Marine manganese tailings concrete: advantages and drawbacks

Korea, India and China are moving ahead with plans to develop a marine manganese nodule industry. This industry or a related manganese crust, hydrothermal manganese or existing terrestrial manganese industry will dispose millions of tons of fine grained manganese waste. This disposal presents a significant environmental liability. An ideal solution would be to use this material for a beneficial purpose. One area which uses enough material to offer this potential is aggregate for concrete. A range of experiments using manganese tailings as the fine grained aggregate in concrete were undertaken at the University of Hawaii. These showed that tailings additions in the range of 20% added a series of useful properties to the concrete. These properties included increased strength, decreased porosity, increased density, increased resistance to erosion and increased resistance to algal growth. The last property was of particular significance as it means that the manganese concrete has an inherent antibiofouling capacity. This is meaningful in the construction of pond liners or for use in the marine environment. These results will be highlighted in the presentation. Apart from all these benefits there is a significant drawback to using manganese. This is manganese toxicity. Recent studies have indicated a considerable danger of manganese neurotoxicity in humans at much lower levels than was previously considered. Of particular risk is airborne manganese as a dust or metal fume. Current tailings pond disposal practices used at many mines are unsafe. Handling practices initially envisioned for marine mining operations will never be permitted