1. 1) National institute for Materials Science: Rare metal Tokushu, http://www.nims.go.jp/research/elements/rare-metal/urban-mine/index.html, (2014/2/24).
2. 2) T. Shiratori and T. Nakamura: Journal of MMIJ 123 (2007) 171–178.
3. 3) J. Shibata and A. Okuda: Journal of the Mining and Materials Processing Institute of Japan 118 (2002) 1–8.
4. 4) Y. Iguchi, T. Azakami, S. Banya, A. Kikuchi, K. Sugimoto and T. Yamamura: Extractive Metallurgy, (The Japan Institute of Metals, 1999) p.166.
5. 5) National Institute for Materials Science: Estimation of CO2 Emission and Energy Consumption in Extraction of Metals, Information of Strategic Natural resources, http://www.nims.go.jp/genso/0ej00700000039eq-att/0ej00700000039j5.pdf, (2014/2/24).