Evaporation Behavior of Zinc Chloride in Ar–O2–H2O Atmosphere

Abstract

Evaporation behavior of ZnCl 2 melts and ZnCl 2 -ZnO mixtures in Ar-O 2 -H 2 O atmosphere was observed at 873 K by measuring change of weight and chemical composition. When water vapor or oxygen was added, weight loss of ZnCl 2 decreased, and the effect of water vapor on repression of weight loss was much stronger than that of oxygen. Especially, weight loss stagnated after 20 min at 40 % of weight loss in Ar-5%H 2 O atmosphere. It is considered that the reaction product between zinc chloride and water vapor covered the surface of melt.In the case of ZnCl 2 -ZnO melt, weight loss reached and stagnated at about 60 % of initial weight in Ar and Ar-O 2 atmospheres. This value is close to initial ZnCl 2 content. However, weight loss reached and stagnated at about 50 % of initial weight in Ar-H 2 O atmosphere, and the residue was converted to zinc oxide after 60 min experiments. From these results, formation of zinc oxide by the reaction between zinc chloride and water vapor in Ar-H 2 O atmosphere was confirmed. It is concluded that zinc oxide formed by the reaction on surface of melt prevented the contact between zinc chloride and gas phase, and the evaporation of zinc chloride. This phenomenon caused the stagnation of weight loss with atmosphere containing water vapor.KEY WORDS: evaporation rate; dust; recycling; scrap; zinc chloride; water vapor. experiments, ZnCl 2 was mixed with reagent grade of ZnO at molar ratio of unity (mass ratio ZnCl 2 : ZnOϭ62.61 : 37.39). Figure 1 shows the schematic diagram of experimental apparatus. Water vapor pressure was controlled by bubbling Ar gas in distilled water, which temperature was kept at 313 K to maintain constant water vapor pressure. The path of water vapor was heated by ribbon heater. In the preliminary experiment, the water vapor in the mixed gas was absorbed to CaCl 2 and it is confirmed that the gas is saturated with water vapor from the weight change of CaCl 2 . Oxygen partial pressure was controlled by changing flow rates of Ar and O 2 gases. Each gas flow rate was controlled by mass flow controller. Total gas flow rate was 400 cm 3 /min. Experimental temperature was measured and controlled at 873 K by using Pt-30%Rh/Pt-6%Rh thermocouple. Samples of 1.6 to 2.0 g were held in a mullite boat (Width 12ϫDepth 9ϫLength 60 mm). Experimental time was started when the boat with sample was inserted into the hot zone of an electric furnace. After each experiment, weight of the boat with sample was measured in a glove box filled with dry Ar gas. The chemical compositions of residues in the boat were determined. Zinc content was analyzed by ICP-AES. Chlorine content was analyzed by titration method with silver nitrate (Mohr method) or gravimetry. Oxygen content was analyzed by LECO TC-600 combustion analyzer. Table 1 shows the experimental conditions and results in Ar-H 2 O atmospheres at 873 K. Fraction of weight loss was defined as quotient of weight loss by initial weight of sample. Figure 2 shows the fraction of weight loss with time in Ar-H 2 O atmosphere. The linear re...

Selective Chlorination Reaction of Cu2O and FeO Mixture by CaCl2

“…Some investigations have been made on the removal of copper in melt using sodium sulfide or sodium sulfate fluxes, 1,2) or from solid scrap by O2-Cl2 gas mixtures reaction, 3) or from carbon saturated molten iron by FeCl2 4) or oxidative removal via Ag phase. 5) Recently, the selective chlorination [6][7][8][9][10][11][12][13][14][15][16][17][18] has been used to separate Zn and Pb from the steelmaking dust. In our previous works, 16,17) CaCl2 was employed as the chlorinating agent to selectively chlorinate Zn from ZnO-Fe2O3 or ZnFe2O4 system.…”

Chlorination and Evaporation Behaviors of Zinc Oxide in Ar- HCl-O2 Atmosphere

“…Reagent grade ZnO was used as a specimen. The experimental apparatus was almost the same as that employed in our previous study [16]. The partial pressures of hydrogen chloride and oxygen were controlled by changing the flow rates of Ar, HCl and O 2 gases.…”

“…However, the effect of water vapor on the chlorination and evaporation behaviors of heavy metal elements has not yet been fully clarified because of the formation of oxychlorides in oxidizing and chloridizing atmospheres. In our previous study [16], the effect of water vapor on the evaporation behavior of zinc chloride was investigated at 873 K. The weight loss of zinc chloride decreased with water vapor addition and saturated in an Ar-0.05 atm H 2 O atmosphere 20 min after the reaction started. However, the reaction mechanisms between metal oxides and a chloridizing atmosphere containing water vapor are not yet understood.…”

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.…”