An insight into the carbonation of calcined clayey dolomite and its performance to remove Cd (II)

Highly active porous materials composed of calcite and periclase nanoparticles was prepared by the carbonation of thermally treated clayey dolomite, having great potential for heavy metal pollution control in water and soil. The effect of coexisting steam and hydration pretreatment on the carbonation of calcined clayey dolomite (CCD) was studied by fixed bed reactor and mass spectrum on-line monitoring. The phase, surface chemistry, thermal activity, pore type and morphology of CCD after carbonation were characterized by XRD, FTIR, TG, N2 adsorption-desorption isotherm and TEM. The results showed that the initial and complete carbonation temperatures of CCD under anhydrous conditions were 400 °C and 600 °C, respectively. The presence of 10% steam decreased the initial and complete temperatures by 100 °C, respectively. The complete carbonation temperature was reduced to 400 °C when the CCD was hydrated and dried before carbonation. However, the hydrated CCD which not dried can be directly carbonated at room temperature, and the carbonation rate (newborn calcite mass fraction) firstly decreased, then increased with the increase of temperature in the range of 50-500 °C. According to the TG results, the decomposition temperatures of the newborn calcite produced by 650 °C carbonation of CCD decreased by 50 °C compared with that of common calcite. The research on cadmium removal showed that the removal efficiency of 50 mg/L Cd (II) by 650 °C carbonation of CCD rapidly reached 99.8% within 1 h, while the equilibrium pH decreased by 2 units compared with CCD without carbonation. The carbonation of CCD formed nano calcite of lower decomposition temperature and also hampered the hydroxylation to decrease the effluent pH. The experimental results displayed carbonation can control the physicochemical property of the CCD, and the carbonated product is potential to be used for the removal of Cd (II) from aqueous solution.