[H-RE13] 資源地質学

[HRE13-09] 硫酸鉛鉱を含む複雑硫化鉱の新規選鉱手法－日本周辺の海底熱水鉱床の将来的な操業に向けて－

*相川 公政¹、伊藤 真由美¹、草野 敦大¹、Jeon Sanghee¹、Park Ilhwan¹、大竹 翼¹、広吉 直樹¹ (1.北海道大学)

キーワード：複雑硫化鉱、海底熱水鉱床、選鉱、硫酸鉛鉱、閃亜鉛鉱

To keep up with the high demand for base metals like Cu, Pb, and Zn, the development of new metal resources is an important issue for the future. Seafloor massive sulfide (SMS) deposits have gained increasing attention because they consist of polymetallic sulfides containing Cu, Pb, Zn, Au, Ag, etc. SMS ores are referred to as modern analogues of volcanogenic massive sulfide (VMS) ores on land (e.g., Kuroko (black ore)) as well as complex sulfides. However, SMS ores obtained from around Japan contain not only common valuable minerals like chalcopyrite (CuFeS₂), galena (PbS), and sphalerite (ZnS), but also soluble minerals like anglesite (PbSO₄) which is not typically contained in complex sulfides. Conventionally, metals are produced from concentrates of each mineral separated from complex sulfides by mineral processing, especially flotation. In practice, flotation of complex sulfide ore is comprised of a two-step process where chalcopyrite and galena are first recovered as froth followed by recovering sphalerite. However, when anglesite coexists like the case of SMS ores, sphalerite would be recovered together with chalcopyrite due to the activation of sphalerite by lead ion released from anglesite. Therefore, the presence of anglesite would make it difficult to separate sphalerite from chalcopyrite and galena in flotation of SMS ores. When the grade of impurities like zinc in copper concentrates increases to more than several percent due to the difficulties in their separation, smelters would not receive the concentrates with high impurities or penalty for impurities would be charged. In addition, anglesite is typically disposed of into the tailings dam and would cause lead pollution in the surrounding environment. Therefore, anglesite contained in SMS ores has detrimental impacts on both economic and environmental sides.
For the development of SMS deposits around Japan, a new approach to solving the problems faced by flotation of SMS ores due to the presence of anglesite was investigated in this study. Prior to flotation, the removal of anglesite by ethylene diamine tetra acetic acid (EDTA) was examined, and the result showed that almost all anglesite (>97%) could be extracted within 30 minutes. When anglesite was extracted by EDTA washing prior to flotation, the recovery of sphalerite decreased from 81% to 28%, while chalcopyrite was well recovered irrespective of EDTA washing. Moreover, Pb²⁺ extracted from PbSO₄ in the leachate after EDTA washing could be recovered as metallic lead by the cementation using zero-valent iron (ZVI) as a reductant.