Attenuation of Metals by Geothermal Muds: A Case Study from the Copahue System

Abstract

Geothermal systems, characterized by unique physicochemical conditions, are increasingly recognized for their potential applications in various fields of biotechnology. However, the specific role of geothermal muds in the natural attenuation of metal contaminants, particularly through adsorption, remains largely unexplored. This study addresses this knowledge gap by investigating the heavy metal retention capacity of four distinct geothermal muds from the Copahue system (Argentina), a region affected by geogenic contamination. Our objective was to characterize their mineralogical composition, geochemical properties, and adsorption efficiency for Cd, Cu, and Cr to elucidate the underlying attenuation mechanisms. Through comprehensive physicochemical analyses (e.g., XRD, XRF, CEC) and batch adsorption experiments, we found that Copahue geothermal muds, rich in clay minerals (e.g., kaolinite, illite) and amorphous iron oxides, exhibit a remarkable capacity to sorb dissolved metals. The muds demonstrated high removal efficiencies, achieving up to 98% for Cd, 96% for Cu, and 99% for Cr under optimal conditions. Adsorption isotherm modelling revealed that both Langmuir and Freundlich models adequately describe the metal uptake, suggesting a combination of monolayer adsorption on heterogeneous surfaces and surface precipitation. Cation exchange capacity and the presence of hydroxylated mineral surfaces were identified as key factors influencing metal retention. These findings highlight the significant potential of geothermal muds as effective natural sorbents, contributing to the immobilization and natural attenuation of heavy metals in active geothermal environments. The study provides novel insights into the biogeochemical cycling of metals in these unique systems and underscores the importance of these natural processes for environmental protection. Furthermore, the demonstrated high adsorption capacities suggest a promising avenue for exploring the application of these geogenic materials in passive remediation strategies for metal-contaminated waters.