Electrochemical leaching of rhenium from single crystal superalloy scrap: Synergistic disruption of oxide-dominated barrier layers with HCl-H2O2

Single crystal superalloy scrap represents an important secondary resource containing rhenium (Re), yet only a very small fraction of high-purity scrap can be directly reused as remelting feedstock, while most of the material must undergo hydrometallurgical processing to enable Re recovery. In hydrometallurgical processes, the formation of oxide-dominated barrier layers hinders effective dissolution. To address this, an electrochemical leaching method using a mixed electrolyte of HCl and H 2 O 2 was developed. The process parameters were optimized to 3 mol·L −1 HCl, 9% ( v /v) H 2 O 2 , a current density of 0.36 A·cm −2 , and an electrolysis time of 2 h. Under these conditions, the current efficiency reached 77% and the Re leaching efficiency was 97.9%. The barrier layers consisted of a chloride deposit layer, a Ta W oxide layer, and a Cr-rich oxide layer. These layers were effectively broken down during the electrochemical process. Specifically, the Ta W oxide layer underwent cracking and spallation, while the Cr-rich oxide layer was progressively destabilized and dissolved under the coupled chemical and electrochemical effects. This method successfully disrupted the oxide barrier layers and significantly enhances Re leaching efficiency. It provides an efficient nitric-acid-free route for recovering Re from single crystal superalloy scrap.