Phosphate removal from aqueous solutions using slag derived from hydrogen plasma reduction of red mud

In this study, the possibility of using slag derived from hydrogen-plasma reduction of red mud (H 2 RMS) as a low-cost adsorbent for phosphate removal from aqueous solutions was investigated. Batch adsorption experiments were conducted to evaluate the effects of contact time, solution pH, sorbent dosage, and initial phosphate concentration under controlled laboratory conditions. Phosphate concentrations were determined spectrophotometrically using the ammonium molybdate method. These results demonstrated that phosphate adsorption onto H 2 RMS is strongly pH-dependent, with maximum removal efficiency achieved under acidic conditions (pH ≈ 2). Adsorption equilibrium was achieved after approximately 18 h of contact time. Increasing the sorbent dosage enhanced phosphate removal efficiency, although improvements became marginal beyond a dosage of 10 g/L. At optimal conditions, phosphate removal efficiency of approximately 90% was achieved. These findings indicate that H 2 RMS shows significant potential as an effective adsorbent for phosphate removal, offering a possible pathway for the valorization of metallurgical waste residues.