Semester

Fall

Date of Graduation

2023

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mining Engineering

Committee Chair

Qingqing Huang

Committee Member

Deniz Talan

Committee Member

Vladislav Kecojevic

Committee Member

Hassan Amini

Abstract

Critical minerals (CMs) are defined as crucial elements for the country's economy due to the development of new cutting-edge applications and the risk of an eventual disruption in their supply chain. The unique chemical and physical properties of the CMs have made these elements decisive in the growth of industries such as telecommunications, army, medicine, Aerospace, etc. In 2022, the US Geological Survey established a list of 50 CMs, including manganese, cobalt, nickel, aluminum, magnesium, and others. Of the total of CMs, 26 are 100% imported from outside the United States (Venditti, 2022).

Driven by the ever-increasing demand for critical minerals (CMs) and the need to diversify their supply chains, extensive research efforts have been devoted to extracting CMs from various secondary sources, such as fossil fuel (coal ash and refuse), mining tailings, refuse piles, water produced by oil and gas industry, electronic waste (E-waste), and acid mine drainage (AMD), among which acid mine drainage and its treatment byproducts proved to be a viable source. Characterization studies of different AMD and sludge materials indicate the occurrence of CMs containing rare earth elements (REEs), cobalt, manganese, nickel, zinc, aluminum, magnesium, etc. In this context, our research aimed to develop an optimized hydrometallurgical process for extracting multiple individual CM concentrates, including cobalt, manganese, and nickel, from acid mine drainage treatment byproducts.

The feedstock used throughout is an REE solvent extraction raffinate loaded with cobalt, manganese, and nickel, with grades corresponding to 38.3 mg/L, 370.7 mg/L, and 69.4 mg/L, respectively, as well as impurity metals such as 3643.1 mg/L of aluminum, 2161.4 mg/L of magnesium, 224.1 mg/L of calcium, and 159.2 mg/L of iron. A hydrometallurgical process developed at the laboratory scale consists of an initial sodium hydroxide precipitation using 2M NaOH until reaching a pH value equal to 5. The approach targeted the upstream removal of impurities such as aluminum and iron and was established by performing stagewise precipitation from an initial pH of 2 to a final value of 12. The optimum pH values were identified by taking samples at each pH setpoint and analyzing the tradeoff between CM recovery and impurity removal. Afterward, a solution with a higher concentration of CMs and lower impurity content was subjected to a new precipitation process with 2M NaOH until reaching pH 10 to generate a precipitated product rich in CMs. The precipitated solids obtained at the pH range of 5 to 10 were treated to separate cobalt and nickel from manganese. The procedure carried out in this stage was a nitric acid washing (HNO3), which was performed under controlled conditions of temperature, time, volume, etc. Two products were obtained in this stage: a dissolved solution with an extractable concentration of cobalt and nickel (393 mg/L and 619.9 mg/L, respectively) and a solid product with a manganese purity of 47.9% by weight. To continue separating cobalt and nickel from remaining impurities, such as magnesium, a new stagewise precipitation with sodium sulfide (Na2S) at 1M was performed to determine the separation feasibility of different elements in the solution. At this stage, three separation steps were determined to generate three solid products: the solid precipitated at the pH range of 1-5 with 5.1 wt.% of cobalt and 8 wt.% of nickel, solids precipitated at pH 5-10 with 20.15 wt.% of manganese, and the solid product at pH 10-12 with 27.49 wt.% of magnesium. Other separation approaches were also evaluated in this study to assess the possibility of separating cobalt from nickel, including oxidative precipitation and solvent extraction. As a result of all these combined studies, the highest cobalt and nickel purity of 9.92 wt.% and 14 wt. % were generated, respectively, in addition to the manganese (47.9 wt. %) and magnesium (27.49 wt. %) products obtained from the developed process.

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