Characterization of Phase Equilibria and Thermodynamics …
345
these phases in complex chemical systems. The availability of the thermodynamic
database enables the systems to be presented and viewed in different ways depending
on the needs of the user.
The example presented in Fig. 4a shows a projection of the matte compositions
in the Pb–Cu–Fe–O–S–Si slag-matte-metal system in equilibrium with SiO 2 on to
the Cu–Fe–Pb composition triangle. Figure 4b contains information on the %PbO
in slag corresponding to these matte compositions. The lines drawn on the figure
correspond to the data provided previously in Fig. 1a for selected compositions
of Cu/(Cu + Pb) in matte. By constructing information in this way, the trends in
chemical behavior can be visualized and more efficiently analyzed. This type of
calculation and representation can be undertaken for any set of process conditions
and bulk chemical compositions to assess the potential outcomes of these multi-phase
equilibrium reactions. For instance, the formation of the matte phase can be a problem
during the bullion tapping in the Kivcet process. Thermodynamic calculations can
provide better understanding of desulfurization reactions in the shaft.
Multi-component Fluxing Diagrams
The thermodynamic database can also be used to construct diagrams that can be
used to assist in the selection of optimum flux additions to slags. Examples of the
application of these diagrams to the optimization of flux additions to complex lead
smelting slags are given in Fig. 5a–d. The effect of the CaO/SiO 2 ratio on the liquidus
temperatures of Pb–Zn–Fe–Al–Ca–Mg–Si–O slags for a given PbO concentration
and Zn/Fe ratio in the slag is given in Fig. 5a. Here, it can be clearly seen that the
slag is fully liquid below 1200 °C for the CaO/SiO 2 weight ratios between 0.1 and
0.6. The liquidus temperature at low flux additions in the spinel primary phase field
corresponds to a Fe/SiO 2 ratio of approximately 0.33–0.37 for the above range of
CaO/SiO 2 ratios. If the flux addition results in sub-liquidus phase assemblage at
these operating conditions, the % solids in the slag can be estimated from Fig. 5c.
Excessive % solids in the slag can lead a practical operating issues, such as difficulties
in tapping due to increased slag viscosity and the loss of operating volume due to the
build-up of solids on the reactor lining. The effect of variable Zn/Fe ratio in slag can
be assessed through the use of a pseudo-ternary section ZnO–“FeO”–(CaO + SiO 2 ),
an example of which is shown in Fig. 5b. Here, the liquidus temperature is shown to
vary with Zn/Fe ratio with the minimum liquidus temperatures occurring at the join
between the zincite, (Zn, Fe) O, and spinel, ZnO · Fe 2 O 3 , primary phase fields.
Process Modelling
Important principles of using thermodynamics in process modelling were outlined
in recent publications. Reliable model predications are important for navigating the
345
these phases in complex chemical systems. The availability of the thermodynamic
database enables the systems to be presented and viewed in different ways depending
on the needs of the user.
The example presented in Fig. 4a shows a projection of the matte compositions
in the Pb–Cu–Fe–O–S–Si slag-matte-metal system in equilibrium with SiO 2 on to
the Cu–Fe–Pb composition triangle. Figure 4b contains information on the %PbO
in slag corresponding to these matte compositions. The lines drawn on the figure
correspond to the data provided previously in Fig. 1a for selected compositions
of Cu/(Cu + Pb) in matte. By constructing information in this way, the trends in
chemical behavior can be visualized and more efficiently analyzed. This type of
calculation and representation can be undertaken for any set of process conditions
and bulk chemical compositions to assess the potential outcomes of these multi-phase
equilibrium reactions. For instance, the formation of the matte phase can be a problem
during the bullion tapping in the Kivcet process. Thermodynamic calculations can
provide better understanding of desulfurization reactions in the shaft.
Multi-component Fluxing Diagrams
The thermodynamic database can also be used to construct diagrams that can be
used to assist in the selection of optimum flux additions to slags. Examples of the
application of these diagrams to the optimization of flux additions to complex lead
smelting slags are given in Fig. 5a–d. The effect of the CaO/SiO 2 ratio on the liquidus
temperatures of Pb–Zn–Fe–Al–Ca–Mg–Si–O slags for a given PbO concentration
and Zn/Fe ratio in the slag is given in Fig. 5a. Here, it can be clearly seen that the
slag is fully liquid below 1200 °C for the CaO/SiO 2 weight ratios between 0.1 and
0.6. The liquidus temperature at low flux additions in the spinel primary phase field
corresponds to a Fe/SiO 2 ratio of approximately 0.33–0.37 for the above range of
CaO/SiO 2 ratios. If the flux addition results in sub-liquidus phase assemblage at
these operating conditions, the % solids in the slag can be estimated from Fig. 5c.
Excessive % solids in the slag can lead a practical operating issues, such as difficulties
in tapping due to increased slag viscosity and the loss of operating volume due to the
build-up of solids on the reactor lining. The effect of variable Zn/Fe ratio in slag can
be assessed through the use of a pseudo-ternary section ZnO–“FeO”–(CaO + SiO 2 ),
an example of which is shown in Fig. 5b. Here, the liquidus temperature is shown to
vary with Zn/Fe ratio with the minimum liquidus temperatures occurring at the join
between the zincite, (Zn, Fe) O, and spinel, ZnO · Fe 2 O 3 , primary phase fields.
Process Modelling
Important principles of using thermodynamics in process modelling were outlined
in recent publications. Reliable model predications are important for navigating the