Influência de lixiviados de mineração no comportamento hidráulico de geocompostos bentoníticos (GCLs)

Abstract

Brazil’s mining industry, a major economic sector, presents high potential for environmental contamination. Conventional geosynthetic clay liners (GCLs) with natural sodium bentonite (NaB) may fail hydraulically when exposed to aggressive mining leachates (high ionic strength/extreme pH), as these liquids reduce osmotic swelling and cause flocculation. Most studies address GCLs with natural sodium and granular bentonites. In Brazil, however, sodium-activated calcium bentonites (CaB) are commonly used due to their abundance, mostly available in powdered form. Bentonite–polymer composites (BPCs) appear as alternatives, but polymer elution remains a concern, and the performance of BPCs with CaB under mining leachates is still little known. This study evaluated the hydraulic performance and viability of GCLs and BPCs produced with sodium-activated calcium bentonite (CaB), both unmodified and modified with linear and/or cross-linked polymers, as alternatives to natural sodium bentonite (NaB). These materials were tested under different mining leachates, saline, and extreme pH solutions. The effects of mineralogy and bentonite grain size were analyzed to understand their influence on GCL hydraulic behavior. Additionally, BPCs using three polymer types were investigated to enhance GCL performance for specific mining applications. Hydraulic conductivity (k) and swell index (SI) tests were performed, including analyses of pre-hydration and granulometry (powder, fine/coarse granular). All bentonites showed reduced swelling and increased k when in contact with mining liquids. GCLs made with sodium-activated calcium bentonites (CaB) generally outperformed those with natural NaB, often meeting the < 5×10⁻¹¹ m/s requirement. CaB mineralogy was less affected, and its powdered granulometry had a stronger impact on performance. Pure CaB GCLs, however, exhibited higher k in aggressive leachates. BPCs, especially those with CaB and linear polymers (Y) or specific combinations, showed improved chemical resistance, maintaining low k (< 5×10⁻¹¹ m/s) due to pore blocking by hydrogels. Fine bentonite particles were crucial under high ionic strength, outweighing mineralogical effects. Pre-hydration in water was also essential for performance. Polymer addition enhanced hydraulic behavior, but the polymer type must match the leachate chemistry. Polymer selection and granulometry determined resistance to elution. Overall, Brazilian sodium-activated calcium bentonites (CaB) in fine granulometry, modified with appropriate polymers, represent a viable and technically effective alternative to NaB in GCLs for aggressive mining leachates.