A hydrometallurgical route to produce ZnO nanoparticles and NiO strips from the spent Ni/ZnO catalyst

A new hydrometallurgical process was proposed for recovering high-purity ZnO nanoparticles and NiO strips from the spent Ni/ZnO catalyst. Extractions of zinc, nickel and iron achieved 98.3%, 95.1% and 72.2%, respectively, after leaching for 60 min at 45 °C with the liquor/solid ratio of 6 mL g− 1 and 15 wt.% HCl, and the leach solution contained 127.87 g L− 1 zinc, 3.23 g L− 1 nickel and 0.77 g L− 1 iron. Iron separation was achieved by adding KMnO4 at an initial pH of 4.75. Taguchi method was successfully used to evaluate the zinc cementation method and the dimethylglyoxime (DMG) precipitation method for nickel removal with two L9 (34) orthogonal arrays. Among these experiments, the attention has been attracted to the DMG precipitation method since it can be performed at lower temperature (60°C), achieve lower Ni2+ residual concentration (0.6 mg L− 1) and recover nickel as 99.04 wt.% NiO strips via one-step thermal decomposition. 99.70 wt.% ZnO nanoparticles were obtained by a thermal decomposition of the basic zinc carbonate which was precipitated by adding NH4HCO3 to the purified solution. A complete hydrometallurgical process flowsheet was proposed.