Fouling due to Calcium Phosphate

Calcium phosphate scaling occurrence is largely reported in reverse osmosis (RO) applications for the reclamation of wastewater (Chesters 2009; Greenberg et al. 2005; Zach-Maor et al. 2008). In municipal wastewater, phosphate levels typically range between 3 and 20 ppm, presenting a major operational challenge for systems designed to operate at high product recoveries. The crystalline forms of calcium phosphate are hydroxyapatite and fluorapatite, which are calcium orthophosphates with varying amounts of OH-, Cl-, and F-groups. Formation of hydroxyapatite occurs through autocatalytic solution-mediated transformation of highly unstable amorphous calcium phosphate, hydrolyzing rapidly to more stable hydroxyapatite microcrystals in water. The lifetime of metastable amorphous phase is strongly governed by the exact solution environment, with the presence of other additive molecules and ions, pH, ionic strength, and temperature affecting the lifetimes. The transformation of amorphous to...