Recycling steel-manufacturing slag and harbor sediment into construction materials

Mixtures consisting of harbor sediment and slag waste from steel industry containing toxic components are fired to produce non-hazardous construction materials. The fired pellets become lighter as firing temperature increases. At a sintering temperature of ≦1050 °C, the fired pellets are in a form of brick-like product, while at 1100 °C, they become lightweight aggregates. Calcium silicate, kyanite, and cristobalite are newly formed in the pellets after firing, demonstrating that calcium oxide acts as a flux component and chemically reacted with Si- and/or Al-containing components to promote sintering. Dioxin/furan content present in the pure slag is 0.003 ng I-TEQ g−1 and, for the fired pellet consisting of slag and sediment, the content appears to be destructed and diminishes to 0.0003 ng I-TEQ g−1 after 950 °C-firing; while it is 0.002 ng I-TEQ g−1 after firing at 1100 °C, suggesting that dioxins/furans in the 950 °C-fired pellets have a greater chance to escape to atmosphere due to a slower sintering reaction and/or that construction of dioxins/furans from molten chloride salts co-exists with their destruction. Multiple toxicity characteristic leaching procedure extracts Cu, Cr, Zn, Se, Cd, Pb, Ba, As, and Hg from all fired products at negligible levels.