CONVERSION OF BLAST FURNACE SLAG INTO HYDROGARNET FOR HUMIC ACID REMOVAL

Abstract

The discharge of humic acid in aqueous environments is a key health and esthetic issue. In this study, blast furnace (BF) slag, a byproduct of iron- and steel-making plants, is converted into a hydrogarnet product under a hydrothermal reaction for humic acid removal. The BF slag is pulverized and passed through sieves of four different sizes, i.e., 100, 100–300, 300–500, and 500–1000 μm. Subsequently, these BF slags are added to NaOH, KOH, and LiOH solutions with 1–4 M NaOH solution/BF slag (= 20, 10, and 4 mL/g) and heated at 80, 120, and 160 °C for 24 h, with or without Al(OH)₃ addition. In the absence of Al(OH)₃, portlandite is synthesized in alkali solutions, and the highest crystallinity of portlandite in the product is obtained in 3 M NaOH at 160 °C. With the addition of Al(OH)₃, katoite, which is a hydrogarnet, as well as tobermorite and hydroxy sodalite are synthesized from BF slag. As the NaOH solution/BF slag ratio increases, the peaks of hydroxy sodalite and tobermorite increase, whereas those of katoite decrease. As the BF slag size decreases, the peaks of katoite increase because of the increase in Ca supply from the BF slag. The product, including katoite, can remove humic acid.