Phosphorus Removal by Crystallization for Scallop Shell Adsorbent
Kohei YOSHIMURA and Haruhisa SHIOMI
Abstract:The feasibility of recycling scallop shell as an adsorbent was evaluated. Crushed shells were encased in plaster, which acts as a source of calcium. The effects of shell particle size and volume fraction in consolidated body on phosphorus removal capacity were investigated. The crystalline phase precipitated on the scallop shell surface after immersing in KH2PO4 aqueous solution with hydrated gypsum was characterized by powder X-ray diffraction and thermogravimetry-differential thermal analysis. The phosphorus removal capacity of the shell powder -plaster composite increased with increasing the volume fraction of shell powder up to 30vol/%. However, there was little difference in phosphorus removal efficiency between samples containing 30vol/% and 50vol/% shell powder, and these samples removed more than 90% of 50ppm phosphorus in 10 days. Small particle size of shell powder was effective for phosphorus removal. By the use of the shell powder below 0.125mm, more than 80% of 50ppm phosphorus was removed in 4days. The results of XRD and TG-DTA showed that DCPD(CaHPO4E2H2O) precipitated on the surface of the scallop shell and grew with increasing immersion time. It was concluded that the phosphorus removal would proceed through the precipitation of DCPD seed crystals and its growth on the surface of scallop shell. Key Words:Crystallization, Scallop, Phosphorus, Calcium, Consolidated body, DCPD crystal