Kinetics of silver anodic dissolution in thiosulfate electrolytes

Bek, R. Yu.; Shevtsova, O. N.

doi:10.1134/s1023193511030037

Cited by 7 publications

(2 citation statements)

References 9 publications

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“…Also, these curves show a plateau on which the current depends on the sulfi te concentration and solution temperature. The run of the dependences is close to that of the voltammetric curves reported for thiocarbamide, thiosulfate, and cyanide electrolytes [23][24][25][26]. As noted in [26], the existence of a plateau indicates that the dissolution rate of silver becomes fully diffusion-controlled and directly proportional to the concentration of the complexing agent.…”

Section: Methodssupporting

confidence: 60%

On anodic dissolution of silver coatings deposited on base metals

2012

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Potentiodynamic polarization and potentiostatic electrolysis techniques were employed to study the anodic oxidation of silver and a number of other metals (copper, iron, nickel, and tin) in sulfi te media, both individually and in Ag-M binary electrodes. The conditions in which silver is dissolved with a nearly 100% current effi ciency were found.It is known [1] that a considerable part of metallic silver used for technical and decorative purposes is in the form of surface fi lms deposited onto various substrates. The role of substrates is played by various metals and metal alloys, including copper, iron, nickel, brass, and tin. The optimal process for recovery of silver from scrap articles of this kind is that in which the substrate metal is not dissolved.The conventional methods for recovery of silver [2][3][4][5] are based on its dissolution in the presence of oxidants in solutions of acids or complexing agents, with the subsequent recovery of silver in the form of insoluble salts or its reduction to the metal. The main shortcomings of these methods are the gross expenditure of reagents and the dissolution nonselectivity: substrate metals pass into solution together with silver.A substantially lower expenditure is characteristic of techniques based on the anodic oxidation of silver. In processing of materials containing considerable amounts of base metals, selective transfer of silver into solution is possible in an alkaline medium in which many transition metals form insoluble hydroxides. An additional advantage of the electrolytic method is that the oxidation of silver may be accompanied by its deposition onto a cathode. The oxidation of silver in alkaline media in the presence of chlorides, nitrates, sulfates, and borates has been extensively studied [6][7][8][9][10][11][12]. However, the formation of passivating fi lms composed of silver oxides on the surface of the metallic phase has been frequently observed. Silver is commonly dissolved in special electrolytes [13], including those containing such complexing agents as thiourea [14], rhodanide [15,16], and amino acids [17].A promising complexing agent for these purposes is sodium sulfi te, because sulfi te complexes of silver(I) are rather stable [18]. Compared with the cyanide widely used in hydrometallurgy of silver, the sulfi te ion forms stable complexes with a substantially smaller number of metal ions [18]. In addition, the sulfi te by itself creates an alkaline medium (pH ≈ 9-10) in solution. All this gives reason to expect a high selectivity in recovery of silver(I) into solutions in the presence of other metals.It is known that sulfi te ions are unstable against atmospheric oxygen. The fi nal oxidation product is the sulfate ion (SO 3 2-+ 2OH --2e = SO 4 2-+ H 2 O, E 0 = -0.90 V [19]). Probably, just the widely accepted opinion about fast oxidation by oxygen has hindered development of methods using sulfi te ions as complexing agents, including those for recovery of silver. The kinetics of SO 3 2-oxidation in aqueous solutions was studied in [20,...

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Section: Methodssupporting

confidence: 60%

On anodic dissolution of silver coatings deposited on base metals

2012

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“…Similar anodic processes with the direct participation of ligands in the elementary act of charge transfer have been also considered previously. [40][41][42][43] Based on the generalized Butler-Volmer kinetic relations, the anodic component of the current density for this process can be represented as follows:…”

Section: Resultsmentioning

confidence: 99%

Analysis of Anodic Linear Sweep Voltammograms Considering Insufficient Lability of Cu|Cu(II), Glycine System

Survila,

Kanapeckaitė,

Gudavičiūtė

2024

J. Electrochem. Soc.

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Anodic LS voltammograms of the alkaline Cu | Cu(II), glycine system were converted into mass-transport corrected Tafel plots considering that the glycinate anion L- takes part in the first stage of copper ionization. The anodic current density was normalized relative to the surface concentration of L- species, which was determined using the mass transfer model of chemically interacting species. The lability of the system was assessed based on available kinetic characteristics and specific experimental data. To linearize the Tafel plots, corrections were made to account for the insufficient mobility of the proton attached to glycine amino group. Obtained Tafel constants indicate that the second step of copper ionization, involving the oxidation of the intermediate copper(I)-glycine complex, is the rate-determining step.

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