Effect of natural dolomite calcination temperature on sorption of borate onto calcined products

摘要

Natural dolomite was calcined at 700-900 °C under air and an Ar gas flow atmosphere to characterize its sorbency potential for borate. A sequential decarbonation occurred with increase in calcination temperature, that is, transformation of CaMg(CO3)2 to MgO and CaCO3 up to 700 °C and CaCO3 to CaO from 700 to 900 °C. The surface molar ratio of Ca/Mg decreased from 1.6 to 0.6 by calcination at more than 700 °C, owing to the crystal growth of MgO toward the surfaces. MgO crystal growth is responsible for hydration leading to borate co-precipitation. The sorption density of borate was greater with the calcined products at 700 °C than 800-900 °C and under an Ar gas flow system rather than for static air at the same temperatures. The surface reactivity of the calcined dolomite with borate in the aqueous phase was affected by CO2 emitted in the decarbonation at higher temperatures.