Comparison of Batch and Column Leaching Conditions for the Environmental Assessment of Waste Foundry Sands Intended for Media Contact Recycling

Driven by the global sand crisis, waste foundry sand (WFS) is increasingly valorized as an alternative aggregate, which makes evaluating its ecological safety important. Regulatory approval usually rests on a single leaching test, which may not represent the range of conditions to which WFS can be exposed. Here, 17 WFS samples were evaluated using three standardized batch tests—neutral water (KLT), an organic acid fluid (TCLP) and an inorganic acid fluid (SPLP)—and an up-flow column test reproducing the conditions under which WFS is assessed for media contact recycling in the Republic of Korea; the column eluates were used for the bioassay. Metal release depended on the test applied, the organic acid condition generally yielding the higher concentrations. Columns packed with 100% WFS could not be completed for seven of the 17 samples and blending with standard sand at 50:50 by volume reduced this to three, indicating that the fine fraction limits the applicability of the procedure. Acute ecotoxicity (Daphnia magna) was resolved in 21 column eluates: 11 showed no effect and 10 were toxic, with four of them above the 2 TU criterion applied to this route. Toxicity was not associated with the metal concentrations measured in the same eluates, nor with phenol, and blending did not reduce it consistently. The physicochemical factors that the test standard requires to be checked before a bioassay—eluate pH, ammonia, conductivity, residual chlorine, turbidity and hardness—were measured and none of them accounts for the responses; speciation excludes un-ionized ammonia in particular. The ecotoxicity of the eluate actually assessed, and the feasibility of obtaining it, may therefore both need review when WFS is evaluated for recycling.