STRATEGIES FOR PROCESSING OF OCEAN-FLOOR MANGANESE NODULES

This paper reviews state-of-the-art technologies available in the lite rature on the treatment of marine maganese nodules. There are, in gene ral, two ways of treating manganese nodules to extract valuable metals such as manganese, nickel, cobalt and copper. They are pyrometallurgi cal treatment and hydrometallurgical treatment. In pyrometallurgical t reatment, nodules are heated along with certain reagents such as chlor ine, sulfur dioxide or other reducing agents. In such processes, resul ting roasted products are frequently subjected to hydrometallurgical t reatment to extract metal values in subsequent steps. On the other han d, hydrometallurgical treatment involves relatively low temperature le aching with reagents such as acids or ammonia, with or without reducin g agents. Autoclave leaching at a temperature above the boiling point of water with acids or ammonia is also regarded as a hydrometallurgica l treatment. Advantages and short-falls of various processes treating manganese nodules are discussed in this paper, Acid leaching is very e ffective in extracting nickel, cobalt and copper selectively, but acid consumption is relatively high due to acid soluble components include d in nodules. This technology provides in general good recoveries of n ot only nickel, cobalt and copper but also rare elements. On the other hand, ammoniacal leaching is selective for these three metals but may not be able to extract other rare elements. High temperature autoclav e leaching is very attractive due to fast rate and excellent selectivi ty but maintenance of the autoclave could be costly. It can be conclud ed that pyrometallurgical processes are usually effective in recoverin g manganese, nickel, cobalt and copper, but they require high energy d ue to high moisture content of nodules.