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

Authors: SCOTT, ISIS - Purdue University; Penn, Chad

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2021
Publication Date: 3/11/2021
Citation: Scott, I.C., Penn, C.J. 2021. Estimating the variability of steel slag properties and their influence in phosphorus removal ability. Chemosphere. 276. Article 130205. https://doi.org/10.1016/j.chemosphere.2021.130205.
DOI: https://doi.org/10.1016/j.chemosphere.2021.130205

Interpretive Summary: Dissolved phosphorus (P) losses to surface waters are considered the main cause of surface water eutrophication, such as Lake Erie. P removal structures are large landscape-scale filters for treating drainage water before reaching a surface water outlet. Steel slag is a common P sorption material (PSM) use to filter dissolved P from non-point drainage. Although this material has been used in several P removal structures, there is tremendous variability in P removal among different steel slags. This study examined the variability in P removal among different slags and determined how chemical and physical characteristics can dictate P removal. Slag was also coated with Al in an attempt to increase the P removal capacity. Depending on the steel making process that resulted in co-production of the slag, properties such as total Ca, Mg, electrical conductivity, pH, and particle size varied, causing P removal to vary as well. For regular non-treated slag, P removal could be predicted based on measurements of P electrical conductivity, which is a measurement of total dissolved ions, bulk density, particle density, and total Mg. Treating the slag with Al always increased P removal when tested under fast flow rates (short retention time). These results will be useful in choosing the proper source of slag for P removal structures, as well as the decision regarding Al treatment of slag.

Technical Abstract: 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).