A multistep leaching of nickel-based superalloy scrap for selective dissolution of its constituent metals in hydrochloric acid solutions

A selective two-step leaching for nickel and rhenium from PWA 1484 nickel-based superalloy scrap in hydrochloric acid solutions was investigated. The scrap was easily comminuted under 150 μm by a pyro-metallurgical pretreatment at 1500 °C, viz. the formation of Al3Ni intermetallic compound with aluminum. At the first leaching step at 90 °C and 40 g/L solid-to-liquid(S/L) ratio in 4.0 mol/L hydrochloric acid solution, over 95% of nickel was dissolved in 60 min with aluminum, cobalt, and chromium, whereas 97.6% of rhenium was remained with tantalum in the residue. The leaching percentage of rhenium was increased with the S/L ratio from 2.4% at 40 g/L S/L ratio to 25% at 200 g/L S/L ratio. The second leaching step for rhenium from the residue was carried out using the electrogenerated chlorine as an oxidant at 80 °C, 0.43 mmol/min chlorine supply, and 10 g/L S/L ratio in 4.0 mol/L HCl solution. Over 99% of rhenium was leached in 20 min, leaving tantalum in the residue.