A principle was established to estimate the equilibrium distribution ratio of the impurity element X between NaO
0.5-CO
2-XO
v/
2 slag (
v: the valence of X) and molten copper defined by {(mass% of X in slag)/[mass% of X in metal]}, over a wide range of the slag composition as a function of partial pressures of CO
2 and oxygen. Based on the principle, the following measurements on NaO
0.5-CO
2-AsO
2.5 slag were conducted to estimate the distribution ratio of arsenic.
(1) Activity measurement of NaO
0.5; Activities of NaO
0.5 in the slag were determined by the EMF method using β″-alumina as a solid electrolyte over the composition range of 1>
N>0.8{N=
nNaO
0.5/(
nNaO
0.5+
nAsO
2.5),
n: the number of moles} under the partial pressures of CO
2 of 0.001-0.08 MPa at 1, 423-1, 523 K.
(2) Activity measurement of AsO
2.5; Activities of AsO
2.5 could be calculated from the activities of NaO
0.5 by integrating the Gibbs-Duhem relation. Activities of AsO
2.5 as the initial values of the integration were determined by the distribution equilibrium measurements of arsenic between the slag and molten copper.
From the obtained results, together with the solubility data of CO
2 in the slag reported in the previous study, the equilibrium distribution ratio of arsenic was successfully calculated over the composition range of 1>
N>0.8 as a function of partial pressures of CO
2 and oxygen at the temperatures of 1, 423 and 1, 523 K.
The calculated distribution ratio of arsenic has a considerably large value and increases with increasing the value of
N. The higher oxygen partial pressure and the lower CO
2 partial pressure and the lower temperature are more preferable for the removal of arsenic from molten copper.
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