Utilization of steel-making slag for the uptake of ammonium and phosphate ions from aqueous solution

Steel-making slag, a waste by-product of the Steel Industry, constitutes a major disposal problem. In the present study, excellent adsorbent materials for reducing eutrophication in wastewaters have been prepared from this slag. Heated samples of acid-treated slag and mixtures of slag with kaolinite and Al(OH)₃ were examined to determine their uptake capacities for NH₄⁺ and PO₄^3- from aqueous solutions. In general, the equilibrium pH of the solution increased in comparison to initial pH with the uptake of target ions, the sample activated slag-Al(OH)₃ showing the smallest change. The highest PO₄^3- uptake capacity was obtained with the slag-Al(OH)₃ mixture heated at 900 °C whereas the highest uptake of NH₄⁺ was found in the slag-Al(OH)₃ mixture heated at 800 °C. The uptake rates for PO₄^3- and NH₄⁺ by the slag-Al(OH)₃ mixture heated at 900 °C were 2.91 and 0.65 μmol/(g min), respectively. It was shown that heating slag composites prior to incorporation into wastewater treatment filters resulted in an increased degree of NH₄⁺ and PO₄^3- uptake.