Field data from AMD-impacted sites, including locations in the northeastern parts of India, were used to perform geochemical simulations, employing tools such as PHREEQC and saturation index analysis to predict metal behavior and precipitation potential across varying pH conditions. Principal Component Analysis (PCA) and Ficklin plots supported contaminant source identification and mobility assessment.
Initially treatment schemes were studied with AMDTreat and other design simulations
to understand techno-economical viability. Thereafter, batch and continuous experiments were performed which involved pH-regulated precipitation for iron and aluminum removal, followed by downstream nanofiltration (NF) for sulfate reduction to below 10 ppm. Energy-efficient operation (~0.62 kWh/m³) and minimal sludge generation were achieved. Concurrently, in-situ precipitation of ettringite (Calcium aluminum sulfate) (Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O) was investigated as a sustainable recovery technique for aluminum and sulfate. After successful experimental trials, treatment of AMD water with ettringite recovery was demonstrated in a semi-pilot level prototype which integrated treatment, sludge disposal and value-added product recovery in modular units characterized by a high degree of process intensification.
This combined approach provides a scalable solution that addresses environmental remediation and circular economy goals by enabling water recovery and the stabilization and/or recovery of byproducts.
Keywords: Acid Mine Drainage, Ettringite, Geochemical Modeling, Nanofiltration, Reverse Osmosis, Water Reuse, Sustainability, Resource Recovery