A New Process of Direct Zinc Oxide Production by Carbothermal Reduction of Zinc Ash

Abstract

Zinc ash is a by-product of the hot-dip galvanizing process and the electrolytic zinc process, which is classified as a hazardous waste consisting predominately of zinc oxide that could be recovered as the useful main resource for ZnO preparation. In this work, in order to reduce the energy consumption of the direct reduction process and improve the resource-recovery rate. A new technology for zinc oxide production, by a carbothermal reduction of zinc ash, is proposed. This process includes two steps: high-temperature roasting of zinc ash for dechlorination and a carbothermal reduction of dechlorination ash. Zn in zinc ash is mainly presented in the form of zinc oxide (ZnO), basic zinc chloride (Zn5(OH)8Cl2H2O), and metallic zinc (Zn). Basic zinc chloride can be roasted and decomposed to reduce the chlorine content in zinc ash. The results of a chloride ion removal test show that the optimal roasting temperature is 1000 °C, with a holding time of 60 min. Under the modified conditions, the chloride content in the roasted zinc ash is reduced to 0.021 wt.%, and the dechlorination rate is more than 99.5%, which can meet the requirements of zinc oxide production. The best process conditions for zinc oxide production by carbothermic reduction are as follows: reduction temperature of 1250 °C, reduction time of 60 min, and reduction agent addition of 22 wt.%. Under the best reduction process, the purity of zinc oxide product is 99.5%, and the recovery of zinc is more than 99.25%. Needle-like zinc oxide obtained by carbothermic reduction has high purity and can replace zinc oxide produced by an indirect process.

Oxalate‐Assisted Synthesis of Hollow Carbon Nanocage With Fe Single Atoms for Electrochemical CO2 Reduction

“…According to thermodynamic data, ZnO cannot be reduced by carbon at 600°C, but ZnO in the the hollow structure was not observable. [39] This contradiction indicates that ZnO was not present before calcination, but was generated by the combination of Zn atoms from ZIF-8 and oxygen atoms from carbon materials during calcination. At 600°C, oxygen atoms in carbon materials would be lost by generating CO or CO 2 with adjacent carbon atoms, making it impossible for zinc atoms to combine with oxygen atoms to generate ZnO [40][41] .…”

Mineral Phase Reconstruction and Separation Behavior of Zinc and Iron from Zinc-Containing Dust

“…The current treatment of electric-furnace dust in steel companies is based on recycling, including hydro-and pyrometallurgical treatment methods [3,[6][7][8][9][10][11][12][13][14][15][16][17]. The direct recycling of zinc-containing dust in steel companies is achieved using electric-furnace dust as a raw material for the sintering processes [18][19][20].…”