Novel Aqueous Processing of the Reverted Turbine-Blade Superalloy for Rhenium Recovery

Abstract

A preliminary study on the hydrometallurgical recovery of rhenium from an engine-reverted superalloy, CMSX-4, was performed. The novelty of this work dealt with (i) the applicability of electro-generated Cl2 in rhenium leaching and (ii) the maneuvering of the organic extractants based on the metal speciation in leach liquor. In a two-step HCl leaching, more than 98% rhenium was selectively leached in the presence of dissolved chlorine (Cl2aq. and Cl3aq. –) in the second step, which was performed after a leaching of thermal-barrier and base-alloy elements in 4 mol L–1 HCl. The leaching kinetics of rhenium indicated a shift from surface diffusion to a chemically controlled reaction with a variance in temperature from 313 to 353 K. The first use of phosphinic acid in molybdenum separation from rhenium in the leach liquor yielded a high separation value (βMo/Re = 839) using 0.067 mol L–1 extractant; whereas the mixed-phosphine oxides showed a tremendous selectivity for separating rhenium from the base-metal impurities in the Mo-depleted solution. The extraction of rhenium increased from 9% to 98% with an increase in extractant concentration from 0.005 to 0.08 mol L–1 in the organic phase. On a metal-to-metal basis, the recovery value of 93% rhenium as NH4ReO4 (9.5 g L–1 Re in the solution) demonstrated the potential of the present process.

Bio-Reclamation of Strategic and Energy Critical Metals from Secondary Resources

“…Rhenium, one of the energy-critical elements has a prime use in Pt-Re catalysts [103]. A study on rhenium extraction from spent Pt-Re catalyst using Bacillus megaterium as a cyanogenic bacterium has been reported by Motaghed et al [104].…”

Selective anodic treatment of W(WC)-based superalloy scrap

“…Complete dissolution can be realized chemically, by treating with hot sulfuric acid [7], hydrochloric acid [7,11], hydrochloric acid with chlorine purging [7,12] or thermal reduction with carbon [7]. Pyrometallurgy methods are also used [7].…”

“…Selective treatment in mixed metal melt [5], and also in molten zinc [12] has been proposed. During treatment, the metal binder is dissolved and the metal solvent is removed under vacuum.…”

On the Fabrication of Metallic Single Crystal Turbine Blades with a Commentary on Repair via Additive Manufacturing

“…Compared to the re-melting process, leaching is more sustainable and generally recovers a larger percent of the material [84]. Specifically, one study found a recovery of > 99% for both Re and Ni [85].…”