Filtration Studies for Geotextile Selection to Produce Rare Earth Elements Preconcentrate

This research investigates geotextile filtration efficiencies for large-scale dewatering of a two-stage selective precipitation acid mine drainage (AMD) treatment process to recover rare earth elements (REE) sludge. The REE precipitate contained particle sizes of 8.5 × 10^–5 mm, which are much smaller than the typical AMD single-split particle size flocs that are filtered and dewatered using geotextiles for treatment. Laboratory tests involved vertical column filtration experiments incorporating woven and nonwoven geotextiles under falling head permittivity tests with different AMD precipitate solutions. Treatment protocol variations included polymer dosage added at each supernatant split (ppm), physical condition of the precipitate (raw/sheared/not sheared), and total solids generated as flocculated precipitate. The testing matrix contrasted the geotextile type (woven vs. nonwoven) with the selective precipitate to evaluate geotextile, filtration efficiency, precipitate filter cake formation, and system hydraulic conductivity. The nonwoven geotextiles included apparent opening size (AOS) of 0.149 mm, and 0.21 mm, while the woven geotextile had an AOS of 0.41 mm. Findings indicated that the nonwoven geotextile demonstrated the highest filtration efficiency (> 90%) in comparison to a standard woven geotextile (30%) in worst case scenario treatment. The results also showed no significant difference in the hydraulic conductivity of the filter cake/geotextile for a test sample when varying flocculation.