Estimating the variability of steel slag properties and their influence in phosphorus removal ability

Steel slag has been proven to be an effective phosphorus (P) removal media, and a potential aid to mitigate point and nonpoint P pollution in freshwater systems. However, the behavior of steel slag as a P sorption material (PSM) is often oversimplified through the generalization of its chemical and physical properties, preventing proper design of P removal structures. In this work, we tested eighteen steel slag samples from different batches, production processes, and steel-making plants, for the purpose of relating slag origin and chemical and physical properties to P removal ability, under two different flow regimes. Slag samples were also coated with aluminum (Al) and tested for P removal. Characterization included elemental composition, particle density, buffer capacity, and P removal ability. There was great variability in the evaluated properties across slag sources and origin, compelling the individual characterization of steel slag samples, since their intrinsic characteristics were key variables in determining their potential P removal capacity. Specifically, electrical conductivity (EC), bulk density, particle density and magnesium (Mg) content could explain around 70% of the variability of P removal by uncoated steel slags. Increasing residence time (RT) always increased P removal for uncoated slags. Steel slags showed a high variability in their P removal ability, but such variability was considerably decreased by coating the slags with Al. Additionally, the Al-coating process significantly improved P removal performance under more rapid flows (lower RT).