An Experimental Study of Carbon Sequestration via Mineralization of Flue Gas Desulfurization (FGD) Gypsum

Abstract

Abstract

Carbon sequestration is the process of capturing and storing CO₂ emissions in a geologic repository. Flue gas desulfurization (FGD) gypsum is a waste product that is produced and typically stockpiled at coal-burning power plants, and is the sequestration repository investigated by this study. This sequestration technology potentially provides a permanent chemical storage option in which carbon dioxide is bound in a carbonate mineral. The mineralization process mimics natural weathering wherein calcium-bearing minerals are converted to calcium carbonate.

In 2014, the United States emitted 1,562 million metric tons of CO₂ at coal-burning power plants, which accounted for 76% of total emissions. In the same year, 24.3 million metric tons of FGD gypsum was produced at these power plants; only 36% of the FGD gypsum was recycled while 64% was landfilled. The goal of this study is to experimentally evaluate the feasibility of carbon sequestration by mineralization, using a common waste material produced by power plants.

Initial tests have been performed at room temperature and 1 bar pressure, and varying solid-to-liquid ratios and pH to determine baseline conditions for the conversion of FGD gypsum to calcite. A stirred reactor is then utilized to determine optimal conditions for the precipitation of calcite, varying the solid-to-liquid ratio (1:2, 1:3, 1:4, 1:6, 1:10), pH (6-14), and pressure (1-300 bar).

After the carbonation reaction is completed, the solid and liquid components are separated for analyses. The solid carbonated product is first viewed under a Scanning Electron Microscope (SEM) to identify dissolution surfaces and calcite crystal growth on the surface of FGD gypsum crystals. X-ray Diffraction (XRD) is then used to quantify the relative amount of calcite precipitated in the carbonated product. Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) is used to identify and quantify trace elements that are released to the aqueous phase during the conversion of FGD gypsum to calcite.

The results from this study demonstrate that mineral carbon sequestration via FGD gypsum carbonation is a chemically feasible method to help reduce CO₂ emissions and utilize this waste product for a beneficial purpose at coal-burning power plants.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016