Polymetallic nodule contains considerable amount of valuable metals, such as nickel cobalt and copper etc., it, therefore, can be future important metal supply. The survey of polymetallic nodule covering wide area of CCZ (Clarion Clipperton Zone) was conducted from the 1980s, then, DORD signed the exploration contract with ISA in 2001, and has been continuing the survey. Not only resource survey, various research and development of mining and processing technologies have been conducted during that period. This paper describes a review of Japanese research and development that have been conducted for recovering valuable metals from polymetallic nodules, and problems and improvements of some processes of smelting and hydrochloric acid leach method are discussed.

It was known that polymetallic nodules could not be treated by the conventional process, the same as terrestrial resources, the processing technology of the manganese nodule, therefore, was studied actively from 1970s in the world. Various studies including examinations by laboratory work were conducted for processing of polymetallic nodules mainly during the periods from 1989 to 1995 in Japan. At first, for developing the suitable metallurgical method of polymetallic nodule, five promising methods were selected from various methods of already existing in the world at that time and they are:

  1. Gas reduction and ammoniacal leaching,

  2. Cuprion ammoniacal leaching,

  3. HCl reduction roast and acid leaching,

  4. High temperature and high pressure H2SO4 leaching, and

  5. Smelting and H2SO4 leaching. Out of these five methods, three methods were selected for making further improvement and smelting and hydrochloric acid leach method was finally selected. This paper includes results of re-consideration of each process of the smelting and chlorine leaching method from a viewpoint of total optimization. The results of examination for finding possibility of incorporating REE recovery with this method were, also, given in this paper.

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