The Electrical Conductivity of Molten Oxide-Fluoride Cryolite Mixtures.

Pavel Arkhipov,Olga Tkacheva

doi:10.3390/ma14237419

Pavel Arkhipov, Olga Tkacheva

Open Access

https://doi.org/10.3390/ma14237419

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Journal: Materials	Publication Date: Dec 3, 2021
Citations: 2	License type: CC BY 4.0

Affiliation: Institute of High Temperature Electrochemistry

Abstract

A new way to reduce the energy consumption during the operation of powerful aluminum reduction cells is suggested via reducing the resistance of the electrolyte, i.e., increasing its electrical conductivity. The electrical conductivity of molten cryolite mixtures NaF-AlF3-CaF2-Al2O3 with cryolite ratio (CR) of 2.1–3.0 and content of CaF2 and Al2O3, up to 8 wt%, was measured at the temperatures from liquidus to 1300 K. Based on the experimental results, a multifunctional equation for the electrical conductivity of oxide-fluoride cryolite melts was evaluated. The experimental and calculated values of the electrical conductivity agree within 1.5%. The activation energy of the electrical conductivity of the NaF-AlF3-CaF2-Al2O3 melts was estimated. The activation energy of electrical conductivity for molten NaF-AlF3 mixtures with CR 3.0 and 2.1, determined by the most mobile cations Na+, increased from 15.8 kJ/mol up to 18.5 kJ/mol. It was found that CR had a greater impact on the activation energy than the changes in the Al2O3 or CaF2 concentrations. Based on the ratio of the activation energies of the electrical conductivity and the viscous flow, the correlation between the electrical conductivity and viscosity of molten cryolite mixtures NaF-AlF3-CaF2-Al2O3 was illustrated.

Highlights

A distinctive feature of the primary aluminum electrolytic production is a high specific power consumption
The electrical conductivity of the molten NaF-AlF3 system was found to increase as the temperature and the cryolite ratio increased, whereas the content of alumina and calcium fluoride decreased
The activation energy of electrical conductivity for molten NaF-AlF3 mixtures increases from 15.8 kJ/mol up to 18.5 kJ/mol

Summary

Introduction

A distinctive feature of the primary aluminum electrolytic production is a high specific power consumption. 15,300 kWh/t Al (for cells with side current supply) to 16,000 kWh/t (for cells with the upper current lead), and only 40% of this electricity is consumed directly for the aluminum production; the rest is spent on heating the cell and heat losses [1,2]. Twenty-seven out of thirty-four large aluminum companies in China use Cell technology 400–500 kA. China Hongqiao Group and Shanxi NonFerrous Co. Ltd., implement Cell technology 600 kA [6]. The Shandong Xinfa Aluminum and Electricity Group have built three new 660 kA power lines, which are operating in Liaocheng (Chipin dong province, China). The capacity of the 660 kA aluminum smelter is 1.15 million tons per year [7]

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