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−.