AlCl₃-BMIC离子液体电解精炼铝中杂质行为研究

【作者】 裴启飞；

【导师】 华一新；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2012， 博士

【摘要】 随着铝需求量的不断攀升和铝矿产资源的日益枯竭,铝的再生问题越来越受到人们的重视,尤其是再生铝的提纯问题已成为发展再生铝工业的研究热点。再生铝原料绝大部分是铝合金,通过目前的熔炼方法很难完全除去其中的金属杂质,主要通过再生处理生产铸造铝合金,大大限制了再生铝的应用范围。而采用离子液体电解精炼再生铝提纯得到金属铝可以扩大再生铝的应用范围。本文以x(AlC13)=0.667的AlCl3-BMIC室温离子液体作为电解质应用于再生铝的电解精炼,系统研究了再生铝中主要杂质金属及水在离子液体电解精炼铝过程中的行为。铝电极在AlCl3-BMIC离子液体中的阳极极化研究表明,铝电极电化学溶解会产生阳极钝化,阐明了AlCl4-浓度降低和Al2Cl7-浓度升高导致固体AlCl3在电极表面析出阻碍铝溶解的钝化机理,增加搅拌、升高温度、降低x(AlCl3)均有利于增加阳极极限氧化电流密度。恒电位库伦分析结果表明,再生铝中杂质金属Mn、Zn、Fe、Ni、Pb、Cu在AlCl3-BMIC离子液体中阳极氧化时,Mn、Zn、Fe、Ni、Pb以二价离子的形式,而Cu以一价离子进入离子液体。进一步测定了Zn(Ⅱ)/Zn、Pb(Ⅱ)/Pb、Fe(Ⅱ)/Fe、Cu(Ⅰ)/Cu、Ni(Ⅱ)/Ni相对与Al(Ⅲ)/Al参比的平衡电极电势,分别为0.02、0.21、0.32、0.63、0.64和0.86V；且发现它们的电化学活性顺序也与水溶液的Mn>Zn>Fe>Ni>Pb>Cu不同,为：Mn>Zn>Pb>Fe>Cu>Ni。测定了不同温度下Mn、Cu、Zn、Fe、Pb、Ni在AlCl3-BMIC离子液体中的腐蚀速率。在323-363K温度范围内,金属的腐蚀速率由大到小的顺序为Mn>Cu>Zn>Fe>Pb>Ni;而超过363K时,Ni的腐蚀速率超过了Pb。Mn、Cu、Zn、Fe、Pb、Ni在离子液体中的腐蚀活化能分别为52.23、66.42、53.02、50.42、41.11、60.55kJ/mol。电化学分析表明,进入离子液体中Cu(Ⅰ)、Zn(Ⅱ)和Ni(Ⅱ)对阴极Al(Ⅲ)的电还原具有去极化作用；Fe(Ⅱ)和Pb(Ⅱ)表现为极化作用；Mn(Ⅱ)浓度低于50mg/L时,表现为去极化作用,浓度为100mg/L时,呈现极化作用；Li(Ⅰ)、Na(Ⅰ)、K(Ⅰ)、Ca(Ⅱ)、Mg(Ⅱ)对Al(Ⅲ)的电还原影响不显著。采用恒电流电解精炼Al-Cu、Al-Zn、Al-Fe、Al-Mn、Al-Ni和Al-Pb合金,阴极铝纯度超过99.9%;离子液体中Li(Ⅰ)、Na(Ⅰ)、K(Ⅰ)、Ca(Ⅱ)、Mg(Ⅱ)浓度即使达到2000mg/L,电沉积铝时也不会在阴极析出；另外,电解精炼再生铝合金(铝含量为75.33wt%),在铜基体上得到了纯度超过99.8%的金属铝,电流效率超过93.8%,直流电单耗在1.59-1.82kW·h/kg-Al之间,再生铝中各主要金属杂质均可通过电解精炼除去。因此,离子液体电解精炼铝是可行的。随着含水量的增加,AlCl3-BMIC离子液体的黏度增加、电导率降低。恒电流电沉积实验表明,离子液体中含水量不超过1.39mol/L时,水的存在可以细化沉积层铝颗粒,改善铝的沉积层质量,使沉积层变的致密均匀,当含水量较高达至1.67mol/L时,沉积层变得疏松、易脱落。更多还原

【Abstract】 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.更多还原