The effectiveness of sodium-geosynthetic clay liner (Na-GCL) to control the low-pH leachate from metal industries

Purpose

This study investigates the effectiveness of sodium-bentonite geosynthetic clay liners (Na-GCLs) in controlling low-pH leachate from metal industries, simulating conditions in tailings impoundments at zinc and copper mines.

Methods

An experimental setup comprising five chambers was used to test Na-GCL performance under 100 kPa pressure with synthetic leachate at four pH levels (1, 3, 5, and 7) and deionized water as a control. The Na-bentonite was characterized using FE-SEM, FTIR, EDX, XRD, swelling index (SI), and pHpzc tests. Hydraulic conductivity (k) was modeled using the Katsumi approach. Leachate samples were collected every 14 days over a 4-month period and analyzed for heavy metal concentrations using ICP-OES.

Results

The swelling index of Na-GCL dramatically decreased from 16 to 2 mL/2 g when exposed to low-pH leachate, significantly impacting its performance. The point of zero charge (pHpzc) was determined to be 4.1. Adsorption capacity for heavy metals (Cu, Mn, Fe, Ni, Zn, and Pb) increased with higher pH values. The Katsumi model parameters for the relationship between hydraulic conductivity (k) and swelling index (SI) were a = -0.3, b = 8.69 mL/2 g-Solid, and R² = 0.875. FTIR analysis revealed subtle changes in OH vibrational peaks between pre- and post-leachate exposure bentonite.

Conclusion

Na-GCL performance is significantly affected by pH conditions, with decreased effectiveness in highly acidic environments typical of mining and metal industry waste. This highlights the need for careful consideration of leachate pH when selecting and implementing GCLs in landfill applications.