Author ORCID Identifier

https://orcid.org/0009-0003-6042-5027

Semester

Fall

Date of Graduation

2024

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mining Engineering

Committee Chair

Deniz Talan

Committee Member

Qingqing Huang

Committee Member

Deniz Tuncay

Abstract

Coal fly ash (CFA), a byproduct of coal combustion, represents an innovative opportunity to address the rising demand for critical minerals and the need to reduce CO2 emissions due to its significant concentrations of calcium and magnesium. By providing insights and preliminary data, this study aims to contribute to the foundational understanding necessary for future development.

A multidisciplinary approach was employed to assess CFA’s potential, including detailed chemical and mineralogical characterization using X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). XRD analysis revealed crystalline phases in the CFA samples. At the same time, SEM imaging identified the characteristic morphology of coal fly ash, with particle sizes ranging from submicron to several micrometers. These analyses provided a comprehensive elemental and mineralogical profile for optimizing mineral recovery and carbonation processes.

Experimental tests involved roasting, precipitation, and leaching under acidic, basic, and aqueous conditions, followed by carbonation experiments. These investigations evaluated extraction efficiency, selectivity, and operational parameters quantified for critical minerals recovery and carbon capture capacity. HCl leaching outperformed other methods in terms of total REE (TREE) recovery (>90%), followed by NaOH and water leaching at elevated temperatures (~40%) and NH4Cl (~30%). NaOH leaching demonstrated the best selectivity (low contamination), followed by NH4Cl, while HCl leaching showed poor selectivity. Water leaching with pre-treatment (roasting) improved selectivity for metals but not for TREE. Overall, HCl leaching at 1 M and 3 hours balanced high TREE recovery and operational practicality, making it the most suitable choice for subsequent carbonation tests. For carbonation, the best results were obtained using 5M NaOH and reaction at 50°C with CO2 pressure of 80 psi and an inlet flow rate of 1 L/min, achieving up to 60% recovery for TREE and calcium and selectivity of targeted pH of 4 and 7.

These findings underscore CFA's potential to address environmental challenges associated with coal combustion residues while advancing circular economy principles by converting waste into valuable resources. By providing a robust foundational framework, this research marks a pivotal step toward harnessing CFA's capabilities to tackle environmental and resource-related issues.

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