Distribution equilibria of Pb and Cu between CaO-SiO 2 -Al 2 O 3 melts and liquid copper
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I. INTRODUCTION
A large amount of ash is generated when municipal wastes are incinerated, and dumping of such ash is a serious issue from an environmental viewpoint. Smelting and coagulating processes for the ash have been developed to reduce the residue volume and to stabilize heavy metals in the slag melts. In these processes, evaporation of poisonous heavy metals and their compounds is a huge problem that should not be ignored. Its resolution requires knowledge of the thermodynamic properties of the components in the slag. Studies on the behavior of lead in slag, however, are quite limited, and most of them have focused on copper or lead smelting. Nagamori et al.[1] measured the lead partition between an FeO-Fe2O3-SiO2-Al2O3 slag and liquid copper at 1473 and 1573 K by the chemical equilibration technique, under a CO-CO2 atmosphere. The distribution ratio of lead was a function of the oxygen potential, and the lead solubility in the slag increased with increasing Al2O3 content. Takeda et al.[2] measured the distribution equilibria of lead between an FeO-Fe2O3-SiO2 or FeO-Fe2O3-CaO slag and liquid copper at 1523 K under a CO-CO2 atmosphere. The distribution ratio of lead, defined by (pct Pb in slag)/ [pct Pb in metal] was larger in an iron-silicate slag than in a calcium-ferrite slag by a factor of about 10. Taskinen et al. measured the activities of PbO in PbOCaO-SiO2,[3] PbO-MgO-SiO2,[4] and PbO-ZnO-SiO2[5] slags using a solid electrolyte with calcia/yttria–stabilized zirconia. The activity of PbO increased with an increasing XPbO /XSiO2 ratio in each slag system. The addition of CaO or MgO to the slag increased the activity of PbO, whereas the addition of ZnO decreased it with XPbO /XSiO2 5 4 and then slightly increased it with lower XPbO /XSiO2 ratios. Kim and Sohn[6] examined the effects of CaO, Al2O3, and MgO additions on the distribution of lead between an ironsilicate slag and liquid copper under a CO-CO2 atmosphere and found that the distribution was not significantly affected by the additives. The governing factors of lead solubility in KENJI MATSUZAKI, formerly Research Associate, Department of Materials Science and Engineering, Waseda University, is with Mitsui Mining & Smelting, Saitama 362-0021, Japan. TAKAAKI ISHIKAWA and TAKAYUKI TSUKADA, Graduate Students, and KIMIHISA ITO, Professor, are with the Department of Materials Science and Engineering, Waseda University, Tokyo 169-8555, Japan. Manuscript submitted February 10, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS B
the slag were the oxygen partial pressure, the basicity of slag, and the ratio of FeOx /SiO2. Moon et al.[7] investigated the phase equilibria between lead and a PbO-FeOx-CaO-SiO2 or PbO-FeOx-CaO-SiO2ZnO slag at 1423 K using a solid electrolyte with calciastabilized zirconia. The activity coefficient of PbO increased with the addition of CaO, whereas the effect of the FeOx or ZnO concentration on it was small. In the present study, the distribution ratios of lead and copper between a CaO-SiO2-Al2O3 melt, which is a typical slag sy
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