Effect of Chlorine on the Vaporization Behavior of Zinc and Lead during High Temperature Treatment of Dust and Fly Ash

Abstract

Smelting process is a practical method to treat incineration ash of solid wastes in terms of volume reduction and decomposition/immobilization of toxic materials. In this process, chlorine is a key element to determine the removal ratio of heavy metals such as zinc and lead. The present paper is aiming to give a general review of researches on the effect of chlorine on the vaporization behavior of zinc and lead in molten slag. First, the basic information such as solubility/activity of chlorine in the slag, vaporization mechanism and kinetics relating to chlorides during heat treatment of fly ash are summarized. Then, the vaporization behaviors of zinc, lead and their chlorides during heating are discussed together with important process factors such as atmosphere, temperature, chemical composition and slag matrix. Further, some information on the oxychlorides of Zn and Pb are introduced.KEY WORDS: vaporization behavior; heavy metals; chlorine; molten slag. * Heavy metals: There has not been a unified definition for them. Generally, it refers to compounds of metals, such as lead, zinc and copper, which become toxic when concentrated in the environment.12) Further, it is often used as a group name for metals and semimetals (metalloids) associated with contamination and potential toxicity.

Separation and Recovery of Antimony from High Arsenic-bearing Flue Dusts through Selective Oxidation Using MnO₂

“…[1][2][3] Among them, an arsenic-bearing flue dust is one of the most important secondary resources, which contains a large amount of valuable metals, such as lead, antimony and indium. [4][5][6][7] Composition of arsenic-bearing dusts varies mainly according to the type of reactor and the raw material used.…”

Kinetics of Zn Removal from ZnO–Fe2O3–CaCl2 System

“…Various new selective chlorination and evaporation processes have been proposed. [8][9][10][11][12][13][14][15][16][17][18][19] The Cl 2 gas was used as the chlorination resource in these investigations. However, CaCl 2 is a more selective chlorinating agent for volatilizing Zn, Pb and so on.…”

Vapor Pressure of Zinc and Zinc Chloride in the Fe<SUB>t</SUB>O-CaO-SiO<SUB>2</SUB>-Al<SUB>2</SUB>O<SUB>3</SUB> Slag System

“…The advantages of this process are as follows: (1) volatile metal elements such as zinc and lead can be separated from the residue by evaporation; (2) recovered heavy metals can be reutilized by conventional metallurgical processes; and (3) oxide residue, sometimes referred to as slag, could be inert to the environment. Since toxic organic compounds in wastes are completely destroyed due to a long residence time at high temperatures, permanently safe slag products can be achieved if the heavy metals are appropriately removed.…”

“…Chlorine-bearing slag/salts are of particular interest from industrial point of view, since the high temperature behaviors of heavy metals strongly depend on the chlorine content or potential. 1) So far, some experimental researches have been performed on the partitioning of heavy metals under incineration and combustion condition (at 873 K-1273 K), [2][3][4][5] along with some thermodynamic equilibrium calculations for the formation of vapor species. 6,7) However, the basic thermodynamic knowledge regarding vapor pressures, activities, and interactions in molten slag or salt of these metals is limited due to experimental difficulties.…”