Preparation of ZnO Nanoparticles from Zn-containing Rotary Hearth Furnace Dust

To solve the problem of the low added value Zn-containing rotary hearth furnace (RHF) dust, two deep eutectic solvents (DESs) were employed, such as choline chloride-urea (ChCl-urea) and choline chloride-oxalic acid dihydrate (CC—OA) solvent and Zn-containing RHF dust (water-washed) as the research target. Then, we prepared ZnO nanoparticles using two DESs or their combination, namely, ChCl-urea (Method A), CC—OA (Method B), first CC—OA and then ChCl-urea (Method B-A) and first ChCl-urea and then CC-OA (Method A-B), respectively. The effects of these methods on the properties of as-obtained precursors and ZnO nanoparticles were investigated in detail. The results indicated that the precursor obtained by Method A was Zn 4 CO 3 (OH) 6 ·H 2 O, and those by Methods B, B-A, and A-B were all ZnC 2 O 4 ·2H 2 O. Moreover, the decomposition steps of the last three methods were similar. The ZnO contents of 95.486%, 99.768%, 99.733%, and 99.76% were obtained by Methods A, B, B-A, and A-B, respectively. Methods A, B, and B-A led to the formation of spherical and agglomerated ZnO nanoparticles with normal size distributions, where Method B showed the best distribution with an average diameter 25 nm. The ZnO nanoparticles obtained by the Method A-B did not possess good properties.