Performance and Field Testing of Geotextiles for dewatering Rare Earth Element Hydraulic Preconcentrate from Hardrock AMD

Author

Ian R. Bird, West Virginia UniversityFollow

Semester

Fall

Date of Graduation

2024

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

John Quaranta

Committee Member

Hema Siriwardane

Committee Member

Leslie Hopkinson

Committee Member

Nathan DePriest

Abstract

As part of ongoing efforts to develop a domestic Rare Earth Elements (REE) supply chain the Hydraulic Preconcentrate (HPC) produced at the Horseshoe bend treatment plant (HsB) was manufactured and evaluated as a potential source for feedstock. After the existing clarifiers on the site were flipped to the desired pH set points, HPC was manufactured and pumped to 24 geobags. The geobags were then passively dewatered to increase the total solids percentage. The geobags evaluated were comprised of: Woven geotextiles, composite (woven and non- woven), and geobags augmented with Capillary Channel Fiber (CCF). Column Filtration Tests (CFTs) were performed onsite to provide laboratory values for hydraulic conductivity. Throughout the dewatering, the geobags were sampled periodically to determine their rate of dewatering. Samples of influent taken from HsB were tested for Specific Gravity (Gs), Atterberg limits, and Grain Size Distribution (GSD). The GSD indicated a gap graded material with the vast majority of particles having a diameter of between 0.5-0.05 mm. Hydraulic conductivity values for the filter cakes developed on the woven and nonwoven geotextiles during Column Filtration Testing ranged from 0.5 to 2.5 m/d (5.43x10-3 to 2.89x10-3 cm/s). With these material properties, the HsB HPC is most equivalent to an ML-Silt using standard USCS soil classification. During the year of passive dewatering the geobags increased the total solids percentage (TS%) of the HPC from an average influent of 9.7% to a final average of 62.4%. With a mean and total solids percentage of approximately 40% across all samples after approximately 40 days of dewatering. Field sampling of the geobags also uncovered considerable cracking of the material within the geobags.

Recommended Citation

Bird, Ian R., "Performance and Field Testing of Geotextiles for dewatering Rare Earth Element Hydraulic Preconcentrate from Hardrock AMD" (2024). Graduate Theses, Dissertations, and Problem Reports. 12687.
https://researchrepository.wvu.edu/etd/12687