Fabrication of Phosphorus Adsorbent by Carbonation of Calcium Hydroxide Derived from Scallop Shell

Abstract

Previously, the authors reported the possibility for the use of scallop shell powder-gypsum composites as a crystallization-type phosphorus remover. However, these composites broke partially on immersing in a phosphorus solution for a prolonged time due to dissolution of gypsum. In this study, in order to improve durability of the composites in the solution, scallop shell powder-Ca(OH)₂-gypsum composites were prepared and carbonated to convert Ca(OH)₂ into CaCO₃. The surface of the carbonated specimens were covered with dense layers composed of fine CaCO₃ particles, and therefore the dissolution rete of Ca from gypsum was reduced. The thickness of CaCO₃ layer increased with increasing number of carbonation. Although the carbonated specimen showed low phosphorus removal properties in the early period due to the low Ca dissolution rete, about 80% of phosphorus was removed after 10 days immersion in 50ppm phosphorus solution because Ca²⁺ concentration gradually increased. Moreover, the carbonation specimen had higher durability compared with the scallop shell powder-gypsum composite in the phosphorus solution.