Dissolution of dehydroxylated lizardite at flue gas conditions: I. Experimental study

The direct mineralization of flue gas CO2 yields serviceable carbonates, thus combining CO2 utilization with its permanent storage. Such a process requires the rapid dissolution of a magnesium or calcium source at lean operating conditions. Motivated by its worldwide abundance, we have studied the dissolution kinetics of a lizardite-type serpentine that was 75% dehydroxylated by thermal pretreatment to maximize its reactivity. A continuous stirred liquid and gas flow-through setup was designed to perform far-from-equilibrium dissolution experiments at moderate temperatures ð30 C 6 T 6 120 CÞ; low CO2 partial pressures ð0:1 bar 6 pCO2 6 2 barÞ, using two different particle size fractions, and using a mineral acid instead of CO2 to vary the solution pH. Dissolution was measured to be non-stoichiometric and did not reach steady state within 10 h. Up to 83% of the magnesium (Mg) and 72% of the silicon (Si) dissolved within the first 100 min, where the dissolution rate for both Mg and Si increased with temperature and pCO2. This fast stage was followed by a period with much reduced dissolution rates. The key observations are rationalized with regard to the physical morphology and chemical properties of the thermally activated mineral, and discussed in view of the design of a process that combines CO2 capture and storage by mineralization.