Abstract
In laboratory experiments using powder converter slag (particle size, 53-75 μm), produced in steel production process, the removal of phosphorous in sea water was examined. The elution of a small amount of phosphorous in the slag was also examined, because the slag contains the small amount of phosphorous.
About 30% of phosphorous originally contained in the slag was possibly eluted in sea water. The net phosphorous removal by the slag was expressed by the Freundlich absorption isotherm at pH7,8 under both aerobic and anaerobic conditions. Although the isotherm was valid for lower phosphorous concentration at pH9, higher removal efficiency was achieved at higher phosphorous concentration due to the precipitation of calcium phosphate. Most of the phosphorous adsorbed on the slag (77%) was held without elution, suggesting chemical adsorption.
Examination of slag surface by a X-ray microanalyzer indicated that (1) the slag could De divided into 3 regions (A, B and C) with relatively the same percentages, (2) phosphorous in the slag was originally contained in the C region, which consisted mainly of CaO and SiO2, and (3) phosphorous removal was also achieved in the C region.
To confirm phosphorous removal in sea water, converter slags of 1cm cube were submerged on the bottom sediments in a bay for nearly 2 years. Phosphorous removal was achieved in the C region, not only on the surface but also at 5mm deep into the slag. P2O5 content in the C region increased from 3.0% to 6.0% (surface) and to 5.2% (5mm deep) after 692 days.
