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Scale Formation Under Blended Phosphate Treatment for a Utility With Lead Pipes
Author(s) -
Wasserstrom Lauren W.,
Miller Stephanie A.,
Triantafyllidou Simoni,
Desantis Michael K.,
Schock Michael R.
Publication year - 2017
Publication title -
journal ‐ american water works association
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.466
H-Index - 74
eISSN - 1551-8833
pISSN - 0003-150X
DOI - 10.5942/jawwa.2017.109.0121
Subject(s) - amorphous solid , corrosion , materials science , scanning electron microscope , aluminium , chemical engineering , phosphate , metallurgy , lead (geology) , amorphous calcium phosphate , solubility , calcium , chemistry , composite material , geology , crystallography , organic chemistry , geomorphology , engineering
US corrosion control practice often assumes that the orthophosphate component of blended phosphate corrosion inhibitors causes the formation of low‐solubility lead–orthophosphate solids that control lead release into drinking water. This study identified the solids that formed on the interior surface of a lead service line and a galvanized steel pipe excavated from a system using a proprietary blended phosphate chemical. The scale was analyzed by X‐ray diffraction, X‐ray fluorescence, and scanning electron microscopy/energy dispersive spectroscopy. Instead of crystalline lead–orthophosphate solids, a porous amorphous layer rich in aluminum, calcium, phosphorus, and lead was observed at the lead pipe scale–water interface. Thus, the mechanism inhibiting lead release into the water was not a thermodynamically predictable passivating lead–orthophosphate scale, but rather an amorphous barrier deposit that was possibly vulnerable to disturbances. Galvanized pipe scales showed relatively crystalline iron and zinc compounds, with additional surface deposition of aluminum, phosphorus, calcium, and lead.