Equilibrium oxygen pressures of iron silicate slags
- PDF / 207,351 Bytes
- 3 Pages / 603.28 x 783.28 pts Page_size
- 38 Downloads / 240 Views
relationship between log pO2 and the concentration ratio of ferric and ferrous irons, given by Eq. [lc]. Oxygen partial pressures can be calculated from pCO2/pCO ratios through the following relationships:
Equilibrium Oxygen Pressures of Iron Silicate Slags
2CO +
Equilibrium oxygen pressures are one of the important properties of pyrometallurgical systems. They are measures of the oxidation states of slags and mattes, and their influences on slag losses and impurity elimination in copper smelting are well documented. In lead smelting and in the making of iron and steel, oxygen pressures play equally important roles. This technical note compares two methods for estimating equilibrium oxygen pressures in iron silicate slags. The oxidation states of slags in the iron-oxygen-silica system are controlled by the redox reaction between ferrous and ferric iron, given by Eq. [ 1].
K = aFeo, ~ [aFeo (pO2) ~ log K = - 2 . 8 3 + 6 6 3 0 / T m log pO2 = const. + 4 log (Fe3+/Fe z+)
2CO2
AG ~ = - 5 6 5 , 0 0 0 + 173 T 1sJ
J.W. MATOUSEK
FeO + 0.25 0 2 = FeO15
0 2 ~---
[31 [3a]
log pO2 = 2 log (pCO2/pCO) - 29,500/T + 9.03
[3b]
log (pCO2/pCO) = 0.5 (log p O 2 + 2 9 , 5 0 0 / T - 9.03)
[3c]
[la]
where G is the Gibbs free energy in joules, T is in kelvins, and pressures are in atmospheres. If the independence of the pCO2/pCO ratios and temperature holds outside the range of silica saturation, Eq. [2] for log pO2 at 1250 ~ and Eq. [3b] may be combined to yield a general expression for oxygen pressures in terms of composition and temperature. For a slag of fixed composition--FeO, Fe203, and SiO2--at two temperatures,
[lb]
log (pCO2/pCO)r, = log (pCO2/pCO)r2
[1]
[lc]
K is the equilibrium constant, where T is the temperature in kelvins, and pO2 is expressed in atmospheres. Theoretically, the term in parenthesis in Eq. [lc] is a ratio of chemical activities; in practice, as discussed later, it has been found that the oxidation states of iron silicate slags are satisfactorily defined when chemical compositions are used. Commercial slags of the copper smelting industry typically contain iron and silica in ratios between 1 and 2 and have iron plus silica contents equal to approximately 75 wt pct. For these slags, at a temperature of approximately 1250 ~ an empirical relationship between the logarithm of the equilibrium oxygen pressure and slag composition has been proposed--first in graphical form and then as the mathematical expression given by Eq. [2]. [2'3'41
[4a]
From Eq. [3c], 0.5 (logpO2 + 29,500/Tz - 9.03)r, = 0.5 (logpO2 + 29,500/T2 - 9.03)r2
[4bl
For T~ = 1250 ~ (1523 K), log pO2 = Eq. [2]; substituting Eq. [2] into Eq. [4b], (Eq. [21 + 29,500/1523 - 9.03)1523 K = (log pO2 + 29,500//'2 -- 9.03)r~
[4cl
[--3.1 + 4 log (Fe3+/Fe 2+) - pct (Fe)/pct (SiO2) + 19.41 = (log pO2 + 29,500/Ta)r2
[4d]
log pO2 = 16.3 + 4 log (Fe3+/Fe 2+) - pct (Fe)/pct (SiO2) - 29,500/T
[4e]
An equivalent form of this equation was derived in a relogpOz = -3.1 + 4 log (Fe3+/Fe2+) - pct (Fe)/pct (SiOe)
[2] at a temperature of 1250 ~ (
Data Loading...
