Efficient decomposition of perchlorate to chloride ions in subcritical water by use of steel slag.

Decomposition of perchlorate (ClO4-) in subcritical water in the presence of steel slag, a by-product of the steel industry, was investigated. Reactivity of ClO4- was low in pure subcritical water state up to 300 °C, whereas adding steel slag efficiently accelerated the decomposition of ClO4- to Cl-, with no leaching of heavy metals such as chromium and other environmentally undesirable elements (boron and fluorine). When the reaction was performed in subcritical water at a relatively low temperature (250 °C) for 6 h, virtually all ClO4- ions were removed from the reaction solution. The concentration of Cl- after the reaction was well accounted for by the sum of the amount of Cl- ascribed to the decomposition of ClO4- and the amount of Cl- leached from the slag. This method was successfully applied to decompose ClO4- in water samples collected from a man-made reflection pond following a fireworks display, even though these samples contained much higher concentrations of Cl- and SO42- than ClO4-.