Zero-waste processing of polymetallic deep-sea nodules from the German license for complete manganese recovery

This dissertational thesis details the development and investigation of a pyrometallurgical process to extract valuable metals from polymetallic deep-sea manganese nodules (PMN) with an emphasis on a zero-waste goal. The continually increasing demand for industrially and technologically important metals has once again given focus onto deep-sea resources as a viable metal-source. The deep-sea nodules found in abundance on the sea floor mainly contain the industrially important metal manganese. Additionally, they contain enriched amounts of nickel and copper as well as other valuable extractable metals such as cobalt and molybdenum, whose demand has increased significantly in the past decades.The study of the state-of-the art in PMN processing shows that in most cases a three-metal processing scenario is pursued. In these processes only nickel, copper and cobalt are extracted and produced as marketable products. This is true especially for hydrometallurgical processes. These approaches leave more than two-thirds of the processed deep-sea nodules unused, which would mean an enormous amount of waste to be landfilled and are thus very questionable from an ecological perspective. This makes a pyrometallurgical process with a zero-waste target advantageous.A three-stage reduction process is proposed. In the first stage the use of optimised slag design for a complete separation of the manganese bearing stream in the slag and the extraction of an iron alloy containing all valuable metals (nickel, copper, cobalt and molybdenum) is demonstrated in models and verified experimentally. Additionally, the manganese enriched slag allows the duplex extraction of both ferro- and silicomanganese, which could be experimentally verified. The optimized first stage to extract target metals from PMN in a FeNiCuCo alloy showed that fluxing is essential to achieve a high manganese separation in the slag and simultaneously improved extraction rates (> 95% Ni, Cu, Co). Manganese is concentrated in the slag and reduction rates are well below 2%. As a second stage thorough laboratory trial series for selective FeMn reduction have conclusively shown that the production of a standard HC ferromanganese is conceivable. Optimally, reduction temperature is between 1520 – 1560°C. The resulting FeMn slag holds MnO concentrations of 25 – 35 wt%, making a duplex extraction of SiMn in the third stage realizable. Best results in terms of Si-extraction were achieved at 1650 – 1700°C. MC silicomanganese was successfully generated from the FeMn slag showing that the adaptation of the industrial duplex process is transferrable to the treatment of enriched manganese PMN slag. The produced calcium-silicate slag is heavy metal free and comparable to slags from industrial manganese smelting operations or steel blast furnace slags. Thus, the zero-waste approach could be realised scientifically