Prediction and measurement of multi-metal electrodeposition rates and efficiencies in aqueous acidic chloride media

A novel process is being developed for metal recovery from waste electrical and electronic equipment (WEEE) and involving a leach reactor coupled to an electrochemical reactor. Metals such as Ag, Au, Cu, Pb, Pd, Sn, etc. are dissolved from shredded WEEE in an acidic aqueous chloride electrolyte by oxidizing them with aqueous dissolved chlorine species. In the electrochemical reactor: (i) chlorine is generated at the anode for use as the oxidant in the leach reactor, and, simultaneously, (ii) at the cathode, the dissolved metals are electrodeposited from the leach solution. The Butler-Volmer equation was used to provide predictions of the electrode potential dependences of partial current densities, and hence total current densities, current efficiencies and alloy compositions, for acidic aqueous chloride electrolytes containing Ag(I), Au(III), Cu(II), Fe(III), Pb(II), Pd(IV) and Sn(IV) species, together with dissolved chlorine. With judicious choice of kinetic parameters, the predicted total current density—electrode potential behaviour of such solutions was in good agreement with experimental data for a rotating Pt disc electrode. Reduction of dissolved chlorine at a Pt rotating disc electrode exhibited mass transport controlled behaviour, in agreement with Levich's equation over the potential range 0.3-0.9 V (SHE). This could form the basis of a linear sensor, possibly using a microelectrode for measurement and control of the dissolved chlorine concentration in the efflux of leach reactors and inlet to cathodes of the electrowinning reactors, in the envisaged process.     

Recovery of Platinum and Palladium from Chloride Solutions by a Thiodiglycolamide Derivative

The liquid-liquid extraction of platinum(IV) and palladium(II) from hydrochloric acid media was carried out using N,N’-dimethyl-N,N’-dicyclohexylthiodiglycolamide (DMDCHTDGA) in 1,2-dichloroethane (1,2-DCE). Pt(IV) is efficiently extracted from 5 M HCl onwards (%E ≥ 97%), whereas Pd(II) is quantitatively recovered from 1 to 8 M HCl solutions. Both Pt(IV) and Pd(II) can be successfully stripped from the loaded organic phases, the former with a 1 M HCl solution, the latter with 0.1 M thiourea in 1 M HCl. The maximum loading capacity of DMDCHTDGA for Pt(IV) could not be determined but it is high, since molar ratios extractant:Pt(IV) within 2 and 3 have been achieved. Data obtained from successive extraction-stripping cycles suggest a good stability profile of DMDCHTDGA towards Pt(IV) recovery. Attempts to replace 1,2-DCE by more environmentally-friendly diluents showed, in general, comparable %E for Pt(IV). The study of the influence of acidity, as well as chloride ion and DMDCHTDGA concentrations, allows a proposal for the composition of the Pt(IV) species formed upon extraction. Results obtained with binary metal ion solutions point out that Pt(IV) and Pd(II) can be efficiently separated from DMDCHTDGA loaded organic phases through sequential selective stripping.     

A preliminary evaluation on the use of the cyclam functionalized resin for the noble metals sorption

A new resin has been prepared through a reaction between the vinylbenzyl chloride–divinylbenzene copolymer and the 1,4,8,11-tetraazacyclotetradecane (cyclam). This resin has been investigated after the characterization of the FTIR, batch and the dynamic sorption behavior of Au(III), Pt(IV) and Pd(II) ions took place. The sorption has been optimized with respect to HCl solutions. The maximum sorption properties were achieved from the solution of 0.1 M HCl. The sorption of Au(III), Pt(IV) and Pd(II) ions during a dynamic procedure in the presence of the 20-fold excess metals i.e. Cu, Fe, Ni resulted in an outcome of up to 400 mg of noble metals per gram of dry resin. The study of the noble metal loading was carried out over a wide range of the HCl concentration and in media of various multicomponent solutions of common metals.     

Electrochemical studies with tin electrodes in citric acid solutions

The electrochemical behaviour of tin in 0.5 M citric acid solution (pH=1.8) was studied by means of the potentiodynamic method. TheE-I profiles show an anodic current peak associated with a dissolution of the metal and the formation of a passivating film, and two cathodic current peaks which are related to the reduction of soluble Sn(II) species and reduction of the film. During the potential sweep in the cathodic direction, an anodic current peak can be observed and is interpreted in terms of a reactivation process. The data suggest that the passivation of tin in this medium occurs by a dissolution-precipitation mechanism. Depending on the potential sweep rate, the process is controlled either by mass transport or by the solution resistance in the pores of the film.     

SOLVENT EXTRACTION OF ANTIMONY (III), BISMUTH (HI), LEAD (II) AND TIN (IV) WITH BIS(2,4,4-TRIMETHYLPENTYL)PHOSPHINODITHIOIC ACID (CYANEX 301®)

The solvent extraction of antimony (in), bismuth (111), lead (II) and tin (IV) from aqueous hydrochloric acid solutions by bis(2,4,4-trimethylpentyl) phosphinodithioic acid (Cyanex 301® denoted HL) in kerosene + 10 % v/v n-decanol was investigated. Lead (II), tin (IV), bismuth (III) and antimony (III) are efficiently extracted by Cyanex 301® up to about 5, 6, 9 and 11 mol.L^1? HCl, respectively. The corresponding extracted species were identified as PbL₂, SnCl₂L₂, BiL₃ and SMvj. However, it was observed that Sn (IV) can be moderately extracted from the aqueous phase by the mere mixture of kerosene and n-decanol above 9 mol.L^1?HCl. In all cases, extraction equilibrium was reached within a few minutes. Finally, a thermodynamic modelling of the extraction system was developed in the particular case of lead (II).     

Codeposition of copper and tin from acid sulphate solutions containing polyether sintanol DS-10 and benzaldehyde

Cu(II) and Sn(II) reduction in acid sulphate solutions containing polyether laprol DS-10 and benzaldehyde (BA) was studied by means of impedance, voltammetric, XPS and XRD techniques. Both additives demonstrate weak surface activity on copper substrate in Cu(II) solutions in the absence of halide impurities. In contrast, their effect is overwhelmingly higher in the Sn|Sn(II) system. The additives induce a significant increase in Sn-electrode impedance and simultaneous strong inhibition of Sn(II) reduction over a wide range of cathodic polarizations. The effects of sintanol and BA in mixed Cu(II) and Sn(II) solutions demonstrate a kind of synergism. Underpotential deposition of tin on foreign (copper) substrate is observed at potentials more positive than the equilibrium potential of the Sn|Sn²⁺ system. Incorporation of tin into the Cu crystalline lattice results in the formation of multiphase material containing pure copper, α-CuSn phase, and intermediate hexagonal hcp phase. Formation of the pure tin phase occurs at more negative potentials and results in a strong inhibitive adsorption that manifests itself in the development of a deep voltammetric minimum. The tin content in the coatings depends on BA concentration and, particularly, on the electrode potential.     

Polybenzimidazole resin based new chelating agents. Palladium(II) and platinum(IV) sorption on resin with immobilized dithiooxamide

Microporous polybenzimidazole (PBI) of 250–500 μm bead size has been epoxidized and subsequently reacted with dithiooxamide in the presence of a phase-transfer catalyst to obtain a sorbent with immobilized dithiooxamide, EPBI(DTOX). The sorption of Pd(II) and Pt(IV) in HCl solutions has been measured on both PBI and EPBI(DTOX) resins, employing the sorbate species singly, in mixtures, and in the presence of a number of base metal ions, which include Cu(II), Ni(II), Zn(II), Co(II), Fe(II) and Fe(III). The saturation sorption capacities (mg/g dry resin) of PBI for Pd(II) and Pt(IV) in 0.1 N HCl are 276 and 288, respectively, the corresponding values for EPBI(DTOX) being 157 and 168. The sorption capacities decrease with the acid strength of the medium, the change, however, being relatively more pronounced for PBI, so much so that in concentrated (> 1 N) acids the sorption of EPBI(DTOX) is higher than that of PBI. In mixtures of Pd(II) and Pt(IV) with 10-fold molar excess of Pt(IV), PBI and EPBI(DTOX) show, respectively, 80% and 85% selectivity for Pd(II). While EPBI(DTOX) exhibits high selectivity (> 85% and > 80%, respectively) for Pd(II) and Pt(IV) in the presence of 100-fold molar concentration of any of the above base metal ions, on PBI, however, the Pd(II) and Pt(IV) selectivities are reduced to 50% and 20%, respectively, by 100-fold molar concentration of Fe(II).The neutral chelating ligand thiourea causes rapid stripping of Pd(II) and Pt(IV) from PBI and EPBI(DTOX) resins. The sorbed metal ions on PBI, being bound as complex anions by ionic forces, are more easily stripped by strong acids than the sorbed metal ions which are bound to EPBI(DTOX) by chelation. Having a relatively lower binding constant, Pt(IV) is however more easily stripped than Pd(II), thus permitting a selective stripping of Pt(IV) on PBI. On the other hand, a selective stripping of Pd(II) can be achieved with a strong solution of thiocyanate, which prevents stripping of Pt(IV) while allowing that of Pd(II). Thus, separation of Pd(II) and Pt(IV) in mildly acidic solutions in the absence of Fe(II) can be conveniently achieved by sorption on PBI followed by stripping with a strong solution of thiocyanate. EPBI(DTOX), on the other hand, is more useful for separation in concentrated acid solutions and in the presence of large concentrations of base metal ions including Fe(II).     

Separation of Precious Metals through a Trioctylamine Liquid Membrane

Abstract

The extraction behavior of precious metals (PMs) from HCl media has been studied using trioctylamine (TOA) in kerosene. The extraction sequence of PMs was found to be Au(III) > Pd(II), Pt(IV), Ir(IV) > Ir(III). Ru. Transport of PMs was performed through a supported liquid membrane (SLM) impregnated with TOA as a mobile carrier from the HCl feed solution into the HClO₄ or HNO₃ product solution. Selective transport; and recovery of PMs from certain mixtures were accomplished across the TOA-SLM on the basis of differences in extraction equilibria and kinetics.     

Electrochemical reduction of trinitrotoluene on core-shell tin-carbon electrodes

In this work, we studied the electrochemical process of 2,4,6-trinitrotoluene (TNT) reduction on a new type of electrodes based on a core-shell tin-carbon Sn(C) structure. The Sn(C) composite was prepared from the precursor tetramethyl-tin Sn(CH₃)₄, and the product contained a core of submicron-sized tin particles uniformly enveloped with carbon shells. Cyclic voltammograms of Sn(C) electrodes in aqueous sodium chloride solutions containing TNT show three well-pronounced reduction waves in the potential range of −0.50 to −0.80 V (vs. an Ag/AgCl/Cl⁻ reference electrode) that correspond to the multistep process of TNT reduction. Electrodes containing Sn(C) particles annealed at 800 °C under argon develop higher voltammetric currents of TNT reduction (comparing to the as-prepared tin-carbon material) due to stabilization of the carbon shell. It is suggested that the reduction of TNT on core-shell tin-carbon electrodes is an electrochemically irreversible process. A partial oxidation of the TNT reduction products occurred at around −0.20 V. The electrochemical response of TNT reduction shows that it is not controlled by the diffusion of the active species to/from the electrodes but rather by interfacial charge transfer and possible adsorption phenomena. The tin-carbon electrodes demonstrate significantly stable behavior for TNT reduction in NaCl solutions and provide sufficient reproducibility with no surface fouling through prolonged voltammetric cycling. It is presumed that tin nanoparticles, which constitute the core, are electrochemically inactive towards TNT reduction, but Sn or SnO₂ formed on the electrodes during TNT reduction may participate in this reaction as catalysts or carbon-modifying agents. The nitro-groups of TNT can be reduced irreversibly (via two possible paths) by three six-electron transfers, to 2,4,6-triaminotoluene, as follows from mass-spectrometric studies. The tin-carbon electrodes described herein may serve as amperometric sensors for the detection of trace TNT.     

Imprinted polymer-based extraction for speciation analysis of inorganic tin in food and water samples

In this study, an ion imprinted polymer (IIP), tin (IV)–4-(2-pyridylazo) resorcinol (PAR) complex (Sn(IV)–PAR–IIP) has been synthesized for speciation and selective solid-phase extraction (SPE) of tin species from food and water samples. For this purpose, copolymerization of Sn(IV)–4-(2-pyridylazo) resorcinol (PAR) complex was performed using methacrylic acid (MAA), ethylene glycol dimethacrylate (EGDMA), and 2,2′-Azobisisobutyronitrile (AIBN) as functional monomer, cross-linking agent, and initiator, respectively. The polymer particles were characterized by FT-IR, and thermogravimetric (TG) analyses. The effects of different variables such as solution pH, mass of the polymer, extraction and elution time, and type and volume of the eluent for elution of tin were evaluated by Box–Behnken design and response surface methodology. The significance of independent variables and their interactions were tested by the analysis of variance (ANOVA) with 95% confidence limits. The optimal conditions at extraction step were 8, 70 mg, and 25 min for solution pH, amount of polymer, and extraction time, respectively. Also, the optimal values for the elution step were 6.5 mL of HCl (4 M) as the eluent volume and type and elution time of 120 min. The detection limit of the proposed method was found to be 1.3 μg L^?1 and a linear dynamic range (LDR) in the range of 5–200 μg L^?1 was obtained. The influence of various cationic interferences on recovery percentage of Sn(IV) was studied. The method was applied to recovery and determination of tin species in different real samples.     

Effects of additives on the electrodeposition of tin from an acidic Sn(II) bath

Additive effects of formaldehyde, propionaldehyde and benzaldehyde on the deposition of tin in acidic solution of tin(II) sulfate have been investigated. The effects of these additives on cathodic polarization and a.c. impedance was measured by galvanostatic or potentiostatic methods, respectively. The reduction products of the aldehyde during the deposition and the diffusion coefficient of Sn(II) in various solutions were also determined.     

Corrosion resistance of Pb–Sn composite coatings reinforced by carbon nanotubes

Carbon nanotubes/Pb–Sn composite coatings were prepared by electrodeposition technology. The polarization curves and electrochemical impedance of the Pb–Sn coatings and carbon nanotube/Pb–Sn composite coatings were studied in 3.0 wt% HCl, 10 wt% NaOH, and 3.5 wt% NaCl electrolyte solutions, respectively. The results show that the corrosion potential of carbon nanotubes/Pb–Sn composite coatings were improved in the three kinds of corrosive medium, especially in 3.5 wt% NaCl electrolyte solution, where it increased significantly from −0.592 V (vs SCE) to −0.535 V (vs SCE). In addition, composite coatings have higher electrochemical impedance. Carbon nanotubes can improve the corrosion resistance of lead–tin electroplated coatings.     

Quaternary Amine Modified Persimmon Tannin Gel: An Efficient Adsorbent for the Recovery of Precious Metals from Hydrochloric Acid Media

Persimmon tannin was chemically modified to prepare a quaternary amine type of adsorption gel, named as quaternary amine modified persimmon tannin (QAPT) gel. The QAPT gel has been used to investigate the adsorption behaviors for Au(III), Pd(II), and Pt(IV) from HCl media. It was found that the gel exhibited good selectivity towards precious metals over a wide concentration range of HCl. However, it exhibited poor affinity towards base metals such as Cu(II), Fe(III), Ni(II), and Zn(II). The adsorption isotherms of the gel for precious metal ions were described by the Langmuir model. The maximum adsorption capacities for Au(III), Pd(II), and Pt(IV) were evaluated as 4.16, 0.84, and 0.52 mmol g^?1, respectively. Although the anion exchange is the main mechanism for the adsorption of anionic species of Au(III), Pt(IV), and Pd(II), adsorption of Au(III) is followed by subsequent reduction, which results in the extraordinary high adsorption capacity for Au(III). Adsorption behavior of QATP gel for Au(III) was also compared to that of the persimmon tannin, the feed material.     

Electrochemical preparation of a Pt-Ru alloy

The electrochemical reduction of Pt(IV) and Ru(III), in separated and mixed solutions, has been studied on a platinum electrode in 1 N HCl solution. The chronoamperometric and chronocoulometric results showed that the simultaneous reduction of Ru(III) and Pt(IV) occurs, leading to alloy formation. The voltammogram of the obtained alloy is in agreement with such a conclusion.     

Liquid-Liquid Extraction of Ruthenium from Chloride Media by N,N'-Dimethyl- N,N'-Dicyclohexylmalonamide

Abstract

Research on the solvent extraction of ruthenium from hydrochloric acid media has been carried out using N,N'-dimethyl-N,N'-dicyclohexylmalonamide (DMDCHMA) dissolved in 1,2-dichloroethane. Ruthenium extraction percentages (%E) ranging from 50% to 80% have been achieved for HCl concentrations between 5 M and 7 M. Extraction curves exhibiting the dependence of the %E ruthenium on HCl concentration in the aqueous phases are presented, the latter solutions being obtained by dissolution of either Ru(III) or Ru(IV) salts. The influence of some experimental parameters on the %E Ru, such as the equilibration time, extractant concentrations, and hydrogen-ion activities, has been thoroughly investigated. Additionally, DMDCHMA is also adequate for extracting Pd(II) from 5 M to 7 M HCl solutions and under similar experimental conditions, %E Rh(III) is below 5%, and Pt(IV), Ir(III), and Ir(IV) cause the formation of third phases. Both Ru and Pd(II) can be successfully stripped from the loaded organic phases with water. A partition scheme to isolate Ru from a number of some associated elements has also been attempted.     

CHARACTERISATION OF METALFIX-CHELAMINE AND ITS APPLICATION IN PRECIOUS METAL ADSORPTION

ABSTRACT

The physical and chemical characteristics of the chelating resin Chelamine, which contains a pentamine ligand, are investigated in order to consider its application in the separation of precious metals- Adsorption isotherm experiments for Pt, Pd and Au and kinetic experiments were carried out under batch procedures. The resin presents a high level of adsorption selectivity for Pt(IV), Au(III) and Pd(II) giving a capacity of 2.8 mmol/g, 3.1 mmol/g and 2.0 mmol/g respectively. Acidic solutions, complexing agents, lipophilic anions and ammonia were used for metal elution. NaClO₄ solutions are the most effective eluting agents for Pt(IV) while thiourea is the best stripping agent for both Pd(II) and Au(III). Selective separation of the three metals can be achieved by sequential elution from the resin with NaClO₄ solutions in different HCl concentrations and thiourea 0.5 M.     

Adsorptive Recovery of Palladium(II) and Platinum(IV) on the Chemically Modified-Microalgal Residue

A biomass waste of microalgae was chemically modified by immobilizing the functional group of polyethyleneimine to prepare a new type of adsorbent. The adsorption test revealed that this adsorbent exhibited remarkably high selectivity for Pd(II) and Pt(IV) over base metal ions in HCl solution. From the adsorption isotherm, its maximum adsorption capacity for Pd(II) and Pt(IV) was evaluated as 2.0 and 0.8 mmol/g, respectively. This adsorbent also exhibited high affinity and selectivity for Pd(II) and Pt(IV) even in the presence of high concentrations of base metals in actual leach liquor.     

The Solvent Extraction Performance of N,N’-Dimethyl-N,N’-Dibutylmalonamide Towards Platinum and Palladium in Chloride Media

The solvent extraction performance of N,N’-dimethyl-N,N’-dibutylmalonamide (DMDBMA) in 1,2-dichloroethane (1,2-DCE) towards platinum(IV) and palladium(II) in hydrochloric acid media was systematically evaluated. Pt(IV) extraction (%E) increases with the HCl concentration in the aqueous phases, being always higher than 72%, whereas Pd(II) extraction decreases from 65% at 1 M HCl to 22% at 8 M HCl. Several stripping agents for the two metals were tested: Pt(IV) is successfully recovered by a 1 M sodium thiosulfate solution, whereas the best result for Pd(II) was achieved with 0.1 M thiourea in 1 M HCl. The loading capacity of DMDBMA for Pt(IV) is high, and data obtained from successive extraction-stripping cycles suggest a good DMDBMA stability pattern. Attempts to replace 1,2-DCE by more environmentally-friendly diluents showed, in general, worse %E for Pt(IV). The dependence of Pt(IV) distribution coefficients on DMDBMA and chloride ion concentrations, as well as on acidity, are the basis of a proposal for the composition of Pt(IV) extracted species.     

Separation,Preconcentration, and Recovery of Pd(II) Ions using Newly Modified Silica Gel with Bis(3-Aminopropyl)Amine

Bis(3-aminopropyl)amine bonded silica gel (BAPA-SG) was synthesized and characterized by elemental analysis and FT-IR spectroscopy, and tested for adsorption, preconcentration, and recovery of Pd(II) ions. The effective parameters on the preconcentration of Pd(II) ions such as pH, volume, and flow rate of the Pd(II) solution, and the type and volume of eluent solution, and also matrix ions such as alkaline and heavy metals were investigated. Flame atomic absorption spectrometry was used for the determination of Pd(II) concentration. The modified silica gel could adsorb Pd(II) ions quantitatively from the solutions up to 400 mL at pH 1.0 by the flow rate of 5 mL/min. The retained Pd(II) ions could be easily eluted by using 5 mL of 1% (m/v) thiourea in 1.0 M HCl solution. The recovery of Pd(II) ions was 95 ± 2% at 95% confidence level. The analytical detection limit of Pd was found to be 0.36 µg L^?1 at the preconcentration factor of 80. Selective adsorption of Pd(II) ions over some base metal ions was also investigated. The developed method was applied to spent auto catalyst for palladium recovery, and a certified ore sample for the determination of palladium content.     

四辛基锡中锡(Ⅱ)的测定

研究了四辛基锡中锡(Ⅱ)含量的测定方法。试样经浓硫酸高温碳化,以金属铝还原锡(Ⅳ)为锡(Ⅱ),铁粉消除溶解氧的影响,淀粉为指示剂,碘酸钾标准滴定溶液滴定锡(Ⅱ)。该方法的标准偏差为0.179,回收率在98.46%~100.70%之间,试样中共存的其它元素均不干扰测定。