Condensation of zinc vapor on solid media in Zn (g) -CO-CO 2 -Ar mixtures
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Condensation of Zinc Vapor on Solid Media in Zn(g)-CO-CO2-Ar Mixtures N.X. FU, T. TAMAGAWA, M. KOBAYASHI, and M. TANAKA The condensation experiments of zinc vapor on the solid media in Zn(g)-CO-CO2-Ar mixtures were conducted in a flow reactor at 800 °C to 1000 °C under a zinc partial pressure of 0.6 to 7.9 kPa. The condensates were weighed, and the zinc contents and their morphology were analyzed to investigate the effects of various factors on the condensation. It was found that the initial temperature of the media should be as low as possible in liquid condensation for the efficient recovery of zinc. The condensation is enhanced with zinc partial pressure of the gases. The medium made of silica with a smooth surface is favorable for the efficient condensation. In the gases not oxidizing to zinc vapor, metallic zinc can be obtained on the medium with an initial temperature over the range of 120 °C to 400 °C. For obtaining metallic zinc, it is necessary to raise the temperature of the gases, appropriately limit the zinc partial pressure, or maintain a sufficient CO/CO2 ratio to avoid the oxidation of zinc vapor.
I. INTRODUCTION
CURRENTLY, the quantity of crude steel produced by the electric arc furnace (EAF) approaches 30 million tons each year in Japan, which amounts to about 30 pct of the total output of crude steel. At the same time, over 0.5 million tons of dust from the EAF exhaust gases are generated annually.[1,2] The dust containing about 33 pct iron, 20 pct zinc, and small amounts of other valuable metals is considered a significant resource. About 60 pct of the dust is treated via the processes of the Waelz kiln at 1100 °C and the Mitsui furnace and electric distillation both at 1300 °C, in which zinc oxide is reduced by coke followed by the evaporation of zinc and the reoxidation of zinc vapor to produce crude zinc oxide or zinc white with low commercial value.[3] These processes are complex and require a large quantity of energy. Additionally, about 30 pct of the dust is disposed of by landfilling after stabilization, and 10 pct is used as raw materials for cement. To save energy and minimize environmental load, a new process to recover iron and metallic zinc with a yield of more than 80 pct directly from the EAF exhaust gases is being developed by the Japan Research and Development Center for Metals (JRCM).[4,5] In this process, the hot exhaust gases from a sealed EAF are first treated by a moving coke bed filter to deposit iron, and second by a condenser to recover metallic zinc on falling ceramic balls with an average diameter of 0.5 mm. Efficient condensation of zinc vapor as metallic zinc is critical to the success of developing the process. The potential for zinc vapor to be oxidized by CO2 on cooling obstructs the acquisition of the metallic zinc. These are influenced by various factors including (1) temperature, flow rate, and N.X. FU, Visiting Researcher, Metals Recovery Group, T. TAMAGAWA, Technical Staff Member, M. KOBAYASHI, Principal Research Scientist, and M.
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