Improvement of Carbon Dioxide Sequestration of Anorthite through Bacterial: Release of Calcium and Destruction of Crystal Structure

Abstract

Carbon dioxide sequestration by minerals containing calcium or magnesium is a safe and stable approach to reduce the concentration of CO2 in the atmosphere. In this work, the bioleaching method was applied to pretreat the anorthite, aiming to improve the carbonation conversion rate of anorthite with low energy consumption, low cost, and no pollution. A bacteria named Herbaspirillum huttiense W-01 was found and selected as the strain. The effects of the bacterial strain on the Ca2+ leaching behavior of anorthite and the corresponding carbonation conversion rate were investigated. Then, the strengthening mechanism of the bacteria was clarified from the Ca2+ leaching rate and the crystal structure of anorthite. The bioleaching results showed that after 9 days of treatment, the pH value of the fermentation solution decreased to 6.01 from 7.20, and the concentration of Ca2+ was 8.1 mmol/L with a 4.65% leaching rate, which was about twice that of sterile medium. During the pretreatment period of one to 9 days, the carbonation conversion rate of different systems (A1: anorthite and bacteria, B1: anorthite and medium, C1: anorthite and distilled water, D1: anorthite and bacteria, cleaning step to remove the medium components) increased with time. After 9 days, the carbonation conversion rate of system D1 reached 18.74%, which was 3.46% higher than that of system C1, suggesting a better carbon sequestration effect of anorthite after the bioleaching pretreatment. In addition, a bioleaching residue with weakened thermal stability and decreased crystallinity was formed after the microbial pretreatment. Furthermore, it can be seen that the surface of the bioleaching residue was rough and showed obvious corrosion at the edges, and the specific surface area increased from 0.5187 m2/g to 0.9883 m2/g. It is precisely because of the changes in the crystal structure of anorthite caused by bioleaching, especially in mineralogy and morphology, that the carbonation activity of anorthite was enhanced. This research may provide a reference for the enhancement of carbon dioxide mineralization by basic or ultrabasic rocks through microbial methods.