Phosphate removal and recovery from aqueous solutions using iron-coated steel slag

Abstract

Phosphate pollution from human activities significantly contributes to the eutrophication of aquatic ecosystems. Additionally, phosphorus is a finite, irreplaceable resource, making its management and recovery critical. This study explores the use of iron-coated steel slag (ICS) as a cost-effective material for phosphate removal and recovery from water. Ferric chloride was used to coat electric arc furnace slag via oven drying under various conditions. Batch adsorption tests evaluated phosphate adsorption, and the optimum coating conditions were identified as 0.5–1 mm slag, 0.5 M FeCl₃, and coating pH 1. The effect of solution pH and coexisting ions on phosphate removal were also evaluated. The adsorption of phosphate onto ICS was characterized by the Langmuir isotherm and the pseudo-second-order model and the calculated maximum adsorption capacity of the optimum ICS was 3.99 mg P/g. The optimum ICS achieved cumulative removal capacities of 2.80, 2.71, and 2.65 mg/g over three adsorption cycles in fixed-bed column tests. Sodium hydroxide (0.1 M) effectively desorbed phosphate, with recovery efficiencies of 83.4 %, 72.2 %, and 73.0 % across three cycles. Overall, the results highlight ICS as a sustainable and cost-effective solution for phosphate removal and recovery, contributing to improved stormwater and wastewater management.