Different Sorption Approaches and Leachate Fluxes Affecting on Mn²⁺ Transport through Lateritic Aquifer

Abstract

Problem statement: Contamination of the underlying aquifer beneath a mining area is usually of great concern even when a prevention plan has been implemented. Approach: To assess the potential risk of heavy metal contamination, the simulation of heavy metal transport was carried out with different leachate fluxes and sorption parameters derived from equilibrium models with linear and Langmuir isotherms and chemical non-equilibrium two-site model. The HYDRUS-2D numerical model was applied to simulate the transport of Mn²⁺ under single- and multi-metal systems with two variable leachate fluxes (0.002 and 0.0026 m day^-1) through the lateritic aquifer, approximately 5 km down gradient of the tailing pond. The model assumed that the compacted clay layer of the Tailing Storage Facility (TSF) had been cracked and led to contamination of the shallow ground water. Results: The simulation showed that the time required to reach the Thailand drinking water standard at a specific location of Mn²⁺ for multi-metal system were faster than those for single metal systems, although different models were applied. The Mn²⁺ concentration fronts derived from simulation with chemical non-equilibrium two-site model came earlier than those of both equilibrium models under single and multi-metal systems. In addition, with a 30% increase in the leachate flux, from 0.002-0.0026 m/day, the time required to reach the drinking water standard at the nearest well, 1 km down-gradient from the source (well 1) decreased. It took about 57 and 106 years (a 17 and 19% decrease, respectively) for Mn²⁺ under multi- and single-metal systems, respectively. Conclusion: In conclusions, sorption parameters and leachate fluxes should be carefully determined and these predictive patterns used as a management tool for planning water well installations under field conditions.