Effects of pH on phosphorus removal capacities of basic oxygen furnace slag

•BOF-slag had high PRCs at acidic, neutral and alkaline pH.•Chemical extraction was used to analyze effects of pH on phosphorus removal paths.•Weak adsorption and Ca-P precipitates were main removal paths at alkaline pH.•Adsorption on Fe-oxys was main removal path at neutral and acidic pH.

Phosphorus removal capacities (PRCs) of basic oxygen furnace slag (BOF-slag) in different pH ranges were investigated using batch experiments. The fractions of different phosphorus containing compounds in fresh and reacted BOF-slag were measured by chemical extraction methods. Fresh and reacted BOF-slag was characterized through combining several methods. The results show that BOF-slag had high PRCs (21–30 mg P/g) and that the PRCs of BOF-slag at alkaline pH were comparable to the ones at neutral and acidic pH. At alkaline pH, phosphorus removal occurred via both the weak adsorption onto BOF-slag and the precipitation of calcium phosphates. At neutral and acidic pH, phosphorus removal was achieved through the chemical adsorption onto Fe containing minerals in BOF-slag. Influences of the pH on weakly bound phosphorus, Ca associated phosphorus, and Fe associated phosphorus in the reacted BOF-slag were also discussed in detail.

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