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3. CO2mineralization by typical industrial solid wastes for preparing ultrafine CaCO3: A review

Author

Xu, Run, Zhu, Fuxia, Zou, Liang, Wang, Shuqing, Liu, Yanfang, Hou, Jili, Li, Chenghao, Song, Kuntong, Kong, Lingzhao, Cui, Longpeng, and Wang, Zhiqiang

Abstract

Mineral carbonation is a promising CO2sequestration strategy that can utilize industrial wastes to convert CO2into high-value CaCO3. This review summarizes the advancements in CO2mineralization using typical industrial wastes to prepare ultrafine CaCO3. This work surveys the mechanisms of CO2mineralization using these wastes and its capacities to synthesize CaCO3, evaluates the effects of carbonation pathways and operating parameters on the preparation of CaCO3, analyzes the current industrial application status and economics of this technology. Due to the large amount of impurities in solid wastes, the purity of CaCO3prepared by indirect methods is greater than that prepared by direct methods. Crystalline CaCO3includes three polymorphs. The polymorph of CaCO3synthesized by carbonation process is determined the combined effects of various factors. These parameters essentially impact the nucleation and growth of CaCO3by altering the CO2supersaturation in the reaction system and the surface energy of CaCO3grains. Increasing the initial pH of the solution and the CO2flow rate favors the formation of vaterite, but calcite is formed under excessively high pH. Vaterite formation is favored at lower temperatures and residence time. With increased temperature and prolonged residence time, it passes through aragonite metastable phase and eventually transforms into calcite. Moreover, polymorph modifiers can decrease the surface energy of CaCO3grains, facilitating the synthesis of vaterite. However, the large-scale application of this technology still faces many problems, including high costs, high energy consumption, low calcium leaching rate, low carbonation efficiency, and low product yield. Therefore, it is necessary to investigate ways to accelerate carbonation, optimize operating parameters, develop cost-effective agents, and understand the kinetics of CaCO3nucleation and crystallization to obtain products with specific crystal forms. Furthermore, more studies on life cycle assessment (LCA) should be conducted to fully confirm the feasibility of the developed technologies.

Published
2024
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6. Bioavailability of metal(loid)s in mining wastes by amphipod C. volutator with an emphasis on arsenic

Author

Cui, Longpeng

Subjects
595.378
Abstract

In this thesis, 10-day sediment-based static bioassay tests on the amphipod Corophium volutator (Pallas, termed C. volutator) were initially designed and set up, in order to investigate mobility, bioaccumulation and toxicity of the metals with an emphasis on arsenic in arsenic sulphides (AsS, As2S3, and Fe[AsS]) and coal-mining spoils (from Kirkcaldy, Scotland and Huainan, China). The marine amphipod is sensitive to metals (As, Cd, Pb, and Ba), which were generally recognised as the most important metals in the drainage water of coal-mining spoils. C.volutator, under the designed test, could indicate the release of contaminants derived from the arsenic sulphides and the spoils for environmental implications, and is of potential applicability in characterising the sulphide-bearing spoils in terms of toxicology monitoring. Toxicity and arsenic bioaccumulation in C.volutator varied greatly between different exposure minerals, in decreasing order: AsS≥As2S3>>Fe[AsS], in association with the 10-day LD50 (referring to mineral-spiked ratio in test sediment) of 0.032-0.073%, 0.050-0.097%, and 0.245-0.289%, respectively and 10-day LC50 value (referring to test media) of 0.42-0.95 mg As L-1 to the bio-indicator. It was found that there is an inverse logarithmic correlation between BAFs and arsenic concentrations in the media. The presence of predominantly arsenite (AsIII) in the mineral leachates and bioaccumulation of inorganic arsenic (AsIII and AsV) associated with eliminated biomethylation (to DMAV) in exposed organism have a close linkage to the relatively lower LC50 values during 10-day exposure duration. This infers that the arsenic-sulphur complex in the exposure media may plays a key role for mineral release and biological-effect of toxic arsenic.

Published
2007

7. Experimental Investigation and Mechanism Analysis of Direct Aqueous Mineral Carbonation Using Steel Slag.

Author

Zhu, Fuxia, Cui, Longpeng, Liu, Yanfang, Zou, Liang, Hou, Jili, Li, Chenghao, Wu, Ge, Xu, Run, Jiang, Bo, and Wang, Zhiqiang

Abstract

The carbonation of industrial calcium-rich byproducts such as steel slag demonstrates significant potential for CO2 sequestration. This technique aids in reducing carbon emissions while also promoting waste recycling. Despite its advantages, gaps remain in the understanding of how steel slag characteristics and operational parameters influence the carbonation process, as well as the underlying mechanism of direct aqueous carbonation. We evaluated the carbonation performance of three types of steel slag at temperatures below 100 °C. The slag with the highest CO2 sequestration capacity was chosen for a systematic evaluation of the effects of operating conditions on carbonation efficiency. Thermodynamic analysis indicated that the reactivity of CaO and Ca(OH)2 with CO2 exceeded that of CaO·SiO2 and 2CaO·SiO2. Under conditions of 85 °C, a particle size less than 75 μm, an initial CO2 pressure of 0.5 MPa, a liquid-to-solid ratio of 5 mL/g, and a stirring speed of 200 rpm, the steel slag achieved a sequestration capacity (K) of 283.5 g(CO2)/kg and a carbonation efficiency (ζCa) of 51.61%. Characterization of the slag before and after carbonation using X-ray diffraction, SEM-EDS, thermogravimetric analysis, and Fourier transform infrared spectrometry confirmed the formation of new carbonates. Mechanistic analysis revealed that the rate-limiting step initially involved the mass transfer of CO2, transitioning to Ca2+ mass transfer as time progressed. Our research provides a viable technique for CO2 capture and a beneficial approach for reutilizing waste steel slag. Furthermore, solid residues after capturing CO2 have the potential for conversion into carbon-negative building materials, offering a sustainable strategy for steel companies and other enterprises with high carbon emissions. [ABSTRACT FROM AUTHOR]

Published
2024
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