铝酸盐结构的稀土荧光粉碱熔机理及应用

发布时间：2018-06-15 11:21

本文选题：铝酸盐结构荧光粉 + 碱熔　；参考：《北京科技大学》2017年博士论文

【摘要】：从废旧稀土荧光粉中回收稀土元素,可以有效解决我们所面临的稀土资源问题。铝酸盐结构的稀土荧光粉具有很好的发光效率和实用价值,是被广泛应用的荧光粉。铝酸盐结构的稀土蓝粉和绿粉结构稳定,难以回收其中的稀土元素,导致稀土回收率低。碱熔是一种有效处理铝酸盐结构荧光粉的工艺手段,两步酸解法工艺主要采用碱熔方法处理难溶废旧荧光粉,有效提高了稀土浸出率。但是现阶段碱熔机理并不完善,碱熔工艺流程还可以进一步改进。本文通过对蓝粉和绿粉碱熔过程的物相分析,计算碱熔反应的活化能,对整个碱熔过程进行热力学分析。通过蓝粉、绿粉分别和不同碱熔剂(KOH,NaOH,Ca(OH)2,NaCl,Na2CO3和Na2O2)的对比反应,从离子作用的角度解释反应过程。本文认为破坏铝酸盐荧光粉的官能团是含氧阴离子(OH-,CO32-,O22-),稀土离子与游离的含氧阴离子结合以逃离结构,导致荧光粉结构被破坏。这一观点可用来解释蓝粉和绿粉中稀土元素的回收原理及移动轨迹。本文在实验分析的基础上,提出阴-阳离子协同作用理论,更加全面的说明铝酸盐荧光粉的碱熔理论。在铝酸盐稀土荧光粉碱熔时,阳离子会取代镜面层的稀土离子,而阴离子的存在会保证取代能够发生,由于电价不匹配,晶体结构发生畸变,结构崩塌。这一理论说明了铝酸盐结构荧光粉结构变化的过程,补充了碱熔的基础理论。通过中试实验和模拟实验的结果,本文评价了两步酸解法工艺的可行性。基于处理1t废旧荧光粉的中试实验结果,经济分析表明产品价值约为直接输入消耗的4倍,说明工艺本身是富有价值的;环境评价指出,工艺对环境最大的影响来自水资源的消耗以及能源消耗产生的温室气体。根据工艺的评价分析,提出了荧光粉除硅预处理,来改进两步酸解法工艺。对废旧荧光粉进行300目物理筛分,可除去56%的二氧化硅,可节省0.215 t的片碱,0.538 t盐酸和0.8 m3的水。废水和废渣的产生量也会相应地减少,由硅酸胶体吸附导致的稀土元素损失也会降低。稀土资源短缺是世界面临的共同问题,从替代、法规、减量和循环等方面对稀土资源管理进行合理安排,加强对基础理论和回收工艺的研究,对我们应对类似的资源短缺问题有重要意义。
[Abstract]:The recovery of rare earth elements from waste rare earth phosphors can effectively solve the problem of rare earth resources. The rare earth phosphors with aluminate structure have good luminescence efficiency and practical value and are widely used as phosphors. The structure of rare earth blue powder and green powder with aluminate structure is stable, so it is difficult to recover rare earth elements, resulting in low recovery of rare earth elements. Alkali melting is an effective process for the treatment of aluminate structure phosphors. The two-step acid hydrolysis process is mainly used to treat refractory waste phosphors, which effectively improves the leaching rate of rare earths. However, the mechanism of alkali melting is not perfect at present, and the technological process of alkali melting can be further improved. In this paper, the activation energy of alkali melting reaction is calculated by analyzing the phase of alkali melting process of blue powder and green powder, and the thermodynamic analysis of the whole alkali melting process is carried out. The reaction process was explained from the point of view of ion action by comparing the blue powder and green powder with different alkali fluxes (Koh) and NaCl-Na _ 2CO _ 3 and Na _ 2O _ 2 respectively. It is considered that the functional group that destroys the aluminate phosphors is the oxygen anion (OH-OH-CO32-O22-N). The rare earth ions combine with the free oxygen-containing anions to escape from the structure, resulting in the destruction of the phosphor structure. This view can be used to explain the recovery principle and moving track of rare earth elements in blue and green powder. On the basis of experimental analysis, this paper puts forward the theory of anion-cation synergistic action, and explains the alkali melting theory of aluminate phosphors more comprehensively. In the alkaline melting of aluminate rare earth phosphors, cations will replace the rare earth ions in the mirror layer, and the existence of anions can guarantee the substitution. Because of the mismatch of electricity price, the crystal structure is distorted and the structure collapses. This theory explains the process of structure change of aluminate phosphors and complements the basic theory of alkali melting. In this paper, the feasibility of two-step acid hydrolysis process is evaluated by the results of pilot and simulation experiments. Based on the pilot experiment results of treating 1 t waste phosphor powder, the economic analysis shows that the product value is about 4 times of the direct input consumption, which shows that the process itself is of great value, and the environmental evaluation indicates that, The greatest impact of technology on the environment comes from the consumption of water and the greenhouse gases generated by energy consumption. According to the evaluation and analysis of the process, the pretreatment of removing silicon from phosphor powder was put forward to improve the two-step acid hydrolysis process. By physical screening of waste phosphors for 300 mesh, 56% of silica can be removed, and 0.215 tons of tablet alkaloid 0.538 t of hydrochloric acid and 0.8 m3 of water can be saved. The amount of waste water and waste residue will be reduced correspondingly, and the loss of rare earth elements caused by silica colloid adsorption will also be reduced. The shortage of rare earth resources is a common problem facing the world. The management of rare earth resources should be rationally arranged from the aspects of substitution, regulation, reduction and circulation, and the research on basic theory and recycling technology should be strengthened. It is important for us to deal with a similar shortage of resources.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ422

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