Distribution and mobilization of heavy metals at an acid mine drainage affected region in South China, a post-remediation study

Chen Luo,Joyanto Routh,Mårten Dario,Soumyajit Sarkar,Lezhang Wei,Dinggui Luo,Yu Liu

doi:10.1016/j.scitotenv.2020.138122

Abstract

Dabaoshan Mine Site (DMS) is the largest polymetallic mine in South China. The Hengshi River flowing next to DMS receives acid mine wastes leaching from the tailings pond and run-off from a treatment plant, which flows into the Wengjiang River. This study focuses on spatiotemporal distribution and mobilization of As, Cd, Pb, and Zn along the Hengshi River, groundwater, fluvial sediments, and soils, with a focus on As due to its high toxicity and the fact that mining is one of the main sources of contamination. Geochemical analyses (heavy metals, grain-size, X-ray diffraction, organic carbon and sulfur content) followed by geochemical modeling (PHREEQC) and statistical assessment were done to determine the physicochemical characteristics, toxicity risks, and behavior of heavy metals. Near the tailings pond, heavy metal concentrations in surface water were 2–100 times higher than the Chinese surface water standard for agriculture. Although water quality during the dry season has improved since the wastewater treatment plant started, heavy metal concentrations were high during rainy season. In groundwater, heavy metal concentrations were low and pose little risks. Soils along the Hengshi River were disturbed and they did not show any specific trends. The potential ecological risk of heavy metals was ranked as Cd > As > Cu > Pb > Zn in sediments and Cd > Cu > Pb > As > Zn in soils indicating multi-metal contamination and toxicity. As(III) was the predominant species in surface water during the dry season, whereas As(V) dominated during the rainy season. Arsenic levels in most sites exceeded the Chinese soil standard. Although As is assumed to have a moderate ecological risk in sediments and low risk in soils, anthropogenic activities, such as mining and land-use changes contribute to the release of As and other heavy metals and pose a risk for local residents.

Highlights

Acid mine drainage (AMD) is a well-known environmental problem in many sulfidic mines (Cheng et al, 2009; Johnson and Hallberg, 2005)
The concentration of As, Cd, and Pb were 173, 380, and 2070 μg/L, respectively. pH in surface water increased along the Hengshi River, whereas electrical conductivity (EC), salinity, and total dissolved solids (TDS) decreased as distance increased from the tailings pond and treatment plant
The behavior of As and other heavy metals at Dabaoshan Mine Site (DMS) affected by AMD is a complex and dynamic process where several factors play a role

Summary

Introduction

Acid mine drainage (AMD) is a well-known environmental problem in many sulfidic mines (Cheng et al, 2009; Johnson and Hallberg, 2005). Oxidation of sulfide-rich minerals such as pyrite (FeS2) is the main cause of AMD (Johnson, 2003). This process happens naturally, especially where large outcrops of sulfidic minerals are exposed to weathering and there is access to surface water and/heavy precipitation. The damage to the surroundings is mainly due to acidification and leaching of heavy metals, and the area around AMD sites consists of contaminated surface and groundwater and soils that affect the flora and fauna (Bhattacharya et al, 2006; Gray, 1997; Herlihy et al, 1990; Simate and Ndlovu, 2014). The AMD sites pose an environmental health hazard and a major challenge for cleaning up toxic contaminants and implementing on-site restoration activities (Gray, 1997; Simate and Ndlovu, 2014)

Objectives

Methods

Results

Discussion

Conclusion