Determination of the Electrochemical Dissolution Feasibility of a Superalloy Used in Turbine Components in Alkaline Solutions With Additives

ENG: The object of this study was an electro-chemical anodic dissolution of a heat-re-sistant nickel-based superalloy (≈62 wt.%),recovered from destroyed components of spe-cial-purpose equipment, which contains valu-able metals such as Re (≈4 wt.%), Co, W, Mo, Ta, Nb, and others. The research addressed the problem of the lack of an effective elec-trochemical method for selectively extract-ing these components, particularly rhenium and other valuable elements, from such an alloy in alkaline media. The anodic behav-ior of the alloy was experimentally studied in 0.5 M NaOH in the presence of various com-plexing and activating additives (NaCl, cit-ric acid, EDTA salt, and Na2H2P2O7). It was shown that none of the additives provided a significant acceleration of anodic dissolu-tion. This was demonstrated by the fact that the increase in the average specific charge calculated for five cyclic voltammetry scans that contributed to alloy dissolution did not exceed 8%. In other cases, the values were sig-nificantly lower than in the base solution con-taining only alkali. It was established that the anodic dissolution process has a surface-selec-tive nature: Ni, Co, Cr, Re, and Al are leached into the electrolyte, while a residual surface layer enriched in W, Ta, Nb, and Mo forms, hindering further dissolution. X-ray fluores-cence analysis data confirmed changes in the chemical composition(Ni content decreased to ≈48 wt.%, W increased from ≈9to≈20wt.% on the surface). Theoretical justification of the results is provided, based on the physico-chemical properties of compounds that may form during anodic dissolution in the pres-ence of additives. The absence of an activating effect from the additives suggests the need for further studies on pure NaOH. The obtained data are of practical importance for the selec-tive separation of superalloy elements before further processing.