The treatment of Basic Oxygen Furnace (BOF) slag with concentrated solar energy

•The treatment of BOF (Basic Oxygen Furnace) slag with concentrated solar energy (CSE) was investigated.•BOF slag is characterized by its high free lime and iron contents which limits its use in construction and cements.•Concentrated solar energy would allow treating BOF slags to give them new uses.•CSE allows obtaining a product with neither free lime nor free magnesia.•Iron oxides from BOF slags can be transformed into magnetic iron oxides using CSE. Basic Oxygen Furnace (BOF) slag is one of the sub-products generated in the steelmaking process. This waste is characterized by its free lime and free magnesia contents that limit its application in construction. Moreover, the iron content in BOF slag of 14–30 wt% is a quantity which is problematic in the manufacture of cements. On the other hand, BOF slag is a source of available iron in the steelmaking industry. Concentrated solar energy offers a great potential in high temperature applications, so we used it to treat BOF slag. In this way, the slag was treated to stabilize it combining the free lime and free magnesia to give other phases (silicates, aluminates, and complex oxides), but also to transform iron into a magnetic phase that could be recovered through magnetic methods. The results demonstrate that the free lime and free magnesia reacted with silicates, aluminates, and ferrites to form stable phases which are not hydrated in the presence of water. Due to this, the treated BOF slag might find application in the construction industry. Furthermore, the iron was transformed into magnetite/maghemite, i.e. phases with magnetic properties.