Study On Electrolytic Refining Of Aluminum In AlCl₃/urea Ionic Liquid

With the increasing amount of aluminum scrap,the issue of aluminum regeneration has attracted attention.At present,the smelting method is usually used to recycle aluminum scrap,but this method has problems such as high-temperature,multiple processes and exhaust gas pollution,which makes the green recycling technology of aluminum scrap become the research hotspot.In recent years,the electrorefining of aluminum alloy scrap in ionic liquids has received widespread attention,but traditional ionic liquids generally suffer from the disadvantages of expensive raw materials and complex synthesis.Ionic liquid analogs are a new type of green solvent with significantly lower raw material costs than traditional ionic liquids,and the synthesis is simple.Herein,aiming at the problems existing in smelting method and traditional ionic liquid purification of aluminum alloy scrap,this paper proposed a new method to recover aluminum by electrorefining aluminum alloy scrap in Al Cl₃/urea ionic liquid analogs（ILAs）.The physicochemical properties of Al Cl₃/urea ILAs,the anodic dissolution behavior and cathodic reduction process of aluminum and co-existing impurity metals in Al Cl₃/urea ILAs,the effect of process parameters on electrorefining of aluminum-silicon alloy scrap,and the influence mechanism of the presence of impurity metal ions in electrolyte on the electrorefining of aluminum were systematically investigated.The main research results are as follows:（1）When the Al Cl₃/urea molar ratio≥1.1:1.0,the main anions in the electrolyte were Al Cl₄^-and Al₂Cl₇^-,and the electrolyte was Lewis acidic.As the molar ratio of Al Cl₃/urea increased from 1.1:1.0 to 1.6:1.0,the melting point gradually decreased,the conductivity firstly increased and then decreased,reaching the maximum at 1.3:1.0,and the viscosity firstly decreased and then increased,reaching the minimum at 1.3:1.0.The highest cathodic current efficiency and lowest energy consumption were obtained by electrolysis of aluminum in Al Cl₃/urea ILA with a molar ratio of 1.3:1.0.（2）Aluminum passivation occurred during electrochemical dissolution in Al Cl₃/urea（1.3:1.0）ILA.The surface of the dissolved aluminum anode was porous and microporous uniformly,and the generation of Al Cl ₃（s）contributed to the passivation in the aluminum anode dissolution process.The dissolution process of aluminum in Al Cl₃/urea（1.3:1.0）ILA was the charge transfer at aluminum/electrolyte interface→the spontaneous formation of passivation film on electrode surface→the generation of soluble aluminum complex ion layer.（3）The major metals in aluminum alloy,Al,in the form of trivalent,Mn,Zn,Pb,Fe,Ni,in the form of divalent,Cu,in the form of monovalent,and Si,in the form of tetravalent ions,entered into Al Cl₃/urea（1.3:1.0）ILA.The equilibrium electrode potentials of co-existing impurity metals Mn,Zn,Pb,Cu,Fe,Ni and Si relative to Al（III）/Al were 0.03,0.20,0.27,0.60,0.65,0.87,and 1.65 V.The order of metallic activity of the co-existing impurity metals in the electrolyte was:Mn>Zn>Pb>Cu>Fe>Ni>Si.（4）The reduction of Al（III）in Al Cl₃/urea（1.3:1.0）ILA was a quasireversible process controlled by diffusion.The mechanism by which the presence of impurity metal ions Mn（II）,Zn（II）,Pb（II）,Cu（I）,Fe（II）,and Ni（II）in Al Cl ₃/urea（1.3:1.0）ILA affected the aluminum electroreduction showed that Mn and Al can be readily deposited as alloy,whereas Zn,Pb,Cu,Fe,and Ni can be deposited both as mono metals as well as alloys of Zn,Pb,Cu,Fe,Ni and Al.（5）The optimum process parameters for electrorefining YL113 aluminum-silicon alloy scrap in Al Cl₃/urea（1.3:1.0）ILA were T=333 K,i=5 m A·cm^-2,r=400 r·min^-1,and t=2 h.Under the optimum process parameters electrorefining YL113 aluminum-silicon alloy scrap,the cathode current efficiency was 93.39%,the energy consumption was1.883 k W·h·kg^-1-Al,and the product aluminium purity was 99.6595%,which reached the national industrial pure aluminum purity standard.（6）The presence of trace impurity metal ions Mn（II）,Zn（II）,Pb（II）,Cu（I）,Fe（II）,and Ni（II）in Al Cl₃/urea（1.3:1.0）ILA caused them to precipitate at cathode,reducing product aluminum purity,decreasing cathode current efficiency,increasing energy consumption,and promoting the growth of product aluminum on（111）crystal plane.The presence of Mn（II）,Pb（II）,Fe（II）and Ni（II）in the electrolyte increased the cell voltage,the presence of Zn（II）decreased the cell voltage,and the presence of Cu（I）had little effect on the cell voltage.The presence of Mn（II）,Cu（I）and Fe（II）favored the product particle size refinement,the presence of Zn（II）and Pb（II）decreased the product densification,whereas the presence of Ni（II）had little effect on the product.