Precipitation: insoluble silicates, mechanism

Hock and colleagues [13] have suggested a more complex mechanism to explain why cement stabilizes lead the formation of lead carbonates. When cement is added to water, the carbonates are soluble. Meanwhile, the lead ions become soluble because lead hydroxides and lead oxides dissociate. These lead ions react with the carbonates in the solution and precipitate as lead carbonates, which have limited solubility. Over time, the environment in the concrete changes the lead carbonates dissolve, and lead ions react with silicate to form an insoluble, complex lead silicate. The authors point out that no concrete evidence supports this mechanism however, it agrees with lead stabilization data in the literature. 

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