concentrations of determined elements of 10^-9-10^-7 M, and pressure of 10–20 mm Hg, the complexes are nearly quantitatively sorbed on a polyamide membrane disk (d = 1 cm,m = 2.7 mg, andl = 0.1 mm). The influence of the composition of the test solutions on the formation of the analytical signal in the solid phase is studied. Rapid sorption-spectrometric procedures are developed for the determination of Pt, Pd, Au, Ag, and Hg with the detection limit 5–30 ng of the element in the sorbent zone     

Preconcentration of noble metals with the POLYORGS 4 complexing sorbent under the action of microwave irradiation

The sorption of Au(III), Pd(II), Pt(IV), Rh(III), and Ir(IV) with the POLYORGS 4 complexing sorbent in the static mode was studied at room temperature and on thermal and microwave heating. It was demonstrated that the sorption of noble metals from 1 M HCl and 1 M HNO₃ solutions can be substantially accelerated under the action of microwave irradiation. Based on the obtained data, the conditions of the group preconcentration of noble metals for their subsequent determination by the ETAAS and ICP AES methods were selected. The preconcentration procedure was used for the analysis of certified reference material SARM-7B (platinum-containing ore), VT-1 (copper-nickel sulfide ore), and the alloy of copper with noble metals.     

Application of an imidazoline group-containing chelating fiber for the determination of trace noble metals in superhigh-temperature alloys

An imidazoline group-containing chelating fiber was prepared by means of the reaction of nitrile groups with ethylenediamine in an hydrazine-modified polyacrylonitrile fiber. The adsorption properties of the chelating fiber for Au(III), Pd(II), Pt(IV), Ir(IV), Os(IV), Rh(III) and Ru(IV) ions, such as binding capacity, distribution coefficient, sorptive rate and quantitative elution of Au(III), Pd(II) and Pt(IV) ions were investigated. The imidazoline group-containing chelating fiber possessed high binding capacities and good adsorption kinetic properties, exhibited high affinity for noble metals in 0.1–1.0 mol/L HCl and could be efficiently re-used. After the separation of trace Au(III), Pd(II) and Pt(IV) ions from a matrix using the chelating fiber, these ions could be determined by ICP-AES with satisfactory results, and the relative standard deviation for Au(III), Pd(II) and Pt(IV) ions was less than 6%. Received: 5 July 1999 / Revised: 4 October 1999 / Accepted: 4 October 1999     

Specificity of noble metals dynamic sorption preconcentration on reversed-phase sorbents

The reversible sorption preconcentration of noble metals (NMs) using different schemes “sorbent–reagent–eluent” was investigated. The extraction of Au, Pd, Pt, Ir, Rh and Ru chlorocomplexes from hydrochloric acid solutions on hyper-crosslinked polysterene MN-200 in the form of ion associates with tributylamine (TBA) and 4-(n-octyl)diethylenetriamine (ODETA) was investigated. It was found that Pd, Pt and Au were quantitatively and reversibly extracted using TBA on hyper-crosslinked polysterene; the appropriate eluent for desorption was 1 M solution of HCl in ethanol. Ir, Rh and Ru under these conditions were not sorbed quantitatively. It was found that sorbent hydrophobicity is not the main characteristic that defines the efficiency of sorption of a particular NM ion associate. Different efficiencies of hyper-crosslinked polysterene MN-200 for sorption of square-planar chlorcomplexes of Pt, Pd and Au and octahedral complexes of Ir, Rh and Ru were found. For the first time, the sorbents with their own N-atoms – StrataX and StrataX-AW – were used for the sorption of Ir, Rh and Ru. Using these sorbents, the sorption of Ir was increased up to 95%, and the sorption of Ru and Rh was increased to about 40%. We can explain these results by nonspecific interaction of chlorcomplexes of Ir, Rh and Ru with ethylenediamine groups of the sorbent. Weak bases with large anions may be applied for desorption of Ir, Rh and Ru. Two schemes of dynamic sorption preconcentration of NMs from hydrochloric acid solutions were proposed – hyper-crosslinked polysterene MN-200 for the determination of Au, Pd, Pt, and StrataX-AW for Ir, Rh and Ru.     

Vinyl 2-hydroxyethyl sulfide polymers and their sorption properties with respect to transition metals

Vinyl 2-hydroxyethyl sulfide (VHES) homopolymer and the homopolymer and vinyl 2-hydroxyethyl sulfide-acryl amide copolymer cross-linked by bisacrylamide were prepared by radical polymerization. The sorption of Au(III), Ag(I), Pd(II), Pt(IV), Hg(II), Pb(II), Fe(III), Ni(II), Cu(II) on these polymers under the static conditions was studied in relation to the solution pH. The polymers are highly selective and efficient sorbents for Au(III), Ag(I) and Hg(II).