Calcium orthophosphate, amorphous

Phosphate is sometimes present in MU water sources (say, 1-2 ppm or more) usually as a result of field and factory run-off or from the deliberate addition as a city water threshold agent to prevent corrosion and deposition in the mains. The steady growth in the reuse of secondary water sources such as municipal and industrial waste waters means that phosphate is increasingly likely to be present in MU. If the phosphate remains undetected, it likely will scale and foul FW lines by forming amorphous calcium orthophosphate [tricalcium phosphate Caj(P04)2] sludge before it reaches the boiler section. 

Calcium phosphate will ordinarily precipitate at concentrations typically exceeding 5 ppm PO4 or less, forming amorphous calcium orthophosphate (tricalcium phosphate) sludge, Ca3(P04>2, in the bulk water and crystalline hydroxyapatite, Caio(OH)2(P04)2, at heat-transfer surfaces. 

Dorozhkin, S.V. (2012) Amorphous calcium orthophosphate nature, chemistry and biomedical applications. Int. J. Mater. Chem., 2 (1), 19-46. 

Heughebaert, J.C. (1977) Contribution a l etude de revolution des orthophosphates de calcium precipites amorphes en orthophosphates apatitiques. Ph.D. thesis. Institut National Polytechnique, Toulouse, France. 

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