Activity of arsenic in copper
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TIIE arsenic bearing minerals arsenopyrite FeAsS, e n a r g i t e C u 3 A s S 4 and
tennantite (Cu, Fe, Zn, Ag) ~2As4S~3are frequently encountered in copper concentrates. During smelting arsenic enters the reverberatory slag and matte even though a substantial fraction of the arsenic is eliminated in the roaster and reverberatory furnace as arsenic trioxide vapor. At one custom smelter of arsenious concentrates arsenic concentrations in reverberatory slag as high as one weight percent have been reported, although concentrations less than 0.3 wt. pct are more typical. The distribution coefficient for arsenic between molten copper and slag and molten copper and white metal are approximately 300 and 12 respectively. 14 The high values of the distribution coefficients reflect the strong chemical affinity copper has for arsenic. Although the typical concentrations of arsenic in slag and matte are low, contact between blister copper and arsenious slag and matte can lead to the dissolution of arsenic in the copper. Arsenic in copper is generally considered undesirable. All impurities tend to lower the electrical conductivity of copper, but the worst offenders are those which form solid solutions in the annealed copper. Arsenic is known to form C u 3 A s in the annealed state and will reduce the electrical conductivity by 23 pct when 0.1 wt. pct As is present in the metal2 Arsenic also reduces the thermal conductivity by a similar amount and the addition of 0.5 wt pct arsenic to copper adversely affects the annealing properties by raising the softening temperature by more than 100 K. 5 For the above reasons, the removal of arsenic from blister copper is desirable and thus a knowledge of the activity of arsenic in copper is important. Several investigators 6-8 have measured the activity of arsenic in copper and evaluated the Henrian activity coefficient. These investigators have reported that the Henrian activity coefficient ranges from 1.45 9 10-4 D. C. LYNCH is Assistant Professor of Metallurgy, Department of Mining, Metallurgical and Ceramic Engineering, University of Washington, Seattle, WA 98195. Manuscript submitted March 3, 1980.
to 5 9 10 -7 at temperatures between 1273 and 1573 K. The discrepancy this poses is illustrated by the data plotted in Fig. 1. The works of Azakami and Yazawa 6 and Jones and Philipp, 7 present the greatest discrepancy. In this study their results are reevaluated in light of new information regarding the vapor of arsenic at elevated temperatures. The results of the new analysis presented in this study are plotted in Fig. 2. Figure 2 illustrates that the data of Azakami and Yazawa and Jones and Philipp are in general agreement. The new analysis presented in this study also suggests that the negative departure of arsenic in copper from ideality, while substantial, is less than originally though to exist. VAPOR PRESSURE D A T A The activity of arsenic is defined by the following equations: "
aAs ="
As,]
po
=
AJ
|L~221
po
AJ
=
=
PAs
[11
where P~s,, poAs~,poAs2and P~s are the satur
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