The amounts of “Electronic wastes” including heavy metals are increasing day by day. Such waste is in the rich resource of various metals having the precious metals. Therefore, these wastes are considered as urban mine, if people successfully can separate them to each source. In sustainable viewpoints, separation technologies applied for such electronics waste are essential and important to efficiently recover various metals at a low concentration from these sources. This chapter reviews functional adsorbents made of polymers, ionic liquid, and dendrimer. Also, membrane technology is introduced as separation toll for heavy metals. Among them, topics of phytoremediation are made as an effective sustainable method, utilizing certain plants to clean up the environmental contaminants. Here, plants are able to remove harmful chemicals such as metals, which are present in the soil, when their roots absorb water and nutrients from the contaminated soil, sediment and surface, or ground water. The contaminants are removed by trapping them into harvestable plant biomass. Furthermore, cleanup methods of environments and recovery of precious and rare metals are mentioned for sources of urban and submarine mines with low cost and high recovery efficiency.
TopIntroduction
In Brundtland’s Commission, World Commission on Environment and Development in United Nations following has submitted, “sustainable development is development that which meets the needs of the present without compromising the ability of future generations to meet their own needs” (Brundtland, 1987). There are several environmental problems in the sustainable society in coming our future. Among them, the metal elements are heterogeneously distributed all over the earth. Humans have used Au, Ag, Cu, and Fe since the earliest our history. Precious metals, such as Au, Ag, Pt, Pd and so on, are widely used in several fields, for example, in catalysts in various chemical processes, electrical and electronic materials, medicine and jewelry (Ramesh, Hasegawa, Sugimoto, Maki, & Ueda, 2008). Recently, precious metals become very important because various high tech industries require and consume them for advanced technology. Under the circumstance of technological innovation and market expansion, these products strongly are concerned with economic growth. However, the increase in waste has caused environmental problems (He, Li, Ma, Wang, Huang, Xu, & Huang, WEEE, 2006).
The separation and purification of the metals are key technologies needed with reducing the energy consuming to effect the separation processes. In addition, much attention has been paid to the decontamination technologies in the environmental conservation aspects. For instance, adsorption of metal ions using low cost natural adsorbents such as agricultural waste, clay materials, biomasses and seafood processing waste is one of the technologies to maintain the sustainability of the human society (Yang & Zall, 1984). As shown in Figure 1, cycling process of metals in our human society composed of producing and wasting in industries. In these most of things, our life faces many kinds of metals. The metals mainly come from mine and the products have been spread to human societies from industries. In the cycle, “electronic wastes (e-waste)” can be found in discarded computers, office electronic equipment, entertainment electronic devices, mobile phones, television sets, and refrigerators, which are increasing the quantity of disposal day by day. It is important to note that such electronic waste becomes the rich resource of various metals including the precious metals. Therefore, these wastes are considered as urban mine (Sthiannopkaoa & Wongb, 2013). The recycling process of urban ore is different from the smelting process of natural ore, that is, in the points of view of the required energy and material inputs (Yamasue, Minamino, Numata, Nakajima, Murakami, Daigo, Hashimoto, Okumura, & Ishihara, 2009). For example, the amount of the rare metals in urban mines in Japan corresponds approximately to leading natural mines. An estimated 50 million tons of e-waste are produced each year globally as indicated by International Environmental Technology Center (URL2013). The estimation of the accumulated amounts of several elements in Japanese urban mines was Au 16%, Ag 22%, In 61%, Ti 42% and Ta 10% as percentages of the world’s known deposite (Harada, 2008).
Figure 1. Cycling drawing of metals in producing, wasting and removing processes against metal pollutings