Fabrication of Phosphorus Adsorbent by Waste Gypsum Board

Abstract

From a viewpoint of creation of a recycling society, it is essential to establish a method for recycling waste gypsum boards because large amount of gypsum board are scrapped with rehabilitation of architectural structure. In this study, we tried to reuse the gypsum board as a phosphorus adsorbent. Test pieces cut out from a commercial gypsum board were immersed in Na₂CO₃ aqueous solutions of various concentrations to precipitate CaCO₃ as crystallization sites of calcium phosphate on the surface of the specimens. The amount of CaCO₃ precipitated on the surface increased with increasing Na₂CO₃ concentrations. Therefore, the specimens carbonated in the highly concentrated Na₂CO₃ aqueous solution showed the higher removal ratio in the early stage of phosphorus removal, but the surface layer of the specimens peeled off after long-term immersion in the phosphorus solution due to the dissolution of gypsum. On the other hand, the specimens carbonated in a dilute Na₂CO₃ aqueous solution showed the lower phosphorus removal ratio in the early stage of phosphorus removal but kept the original shape even after long-term immersion in the phosphorus solution. The phosphorus removal efficiency after immersion in the phosphorus solution for 10 days was about 95% regardless of Na₂CO₃ concentration, that is, the amount of CaCO₃ precipitate on the surface of the specimens.