(647e) Carbon Capture and Utilization By Three-Step Aqueous Phase Mineralization

The
increase in greenhouse gasses concentration in the atmosphere has contributed
to global warming in recent decades. Carbon sequestration is one of the
solutions to control the CO₂ concentration in atmosphere.  A
pH-swing mineral carbonation is the process of extracting magnesium or calcium
from mineral rock, followed by precipitation of extracted minerals in separate
reactors. The process was found to be feasible method for potential industrial
application to reduce CO₂ emission by carbon sequestration. This
study investigates production of value-added materials for a three-series mineralization
reactor in aqueous phase. Magnesium, iron and small portions of some other
minerals were extracted from magnesium silicate rock, were precipitated in two
steps by increasing the pH from 0.5 up to 10. Product analysis showed that in
each step, high purity stable solids such as silica, iron hydroxide II and III,
hydrated magnesium carbonate were produced. The CO₂ source was Na₂CO₃
which was the product generated from the scrubbing reaction between a power
plant's flue gas and NaOH to serve as a potential carbon capture method. Mass
balance for the mineral sequestration process was investigated for future scale
up. CO₂ uptake was determined by magnesium carbonate elemental
analysis.  It was calculated that for each ton of sequestrated CO₂
approximately 3.22 ton of serpentine rock (mainly (Mg₃Si₂O₅(OH)₄)
was required and also 25 m³ of 1M NaOH, 35 m³ of 1M Na₂CO₃
and 80 m³ of 1M HCl were utilized. The resultant value-added
products from the process would be 3.1 ton of 99.74% pure nesquehonite (Mg₂CO₃∙3H₂O)
and 0.82 ton of iron oxide and hydroxide with 90% purity. Crystalline structure,
particle size distribution and morphology of hydrated magnesium carbonate
produced, were strongly dependent on the last precipitation reactor conditions
including temperature, feeding flow rate, mixing speed and base concentration. Additionally,
different composition and crystalline structure of magnesium carbonate produced
in the last precipitation step in different temperature ranging 0 to 60 ºC, shows
that the process is capable of producing value-added products including
nesquehonite, hydromagnesite and dypingite under a wide range of ambient
temperature.  In future investigations, carbon footprint of the process chain
will be studied.