A multiple isotope (S, H, O and C) approach to estimate sulfate increasing mechanism of groundwater in coal mine area

Pinghua Huang; Yanni Zhang; Yuanmeng Li; Hongfei Gao; Mengke Cui; Shuangwei Chai

doi:10.1016/j.scitotenv.2023.165852

A multiple isotope (S, H, O and C) approach to estimate sulfate increasing mechanism of groundwater in coal mine area

Sci Total Environ. 2023 Nov 20:900:165852. doi: 10.1016/j.scitotenv.2023.165852. Epub 2023 Jul 28.

Authors

Pinghua Huang¹, Yanni Zhang², Yuanmeng Li³, Hongfei Gao³, Mengke Cui³, Shuangwei Chai³

Affiliations

¹ School of Resources and Environment Engineering, Henan Polytechnic University, 454000 Jiaozuo, China; Collaborative Innovation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region, 454000 Jiaozuo, China. Electronic address: hph2001@hpu.edu.cn.
² School of Resources and Environment Engineering, Henan Polytechnic University, 454000 Jiaozuo, China. Electronic address: zynhpu2017@163.com.
³ School of Resources and Environment Engineering, Henan Polytechnic University, 454000 Jiaozuo, China.

PMID: 37517724
DOI: 10.1016/j.scitotenv.2023.165852

Abstract

Groundwater in North China type coal mine area is an important source of domestic, industrial and agricultural water. To explore the sulfate increasing mechanism of groundwater in mining area and identify key influencing factors. In this paper, hydrochemistry and multi-isotope tracer techniques such as δ³⁴S_SO4, δ¹⁸O_SO4, δ²H_H2O, δ¹⁸O_H2O and δ¹³C_DIC were used to study the groundwater circulation law and the migration and transformation mechanism of sulfate and carbonate in coal mine area. The results show that: the hydrochemical types of groundwater in the coal mine area are mainly HCO₃^- and SO₄^2- anions, while the cations are mainly Ca²⁺ and Mg²⁺. The sulfate content is significantly increased, and the pH shows weak alkalinity; the relationship between δ¹⁸O_H2O and δ¹⁸H_H2O shows that the dynamic field of groundwater changes significantly after coal mining or closure, and limestone water mainly comes from surface water recharge through 'skylight' infiltration. The relationships between δ¹⁸O_SO4 and δ¹⁸O_H2O, δ³⁴S_SO4 and δ¹⁸O_SO4 show that the sulfate in groundwater of coal mine area is mainly derived from sulfide oxidation. The ∆δ¹⁸O_SO4-H2O value of groundwater in coal mine area is greater than 8 ‰, and the oxygen content in sulfate is 25 %-75 % from oxygen in water, indicating that coal mining has disturbed the groundwater in the study area from reducing environment to oxidizing environment, promoted sulfide oxidation, and accelerated the dissolution of carbonate minerals. The δ¹³C_DIC value and δ³⁴S_SO4 value in the coal mine area are inversely proportional. The δ¹³C_DIC of groundwater in the coal mine area is affected by the δ³⁴S_SO4 value to a certain extent. Sulfuric acid participates in the dissolution of carbonate minerals, making the pH value weak and alkaline as a whole. This paper expounds the migration and transformation law of sulfate in groundwater in coal mine area, which has practical significance for groundwater quality management. The research results can provide theoretical support for the rational development and utilization of groundwater resources in coal mine areas.

Keywords: Coal mining; Groundwater; Limestone aquifer; Multi-isotope; Sulfate increasing mechanism.