Impact of pH, Temperature and Alkalinity on Lead Carbonate Solubility

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Lead carbonate is a white insoluble compound with the chemical formula PbCO3. It is highly corrosive and is used in the manufacture of lead paint, anticorrosion coatings, cosmetics, colored glaze, and dope for tin-lead plating. It is insoluble in cold water, but soluble in hot, acidic solutions. It is incompatible with strong oxidizing agents.

The formation and destabilization of corrosion scales in distribution systems is the main source of lead contaminating drinking water. Many of the parameters that affect this process such as pH, alkalinity, chlorine content and oxidation reduction potential (ORP) are influenced by temperature.

Numerous studies have shown that low pH values increase the corrosivity of water and lead concentrations while high alkalinity levels limit lead dissolution. This is due to the fact that lead complexes formed with hydroxide and carbonate ions are insoluble in the water.

This article aims to investigate the impact of pH, temperature and alkalinity on lead carbonate solubility by performing multiple sets of batch dissolution experiments. Cerussite and hydrocerussite, which are the major dissolved lead species in distribution systems, were used as test species and their dissolution behavior was investigated at different pH values (7.0 – 9.5), temperatures (5 °C vs 20 °C) and alkalinity levels.

The results show that the dissolved lead concentrations of hydrocerussite and cerussite in both alkaline and acidic conditions fluctuated over 45 days. This is most likely caused by frequent transformation of the two species to each other and/or their interaction with free chlorine or alkalinity, which can alter the kinetics of the reaction.