(430b) Directed Mineralization of Waste Carbon to Develop Negative Emission Cements

Direct air capture (DAC) and point source capture (PSC) are current state-of-the-art efforts to close the industrial carbon balance. These processes fight against thermodynamics, as they capture dilute atmospheric carbon dioxide (400 ppm) for it to be concentrated and upcycled to consumer chemicals.

Alternatively, the United States produces 292 million tons of municipal solid waste (MSW) with nearly 80% organic biomass. Traditional waste management produces nearly 8% of the national anthropogenic emissions. This study aims to leverage the organic fraction of MSW as a pre-concentrated source of carbon and optimize reaction thermodynamics and kinetics to develop a competitive net-negative alternative cement. This net energy-positive, carbon-negative process relies on hydrothermal mineralization (HTM), a patent-pending process that converts wet organic waste into thermally stable calcite (CaCO3). First, the use of supercritical water oxidation (SCWO) is a high-temperature, high-pressure process that allows for the combustion of organic carbon under supercritical conditions (374°C, 22.4 MPa). Waste has a significant energy content (24-40 MJ/kg) and can operate as a source of bioenergy. In some cases, energy can be exported from the process. The second oxidative step drives the high-pressure CO₂ produced from the SCWO and mineralizes calcium hydroxide (Ca(OH)­₂) to the most stable calcite (CaCO­₃) form.

Ordinary Portland Cement (OPC) is the current industrial standard for cementitious materials. It relies on the mining and calcination of CaCO3 to form calcium oxide (CaO), which is a key component of the primary strength source. This work then looks at the capability to integrate HTM with trailblazing work to develop a competitive alternative cementitious material (10 MPa) that acts as a calcite sink and relies on polymer binding for strength, instead of traditional cement that uses CaCO₃ as a feed. This work was modeled in ASPEN/HYSYS and GREET, a lifecycle analysis software, and found that in offsetting traditional cement production, this pathway offers a substantial net-negative alternative to two of the largest global polluters.