Boric Acid Production from Colemanite Together with ex Situ CO2 Sequestration

In this work, boric acid (H3BO3) production from the mineral colemanite (Ca2B6O11 center dot 5H(2)O) 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 mu m) of colemanite are tested. Reactions were carried out for different reaction times and at 40-70 degrees 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.