Preparation of High Purity Zinc Oxide from Zinc Metal Scrap

抄録

Pyrometallurgical process is utilized to recover zinc in the form of high purity zinc oxide from a kindof zinc metal scrap containing 92.49 wt% zinc. The process uses tube-type furnace, where the reactor isdivided into volatilization zone and oxidization zone by flowing nitrogen gas and air. In the process, zinc isfirstly volatilized to vapor in inert atmosphere of nitrogen gas and carried forward to oxidization zone bynitrogen gas, then oxidized to zinc oxide in air atmosphere. The effect of temperature, air and nitrogen gasflow-rates, and reaction time on both purity and yield of the product is investigated in detail in this study.Subsequently, the characteristics of the products are examined by X-ray diffractometer and scanning electronmicroscope. The obtained results demonstrated that both the purity and the yield of the product haverelationships with the operation parameters. The contents of the impurities grow with the rise of temperature, with the increase of nitrogen gas or air flow-rate, and also with the extension of reaction time. However, theyield decreases with the decrease of temperature, with the reduce of nitrogen gas flow-rate, with the rise ofair flow-rate, and also with the diminishment of reaction time. In addition, very low air flow-rate resultedin the increase of metallic zinc in the product and the decrease of the yield of the product at the same time.Zinc oxide with purity of 99.97wt% and yield of 94.45% in nano-grade dimension can be obtained inpresence of 300 ml/min N₂ flow-rate and 800 ml/min air flow-rate for 12 minutes at 1253 K, whereas theimpurity content of Al, Fe, Cu, Pb and Cd is 0.0072wt%, 0.00060 wt%, 0.00096wt%, 0.0048wt% and 0.00031wt%, respectively, which approaches the quality demands of the first-grade-zinc oxide in JIS (Japanese Industrial Standard) K 1410-1995.