Synthesis of Hydrocalumite-like Compound from Blast Furnace Slag by Alkali Fusion using Waste Molten-Slag Heat, and Its Anion Removal Ability

Abstract

Blast furnace (BF) slag is a byproduct of iron- and steel-making plants and is produced by the forced cooling of the 1500°C molten state. The ability to create value-added products from BF slag has become an important sustainability issue. In this study, we converted this slag into a hydrocalumite-like compound capable of removing pollutant ions from water through alkali fusion using the waste heat of the melting slag. The molten slag was transformed into a precursor with reactive phases by alkali fusion at 1500°C, after which the cooled melting slag was crushed and added to distilled water containing NaAlO₂ and stirred at room temperature to produce the hydrocalumite-containing product. The effects of the type of alkali salt, the Na₂CO₃-to-slag mixing ratio (Na₂CO₃/slag ratio), heating time, amount of added NaAlO₂, and the ability of the product to remove certain ions from aqueous solution were examined. Na₂CO₃ was used to alkali fuse slag at 1500°C, and the optimal conditions for the synthesis of hydrocalumite were found to include a Na₂CO₃/slag ratio of 2:1, a heating time of more than 10 min, and a 60 g/L concentration of NaAlO₂. The product was shown to remove more F^– and PO₄^3– than BF slag. These results suggest that a hydrocalumite-like adsorbent capable of removing pollutant ions from aqueous solution can be synthesized from BF slag through alkali fusion using waste slag-production heat.