Fractionation of Phosphorus in Steelmaking Slags and Aquatic Particulate Materials Using a Sequential Extraction Technique

We measured the concentrations and chemical forms of phosphorus (P), an essential nutrient in marine ecosystems, in steelmaking slag (Slag) to determine whether use of Slags as a basal medium for artificial tidal flats and seagrass beds was an environmentally acceptable option for the reuse and recycling of Slags. We tested six Slag samples, including dephosphorization slags and converter slags. The total P concentrations were one order of magnitude higher in the Slags than in the aquatic particulate materials. We used a sequential extraction technique in which the strength of the extractants was increased stepwise in order to separate the P pools in the Slags into four fractions; exchangeable P, Fe (III)-bound P, authigenic P-like component, and detrital P-like component. We considered P contained in the first two fractions to be easily mobilized under the conditions found in some marine environments, such as the highly reduced zones of subsurface sediments. The mobile P accounted for 55–660 μmol P g–1 and for 56–81% of the total P in the Slags. The results strongly suggested that Slags have substantial potential to function as a P source that could sustain biological productivity in artificial tidal flat and seagrass bed ecosystems. On the other hand, Slags also have the potential to mitigate intense and rapid release of P from basal media, because mechanisms exist for adsorption and co-precipitation of phosphate with major components of Slags, including iron, calcium, and magnesium.