Boric Acid Production from Colemanite Together with ex Situ CO2 Sequestration
2016
Gönen, Mehmet | Nyankson, Emmanuel | Gupta, Ram B.
In this work, boric acid (H₃BO₃) production from the mineral colemanite (Ca₂B₆O₁₁·5H₂O) with carbon dioxide (CO₂) sequestration is investigated. CO₂, a known greenhouse gas, is used as a raw material in the leaching of boric acid from colemanite, and the residual calcium is converted into the thermodynamically stable carbonate form. Experiments are carried out in a high pressure stainless steel reactor equipped with stirring and ultrasonic mixing. The solid/liquid ratio is kept at 0.1 g/mL considering the solubility of boric acid extracted, and two different particle sizes (45 and 75 μm) of colemanite are tested. Reactions were carried out for different reaction times and at 40–70 °C and at 4–12 MPa. Characterization of the products by FTIR, XRD, and TGA confirmed that boric acid is extracted from colemanite and CO₂ is converted into calcium carbonate. The conversion favorably increases with the addition of CO₂ pressure up to 8 MPa. The use of 20–25 kHz ultrasound in this heterogeneous reaction increased the extraction efficiency from approximately 70% to 90% due to enhanced mass transfer. CO₂ storage capacity of colemanite is measured as 0.17 as compared to the theoretical value of 0.21 kg CO₂/kg mineral. The utilization of CO₂ in boric acid production can sequester a significant amount of CO₂ while improving the environmental performance as compared to traditional sulfuric acid-based processes.
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