Enhancement of accelerated carbonation of alkaline waste residues by ultrasound

Research status and future challenge for CO2 sequestration by mineral carbonation strategy using iron and steel slag

Mineral carbonation can simultaneously realize the effective treatment of CO₂ and iron and steel slag; thus, it is of great significance for the low carbon and sustainable development of iron and steel industry. In this article, the researches of mineral carbonation process using iron and steel slag as feedstock are reviewed, and the carbonation reaction mechanism and the parameters affecting the reaction rate and carbonation degree are analyzed. Furthermore, the effect of different enforcement approaches, such as ultrasonic enhancement, mixed calcination, microbial enhancement, and cyclic coprocessing on mineral carbonation reaction, is introduced. The additional effects of mineral carbonation, such as solving the problem of poor volume stability of steel slag, weakening the leaching of heavy metal ions, and reducing the pH of the leachate, are also illustrated. Moreover, issues related to mineral carbonation technology that should be emphasized upon soon, such as the production of valuable products, use of industrial wastewater, aqueous phase recycling use, multiparameter coupling analysis, and research on the properties of carbonation residues, are also discussed, which contribute some perspectives to the future development of mineral carbonation of iron and steel slag.

Influence of Hydrothermal Pretreatment Temperature on the Hydration Properties and Direct Carbonation Efficiency of Al-Rich Ladle Furnace Refining Slag

The influence of hydrothermal pretreatment temperature on the hydration products and carbonation efficiency of Al-rich LF slag was investigated. The results showed that the carbonation efficiency was strongly dependent on the morphology of hydration products and the hydration extent of the raw slag. Hydrothermal pretreatment at 20 °C or 80 °C favored the formation of flake-shaped products with a higher specific surface area and therefore resulted in a higher CO2 uptake of 20 °C and 80 °C-pretreated slags (13.66 wt% and 10.82 wt%, respectively). However, hydrothermal pretreatment at 40 °C, 60 °C or 100 °C led to the rhombohedral-shaped calcite layer surrounding the unreacted core of the raw slag and the formation of fewer flake-shaped products, resulting in a lower CO2 uptake of 40 °C, 60 °C and 100 °C-pretreated slags (9.21 wt%, 9.83 wt%, and 6.84 wt%, respectively).

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 C3AHX was formed in pretreated slags because of C12A7 hydration, which could remove part of S. After carbonation, most of the C3AHX in pretreated slags produced crystalline CaCO3 bonded by amorphous Al(OH)3 (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 C3AHx, 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 Ca2SiO4.

A review on steel slag valorisation via mineral carbonation

Alkaline slags, a waste product of steel industry, provide an opportunity for carbon sequestration and creation of value at the same time. This requires an understanding of the mechanisms of leaching and carbonation.

Recycling of waste autoclaved aerated concrete powder in Portland cement by accelerated carbonation

To recycle waste autoclaved aerated concrete (WAAC) and minimize environmental pollution induced by Portland cement (PC), carbonation curing was performed on cement pastes containing variable replacement levels (0-50%) of waste autoclaved aerated concrete powder. Compressive strength and chloride ion permeability of PC-WAAC specimens were measured and related mechanisms were demonstrated by X-ray diffraction (XRD), ²⁹Si solid-state Nuclear Magnetic Resonance (NMR), thermogravimetry-differential thermal analysis (TG-DTA), mercury intrusion porosimeter (MIP), scanning electron microscope (SEM) and back scattered electron images (BSE) measurements. Results showed that the PC-WAAC specimens presents a higher compressive strength increase than the pure PC specimen after carbonation curing and the optimal dosage of WAAC is 20%. This effect compensates the decreasing strength induced by the incorporation of WAAC. Chloride ion penetration resistance of cement pastes were also improved by carbonation curing due to the refinement of pore structure. Up to 20% of WAAC can be successfully recycled to replace PC without compromising strength and chloride ion permeability. Moreover, around 11.23-19.02% of CO₂ by the total binder weight can be captured. Therefore, this technology has a great environmental potential to both recycling of construction waste and capture of greenhouse gas.

Carbon Mineralization by Reaction with Steel-Making Waste: A Review

Carbon capture and sequestration (CCS) is taking the lead as a means for mitigating climate change. It is considered a crucial bridging technology, enabling carbon dioxide (CO2) emissions from fossil fuels to be reduced while the energy transition to renewable sources is taking place. CCS includes a portfolio of technologies that can possibly capture vast amounts of CO2 per year. Mineral carbonation is evolving as a possible candidate to sequester CO2 from medium-sized emissions point sources. It is the only recognized form of permanent CO2 storage with no concerns regarding CO2 leakage. It is based on the principles of natural rock weathering, where the CO2 dissolved in rainwater reacts with alkaline rocks to form carbonate minerals. The active alkaline elements (Ca/Mg) are the fundamental reactants for mineral carbonation reaction. Although the reaction is thermodynamically favored, it takes place over a large time scale. The challenge of mineral carbonation is to offset this limitation by accelerating the carbonation reaction with minimal energy and feedstock consumption. Calcium and magnesium silicates are generally selected for carbonation due to their abundance in nature. Industrial waste residues emerge as an alternative source of carbonation minerals that have higher reactivity than natural minerals; they are also inexpensive and readily available in proximity to CO2 emitters. In addition, the environmental stability of the industrial waste is often enhanced as they undergo carbonation. Recently, direct mineral carbonation has been investigated significantly due to its applicability to CO2 capture and storage. This review outlines the main research work carried out over the last few years on direct mineral carbonation process utilizing steel-making waste, with emphasis on recent research achievements and potentials for future research.