Improvement of desulfurization efficiency of Al-rich ladle furnace refining slag with an aqueous carbonation method by hydrothermal or ultrasound pretreatment.

Ladle furnace (LF) slag is a type of steel slag, which has limited applications due to its high S content. Aqueous carbonation is a prospective method for desulfurization of the LF slag. However, the Al-rich LF raw slag has very low desulfurization efficiency with carbonation method. This study investigated the improvement of desulfurization efficiency of the Al-rich LF slag with carbonation method by hydrothermal (HP) or ultrasound pretreatment (UP). The results showed that CAH was formed in pretreated slags because of CA hydration, which could remove part of S. After carbonation, most of the CAH in pretreated slags produced crystalline CaCO bonded by amorphous Al(OH) (the other reaction product) in 10 min. In the carbonation process, S removal was mainly determined by carbonation efficiency. The S content was reduced to about 0.40% for the pretreated slags from 1.04% in the raw slag. By contrast, the S content was reduced to only 0.93% for slag without pretreatment under the same carbonation conditions. The possible reason of the improvement of desulfurization efficiency by HP or UP was the formation of thin plate-like CAH, which increased the surface area available for carbonation reaction. The UP slag presented slightly lower S content than the HP slag because high ultrasound energy increased the reactivity of CaSiO.