While precious metals such as Au, Ag, Pt, and Pd are finite materials, they are essential for electronic components and functional materials. Therefore, it is important to separate and extract the necessary precious metals from the final products and recycle them as high-purity precious metals in order to secure resources and reduce costs. Impurities, which must be controlled, include light elements such as carbon, sulfur, oxygen, and nitrogen. For example, Au (gold) used in electronic devices must be at least 99.999% pure.