Inhibitory effect of nitrite on iron sulfide dissolution at high pH

Oxidation reactions of iron sulfide-bearing aggregates have been increasingly recognized as a significant cause of concrete deterioration worldwide. Yet there is a lack of mitigation strategies to control the reactions. This work investigates the effectiveness of nitrate- and nitrite-based admixtures in inhibiting the dissolution of iron sulfides (pyrrhotite and pyrite) in highly alkaline environments, the first step of the deleterious reactions in concrete. Although the addition of nitrate was not found to exhibit a profound influence, the use of nitrite significantly slowed down the dissolution, reducing the overall dissolution extent by nearly 90%. Solid characterization indicated that nitrite may accelerate the formation of a protective passive layer that acts as a diffusion barrier and inhibits further dissolution. The findings demonstrate the potential of nitrite as an inhibiting admixture for controlling iron sulfide dissolution, offering new avenues for developing practical mitigation strategies for related deterioration in concrete.