Electrochemical production of Al–Mn alloys during the electrodeposition of aluminium in a laboratory cell

Omar Awayssa,Geir Martin Haarberg,Rauan Meirbekova,Gudrun Saevarsdottir

doi:10.1016/j.elecom.2021.106985

Omar Awayssa, Geir Martin Haarberg + Show 2 more

Open Access

https://doi.org/10.1016/j.elecom.2021.106985

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Abstract

This study reports the direct production of an aluminium–manganese alloy during aluminium electrolysis in fluoride-based melts. Experiments were conducted in a laboratory cell dedicated for current efficiency measurements. The temperature was varied from 965–980 °C at a cathodic current density (CCD) of 0.9 A/cm2 and a cryolite ratio (CR) of 2.2. The manganese content was up to 3.0 wt%. Manganese was added in the form of Mn2O3. Bath samples were collected regularly and analyzed with ICP-MS to observe the decay of manganese during electrolysis. It was possible to produce Al-Mn alloys of up to 21 wt. % Mn. Current efficiency for the electrodeposition of Al–Mn alloy was estimated to be in the range of 93%. Current efficiencies with respect to aluminium were estimated. The solidified surfaces of the metal deposits were mostly flat, but some were deformed.

Highlights

IntroductionA patent has reported the pos sibility of producing aluminium–manganese alloys directly in the cryolite-based melt
In the Hall–Heroult process liquid aluminium is produced by the electrolytic reduction of alumina (Al2O3) dissolved in an electrolyte containing cryolite (Na3AlF6) at 960–970 ◦C according to the overall electrochemical reaction given by [1]: (1)Manganese is the principal alloying element in the 3xxx aluminium alloys series
It agrees with reports which suggest that a reduction in current efficiency of 1% was recorded for every 5 ◦C increase in the operating temperature [10]

Summary

Introduction

A patent has reported the pos sibility of producing aluminium–manganese alloys directly in the cryolite-based melt. According to this invention, aluminium–manganese alloys containing up to 10 wt. The overall reduction reaction of MnO and MnO2 in fluoride-based melts containing molten aluminium could be given, in order, as: Mn2+ + 2e− = Mn (2). Current efficiency (CE) is a representation of how efficient the supplied electricity has been used to deposit aluminium It can be estimated by metal weight gain relating the actual produced aluminium to the aluminium that would theoretically be produced based on Faraday’s law. This work reports a study on the electrochemical deposition of an aluminium–manganese alloy during aluminium reduction in fluoridebased melts in a laboratory cell implementing industrial standards. The effect of the presence of Mn on the current efficiency with respect to Al, the current efficiency for the alloy, and the shape of the surface of the solidified deposit are discussed

Experimental

Cell performance

Solidified deposit shape and cell voltage behavior

Conclusions