Impact of REE Mining on Coastal Groundwater: Numerical Modelling and Remediation Potential of Clay-Amended Laterites

Abstract

Coastal aquifers are vulnerable to contamination due to extensive beach sand mining and effluents from processing plants, leading to heavy metal dispersion in groundwater. This study integrates hydrodynamic and geochemical modelling to predict contaminant transport and evaluates the effectiveness of clay-amended laterite mixtures in immobilising heavy metals. A 3D transient state finite element model (FEFLOW) was developed to simulate the transport mechanisms of titanium (Ti), iron (Fe), and magnesium (Mg) in the Chavara coastal zone, considering advective–dispersive transport and geochemical interactions. Results indicate significant contaminant plume migration along primary flow paths influenced by macro-scale hydrodynamics (groundwater flow) and micro-scale adsorption kinetics of laterite. Forecasting highlighted significant southwest movement of contaminants with maximum velocities of 18.40 m/day. The 7-year hydraulic modelling scenario predicts dispersion over 6.2–7.1 km2 area, emphasising groundwater vulnerability to pumping rates. Contaminant levels reached concentrations of Fe—180 ppm, Mg—48 ppm, and Ti—0.56 mg/L ppm. Simulation shows a 21.6% reduction in hydraulic head and a 71.34% decrease in storage capture with increased extraction, compared to a 0.61% head reduction from variations in specific storage. The study also explores heavy metal immobilization using laterite soil modified with bentonite, kaolinite, and zeolite clay through Langmuir and Freundlich adsorption models. Bentonite-amended laterites demonstrated the highest adsorption efficiency (K<inf>d</inf>—54.8 L/kg for Ti, 22.1 L/kg for Fe, and 17.9 L/kg for Mg), attributed to its expansive interlayer structure and high cation exchange capacity. This research provides a multiscale interdisciplinary approach offering sustainable solutions for groundwater remediation in industrial coastal regions. © The Author(s), under exclusive licence to Springer Nature Singapore Pte Ltd. 2025.