Flow Injection Electrochemical Quartz Crystal Microbalance with ICP-OES Detection: Recovery of Silver by Electrodeposition with Redox Replacement in a Flow Cell

Abstract

We developed a new on-line hyphenated flow injection analysis technique (FI-EQCM-ICP-OES) that allows electrochemical deposition and stripping with mass detection and elemental analysis. This technique was used to study a new system for electrochemical recovery of silver from a 0.5 mM Ag+/5 mM Cu2+/0.5 M H2SO4 solution by pulsed electrodeposition with redox replacement (EDRR) in a small flow cell. The metal ions in a 500 μl sample are injected into the sulfuric acid carrier stream and deposited onto an electrochemical quartz crystal microbalance (EQCM) electrode housed in a 50 μl flow cell. The deposits are subsequently stripped off electrochemically in the same cell and analyzed downstream in an ICP-OES. The stripped metal layer was found to be composed of Ag with no detectable Cu for a redox replacement time of 10 s, and 91 wt.% Ag–9 wt.% Cu for a redox replacement time of 5 s. Microscopy measurements demonstrated that the electrode was covered with silver particles, some of which contain Cu in the case of the 5 s replacement time. This technique allowed the study of mass changes on the electrode during electrodeposition and open circuit times in each EDRR cycle in flowing solutions.

Flow Injection Electrochemical Quartz Crystal Microbalance with ICP-OES Detection: Electroprecipitation and Stripping of Lanthanum and Neodymium in a Flow Cell

“…In our flow cell with planar electrode, the current density and the diffusion will not be homogeneous. 27,36 From chronoamperometry at potentials between −0.7 V Ag/AgCl and −1.1 V Ag/AgCl , using the same continuously flowing La-Nd solution (see Fig. 6S), we obtained the electroprecipitation rates, shown in Fig.…”

“…This confirms that higher potentials, and thus higher currents, can severely hinder the formation of the lanthanide layer and suggests we should stay near ∼−0.8V Ag/AgCl for electroprecipitation under these experimental conditions. Although the current density and diffusion layers are not homogenous in our flow cell setup, 27,36 Eq. 4 can be used to estimate the increase in thickness of the high-pH layer when the current goes from 0.015 to 0.030 mA, for which we obtain ∼2.5 • 10 −3 cm, which is comparable with the size of the diffusion layer used by Hansen.…”

“…The rest of the micro flow cell assembly and cleaning procedure has been described previously. 27 The calibration of the EQCM micro flow cell was performed as described in section S1, Fig. S1, and Table SI of the Supplementary Information.…”

“…In the case of radioactive f-elements this would be invaluable to decrease operator exposure during sample handling and analysis. 26 In this work, an improved version of our previously-developed flow injection FI-EQCM-ICP-OES technique, 27 has been used to study the electroprecipitation of lanthanum and neodymium ions from acidic solutions with and without supporting electrolyte. This version of the system uses an additional syringe pump and injection valve so that two independent loops with different carrier solutions can be used: one mildly acidic for sample injection and precipitation, and one comprised of 2%-HNO 3 for stripping and ICP-OES detection.…”

Green and Controllable Preparation of Cu/Zn Alloys Using Combined Electrodeposition and Redox Replacement

“…Recently, a novel electrodeposition–redox replacement (EDRR) method has been developed to recover valuable elements such as Au, − Ag, ,− Te, and Pt with minute concentration (ppm or even ppb level) from different complex solutions. Moreover, the EDRR method was found to be promising for the direct production of bimetallic functional materials such as Pt/Ni, Ag/Cu, and Ag/Zn particles, from industrial-type process streams.…”