Comparison of Three Mineral Candidates in Middle and Low-Pressure Condition: Experimental Study

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Abstract

“Greenhouse Effect”, which is scientifically proven to be main caused by the increasing concentration of CO2, has become a topic of national and international concern. Mineral carbonation, such as carbonation of alkaline silicate Ca/Mg minerals, analogous to natural weathering processes, is a potentially attractive route to mitigate possible global warming on the basis of industrial imitation of natural weathering processes. In this paper, three typical natural mineral candidates in China, serpentine, olivine and wollastonite, were selected as carbonation raw materials for direct mineral carbonation experiments under middle and low-pressure. A series number of experiments were carried out to investigate the factors that influence the conversion of carbonation reaction, such as reaction temperature, reaction pressure, particle size, solution composition and pretreatment. The solid products from carbonation experiments were filtered, collected, dried and analyzed by X-ray diffraction (XRD) and field scanning electron microscopy equipped with energy dispersive X-ray analysis (FSEM-EDX) to identify the reaction of mineral carbonation. And the method of mass equilibrium after heat decomposition was used to calculate the mineral carbonation conversion. All the XRD and FSEM analysis validate that carbonation reaction was occurred during the experiments and mineral carbonation is one of the potential techniques for carbon dioxide sequestration. The data of mass equilibrium after heat decomposition was collected and then the conversion formula was used to calculate the carbonation conversion of all the three mineral candidates. The mass equilibrium results show that, for all of the three mineral materials, the carbonation conversion increases with the increasing of reaction temperature. But once the temperature increases above 150°C, the conversion of serpentine decreases a little. Reaction pressure is also an important factor to mineral carbonation process. For all of the three mineral materials, the carbonation conversion increases with the increasing of reaction pressure. Decrease of mineral particle sizes and use of heat treatment before carbonation experiments can effectively improve the carbonation conversion of mineral carbonation. And the addition of NaHCO3, which had a buffering effect that kept the solution pH in a certain range, can also improve the carbonation conversion. In this paper, a highest carbonation conversion of 89.5% was obtained under the condition of T = 150°C, $ {{\text{P}}_{{{\rm{C}}{{\rm{O}}_2}}}} $ = 4.0 MPa, particle sizes <37 μm in 1 h using wollastonite as the raw material. Compared with serpentine and olivine, wollastonite is the most promising material for carbon dioxide mineral carbonation under middle and low-pressure.