Lixiacion Con Acido Sulfurico

Materials Transactions, Vol. 44, No. 12 (2003) pp. 2489 to 2493 Special Issue on New Systems and Processes in Recycling and High Performance Waste Treatments #2003 The Japan Institute of Metals

Leaching of Zinc Oxide in Acidic Solution
Takashi Yoshida
MS Zinc Co., Ltd., Tokyo 105-0004, Japan
Leaching mechanism of zinc oxide is important not only to understand zinc smelting process but alsoto develop of new zinc recycling process. Recycling of zinc is mainly done by treatment of electric arc furnace dust (EAF dust). In Japan pyro metallurgical process is enhanced for EAF dust treatment, however only zinc oxide can be recovered by pyro metallurgical process. Hydro metallurgical process makes it possible to recover high purity zinc directly from EAF dust. One of the main components ofzinc included in EAF dusts is zinc oxide. Thus the mechanism of zinc oxide leaching is important to develop the new hydro metallurgical zinc recycling process. Leaching test of zinc oxide in hydrochloric acid and sulfuric acid solution has been carried out kinetically. Zinc oxide disk was used for leaching test which the reaction area is clear. The experimental parameters of pH, temperature,leaching time and rotating speed of the disk specimen were varied. The results obtained are as follows; (1) The activation energy of leaching reaction by sulfuric acid was 17.5 kJmolÀ1 and 11.6 kJmolÀ1 by hydrochloric acid solutions. (2) The leaching rate increases in proportion to the square root of rotating speed of test specimen. These results indicate that the rate controlling factor of zinc oxideleaching reaction in acidic solution is mass transportation. (Received July 14, 2003; Accepted September 5, 2003) Keywords: leaching, zinc oxide, mass transfer, disk specimen, recycling and acid solution

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Introduction

was investigated. The observation of the surface morphologies is very few in previous studies. 2. Experimental Procedure

The amount of zinc production in the worldhave increased and reached more than eight million tons. The major zinc production process is the hydro-metallurgical process which consists of roasting, leaching and electro-winning. The kinetics of leaching is very important to fully understand the zinc smelting process. Thus several studies1–4) have been done in the leaching kinetics of zinc oxide. On the other hand the recycling has become themajor issue for almost every industry. The one of the major recycling of zinc is done by treatment of electric arc furnace dusts (EAF dust). Pyrometallurgical processes such as Wealz kiln process, MF process and electric thermal process are enhanced for recycling of zinc from EAF dust in Japan.5) These processes recover zinc as zinc oxide. Thus further treatment is necessary to produce high purityzinc metal. Hydro-metallurgical process makes it possible to produce high purity zinc directly from EAF dust. Several hydro-metallurgical processes have been proposed6) however they are not sufficient from the industrial point of view. Thus development of new hydro-metallurgical process for zinc recycling is very much concerned. Zinc included in EAF dust is mainly zinc oxide. Thus the basic study onleaching kinetics of zinc oxide becomes more important for development of new recycling process. Relatively many studies have been done for leaching kinetics of metal sulfide and oxide which controlled by chemical reaction.7–9) Few studies have been made on leaching kinetics which controlled by mass transportation. Leaching of zinc oxide by acidic solution is typical example that the reaction iscontrolled by mass transportation. Previous studies on leaching of zinc oxide in acidic solutions are carried out mainly by using powder samples. In these cases the surface area is not well understood. In this study disk type zinc oxide specimen is used to make sure the surface area and fully understand of leaching kinetics of zinc oxide. Furthermore the changing of surface morphologies

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