Assessment of the effectiveness of a low permeability layer made of sand amended with superabsorbent polymers as a barrier to oxygen and water

ABSTRACT: This study aims to evaluate the feasibility and effectiveness of a low saturated hydraulic conductivity (LSHC) layer composed of natural sand modified with sodium polyacrylate (Na-PA) superabsorbent polymers (SAPs) as an oxygen and/or water barrier in fine tailings impoundment cover systems. A specific type of fine-grained SAP, SAG-M85F, was chosen to amend the sand layer. Saturated hydraulic conductivity (ksat) tests were conducted using varying dosages of SAP in the sand (0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1.0%), along with infiltration tests using instrumented columns. The permeability tests revealed that the ksat of the LSHC layer (sand-SAP mixture) decreased with increasing proportions of SAP, ranging between 10-7 and 10-8 m/s, compared to the ksat measured for the sand alone (control) at 10-5 m/s. This represents a reduction of 2 to 3 orders of magnitude. Furthermore, the instrumented column tests demonstrated that, depending on the SAP dosage, the LSHC layer (sand-SAP mixture) became impermeable to water after the SAP transformed into a gel during rinsing. In addition, The LSHC layer, composed of the fine sand-SAP mixture, effectively acts as a moisture retention layer, achieving the targeted objective of limiting the oxygen flux to less than 1 mol/m²/year. These findings highlight the potential of utilizing a sand-SAP mixture as an LSHC layer in tailings cover systems, offering an effective barrier against oxygen and water infiltration.