Alkali elution behavior of steelmaking slag into seawater by batch test

Synopsis : Kinetic study was carried out in order to clarify effects of slag properties and operation factors on alkali elution of steelmaking slag component into artificial seawater. The seawater was rotated by an impeller in a cylindrical vessel and time change in pH was measured by pH meter. Operating factors such as vessel diameter, seawater volume, slag volumes, rotating speed were varied for various slag diameter and composition. [OH-] increased lineally in the early stages of the experiment. From a theoretical study on pH buffering ability of carbonate in the seawater, it was found that the double-digit [Ca²⁺] increase was achieved compared with [OH-] and that [Ca ²⁺]/[OH-] was kept almost constant. As alkali increase in the seawater resulted from dissolved free CaO of the steelmaking slag, its rate proceeded at the constant rate. When slag diameter was too small, alkali elution rate decreased because the penetration of the seawater in the lower part of slag layer was insufficient, whereas when slag diameter was too large, it also decreased due to the decrease in interfacial area of reaction. Alkali elution rate increased according to 1/3 power of liquid circumferential velocity, increased with free CaO content in steelmaking slag within about 2 % and decreased with an increase in ratio of dredged soil.