Lead contamination in water distribution systems has raised great concerns in US, and adding phosphate can lower the dissolved lead concentrations in tap water. However, lead phosphate precipitates can transport along pipes and their stability is controlled by aggregation. In this study, dynamic light scattering (DLS) was used to investigate the formation and aggregation of lead phosphate particles under various aqueous conditions, including varied total PO4/Pb ratios, ionic strength (IS), pH, in the absence/presence of substituting ions and natural organic matter (NOM). Hydroxylpyromorphite (Pb5(PO4)3OH) was identified to be the main mineral phase by Raman spectroscopy and grazing-incidence wide-angle X-ray scattering (GIWAXS). At neutral pH conditions, the aggregation of lead phosphate particles was inhibited in solutions with high total PO4/Pb molar ratios (&gt; 1), due to phosphate adsorption which made the particles highly negatively charged. This observation indicated that addition of excess amount of phosphate can lower dissolved Pb concentration, meanwhile, increase the stability of lead phosphate particles. The presence of divalent cations (Ca2+ and Mg2+) promoted the aggregation of lead phosphate particles as their adsorption on the particles neutralized the surface charges. The presence of NOM (humic acid and fulvic acid) retarded aggregation of lead phosphate particles, primarily due to steric repulsion caused by the adsorption of NOM onto the particles. Such observations indicated that hardness control and organic removal can affect the efficiency of phosphate addition on lead control. Our findings provided useful information about the formation and aggregation of lead phosphate particles under varied aqueous environments, which can help predict the fate and transport of Pb in lead pipes, therefore aiding the optimization of corrosion control strategies.

Formation and aggregation of lead phosphate nanoparticles: Implication for lead immobilization in water distribution systems

256th National Meeting (2018)

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