Phosphate Recovery from Synthetic Urine with Shell of Mizuhopecten yessoensis

Abstract

Calcium phosphate can precipitate from phosphate in urine and calcium carbonate, which is the main component of Mizuhopecten yessoensis shells. Precipitation tests, analyses of SEM-EDS and XRD were carried out to study the formation of calcium phosphate from the shells and synthetic urine, to identify the products, and to investigate the effect of operation conditions on the form of the obtained products. Two precipitation processes were observed at low Ca/P and at high Ca/P ratios. The former involved an increase in pH and a decrease in concentrations of phosphate and calcium to form dicalcium phosphate dihydrate (DCPD), while the latter involved three steps: 1. a rapid increase in pH and a decrease in the concentrations of phosphate and calcium to form DCPD, 2. a decrease in pH and an increase in the phosphate concentration, causing to change the crystal structure into poorly crystallized apatite, and 3. an increase in pH. The observations of the particle surface by SEM-EDS and powder XRD analysis of precipitates were consistent with these phenomena. Elemental analysis of the cross section of particles showed that the reaction that formed calcium phosphate started from the particle surface and then progressed to inside the particles.