Characteristics of water contamination in abandoned coal mines: a case study on Yudong River area, Kaili, Guizhou Province, China

Xiangdong Li,Qiyan Feng,Jieying Cai,Di Chen

doi:10.1007/s40789-021-00466-w

Abstract

The seasonal and spatial changes in the chemical composition of the water in abandoned mine drainages and rivers in Yudong River area in the years of 2017–2018 were analyzed. The effects of mine water drainage on the seasonality and physicochemical properties of the river water after mine closure were evaluated, and the feasibility of irrigation using river water and the degree of pollution to farmland were assessed using the Water Quality Standard for Farmland Irrigation. The results show that the mine water has low pH value (< 3.5–4) and high levels of total hardness, SO42−, Fe, Al, and Zn. In addition, the pH of the mine water is negatively correlated with the presence of other metal ions. The correlation coefficient between the chemical oxygen demand (COD) and Fe reached 0.989. While the pollution levels of Pinglu and Baishui rivers were low, the confluence region of the two rivers was seriously polluted. However, only the levels of Fe and Cd slightly exceeded the Surface Water Environmental Quality Standard after the confluence of Yudong and Chongan rivers. Overall, the heavy pollution type of the confluent river is consistent with mine water pollution. The water quality is slightly better in the dry season compared than in the high-water period. Sulfate and Fe content decreased by 39 and 16 mg/L, respectively, and Cd content decreased two-fold. Despite these findings, this study shows that from 2017 to 2018, the pH and Cd content of the rivers at the confluence exceeded the irrigation limit and the water quality continued to deteriorate, which may pose a soil contamination risk. Long-term use of the river for irrigation water may cause toxic elements such as Cd, Fe, Mn, SO42−, Al, and F- to enter the food chain, thereby endangering the life and health of villagers in Yudong River area.

Highlights

In recent years, following the imperative for ‘‘clean, green, and low-carbon’’ energy revolution (Huang et al 2017), China has introduced policies to vigorously integrate coalThe large-scale exploitation of coal resources in Yudong River area began in the early 1980s
The Piper diagram of the mine water’s chemical composition shows that SO42- is the main anion in the sample, and it is concentrated in the Ca, Fe, and Al fields (Fig. 3)
This study shows that in the study area, even after the mines were closed, the pollution of Yudong River from mine water persisted

Summary

Introduction

The large-scale exploitation of coal resources in Yudong River area began in the early 1980s. More than 80 recorded coal mines have been worked in Yudong River area. 16 coal mines were merged and reorganized, and 26 privately owned mines were closed by the government or were closed on their own. 16 unnamed small kilns remain; most are privately owned, small-scale, and have henhouse-like structures that have been abandoned for a long time. Coal mines are associated with large amounts of pyrite (FeS2), which, after mine closure, becomes exposed to air or immersed in oxygen-rich water, forming acidic mine water with sulfate-rich ions and severely low local pH values (pH up to 2), producing a series of oxidation reactions (Masindi et al 2016). As the pH values decrease, Fe3? activity increases and further acts on pyrite as below(Nordstrom 2015; Masindi 2016):

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