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近年来，半导体照明（LED）市场规模不断扩大，一方面铟、镓、铜等稀有稀贵金属需求剧增，另一方面其生产与消费过程产生大量的固体废弃物，资源利用效率低。究其原因，过程中产生的固体废弃物的理化特性复杂，定量化解析方法缺乏，资源回收效率低、选择性差。针对这些问题，本论文以LED生产和消费过程固体废弃物为对象开展系统研究，主要研究内容如下：(1) 采用SEM、XRD、EDS、FT-IR及XPS等表征技术，系统表征了金属有机化学气相沉积（MOCVD）废料。MOCVD废料物相组成相对单一，主要是由GaN和铟单质相组成；由于GaN是难溶/熔耐火材料，使得MOCVD废料资源回收难度增加；空气氛围中，热化学信息表明废料发生持续氧化，难溶/熔GaN在800 °C下转变为溶于酸碱的Ga2O3，说明氧化焙烧预处理能够实现废料中镓元素的回收再利用；浸出性表明碱浸能够实现镓元素的选择性浸出；(2) 系统开展了碱浸工艺选择性浸出MOCVD中镓元素。在最佳工艺参数：2 mol/L NaOH浓度，固液比为100 g/L，搅拌速率为500 rpm，反应温度为353 K，浸出时间180 min，镓的浸出率为90.01 %，镓选择性为98.98 %；通过调节浸出液pH，实现Ga(OH)3的沉淀率为99.98 %；(3) 综合分析不同浸出动力学模型的适用范围及其与实验结果的一致性，对碱浸体系的表观动力学进行分析。研究发现：该体系属于未反应收缩核心模型，其控速步骤为反应物通过产物层界面的扩散控制，实验条件下镓元素浸出的反应表观活化能为24.33 kJ?mol-1。 (4) 引入金属关键性评价中资源参数和技术参数以及材料可循环性评价中统计熵和品位等级概念，建立金属可回收性评估四象限图和八象限图，根据固体废弃物所处的象限，综合考虑其回收次序。结果表明：与其它固体废弃物相比，LED处于中等回收难度区域，其中绿色高强度LED位于四象限图中第一象限，具有高资源性和高技术性，经济角度优先考虑回收；蓝色高强度LED具有低回收难度，技术角度优先考虑回收。;With the continuous market expansion of semiconductor lighting (light emitting diode, LED), the demand for rare metals (such as indium, gallium and copper) has been increasing. Additionally, the quantities of the solid waste generated in the production and consumption processes have also been enlarging, and the resource utilization efficiency during these processes is low. The reason for that is the complex physical and chemical properties of such waste, the lack of the quantitative analysis method, the low resource recycling efficiency and the low selectivity. In order to deal with these problems, the solid waste generated in the process of LED production and consumption stage is systematically studied in this paper. The main research contents are as follows:(1) The Metal organic chemical vapor deposition (MOCVD) dust was systematically characterized by SEM, XRD, EDS, FT-IR and XPS. The results show that the physical phases composition of MOCVD waste is relatively simple, mainly composed of GaN and indium elemental phase; The presence of GaN and metallic indium increases the recycling difficulty because of refractory GaN; The thermochemical shows that continuous oxidation occurred during the procedure of analysis, GaN can be converted into Ga2O3, which is soluble in acid or alkaline solution, suggesting that oxidative roasting pretreatment can realize the recovery and reuse of MOCVD. Leaching behaviors indicate that alkaline leaching can achieve the selective leaching gallium from MOCVD dust;(2) Selectively leaching gallium from MOCVD dust using alkaline solution was carried out systematically. Under the optimal parameters: NaOH concentration of 2 mol/L, the solid-to-liquid ratio of 100 g/L, the rotation rate of 500 rpm, the reaction temperature of 353 K, the leaching time of 180 min, the leaching rate of gallium is 90.01% and the selectivity is 98.98%. Through adjusting the pH of the leaching solution, Ga(OH)3 can be obtained and the precipitation rate is 99.98%.(3) Through analyzing the applicability of different leaching kinetic models and their consistency with the experimental results, the apparent kinetic of the alkali leaching system was studied. The results indicate that the leaching system belongs to the unreacted shrinkage core model, and its rate-controlled step is the diffusion control of the reactants through the interface of the product layer. The apparent activation energy of the leaching reaction under the experimental conditions is 24.33 kJ?mol-1.(4) Based on the two index i.e. resource index and technology index in the metal criticality and the two concepts, i.e. statistical entropy and grading in the material recyclability, the four-quadrant map and eight-quadrant map of resource recovery assessment were established, achieving the comprehensive evaluation of metal recycling from end-of-life LED. The results show that LEDs are in the middle recycling difficulty area compared with other solid wastes. Among which, green high-intensity EDLs, locating in the first quadrant in the four-quadrant map, have high resource and technology index, the recycling priority should prefer from the perspective of economic, while blue high-intensity LEDs should be considered first from the point of view of technology owing to the low recycling difficulty.
|方升. LED行业含镓固体废弃物资源化的基础研究[D]. 中国科学院大学,2019.|
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