Dissolution of activated serpentine and precipitation of magnesium carbonates for a flue gas CO_2 mineralization process

摘要

A fully functional Carbon Capture and Storage (CCS) scheme has to ensure a completely safe and permanent storage of the captured CO_2. Ex situ mineralization enables this by storing CO_2 in a chemically stable carbonate form. Magnesium and calcium silicate rocks found in nature are the main source for the metal cations needed for the mineralization process. In an aqueous mineralization process, Mg/Ca ions are leached from the silicate rocks and then precipitated as carbonates. The rate limiting step for this process is the dissolution of the silicate rocks [e.g. 1]. The relatively simple silicate structure and dissolution mechanism of forsterite, the magnesium rich member of the olivine group (e.g. Mg_2SiO_4), has resulted in extensive study of its dissolution under various conditions [e.g. 1-4]. The great abundance of the serpentine group (e.g. Mg_3Si_2O_5(OH)_4) makes it a more attractive feedstock for mineralization than olivine. However, it suffers from slow dissolution kinetics. Thermal activation has shown to accelerate the dissolution kinetics for serpentine [5]. But heat activation is an energy intensive process and adds substantially to costs. The use of direct flue-gas mineralization in aqueous medium avoids the costs associated with the capture of CO_2. In such a process, CO_2 is dissolved into an aqueous solution and the resulting carbonic acid is sufficient to leach Mg ions from the activated material.