Chloride Removal from Stormwater and Lakes Impacted by Road Salt Application: Experimental Assessment of Friedel’s Salt Reactions

Road salt (e.g., NaCl) application in cold-temperature
regions
has increased Cl– concentrations in freshwater.
Removing Cl– from water is challenging because it
is highly soluble. This paper is the first to demonstrate and characterize
the removal of Cl– from stormwater via Friedel’s
salt (Ca4Al2(OH)12Cl2(H2O)4) precipitation (FSP), achieved by adding calcium
oxide (CaO) and sodium aluminate (NaAlO2). Laboratory tests
were done on Cl– removal with FSP using a range
of Ca/Al/Cl ratios in deionized (DI) water and stormwater samples
impacted by road salt. Even the lowest doses resulted in significant
removal of Cl– with maximum removal rates for comparable
Ca/Al/Cl ratios of 72% and 84% in stormwater and DI water, respectively.
Temporal experiments in stormwater and DI water indicate that most
of the Cl– removal occurred within the first 10
min of reaction time. Potential applications of FSP were demonstrated
for two hypothetical scenarios based on a well-characterized, salt-impacted
lake. The first scenario indicates that a 30% reduction in stormwater
Cl– mass is sufficient to maintain concentrations
below 150 mg/L. A second scenario with an initial 300 mg/L lake water
concentration shows the potential for implementing FSP in low-flow
pump and treat systems for the rehabilitation of road-salt-impaired
lakes.