Recovery of Metal Resources from Wastes using Thermal Plasma

本研究的目的是处理从焚化炉产生的飞灰，并利用反应热等离子体从飞灰中回收金属资源。作为一项基础研究，采用热氩等离子体在加入四种气体的条件下处理五种金属氧化物。通过对产物和残余样品的分析，以及对吉布斯自由能变化的计算，推测了反应等离子体与金属氧化物的反应机理。结果表明，反应通道按以下反应进行分类；样品内热分解、表面反应、气相热分解、气相反应。进一步研究了反应机理。选择氧化镁、二氧化硅和氧化铝作为金属氧化物，在热氩等离子体中加入氢。在氧化镁和二氧化硅处理中，氢的加入促进了氧化物样品的减少。质量下降速率与氢浓度根和氢原子发射强度成正比，说明氢原子参与了反应。镁砂等离子体处理可回收镁，但硅不能从二氧化硅中回收。综合实验结果、平衡组成和表面温度，提出了还原和蒸发两种反应机理。在氧化铝处理中，没有观察到样品的重量变化，因为氧化铝在估计的表面温度下热力学稳定。研究将继续使用混合金属氧化物样品，最后提出等离子体处理粉煤灰的回收工艺。

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.