CO2 capture and sequestration by sodium humate and Ca(OH)2 from carbide slag

A new method of carbon capture and sequestration (CCS) by sodium humate (HA–Na) and Ca(OH)2 from carbide slag (CS) solution was proposed. The effects of various operating parameters, such as the additive amount of HA–Na, pH, temperature, gas flow rate, CO2 inlet concentration, and stirring rate on both the Ca ion concentration and Ca conversion rate were investigated in a lab-scale bubbling reactor. The synergistic mechanism of HA–Na and Ca(OH)2 from CS on CCS is also put forward and demonstrated. The experimental results indicate that HA–Na may improve significantly the CCS capability of CS since the Ca conversion rate of CS is increased 10% by HA–Na additive. The pH is a key factor for the CO2 absorption process and HA–Na may lower the rate of pH decrease of Ca(OH)2 solution. The increasing temperature, stirring rate, and CO2 inlet concentration are favorable to CO2 capture, as well as low gas flow rate. Ca(OH)2 from CS mixed with HA–Na solution shows good performance in CO2 uptake, and the Ca conversion rate reaches 99% with 100 mL of Ca(OH)2 (1.5 g/L) solution mixed with 0.1 g HA–Na at 40 °C, a gas flow rate of 0.1 L/min, and an inlet CO2 concentration of 100% at ambient pressure. Moreover, calcite CaCO3 is is identified as the main product of CO2 capture by X-ray diffraction and scanning electron microscopy analysis.