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复盐脱水制备含无水氯化镁的熔盐及其电解性能研究
Alternative TitleStudy on the preparation of anhydrous MgCl2-containing molten salt via dehydration of the complex salts and its electrolytic
张志敏
Subtype博士
Thesis Advisor卢旭晨
2013-05-01
Degree Grantor中国科学院研究生院
Degree Discipline化学工艺
Keyword六水氯化镁   复盐脱水   熔盐电解   金属镁   镁合金
Abstract盐湖、地下卤水和海水的利用过程中产生大量的老卤(主要成分为水氯镁石,MgCl2?6H2O),排放的老卤对环境造成严重的污染。本论文研究利用六水氯化镁制备含无水氯化镁的熔盐,进而电解制备金属镁及镁合金。首先,对六水氯化镁脱水过程中氧化镁和羟基氯化镁的生成与转化进行了基础研究;在此基础上,以六水氯化镁为原料,研究了复盐脱水制备含无水氯化镁的熔盐;通过电解制备金属镁和镁合金的实验研究,评价了复盐脱水制备的熔盐的电解性能。 首先,研究了六水氯化镁脱水过程中羟基氯化镁和氧化镁的生成与转化。结果表明,六水氯化镁在250 ℃、300 ℃、350 ℃和380 ℃脱水时水解生成的主要产物分别为MgOHCl?1.5H2O、MgOHCl?0.8H2O、MgOHCl?0.5H2O和MgOHCl;羟基氯化镁在MgOHCl-NH4Cl固相体系中加热至一定温度时可转化为无水氯化镁。六水氯化镁加热脱水过程中氧化镁的生成主要途径如下:① 400 ℃以上羟基氯化镁分解生成氧化镁;② 无水氯化镁在400 ℃以上与空气中的水蒸气和氧气反应,生成氧化镁;氧化镁可在MgO-NH4Cl固相体系中加热至一定温度时转化为无水氯化镁。探索了无水氯化镁高温下对空气的敏感性。在高温下无水氯化镁对氧气和水蒸气的敏感性非常强,迅速转化为氧化镁;通过有效地隔绝无水氯化镁与空气的接触,可避免无水氯化镁在高温下转化为氧化镁。 研究了六水氯化镁在MgCl2?6H2O-NH4Cl固相体系中通过复盐进行脱水的过程,机理如下:水合氯化镁与氯化铵在300 ℃左右形成复盐NH4Cl?MgCl2?nH2O(6>n≥0),复盐的形成减弱了结晶水与氯化镁的结合,在加热脱水时抑制或减弱了水解反应的发生,可获得氧化镁含量为0.02%的无水氯化镁。 研究了六水氯化镁在MgCl2?6H2O-NH4Cl-NaCl-KCl体系中加热脱水过程,脱水机理如下:300 ℃左右时形成复盐NH4Cl?MgCl2?nH2O(0≤n<6),减弱了氯化镁与结晶水的结合,在加热脱水过程中抑制了水解反应的发生;当温度为400 ℃时,生成复盐KMgCl3;当温度为500 ℃时,生成三元复盐K3NaMgCl6;复盐KMgCl3和K3NaMgCl6在高温较稳定,不易与空气中的氧气和水蒸气发生反应,抑制了无水氯化镁水解反应的发生,保证了产物的纯度;当温度升至550 ℃以上时,复盐体系变为熔体,熔体进一步隔绝了无水氯化镁与氧气和水蒸气的接触,进而得到了高纯度的含无水氯化镁的熔体(氧化镁的含量可达0.016%(以100%氯化镁当量计),完全满足电解镁工业对原料的要求)。 研究了六水氯化镁复盐脱水制备含无水氯化镁熔盐的电解性能。结果表明,电解制备的金属镁纯度大于99%,电流效率大于96.5%,能耗可控制在9000 kW?h/t以下,产品的能谱分析和阴极的XRD分析并未检测到氧元素和氧化镁;同时以六水氯化镁和合金元素的水合氯化物或氧化物为原料,探索了复盐脱水-电解制备镁合金的方法,结果表明,制备的镁合金(Mg-Li、Mg-La、Mg-Zn、Mg-Mn、Mg-Ca、Mg-Zn-Ca、Mg-Li-La)合金元素分布的均匀性良好,电流效率均在80%以上。
Other AbstractThe use of salt lakes, subsurface brine and seawater will produce a great quantity of brine (major constituent is MgCl2?6H2O), which will cause considerable impact on the environment. In this thesis, we prepared anhydrous MgCl2-containing molten salt with MgCl2?6H2O, and then used electrochemical method to prepare magnesium metal and magnesium alloys. Firstly, we carried out basic research into the formation and transformation of MgO and MgOHCl in the process of dehydration of MgCl2?6H2O. Secondly, we prepared the anhydrous MgCl2-containing molten salt by dehydration of the complex salts and by using MgCl2?6H2O as raw material. Finally, we evaluated the electrolytic properties of the molten salt (which was prepared by dehydration of the complex salts) through preparing magnesium metal and magnesium alloys by electrochemical method. At first, we studied the formation and transformation of MgO and MgOHCl in the process of dehydration of MgCl2?6H2O. The results showed that the major products of dehydration of MgCl2?6H2O at 250 ℃、300 ℃、350 ℃ and 380 ℃ were MgOHCl?1.5H2O、MgOHCl?0.8H2O、MgOHCl?0.5H2O and MgOHCl. MgOHCl was transformed into MgO in the MgOHCl-NH4Cl solid state system at certain temperature. There were two main processes of MgCl2?6H2O transformed into MgO by dehydration of MgCl2?6H2O: ① MgOHCl decomposed into MgO at above 400 ℃; ② Anhydrous MgCl2 reacted with O2 and H2O, and produced MgO at above 400 ℃; MgO was transformed into MgCl2 in the MgO-NH4Cl solid state system at certain temperature. We also explored the sensitivity of anhydrous MgCl2 to ambient atmosphere at high temperature. Anhydrous MgCl2 was very sensitive to O2 and H2O at high temperature, and was transformed into MgO rapidly. Therefore, by isolating anhydrous MgCl2 from ambient atmosphere, we can avoid the formation of MgO at high temperature. Secondly, we studied the complex salts dehydration process of MgCl2?6H2O in MgCl2?6H2O-NH4Cl solid state system. The reaction mechanism were as follows: MgCl2?6H2O reacted with NH4Cl at about 300 ℃, and produced NH4Cl?MgCl2?nH2O (6>n≥0). The formation of complex salts weakened the bond between H2O and MgCl2 and suppressed the hydrolysis reaction while heating. The content of MgO in anhydrous MgCl2 could achieve 0.02%. Thirdly, we studied the dehydration process of MgCl2?6H2O in MgCl2?6H2O-NH4Cl -NaCl-KCl system. The dehydration mechanism were as follows: MgCl2?6H2O reacted with NH4Cl at about 300 ℃, and produced NH4Cl?MgCl2?nH2O (0≤n<6). The formation of the complex salts weakened the bond between H2O and MgCl2 and suppressed the hydrolysis reaction while heating; KMgCl3 was formed at about 400 ℃; K3NaMgCl6 was formed at about 500 ℃; KMgCl3 and K3NaMgCl6 didn’t react with H2O and O2 in ambient atmosphere at high temperature, which could suppress the hydrolysis reaction and guaranteed the purity of the products. The complex salts was transformed into anhydrous MgCl2-containing molten salt at above 550 ℃, which could further isolate anhydrous MgCl2 from H2O and O2 in ambient atmosphere and guarantee the purity of the molten salt (the content of MgO in anhydrous MgCl2 could achieve 0.016%, which could meet the challenge of electrolytic magnesium industry) Finally, we studied the electrolytic properties of the anhydrous MgCl2-containing molten salt which was prepared by dehydration of the complex salts with MgCl2?6H2O. The results showed that the purity of the magnesium metal obtained was above 99%, Current efficiency was above 96.5% and energy consumption was under 9000 kW?h/t. The EDS analysis and XRD analysis of the cathodic deposit showed that element O and MgO could not be detected; we explored the dehydration of complex salts-Preparation of magnesium alloys by electrochemical method using MgCl2?6H2O. The results showed that the distribution of the alloying elements in the magnesium alloys obtained were uniform. The current efficiency was above 80%.
Pages149
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/8280
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
张志敏. 复盐脱水制备含无水氯化镁的熔盐及其电解性能研究[D]. 中国科学院研究生院,2013.
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