Steelmaking slag is artificially produced to remove, among others, the phosphorus from molten steel; approximately 120 kg of slag is formed per ton of steel. At present, steelmaking slag is mostly used for road construction and civil engineering materials. However, the slag cannot be sold at a high price and, in advanced countries, its market for civil work is shrinking and regulations to protect the environment are becoming more severe. There are two solutions to the problem of steelmaking slag: one is to decrease the generation of slag, and the other is the development of reuse methods. In this paper, the measures to decrease slag formation are first discussed based on the mass-balance calculation, and then the present and future states of slag valorization in Japan are reviewed. In the first part, the importance of the hot-metal dephosphorization process and the recycling of decarburized slag is clarified. In the second part, as a new field of slag valorization, the use of slag in marine environments is explained. Several studies to extract phosphorus and manganese from slag were also introduced.
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