Modeling and experimental validation of aluminum electrowinning in chloroaluminate ionic liquids at low temperatures

A novel process for aluminum extraction using ionic liquid electrolyte was investigated on multiple scales of experiments and modeling. Ionic liquids [BMIM]Cl and [HMIM]Cl were synthesized and characterized using Coulomb Titration and Nuclear Magnetic Resonance (NMR) techniques. Thermodynamic properties of [BMIM]Cl and [HMIM]Cl ionic liquids were investigated using thermogravimetric analysis (TGA) and differential thermal analysis (DSC).;A 3-D mathematical model for the low temperature aluminum electrowinning in ionic liquid electrolytes was developed. A number of ionic liquid electrowinning process parameters were evaluated for optimal reactor performance, including current and potential distributions, species concentration profiles, fluid flow distribution, and electrode spacing. The results indicated that the electrode configuration significantly affects the electrolyte fluid flow and current density distribution. The parallel electrode configuration (in line with electrolyte inlet) improved the convection and resulted in homogenous current density distribution and electrolyte fluid flow. The electroactive species distribution was most favorable between the electrodes in the case of parallel electrode configuration. Perpendicularly configured electrodes resulted in a more complex fluid flow within electrolyte domain. The optimum electrode distance was determined to be ∼1.0 cm which gave maximum current density. The current density modeling results are in good agreement with experimental data below applied cell voltage of 3.5 volts.;Aluminum was successfully electrowon on copper cathode using AlCl 3-1-hexyl-3-methyl imidazolium chloride ([HMIM]Cl) ionic liquid electrolytes with molar ratio from 1:1 to 1:2 at temperature range 90-140°C and with cell voltage from 2.50 V to 3.50 V. The cell performance variables studied were the current density and current efficiency as a function of temperature, electrolyte flow rate, electrolyte concentration, applied cell voltage, and process operating time. Aluminum electrowinning in batch recirculation cells showed that current density of batch experiments were comparable with previous laboratory experiments in similar conditions. Current density and current efficiency increase when electrolyte flow rate and concentration increase. Maximum current efficiencies were obtained at circulation rate of 20 ml/min. From the present study, it is showed that high applied cell voltage; high flow rate and intermediate concentration ratios are optimum conditions for obtaining high cathode current efficiencies.