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

Decomposition of perchlorate (ClO) in subcritical water in the presence of steel slag, a by-product of the steel industry, was investigated. Reactivity of ClO was low in pure subcritical water state up to 300 °C, whereas adding steel slag efficiently accelerated the decomposition of ClO 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 ClO 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 ClO and the amount of Cl leached from the slag. This method was successfully applied to decompose ClO 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 SO than ClO.