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Mineral carbonation is a promising CO2 sequestration strategy that can utilize industrial wastes to convert CO2 into high-value CaCO3. This review summarizes the advancements in CO2 mineralization using typical industrial wastes to prepare ultrafine CaCO3. This work surveys the mechanisms of CO2 mineralization 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 CaCO3 prepared by indirect methods is greater than that prepared by direct methods. Crystalline CaCO3 includes three polymorphs. The polymorph of CaCO3 synthesized by carbonation process is determined the combined effects of various factors. These parameters essentially impact the nucleation and growth of CaCO3 by altering the CO2 supersaturation in the reaction system and the surface energy of CaCO3 grains. Increasing the initial pH of the solution and the CO2 flow 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 CaCO3 grains, 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 CaCO3 nucleation 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.

Mineral carbonation is a promising CO2 sequestration strategy that can utilize industrial wastes to convert CO2 into high-value CaCO3. This review summarizes the advancements in CO2 mineralization using typical industrial wastes to prepare ultrafine CaCO3. This work surveys the mechanisms of CO2 mineralization 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 CaCO3 prepared by indirect methods is greater than that prepared by direct methods. Crystalline CaCO3 includes three polymorphs. The polymorph of CaCO3 synthesized by carbonation process is determined the combined effects of various factors. These parameters essentially impact the nucleation and growth of CaCO3 by altering the CO2 supersaturation in the reaction system and the surface energy of CaCO3 grains. Increasing the initial pH of the solution and the CO2 flow 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 CaCO3 grains, 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 CaCO3 nucleation 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. [ABSTRACT FROM AUTHOR]

Rare earth elements (REEs) are important geochemical indicators and they can provide a lot of useful pertinent information. The inorganic/organic affinity of REEs in Huadian and Luozigou oil shales from Jilin Province, China, was determined using the float-sink and acid-washing tests and sequential chemical extraction methods. The constituents of REEs were determined employing inductively coupled plasma-mass spectrometry (ICPMS). The results of the float-sink test indicated that the concentration of REEs increased with increasing specific gravity, while during the acidwashing tests, REEs were removed from oil shale. The linear regression of REEs and ash content revealed that the majority of the elements were associated with minerals in coal. In addition, acid washing proved to influence the desorption of REEs. REEs in oil shale exist mainly in the mineral fraction, while the organic fraction plays a major role in their aggregation, especially in case of light rare earth elements (LREEs). REEs in oil shale derived from terrigenous clastic rocks when they were absorbed by organic matter or minerals. [ABSTRACT FROM AUTHOR]