Controllable Production of Ag/Zn and Ag Particles from Hydrometallurgical Zinc Solutions

Abstract

Ag/Zn and Ag particles have been successfully produced from electrolytes simulating zinc process solutions containing a high zinc concentration (65 g/L) and a negligible silver concentration (0.5–50 ppm) using a facile and sustainable electrodeposition-redox replacement (EDRR) method. Results show that the particle size and chemical composition of the deposited Ag/Zn and Ag particles can be readily controlled by varying the operating parameters such as replacement time and agitation. Electrochemical quartz crystal microbalance (EQCM) studies supported with SEM-EDS and TEM results indicate that the EDRR process consists of three regions: (I) zinc pulse deposition; (II) redox replacement between the Ag+ ions and the deposited Zn, formation of a Zn/Ag alloy structure, and competing Zn oxidation by H+ ions; and (III) further replacement between Ag+ ions and Zn (alloy) formed in the previous stage and possible silver reduction by hydrogen. The Zn (alloy) has a higher reduction potential which hinders the competing H+ reduction and sequentially improves the utilization efficiency of the sacrificial metal (Zn). Furthermore, by using the EDRR method, Ag/Zn particles could be successfully obtained from solutions with an extremely low Ag concentration of 0.5 ppm. The promising results demonstrate the feasibility of producing Ag-based functional materials utilizing trace amounts of Ag from zinc process solutions.

Electrochemical Growth of Ag/Zn Alloys from Zinc Process Solutions and Their Dealloying Behavior

“…Moreover, as only a minor amount of Zn is deposited during an ED step in a single cycle (of total number of cycles 400), this allows for more complete diffusion of Ag during the RR steps in each cycle. Consequently, the even distribution of elements remained stable throughout the growth of larger structures when compared to the separate bimetallic particles observed previously, 25 and as a result, the behavior observed with EDRR growth is distinct from Ag/Zn dendrites produced by galvanic replacement using a prefabricated Zn plate in which clear local enrichment of individual elements was observed. 44 The Ag/Zn alloys were electrochemically analyzed with ALSV, as shown in Figure 3b, and it can be clearly observed that the results are dependent on the applied EDRR parameters.…”

“…−1.45 and −0.1 V (vs Hg/Hg 2 SO 4 ), respectively. 19,25,45 In contrast, the distinctive behavior of the anodic peaks/current waves for samples prepared by EDRR can be attributed to the dissolution of specific Ag/Zn mixtures. From Figure 3b, it can be seen that the anodic dissolution of the deposits can be separated into three discrete regions (I−III).…”

“…Earlier investigations have shown that particles (with a diameter < 1000 nm) of mixed Ag/Zn composition can be obtained with a short replacement time, whereas a long replacement time results in nearly pure Ag particles. 25 According to the binary alloy phase diagram of the Ag-Zn system (Figure S1 in the Supporting Information), various Ag/ Zn intermetallic compounds are potentially stable at room temperature. Nevertheless, the crystalline compositions in the Ag/Zn mixtures by EDRR and the extent to which Zn and Ag exist either as independent phases or alloyed Ag x Zn 1−x phases are yet to be confirmed.…”

“…Furthermore, as previously it has only been speculated that Ag and Zn existed in alloyed forms, based on energy-dispersive X-ray (EDS) spectroscopy analysis and electrochemical results, consequently, the exact identity of the associated crystalline phases have remained unverified. 25 Dealloying, or selective removal of less-noble components, is an effective approach to generate new attractive features like porous or dendritic structures for a broad range of applications such as sensors, 39 antimicrobiality, 40 and catalysis. 41 The dealloying behavior of Ag/Zn binary alloys has been studied by several researchers; for example, Luo et al have prepared bimodal nanoporous silver from an Ag 10 Zn 90 precursor, 29 and the porosity evolution of Ag 25 Zn 75 powder particles by chemical dealloying has been investigated by Bhushan et al 30 In addition, Zhang et al have fabricated nanoporous silver structures by dealloying Ag/Zn ribbons, 32 whereas Li et al have utilized Ag/Zn plates and the dealloying kinetics of Ag 25 Zn 75 to produce nanoporous silver.…”

“…According to previous voltammetric studies, the oxidation potential of Zn (alloyed) is very close to pure silver within the Ag/Zn alloys produced by EDRR. 25 This suggests that the chemical dealloying of the Zn component would require a relatively aggressive medium like hydrochloric acid that has the potential to generate hazardous gas (e.g., HCl). Therefore, the current study suggests an alternative electrochemical approach to allow for a tailorable dealloying process for the produced Ag/Zn alloy under milder conditions with dilute sulfuric acid, which has high availability as a byproduct in Zn production and a relatively low environmental impact.…”