Bioremediation of Uranium- and Nitrate-Contaminated Groundwater after the In Situ Leach Mining of Uranium

Rehemanjiang Wufuer,Jia Duo,Jinglong Fan,Xiangliang Pan,Wenfeng Li

doi:10.3390/w13223188

Abstract

Uranium and nitrate are common groundwater pollutants near in situ leach uranium mines. However, we still lack techniques that can simultaneously immobilize uranium and reduce nitrate using a single bacterial species. In this study, the potential of simultaneous uranium immobilization and nitrate reduction by a single AFODN (anaerobic Fe(II) oxidizing denitrifier), Clostridium sp. PXL2, was investigated. Clostridium sp. PXL2 showed tolerance to U(VI) concentrations varying from 4.2 µM to 42 µM. The U(VI) immobilization and nitrate reduction rates in groundwater samples inoculated with this bacterium reached up to 75.1% and 55.7%, respectively, under neutral conditions. Exposure to oxidation conditions led to further U(VI) removal but did not show any noticeable effect on nitrate reduction. The U(VI) immobilization rate reached up to 85% with an increased Fe(II) initial concentration, but this inhibited nitrate reduction. SEM (scanning electron microscopy) coupled with EDS (energy dispersive spectroscopy) showed that the U(VI) immobilization was mainly due to sorption to amorphous ferric oxides. U(VI) and nitrate bioremediation by AFODNs, including Clostridium sp. PXL2, may provide a promising method for the treatment of uranium- and nitrate-contaminated groundwater after the in situ leach mining of uranium.

Highlights

Uranium pollution has become a serious environmental concern because of extensive uranium mining, leaching, and the poor processing of by-products generated during mining activities [1]
ISL techniques were developed in the USA and have been broadly used in Eastern Europe, including the former Soviet Union, and some parts of Asia
The permissible value for uranium in drinking water is set as 2.0 mg L−1 by the World Health Organization [6] and is 30 μg L−1 in the USA [7]

Summary

Introduction

Uranium pollution has become a serious environmental concern because of extensive uranium mining, leaching, and the poor processing of by-products generated during mining activities [1]. The leaching solutions from ISL mines contain high levels of uranium and nitrate, which contaminate nearby aquifers and cause serious pollution to the groundwater. The permissible value for uranium in drinking water is set as 2.0 mg L−1 by the World Health Organization [6] and is 30 μg L−1 in the USA [7]. Nitrate is another common pollutant produced by uranium leaching and processing due to the use of nitric acid or ammonia [8,9]. The guideline value for nitrate in groundwater is set as 10 mg L−1 in many countries [12]

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Results