Etd

A Multi-Faceted Approach to Carbon Mineralization Advancement

Public

Downloadable Content

open in viewer

The levels of carbon emissions in our atmosphere due to a dependence on fossil energy calls for swift action to prevent potentially devastating impacts of climate change. Along with a transition away from fossil energy sources, climate models call for capture of CO2, both at the source of emissions and directly from the ambient air. In both cases, a safe method to permanently store the CO2 is required so that the CO2 is not re-emitted. Carbon mineralization can capture and permanently store CO2 in the form of carbonate minerals by reacting it with alkalinity (i.e., Mg or Ca). The alkalinity can be found in abundant silicate minerals (e.g., olivine, serpentine, plagioclase feldspar), wastes from industrial or mining practices (e.g., steelmaking slags, mine tailings), or geologic formations (e.g., peridotite, basalt). Mine tailings are particularly promising because of their large reactive surface area and because their production is projected to grow by an order of magnitude in the coming century due to increased demand of metals like nickel and platinum for the global energy transition. In this Dissertation, tailings are studied from Sibanye-Stillwater in Nye, Montana, which produces copper, nickel, and platinum group metals (PGM). The tailings were characterized, revealing that they contain alkalinity distributed in several silicate groups, including tecto-, ino-, and phyllo-silicates. Given this heterogeneous nature, it was determined that mineralization would be more effective if the alkalinity is extracted from the tailings prior to reaction with CO2. Three methods were used to extract the alkalinity from the tailings. At ambient conditions, < 3% of Ca and < 1% Mg were extracted, indicating that a process with elevated conditions would be necessary to increase alkalinity extraction. Other processes used were the Alternative ÅA Route and the pH swing process, which extract alkalinity through a thermal reaction with ammonium sulfate and through acidic dissolution, respectively. Using these two processes, top extraction efficiency values ranged 40-81% for Mg and 4-14% for Ca. Extraction of Ca was limited primarily due to the restrictive tectosilicate structure of anorthite, which holds nearly 80% of the Ca in the tailings. Several suggestions for future work are made, which could increase the extraction of Ca while decreasing the consumption of reagents and cost of equipment. A technoeconomic analysis tool was developed to evaluate and compare a variety of carbon mineralization processes. When the tool was used to compare the processes used in this Dissertation, the Alternative ÅA Route was revealed to be more economical than the pH swing at the conditions tested. Despite extracting more Mg, pH swing process economics suffered from high equipment costs, as mineral acids like sulfuric acid require corrosion-resistant equipment, and organic acids like citric acid require longer dissolution times and thus larger equipment volumes. The tool compared the processes optimized in this Dissertation, but removal of simplifying assumptions will be necessary to improve the tool’s usability and robustness. Products of carbon mineralization can be utilized as products in the construction industry. A review of the current state of product utilization reveals that up to three GtCO2 could be avoided if all alkaline feedstock was converted. Further an analysis shows that more than two-thirds of emissions in the U.S. concrete industry could be avoided by decarbonization technologies and techniques, including the use of carbon mineralization products. However, additional research is still needed to demonstrate reliability of the new, relatively unproven products, and government policies are needed to revise outdated regulations that limit innovation in construction materials. It is suggested that public funding should be allocated to researching these areas. To help motivate and enhance understanding of carbon mineralization for policymakers, along with the general public and our youth, a high-level description of the technology has been written.

Creator
Contributors
Degree
Unit
Publisher
Identifier
  • etd-5631
Keyword
Advisor
Orcid
Committee
Defense date
Year
  • 2021
Date created
  • 2021-03-11
Resource type
Rights statement
Last modified
  • 2023-11-03

Relations

In Collection:

Items

Items

Permanent link to this page: https://digital.wpi.edu/show/v692t938d