| As the rising demand for aluminum and the exhaustion of the aluminum mineral resource make the recovery of aluminum concerned, the purification of secondary aluminum has become the focus of researches. The metal impurities of aluminum scrap can not be fully removed by refining in melting furnace. Aluminum scrap is mainly recycled as aluminum alloy by remelting and purifying and mixing with primary aluminum, so its application is limited. Refining of aluminum scrap to pure metal would enable to increase its applications fields. In this paper, the x(AlCl3)=0.667AlCl3-BMIC ionic liquid is served as the electrolyte for the electrorefining of aluminum scrap. The effects of metal impurity of aluminum scrap and water on aluminum electrorefining have been investigated.The anode dissolution of aluminum in AlCl3-BMIC ionic liquid has been studied through linear sweep voltammetry test. The passivation phenomenon is observed. It is caused by formation of solid AlCl3layer at the surface of aluminum electrode resulting from concentration changes of AlCl4and Al2Cl7-. The agitation, increment of temperature and decrement of x(AlCl3) exhibits a notable effect on increasing anodic limiting current density.The controlled-potential coulometry measurement has been carried out to determine the oxidation state of metal species produced by the anodization of metal in ionic liquid. The results indicate that the Mn、Zn、Fe、Ni、Pb are oxidized to generate Mn(Ⅱ)、Zn(Ⅱ)、Fe(Ⅱ)、Ni(Ⅱ)、 Pb(Ⅱ) and Cu is oxidized to generate Cu(Ⅰ). The potentials of Mn(Ⅱ)/Mn, Zn(Ⅱ)/Zn, Pb(Ⅱ)/Pb, Fe(Ⅱ)/Fe, Cu(Ⅰ)/Cu and Ni(Ⅱ)/Ni are0.02,0.21,0.32,0.63,0.64and0.86V vs. Al(Ⅲ)/Al reference electrode respectively, which are much smaller than those in aqueous solutions. The metal activation taxis in AlCl3-BMIC ionic liquid is Mn>Zn>Pb>Fe>Cu>Ni, and is not a usual metal activation taxis.The corrosion of Mn, Cu, Zn, Fe, Pb and Ni in AlCl3-BMIC ionic liquid has been investigated. It is found that the order of metal corrosion rate is Mn>Cu>Zn>Fe>Pb>Ni in the range of323-363K while Ni is faster than Pb when the temperature is above363K. The corrosion activation energies of Mn, Cu, Zn, Fe, Pb and Ni in the ionic liquid are52.23,66.42,53.02,50.42,41.11and60.55kJ/mol respectively.Electrochemical analysis indicates the effects of impurities on electrode reaction are quite different. The Cu(I), Zn(II), Ni(II) are found to depolarize the cathode. The Fe(II) and Pb(II) are observed to polarize the cathode. Polarization of the cathode is noted when Mn(Ⅱ) concentrations are less than50mg/L whereas depolarization of cathode is found when Mn(Ⅱ) concentration is100mg/L. The Li(Ⅰ), Na(Ⅰ), K(Ⅰ), Ca(Ⅱ) and Mg(Ⅱ) have little effect on electrode reaction.The constant current electrolysis experiments results show that the aluminum with purity higher than99.8%is obtained with electrorefining Al-Cu, Al-Zn, Al-Fe, Al-Mn, Al-Ni and Al-Pb alloys. The purity of aluminum deposits is virtually unaffected by Li(Ⅰ), Na(Ⅰ), K(Ⅰ), Ca(Ⅱ) and Mg(Ⅱ) in AlCl3-BMIC ionic liquid electrolytes even though the concentration is up to2000mg/L. The aluminum deposits whose purity is higher than99.8%are obtained at cathode via electrolysis industrial aluminum alloy which aluminum purity is75.33wt%. The current efficiency is kept above93.8%, and the energy consumpution is in the range1.59-1.82kW·h/kg-Al. The metal impurities of secondary aluminum can be removed almost by electrorefining. It is indicate that electrorefining aluminum with AlCl3-BMIC ionic liquid is feasible.The effects of water on the properities of AlCl3-BMIC ionic liquid have been investigated. The results show that the AlCl3-BMIC ionic liquid viscosity increases and electrical conductivity decreases with water content increasing. The deposits from ionic liquid with water became more compact and grain size decreases when the water concentration is increased from0to1.39mol/L, but it become loosen when water concentration is up to1.67mol/L. |
PDF Full Text Request