Abstract
Magnetic separation is an effective method to recover iron from steel slag. However, the ultra-fine tailings generated from steel slag become a new issue for utilization. The dry separation processes generates steel slag powder, which has hydration activity and can be used as cement filler. However, wet separation processes produce steel slag mud, which has lost its hydration activity and is no longer suitable to be used as a cement filler. This study investigates the potential of magnetically separated steel slag for carbonation curing and the potential use of the carbonated products as an artificial reef. Steel slag powder and steel slag mud were moulded, carbonation-cured and seawater-cured. Various testing methods were used to characterize the macro and micro properties of the materials. The results obtained show that carbonation and hydration collaborated during the carbonation curing process of steel slag powder, while only carbonation happened during the carbonation curing process of steel slag mud. The seawater-curing process of carbonated steel slag powder compact had three stages: C-S-H gel formation, C-S-H gel decomposition and equilibrium, which were in correspondence to the compressive strength of compact increasing, decreasing and unchanged. However, the seawater-curing process of carbonated steel slag mud compact suffered three stages: C-S-H gel decomposition, calcite transfer to vaterite and equilibrium, which made the compressive strength of compact decreased, increased and unchanged. Carbonated steel slags tailings after magnetic separation underwent their lowest compressive strength when seawater-cured for 7 days. The amount of CaO in the carbonation active minerals in the steel slag determined the carbonation consolidation ability of steel slag and durability of the carbonated steel slag compacts. This paper provides a reference for preparation of artificial reefs and marine coagulation materials by the carbonation curing of steel slag.
Highlights
Steel slag is produced in the steelmaking process
This study investigated the mechanism of carbonation curing on steel slag tailings after iron recycling and the potential application of carbonated steel slag tailings as artificial reefs
The compressive strength of steel slag powder (SSD) and SSW compacts before carbonation curing were 1.3 and 0.7 MPa, respectively
Summary
Steel slag is produced in the steelmaking process. China produced 160 Mt of steel slag in 2020. Researchers have focused on the study of application of the steel slag in various ways, including aggregates in road construction, fillers of cementitious materials, as well as iron recycling [2]. Steel slag tailings after iron recycling contain a large amount of calcium oxide, calcium hydroxide, calcium silicates, calcium aluminates and calcium ferrates, which are suitable for mineral carbonation [10–13]. Mineral carbonation on steel slag has been investigated in two aspects: indirect carbonation to generate pure CaCO3 [14] and direct carbonation to produce construction materials [15]. Carbonation curing of concrete artificial reefs has recognized steel slag materials as a good strategy to reduce the surface pH, which enhances their attraction to marine organisms [31,32]. The results of this study provide a reference for the utilization of steel slag tailings after iron recycling and the development of carbonated artificial reef concrete
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