Silver electrowinning from silver(I)–calixarene complexes by two-phase electrolysis

Abstract

Results are reported, providing the basis for an elegant new process for metal recovery from acidic solutions, by integrating solvent extraction (SX) and electrowinning (EW) in a single process, rather than operating them separately, as in conventional SX-EW processes. Calixarene-tetramide and its thio-analogue were used for the extraction of silver(I) ions from aqueous phases into dichloromethane, both compounds achieving extraction efficiencies [90%. The effects were determined of extractant and silver(I) concentrations, aqueous phase pH, and the presence of sodium ions, on the distribution of Ag(I) between aqueous and organic phases. Due to the impossibility of stripping the extracted metal conventionally, electro-reductive stripping of silver(I) from the loaded organic phase was carried out in the calixarene/nitric acid two-phase system. The effects were also investigated of current density or electrode potential on silver deposition current efficiencies and cell voltages. Based on experimental data, a new process for silver(I) removal from very dilute solutions was proposed that showed high percentage extractions of silver(I) from the aqueous phase, coupled to direct EW of silver from the calixarene complex in the loaded organic phase, regenerating the extractant for recycle. Current efficiencies in the range from 60% to 90% and cell voltages \3.5 V were achieved simultaneously in this process.

Recovery of High-Purity Silver from Spent Silver Oxide Batteries by Sulfuric Acid Leaching and Electrowinning

“…Specific energy consumption was ca. 1.0 kW h/kg of silver, which is slightly higher than that of industry practice in silver nitrate solution (ca 0.8 kW h/kg) but much lower than that from cyanide bath (4.56 kW h/kg), as in the previous study …”

“…Specific energy consumption was ca. 1.0 kW h/ kg of silver, which is slightly higher than that of industry practice in silver nitrate solution (ca 0.8 kW h/kg) 45 but much lower than that from cyanide bath (4.56 kW h/kg), as in the previous study. 46 MnO 2 was obtained on the anode, although there is slight contamination of sulfate solution indicated by the detection of S element.…”

Solvent extraction of silver from nitric acid solutions by calix[4]arene amide derivatives

“…As a power supplier a computer controlled potentiostat/galvanostat (Autolab PGstat 30, Eco Chemie B.V.) was employed. The electrowinning experiments were performed in both the potentiostatic and glavanostatic mode of operation [22,25].…”

“…To avoid any anodic destruction of the calixarenes, the electrochemical experiments were conducted using a previously proposed two-phase electrowinning method [21,23]. The experimental procedure and the obtained results are described in detail elsewhere [22,25]. Hence, only a brief description of the stripping process and the electrowinning results will be presented in this paper.…”

“…The application of two-phase electrolysis in the electrochemical synthesis of organic substances has been shown to be an attractive method having several technological advantages [21,23]. For metal recovery, this method has not yet been applied and this is the first attempt also described in [25].…”