Comprehensive utilization of red mud and blast furnace dust: Synergistic preparation of direct reduced iron and functional ceramsite

The aluminum and steel industries produce a large amount of solid waste in the form of red mud and blast furnace dust, respectively. Stacking solid waste can lead to environmental pollution and the wastage of iron resources. This study proposes a new method for the comprehensive utilization of red mud and blast furnace dust through synergistic preparation of direct reduced iron (DRI), and the slag produced during the preparation of DRI is then prepared into functional ceramsite, which is used for the adsorption and removal of phosphorus from wastewater. Under the optimal roasting reduction process, direct reduced iron can be obtained with an iron grade of 92.04 % and an iron recovery rate of 90.33 %. Pre-making ceramsite was prepared by mixing slag, bentonite, and CaCO3 in a mass ratio of 6:2.5:3, followed by preheating at 400 °C for 10 min and then sintering at 1150 °C for 20 min to obtain functional ceramsite. Under optimal conditions, with an initial pH of 2, a ceramsite dosage of 20 g/L (±0.5), and an adsorption time of 24 h, this functional ceramsite can achieve a 96.26 % removal rate of phosphorus in wastewater. XRD and SEM-EDS analyses showed that a roasting temperature of 1260 °C was optimal for the production and growth of DRI, and the addition of CaCO3 was found to be beneficial in transforming the mineral components of functional ceramsite from labradorite to gehlenite, which exhibited favorable adsorption performance towards phosphorus. The DFT results revealed that the gehlenite in functional ceramsite can adsorb H3PO4 and H2PO4− through O–H and Ca-O bonds, and there were two different forms of interaction between surface O atoms and H atoms of adsorbed molecule, the interactions can illustrate the adsorption behavior of ceramsite to phosphorus.