Synthesis of sole gismondine-type zeolite from blast furnace slag during CO2 mineralization process

Abstract

CO2 mineralization is one of the most important strategies for reduction of anthropogenic CO2 emissions. Preparation of high-value products during this process would improve its economy and make it more promising for industrial applications. In this study, sole gismondine-type zeolite (zeolite P) was synthesized during the CO2 mineralization process by using blast furnace slag as feedstock. The optimal experimental conditions and regression model for synthesis of zeolite was determined through Response surface methodology. The results showed that a well-crystallized zeolite was obtained with a short hydrothermal time at high temperature even at low alkalinity. However, too high temperature and alkalinity can promote the formation of sodalite, reducing the relative content of zeolite P in the product. Different analysis methods such as XRD, FTIR, SEM were applied to characterize the products and investigate the synthesis mechanism of zeolite formation. The analysis indicated that zeolite products with a uniform shape of octahedron can be obtained under mild conditions (NaOH concentration of 1.5 mol·L−1, 120 °C, 2∼4 h). The formation of zeolite from blast furnace slag can be divided into four steps, i.e., dissolution of aluminate ions and silicate ions from raw material, formation of the amorphous intermediate aluminosilicate gel precursor, rearrangement of the structure of aluminosilicate precursor to form nuclei of zeolite, and crystal growth. Based on the results in this study, major components of blast furnace slag were utilized fully (Mg and Ca for CO2 storage, whilst Al and Si for synthesis of zeolite), reducing the overall cost of CO2 mineralization.