Gipronickel Institute LLC, St. Petersburg, Russia

E. S. Vladimirov, Leading Engineer, Pyrometallurgy Laboratory, e-mail: VladimirovES@nornik.ru
A. B. Portov, Senior Researcher, Pyrometallurgy Laboratory, e-mail: PortovAB@nornik.ru

Kazzinc Ltd., Ust-Kamenogorsk, Kazakhstan
L. A. Ushkov, Deputy Chief Metallurgist For Pyrometallurgy, e-mail: Leonid.Ushkov@kazzinc.com
E. A. Klassen, Head of Production Management Service, RMC, e-mail: Eduard.Klassen@kazzinc.com

Roasting of low-grade zinc concentrates in fluidized bed furnaces is accompanied by the formation of cakes and skull on the furnace walls, which reduces its productivity and leads to emergency shutdowns. The existing literature data on the causes and mechanism of cake formation in the fluidized bed are heterogeneous and do not provide a complete picture of the process; in addition, effective methods for combating their formation are not proposed. The conducted study determined the conditions for the formation of cakes in the fluidized bed and showed the mechanism of their formation. It was found that two types of cakes are formed in the fluidized bed during roasting of zinc concentrates: porous whitish cakes with a zinc content corresponding to the concentrate and sulfur at the level of the cinder; dark dense cakes, depleted in zinc, with a sulfur content of up to 5%. The former are located on the furnace bottom or in the bed volume, the latter - on the furnace walls. There is not enough oxygen near the furnace walls, and oxidation occurs in two stages: through the formation of metallic zinc, which sublimates into the gas phase at firing temperatures and thereby depletes the resulting cake. As a result of statistical data processing, a regression equation was obtained that allows, taking into account the furnace operating parameters and the lead content in the roasted concentrate, to estimate the minimum feed rate of blast gases at which cakes are not formed in the fluidized bed.
We would like to express special gratitude to T. A. Azekenov, Executive Director for Metallurgy at Kazzinc, and to all employees who participated in the research work.

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