海底熱水鉱石の金属溶出特性―海底鉱物資源開発における環境影響評価―

抄録

Seafloor massive sulfide (SMS) deposit is expected to be an available metal resource; however, it might become a potential source for metal-containing drainage around mining areas to generate metal cations and acids by their oxidative dissolution. In this paper, we reviewed the metal mobilization from various hydrothermal sulfides into seawater and discuss the possibility of metal rich seawater generation during SMS-mining operation. The results from leaching experiment using natural hydrothermal sulfide in seawater showed the metal dissolution behaviors were significantly different with the initial oxidation states of the hydrothermal sulfide surfaces. The non-oxidized samples (i.e., non-exposed to atmosphere) primarily and gradually released Zn and Pb into seawater, whereas the oxidized hydrothermal sulfides rapidly released various metals (Mn, Cu, Zn, As, Cd, Pb) into oxic seawater within several minutes. The result suggests the hydrothermal sulfides in each mining process would have different metal dissolution potentials; once the sulfides are oxidized by air and oxic seawater during lifting from seafloor to the vessel, various metals and metalloids can be released rapidly if the oxidized sulfides are spilled into the ocean.