Recovery of Metal Resources from Wastes using Thermal Plasma

这项研究的目的是测试焚烧炉产生的飞灰，并使用反应热等离子体从飞灰中回收金属资源。作为基础性研究，对五种金属氧化物进行了添加四种气体的热Ar等离子体处理。通过对反应产物和残留样品的分析以及吉布斯自由能变化的计算，对反应等离子体与金属氧化物的反应机理进行了探讨。结果表明，反应过程可分为样品中的热分解反应、表面反应、气相中的热分解、气相中的反应。并对反应机理进行了进一步的研究。选择氧化镁、二氧化硅和氧化铝作为金属氧化物，在热Ar等离子体中加入氢气。在氧化镁和二氧化硅的处理中，氢气的加入促进了氧化物样品的减少。减重速率与氢浓度的根和氢原子的发射强度成正比，表明氢原子参与了反应。从氧化镁的等离子体处理中可以回收镁，但不能从二氧化硅中回收硅。根据实验结果、平衡组成和表面温度，提出了包括脱氧和蒸发在内的反应机理。在氧化铝处理中，没有观察到样品中的重量变化，因为氧化铝在估计的表面温度下是热力学稳定的。将继续使用混合金属氧化物样品进行研究，最后提出等离子体处理飞灰的回收工艺。

The purpose of the research is to teat flyash produced from a incinerator and to recover metal resources from the flyash using a reactive thermal plasma. As a fundamental study, five kinds of metal oxides were treated by the thermal argon plasma with the addition of four kinds of gases. The reaction mechanisms between the reactive plasma and metal oxides were estimated by considering the analyzes of products and residual sample, and calculation of Gibbs' free energy change. The results showed that the reaction passes were classified according to the following reaction ; thermal decomposition in the sample, surface reaction, thermal decomposition in gas phase, reaction in gas phase. The further study was carried out to elucidate the reaction mechanisms. Magnesia, silica and alumina were chosen as a metal oxide and hydrogen was added into the thermal argon plasma. In the treatments of magnesia and silica, hydrogen addition enhanced the decrease in the oxide samples. The weight decreasing rate was in proportion to the root of hydrogen concentration and the intensity of hydrogen atom emission, suggesting hydrogen atom took part in the reaction. Magnesium was recovered from the plasma treatment of magnesia, however silicon was not recovered from silica. According to the consideration of the experimental results, equilibrium compositions, and surface temperature, the reaction mechanisms was proposed including the deoxidation and evaporation. In alumina treatment, no weight change in the sample was observed because alumina was thermodynamically stable at estimated surface temperature. The study will be continued using mixed metal oxide samples and finally the recovery process in the plasma treatment of flyash will be proposed.