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Alternative TitleExploratory Research on Manufacture of Alumina by Potassium Hydroxide Sub-molten Salt
Thesis Advisor张懿 ; 张亦飞
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword氧化铝   一水硬铝石   koh亚熔盐   水合铝酸钾   赤泥
Abstract我国铝土矿资源主要以中低品位、难溶的一水硬铝石为主,铝硅比在4~7间的矿约占总储量的80%。近年来随着我国氧化铝生产规模和技术水平不断提高,我国铝土矿资源进一步贫化,高品位铝土矿资源已逐渐减少。本论文针对我国特有的中低品位一水硬铝石型铝土矿资源,为解决我国氧化铝工业普遍存在的能耗高、投资大以及高碱赤泥污染严重等瓶颈问题,进行了氢氧化钾亚熔盐法制备氧化铝的探索研究与过程优化。本文在以下几个方面取得创新性进展:(1)研究了氢氧化钾亚熔盐法处理一水硬铝石型铝土矿的溶出行为,考察了反应温度、碱矿比、初始KOH溶液浓度、反应时间及添加CaO对溶出过程的影响。实验研究结果表明:在反应温度220 oC、碱矿质量比1.5、初始KOH溶液浓度50 wt%、反应时间1 h的优化条件下,Al2O3的回收率可达到81.4%,赤泥的铝硅比降至1.06。(2)溶出后赤泥中的主要含硅物相是KAlSiO4,溶出过程不需要添加CaO,该工艺所得赤泥量少、矿物普适性强。(3)首次研究了水合铝酸钾初级成核动力学,根据经典成核理论解释了初级均相成核和初级非均相成核两种不同机制,在313 K ~ 353 K内,水合铝酸钾晶体在过饱和铝酸钾溶液中的液固界面张力具有较低的温度相关性,平均值为2.1 mJ/m2;通过单核-多核模型和表面熵因子的判定,证实水合铝酸钾晶体生长过程符合连续生长机理。(4)系统研究了结晶温度和溶液过饱和度对水合铝酸钾晶体形貌的影响,获得的晶体形貌包括十二面块状体、八边形片状及其复合结构、六边形片状及其复合结构,并归纳了不同晶体形貌的转化规律。在不同温度、较低过饱和度下,水合铝酸钾晶体以大尺寸的十二面块状体形貌从溶液中析出;在较低温度、较高过饱和度下,水合铝酸钾晶体以小尺寸的片状形貌从溶液中析出。(5)采用水化学法对赤泥中的氧化铝和氧化钾进行回收。在反应温度260 oC、碱矿比10:1、初始KOH溶液浓度 20wt%、CaO与赤泥中SiO2的摩尔比2:1,反应时间2 h条件下,终赤泥中K2O含量降至3.13%,Al2O3含量降至3.64%。赤泥中的KAlSiO4在稀碱液中与CaO、Fe2O3发生反应,转变为钙铁铝石榴石,达到回收氧化铝和氧化钾的目的。
Other AbstractChinese bauxite resources are characterized by low grade and tough processing diaspore bauxite, which the ore with ratio of alumina to silica between 4 and 7 accounts for about 80% of the total reserves. In recent years, with Chinese alumina production scale and technology level constantly improved, Chinese bauxite resources become further poorly and high grade bauxite reserves decrease greatly. A new green potassium hydroxide sub-molten salt process of alumina manufacture was basically investigated and optimized, which was especially developed to resolve the key problems of high energy consumption, great investment of equipments and pollution of red mud with high alkaline content existing in the alumina industry of China.The achievements and innovative progresses are exhibited as follows: (1) The leaching behavior of diaspore bauxite in potassium hydroxide sub-molten was investigated. The effects of reaction temperature, mass ratio of alkali to ore, initial KOH solution concentration, reaction time and CaO addition were examined. The results indicated that the recovery rate of Al2O3 reached 81.4% and A/S of the red mud decreased to 1.06 under the optimum conditions: reaction temperature at 220 oC, mass ratio of alkali to ore at 1.5, initial KOH solution concentration of 50 wt% and reaction time for 1h. (2) The XRD analysis showed that Si existed in the form of KAlSiO4 in the red mud; no CaO addition was needed in the leaching process. This new process could produce less amount of red mud and have better bauxite adaptation. (3) The primary nucleation of PAT was firstly investigated. According to the classical nucleation theory, the homogeneous and heterogeneous nucleation mechanism was experimentally explained. The interfacial free energy γ of the PAT crystals in the supersaturated potassium aluminate solution at 313 to 353 K had low temperature dependence, with the average value of 2.1 mJ/m2. Normal growth mechanism of PAT crystallization was identified by experiments and the regression of induction times based on the mononuclear and polynuclear model and the surface entropy factor.(4) The effect of nucleation temperature and supersaturation degree of the solution on the morphology of PAT crystallized from supersaturated potassium aluminate solution was systematically investigated. The dodecahedral bulk, the octagonal plate and the composite octagonal plate, the hexagonal plate and the composite hexagonal plate of PAT crystals were reported for the first time. Large size of dodecahedral bulks of PAT crystals preferred to grow in the solution with low supersaturation at various temperatures, while smaller size of plate like crystals did in the solution with high supersaturation at low temperature. (5) A further step to extraction Al2O3 and K2O in the red mud by hydrochemical method achieved good results with 3.13% of K2O and 3.64% of Al2O3 in the final red mud. The KAlSiO4 in the red mud reacted with CaO and Fe2O3 and changed into andradite-grossularite.
Document Type学位论文
Recommended Citation
GB/T 7714
马青霞. 氢氧化钾亚熔盐法制备氧化铝的探索研究[D]. 中国科学院研究生院,2013.
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