Long-term Alkali Elution Behavior from Steelmaking Slag into Seawater by an Open Channel Vessel

Abstract

Steelmaking slag has been used in the coastal area for the purpose of the environmental improvement. Short-term alkali elution behavior induced by free CaO in the steelmaking slag was investigated by a batch and continuous vessel. In this study, long-term alkali elution experiments were done in an open channel vessel with a slag box to make clear the decreasing mechanism of the alkali elution from steelmaking slag into seawater. The experimental period was 44 d (1056 h). The pH values increased just in the beginning of the experiment, and then gradually decreased in about 100 min. They showed almost the same value as that of seawater in 1200 min. As the experimental time passed, the white deposits on the steelmaking slag layer, which were composed of Mg[OH] 2 and CaCO 3 , spread to the lower slag zone in the slag box. The white deposit zone of larger slag size was more rapidly diffused downward than that of smaller one due to larger voidage in the slag layer. While carrying out the batch test with the used slag by the long-term experiment, the alkali elution rate of slag layer on the open channel flow was 0.03-0.11 times decreased compared with the unused slag, whereas that of the lower positioned slag layer was 0.10-0.38 times decreased. From these results, it was found that the alkali elution rate was reduced by the white deposit on the steelmaking slag.