Aluminium Recycling in Single- and Multiple-Capillary Laboratory Electrolysis Cells

Andrey Yasinskiy,Sai Krishna Padamata,Peter Polyakov,Ilya Moiseenko,Bernd Friedrich,Dominic Feldhaus,Srecko Stopic

doi:10.3390/met11071053

Andrey Yasinskiy, Sai Krishna Padamata + Show 5 more

Open Access

https://doi.org/10.3390/met11071053

Copy DOI

Journal: Metals	Publication Date: Jun 30, 2021
Citations: 6	License type: CC BY 4.0

Affiliation: Siberian Federal University, RWTH Aachen University

Abstract

This work is a contribution to the approach for Al purification and extraction from scrap using the thin-layer multiple-capillary molten salt electrochemical system. The single- and multiple-capillary cells were designed and used to study the kinetics of aluminium reduction in LiF–AlF3 and equimolar NaCl–KCl with 10 wt.% AlF3 addition at 720–850 °C. The cathodic process on the vertical liquid aluminium electrode in NaCl–KCl (+10 wt.% AlF3) in the 2.5 mm length capillary had mixed kinetics with signs of both diffusion and chemical reaction control. The apparent mass transport coefficient changed from 5.6∙10−3 cm.s−1 to 13.1∙10−3 cm.s−1 in the mentioned temperature range. The dependence between the mass transport coefficient and temperature follows an Arrhenius-type behaviour with an activation energy equal to 60.5 kJ.mol−1. In the multiple-capillary laboratory electrolysis cell, galvanostatic electrolysis in a 64LiF–36AlF3 melt showed that the electrochemical refinery can be performed at a current density of 1 A.cm−2 or higher with a total voltage drop of around 2.0 V and specific energy consumption of about 6–7 kWh.kg−1. The resistance fluctuated between 0.9 and 1.4 Ω during the electrolysis depending on the current density. Thin-layer aluminium recycling and refinery seems to be a promising approach capable of producing high-purity aluminium with low specific energy consumption.

Highlights

Aluminium is the second most utilised metal in the world, only outranked by steel, due to its outstanding mechanical and metallurgical properties
93% of CO2 emissions can be reduced using secondary aluminium production [2]. Processes such as remelting [3], electrolysis [4], and fractional solidification [5] are used for secondary aluminium production
While remelting has a very low specific energy consumption, capillary thin-layer electrolysis is performed in an electrochemical cell (Al–Me)Al|Al3+|Al with EMF equal to zero, which has been shown in previous work [15], and which makes it possible to produce pure aluminium with much smaller energy consumption than that required for primary production

Summary

Introduction

Aluminium is the second most utilised metal in the world, only outranked by steel, due to its outstanding mechanical and metallurgical properties. Chloride-based molten salts have shown some promising results in aluminium extraction from aluminium alloys [13] It still faces some problems [14] such as: extremely high hygroscopicity of AlCl3; significant volatility of AlCl3. The distance between the two liquid electrodes (aluminium alloy and pure aluminium) was reduced in an attempt to drastically minimize the Ohmic voltage drop and to increase the reaction rates due to overlapping diffusion layers. While remelting has a very low specific energy consumption, capillary thin-layer electrolysis is performed in an electrochemical cell (Al–Me)Al|Al3+|Al with EMF equal (or close) to zero, which has been shown in previous work [15], and which makes it possible to produce pure aluminium with much smaller energy consumption than that required for primary production. The previously used single-capillary cell [15] was improved in terms of simple manufacturing, and the pilot multiple-capillary laboratory cell was designed based on previous data

Experiment

Conclusions