Desorption properties of heavy metals from cement hydrates in various chloride solutions

• We investigate desorption of Pb from cement pastes in chloride solutions.
• A linear relationship is obtained between the adsorption and the desorption amount.
• A small quantity of Pb is desorbed with NaCl, KCl, and LiCl solution.
• A large quantity of Pb is desorbed with CaCl2⋅2H2O solution.
• Cumulative desorption amount of Pb increases by repeating desorption process.

A leaching test of heavy metals for concrete does not take into consideration the long-term deterioration and exposed environments of concrete. Therefore, it is necessary to understand the behavior of heavy metals in concrete exposed to various situations. It is supposed that cement concrete containing heavy metals are exposed to chlorides such as de-icing salt when reused as roadbed materials as well as seawater when used as coastal structures. In this study, the adsorption and desorption properties of cement pastes in various chloride solutions were investigated. Pb was used as the metal for the sorption tests. The results indicate that after lead ions have been adsorbed on the cement hydrate, a large quantity of Pb desorbed from the cement hydrate in a calcium chloride solution, while a very small quantity of Pb desorbed in deionized water and in lithium, sodium, and potassium chloride solutions. In particular about 70% of Pb desorbed when 35% and 40% of calcium chloride solutions were used.