Appraisal of gastropod shell as calcium ion source for phosphate removal and recovery in calcium phosphate minerals crystallization procedure

On the basis of the perspective of wastes recycling and minimization of cost of phosphate removal via the chemical precipitation procedure, the present studies evaluated the ability of waste biogenic Gastropod shell to serve as a source of Ca2+ ion in the removal and recovery of phosphate in calcium phosphate mineral (CPM) crystallization procedure. Phosphate removal efficiency values >99% was achieved when 2 g of snail shell was used in water of phosphate concentrations ranging between 25 and 1000 mg/L. pH and ionic strength exhibited no influence on the phosphate removal efficiency. Concomitant removal of phosphate and organic matter revealed that phosphate removal efficiency was not impacted but the magnitude of the organics removed increased with increase in the organic load. Kinetic analysis showed that second order kinetic model gave a better description of the process. XRD analysis of the derived sludge showed the crystallinity and peaks synonymous with the presence of whitlockite, hydroxyapatite and calcium phosphate hydrate. The FTIR of the sludge showed the disappearance of some naturally occurring functional groups and the appearance of phosphate peaks which confirmed the formation of CPM.

► SS is used for the removal and recovery of P and concomitant removal of organics. ► pH, ionic strength and organic load had no impact on the removal efficiency. ► CPM crystallization process is well described by second order kinetic equation. ► The FTIR spectra of the sludge confirmed the formation of CPM. ► XRD analysis of the sludge showed that the CPM is crystalline.