Current Efficiency
Raw Materials
Cell Operation
Measurements
Theory Table of Contents 3. Properties of the Electrolyte 3.1 Summary
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The properties of the electrolyte which depend on its composition and the bath temperature influence the results of cell operation. The chapter gives equations to calculate these properties and examples to show their applications. The composition of the electrolyte is chemically characterized in several ways: by ratio and concentration values. The chemical laboratory of a plant determines as a matter of routine the aluminum fluoride, calcium fluoride and eventually the aluminum oxide content of the electrolyte. The methods of chemical analysis are described. A section about phase diagrams describes the meaning of some phase diagrams for aluminum production. The following chapters treat the essential properties of the electrolyte like liquidus temperature, electrical conductivity, etc. You find here the relations and equations of mostly several authors that AlPrg and AlWeb are using for the calculations and evaluations.
The properties of the cryolite electrolyte influence many key parameters and processes of the Hall-Héroult electrolysis:
solidus, liquidus temperature:
heat transfer, ledge profile,
electrical conductivity:
bath voltage, energy consumption,
solubility of alumina:
formation and dissolution of sludge,
aluminum, electrolyte densities:
magnetohydrodynamic effects,
vapor pressure:
fluoride emission,
viscosity:
dissolution of alumina, electromagnetic effects,
surface tension:
wetting of carbon anodes, anode effect.
Most of the properties depend on the composition and the temperature of the electrolyte. The following chapters give you the relations and equations for these properties and also indications how you use them. The next Figure 3.1 shows how the AlPrg PC program [Lit.] handles the properties of the cryolite electrolyte. On the Electrolyte Composition part of the page you define the concentration of the electrolyte components. In the Electrolyte Properties part AlPrg lists the corresponding properties values.
3.1 AlPrg: Electrolyte Composition and Properties page and diagrams.
On the upper part of the page (Electrolyte Composition) you find the input fields for the components of the cryolite electrolyte and below AlPrg shows the values of the corresponding properties. On the diagrams part you see little icons representing the dependence of a property (aluminum and electrolyte density) on the bath components and temperature. If you click on one of these icons (Al2O3 in the figure) AlPrg create the corresponding large diagram.
In Figure 3.2 represents the corresponding Electrolyte Properties Interactive Web Page. Compared to the AlPrg page you see the same input and output field, the icon diagrams and large graphical representation all arranged a little bit differently. You can let AlWeb draw the curve electrolyte temperature vs electrolyte composition parameter (Al2O3 concentation in Figure 3.2) into the main diagram. You do this by clicking on the TB button.
3.2 AlWeb: Electrolyte Properties Interactive Web Page.
Compared to the AlPrg version in Figure 3.1 the input and output fields of the AlWeb version are arranged differently to adapt them to the browser screen.
The chapter 3. Properties of the Electorlyte treats its content in the following sections:
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