Aluminum Electrowinning and Electrorefining

(a) Introduction

Aluminum electrolysis at high temperature has been used in industry since last century. Because of the high temperature operation, there are some intrinsic disadvantages, such as pure raw materials, use of expensive refractory and electrode materials, high producing cost, and pollutant emission. Aluminum production using electrolysis in ionic liquid at ambient temperatures is a newly developed environmentally benign method. The input material for electrolysis is an ionic liquid which is a mixture of AlCl3 and MCl, where MCl is an organic chloride. Compared with current producing process of aluminum, the new method is cost effective. The ultimate purpose of the research is to replace the current high temperature electrolysis with near room temperature electrolysis in ionic liquid thereby lowering production costs and environmental pollution.


(b) Aluminum Refining via Electrolysis in Ionic Liquids

Experimental studies on aluminum recycling via electrolysis in ionic liquids were carried out at 105°C. The electrolyte was made from AlCl3 and 1-butyl-3-methylimidazolium chloride (C4mimCl). Aluminum from an impure anode was dissolved and deposited at the copper cathode. The deposited product was analyzed using Optical Microscope, Micro-image Analyzer, XRD, Emission Spectrometer and Atomic Absorption Spectrometer. The electrorefining process yielded a current density in the range of 400-500 A/m2 and a current efficiency of about 95%. Impurities such as Si, Cu, Zn, Fe, Mg, Cr, Ni, Mn and Pb were removed as anode residue. Aluminum from the impure anode was purified from 79.8 to 99.9%. At a cell voltage of 1V, the energy comsumption of about 3 kWh/kg-Al was obtained.


(c) Aluminum Reduction via Electrolysis in Ionic Liquids

Aluminum reduction via electrolysis in ionic liquid at near room temperature was carried out. Anhydrous aluminum chloride was used as the raw material. The electrolyte that was used for recycling aluminum was employed in the reduction. Aluminum was electrowinned at copper cathode and chlorine gas was released at the graphite anode. Experimental temperatures were in the range of 100-140°C. Cathode current density was in the range of 200-700 A/m2. Dense aluminum deposition with thickness of 0.1-0.2 mm was obtained. Effects of temperature, cell voltage and molar ratio of AlCl3 and C4mimCl on the cathode current density and efficiency were also investigated.

Further information on Ionic liquids, their preparation and uses can be obtained from the following literature:

Kenneth R. Seddon: Room temperature ionic liquids: neoteric solvents for clean catalysis

Thomas Welton: Room temperature ionic liquids- Solvents for synthesis and catalysis, Chemical Reviews, vol. 99, No. 8, 1999.

Robin D. Rogers: Room temperature ionic liquids,

Joan Brennecke: Successful ‘Green’ solvents found for problematic chemicals

Peter Koronaios et al: Acidity of Neutral Buffered 1-Ethyl-3-Methylimidazolium Chloride – AlCl3 Ambient Temperature Molten Salts, Inorganic Chemistry, vol. 37, No. 8, 1998. Kenneth R. Seddon, Ionic Liquids for Clean Technology, J. Chem. Tech. Biotech., Vol. 68, 1997, pp. 351-356.