Date

2018

Document Type

Thesis

Degree

Master of Science

Department

Mechanical Engineering

First Adviser

Banerjee, Arindam

Abstract

Solvent extraction was studied for the recovery of Rare Earth Elements (REEs) from refuse coal under static and dynamic conditions. Static extraction was performed using nitric acid (HNO3) digestion at elevated temperatures, up to 90℃. Dynamic extraction was performed in a flow apparatus using HNO3 and a complex prepared from TBP and concentrated HNO3 (TBP-HNO3 complex) in Supercritical Carbon Dioxide (SC-CO2) under high pressures, up to 3,000 psig. The reported recovery efficiency for three targeted REEs from refuse coal, Ce, La and Nd was less than 30% under static conditions and less than 5% under dynamic conditions, despite the fact that these three elements exist in the highest concentrations of all of the REEs in the coal samples. However, a hydrometallurgy method for REEs recovery from coal was investigated, providing the opportunity to understand and identify modifications required by the approach to improve REE recovery efficiency. Additionally, the use of SC-CO2 as a polarity matching stream for REE carry and subsequent reduction, was identified as an important step in a dynamic REE extraction process, which would require process optimization. For static extraction of Ce, La and Nd from refuse coal with heated HNO3 and TBP-HNO3 complex digestion, a temperature and time of 90℃ and 4 hours were identified from these static experiments, which improve the extraction efficiency of Ce and La with TBP-HNO3 complex reaching 18.84% and 26.32%, respectively, while with HNO3, extraction efficiency of 11.90 % and 6.26% were achieved, respectively. Nd was insensitive to this extraction method. For dynamic extraction, with a SC-CO2 flow rate of 2.5 L/min, pressure and extraction time play an important role in using TBP-HNO3 complex to extract REE from refuse coal.

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