Strontium adsorption and desorption reactions in model drinking water distribution systems

Divalent cationic strontium (Sr²⁺) adsorption to and desorption from iron corrosion products were examined in two model drinking water distribution systems (DWDS). One system was maintained with chlorine-disinfected drinking water and the other with the same water with secondary chloramine disinfection. Flow conditions simulated primary transmission lines (constant flow) and residential mains (periods of stagnation). Accumulation of Sr²⁺ to iron corrosion products in model DWDS was independent of disinfection type. Adsorption and desorption mechanisms are discussed. X-ray adsorption near edge structure (XANES) spectroscopy and linear combination fitting determined Sr²⁺ was primarily associated with iron oxyhydroxide corrosion products. At the end of the desorption study, the amount of Sr²⁺ remaining in iron corrosion products equilibrated to approximate levels observed at the end of the constant flow adsorption experiments. These results suggest that enhanced iron corrosion product loading of Sr²⁺ during stagnation could be short lived under constant flow conditions. Differences between adsorption and desorption based on disinfection type (chlorine versus chlorine plus chloramine) cannot be used to control Sr²⁺ desorption.