Occurrence and Removal of Copper and Aluminum in a Stream Confluence Affected by Acid Mine Drainage

Carolina Rodríguez,Eduardo Leiva,Jennyfer Serrano,Enzo Leiva-Aravena

doi:10.3390/w10040516

Abstract

Acid mine drainage (AMD) is an environmental concern characterized by low pH and high concentrations of dissolved metals and sulfate. Yerba Loca Creek in Santiago, Chile, is an AMD-affected water stream that originates in a glacier and, therefore, has a season-dependent flow. This water course is characterized by low pH (3.75 ± 0.13) and high concentrations of aluminum (2.2–2.6 mg/L) and copper (4.8–6.5 mg/L). A field campaign was carried out to study the geochemical behavior around the confluence of the Yerba Loca Creek with the San Francisco River, which has a neutral pH and low concentration of dissolved metals. The results show that the geochemical parameters after the confluence are very similar to those registered for the Yerba Loca Creek, due to its great flow in relation to the San Francisco River. The pH after the mixing zone was controlled by the geochemical conditions and flow of the Yerba Loca Creek; however, the turbidity decreases and stabilizes downstream. We found that, despite the low impact of pH on the precipitation of aluminum and copper phases due to poor neutralization, the dissolved aluminum and copper concentrations are slightly decreased after the mixing zone by natural microscale removal processes or suspended solids formation. Scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDX) analysis of suspended solids indicates the presence of various oxides, hydroxy-sulfates and aluminosilicates, which have a great affinity for adsorption and co-precipitation with dissolved metals (i.e., Al and Cu). A pH-neutralization would favor the formation of more minerals and, therefore, the immobilization of the heavy metals found in these waters. These results contribute to a better understanding of the effect of the confluence of water courses related to pollution by AMD. It is possible that the seasonal variation of the flows has an impact on the composition of water and minerals formed.

Highlights

Acid mine drainage (AMD) is a major problem all over the world
The studied confluence site is strongly influenced by the high flow of the Yerba Loca Creek, which is substantially higher than the flow of the San Francisco River in summer
The water quality of the San Francisco River after the confluence is heavily governed by the geochemical parameters of the Yerba Loca Creek

Summary

Introduction

Acid mine drainage (AMD) is a major problem all over the world. AMD is produced when sulfide-bearing material, from mine sites or natural sources, is exposed to water and oxygen [1,2].The main problem caused by AMD is pollution due to low pH, high concentrations of dissolved metals (i.e., iron, aluminum, copper, lead, zinc and silver, among others), metalloids (e.g., arsenic) and sulfate [3]. Acid mine drainage (AMD) is a major problem all over the world. AMD is produced when sulfide-bearing material, from mine sites or natural sources, is exposed to water and oxygen [1,2]. The main problem caused by AMD is pollution due to low pH, high concentrations of dissolved metals (i.e., iron, aluminum, copper, lead, zinc and silver, among others), metalloids (e.g., arsenic) and sulfate [3]. The level of environmental impact of AMD is dependent on its composition (i.e., which dissolved metals are present) and its pH values, in turn, depend on the geology of the AMD source [3]. Yerba Loca Creek is a natural water course located in Santiago, Chile, and is affected by AMD.

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