Author ORCID Identifier

https://orcid.org/0009-0005-3023-7839

Semester

Spring

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

Oishi Sanyal

Committee Member

Hassan Amini

Abstract

Rare earth elements (REEs) are members of the lanthanide family (atomic number 57 – 71). They are significantly important to the global economy due to their applications in renewable energy, defense, and medical industries. REEs are primarily derived from bastnaesite and monazite but may also be present in xenotime, cerite, alanite, and many other types of mineralization in lesser amounts. Due to the increasing demand for REEs and their criticality in the supply chain, the need to explore secondary sources of REEs has gained tremendous importance.

Secondary sources of REEs include but are not limited to acid mine drainage (AMD), red mud, phospho-gypsum, and coal byproducts. In recent years, the extraction of REEs from AMD has been a significant study area targeting both sustainable mining activities and contributing to environmental conservation efforts. Solvent extraction, leaching, precipitation, and ion exchange have all been investigated as conventional extraction techniques for REEs from AMD. Still, the high cost and environmental impacts of these techniques have posed significant concerns and brought the need for an assessment of other techniques.

Research has demonstrated that adsorption is a simple, cost-effective, and environmentally friendly technique for extracting REEs from aqueous solutions. Biochar, a low-cost and environmentally benign adsorbent, was used in this study to investigate the adsorption process of rare earth elements from aqueous solutions, with the objectives of evaluating different biochar types and their adsorption capacities, physical and chemical properties, and desorption capacities. Biochars derived from Appalachian hardwood (AH), wood chip and chicken litter (WCC), and softwood (SW) were subjected to various pyrolysis temperatures of 675 °C, 700 °C, and 450 °C, respectively, and their adsorption performance was systematically examined.

As samples for simulating AMD solutions, aqueous solutions of lanthanum and a mixed solution of critical metals and REEs were used. The effects of pH, contact time, and initial elemental concentration on REE adsorption were evaluated at room temperature. According to the results, the optimal pH level for the single element (i.e., La-only) adsorption tests was 5, and the optimal contact time was 24 hours. The adsorption capacity of AH was 126.85 mg/g, which was higher than that of WCC and SW. Adsorption kinetics for the La-only system were consistent with a pseudo-second-order reaction, while the Langmuir isotherm provided the best fit for the system. Examination of the changes in biochars surface area and properties before and after the La (III) adsorption was completed using scanning electron microscopy (SEM), Fourier-Emmett-Teller (BET) analysis, and zeta potential measurements. Due to AH's high capacity, it was also used for the mixed solution, and the results indicated a 100% adsorption of REEs from aqueous solution, without any selectivity between different REEs. This indicates that future research must be devoted to functionalizing the biochars to achieve selective adsorption. Lastly, desorption tests were conducted, assessing different methods to support the economic and environmental feasibility of the process. Among the three desorbents studied, nitric acid outperformed hydrochloric acid and sodium hydroxide. Overall, biochar has the potential as an eco-friendly substance for efficiently removing REEs from aqueous solutions.

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