Methodology for enhanced filtration and dewatering of fine-grain AMD precipitate using geocomposites for rare earth elements recovery
Year: 2022
Type: dissertation
Abstract: Research performed by the West Virginia Water Research Institute (WVWRI) in partnership with the Department of Energy (DOE) has identified that coal mining by-products contain significant amounts of Rare Earth Elements (REEs). REEs currently are in high demand, and extraction from coal mining reject presents a potential for commercialization if extraction is feasible. The coal mining reject include Acid Mine Drainage (AMD) in the aqueous phase and sludge from AMD treatment. A novel two split selective precipitation method was implemented to remove gangue metals, increasing the concentration of REEs in the sludge. This process presents a two-fold benefit: 1) treatment and maintenance of AMD producing sites, and 2) creation of an REE precipitate for further metal extraction and separation. Exploring AMD in the aqueous form is beneficial because of its long-term future availability. Underground mines, refuse piles, valley fills are examples of sites providing aqueous sources. This research was performed to produce, collect, and dewater the REE sludge that will feed the extraction and separation phases. The research consists of three phases: 1) augmenting the sludge precipitation with polymer aided flocculants and determining the optimum dosage for the two-split treatment sludge settling and filtration, 2) testing the defined chemical dosages in a bench-scale production, and 3) performing tests to filter and dewater the sludge. The first phase was performed by testing six polymer-aided flocculants and one coagulant to identify the more suitable floc production. The six polymers vary in their charge and density but are equal in structure (linear chain), and the coagulant has a neutral charge. A series of jar tests were performed according to ASTM requirements to evaluate formed floc size, precipitation velocity, supernatant turbidity for each flocculant, and coagulant under different dosages. The selected flocculant candidate was a cationic flocculant with a medium charge. The produced floc sizes ranged from 2 mm to 20 mm, and turbidities ranged from 0.6 to 1.1 NTU. Next, the optimum dosage was defined, envisioning floc dewaterability capability identified by the Specific Resistance to Filtration (SRF) test, producing a floc size of 9mm. The second phase was the proof-of-concept of a continuous operation. A simulation of an AMD treatment station with selective precipitation was designed, built, and commissioned in a 20L clarifier. The operation showed it is possible to maintain the targeted pH of 4.5 and 8.5 +/- 0.2 and precipitate large flocs (5 mm to 8 mm size range) that can
DOI: 10.33915/etd.11444
Author: Iuri Lira Santos
Institution: West Virginia University
Language: English
Subfield: Water Science and Technology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4292249714