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Tremendous CO2 emissions from various industries cause environmental complications such as ocean acidification and global warming. The cement industry contributes to 2.53 billion tCO2/yr emissions globally. In an effort to remedy this problem, this research aims to implement the accelerated weathering of limestone (AWL) process to capture CO2 from cement industry emissions. The AWL absorption process utilizes a counter-current flow with a limestone-packed-bed column height of 0.876 m, a diameter of 0.102 m, and a working limestone packing volume of 0.0056 m3. A correlation study was conducted to study the effect of the liquid-to-gas (L/G) ratio on effluent alkalinity and CO2 capture efficiency. It was found that when the L/G ratio decreases (1 to 0.003), a significant increase in the alkalinity (0.62 to 2.43 mM) and pH (6.34 to 7.32) of the calcium bicarbonate (Ca(HCO3)2) effluent was observed. This was due to the longer retention time under a lower L/G ratio operation. On the flip side, the CO2 capture efficiency (70.82 to 16.98 %) of the AWL system responded negatively to the decrease in the L/G ratio. During a low L/G ratio configuration, the rate at which the system reaches equilibrium is more rapid. Results from the correlation study were used to determine the optimum operating condition simulated via the Design of Expert (DoE) software. Two optimized conditions to obtain maximum alkalinity and maximum CO2 capture efficiency were identified and validated experimentally. The highest possible alkalinity and CO2 capture efficiency obtainable were 2.43 mM and 73.51 %, respectively. Overall, this research serves as a preliminary study for the potential future commercialization of the AWL process. [ABSTRACT FROM AUTHOR]

Rapid industrial development has led to a high discharge of carbon dioxide (CO2) and hazardous industrial wastewater. These industrial wastes are sources of well-known environmental problems such as global warming and pollution. This preliminary study aims to evaluate the potential of using accelerated weathering of limestone (AWL), a low-tech, inexpensive and eco-friendly CO2 capture process for industrial wastewater treatment. This idea stems from the high bicarbonate effluent produced via the AWL process, which can be suitable for heavy metal precipitation. The AWL process was carried out using a counter-current absorption tower packed with limestone chips to capture CO2 from ambient air. Two conditions, continuous flow and semi-batch, were tested to determine the absorption configuration to achieve maximum alkalinity effluent production. The continuous flow condition achieved a higher calcium bicarbonate effluent concentration of 80 mg/L (with 2.20 hrs retention time) compared to the semi-batch operation of 75.00 mg/L (at 2.50 hrs retention time). Hence the continuous flow condition was more favorable for operation. Apart from that, the effluent volume producible by the continuous flow method was 44 % higher compared to a semi-batch process. Thereafter, the bicarbonate effluent was used to evaluate its potential for precipitating zinc (Zn) from industrial wastewater to produce zinc carbonate (ZnCO3) solid. A parametric study on the effect of pH and bicarbonate ion (HCO3−) deficit or excess on Zn removal efficiency was conducted for this evaluation. It was shown that as pH increased from 7 to 8, 9 and 10, it achieves high Zn removal efficiency ranging from 98.79 % to 99.74 %. The precipitation condition with no excess of HCO3− achieved high Zn removal of 96.51%. With excess HCO3−, it precipitated both Zn (89.55 % to 94.83 %) and Ca (8.89 % to 21.78 %). This study shows that the AWL process effluent can be utilized to effectively remove heavy metals from industrial wastewater while achieving carbon capture and storage at the same time. [ABSTRACT FROM AUTHOR]