Reducing conditions increased the mobilisation and hazardous effects of arsenic in a highly contaminated gold mine spoil
Journal
Journal of Hazardous Materials
Journal Volume
436
Date Issued
2022
Author(s)
Abstract
Arsenic (As) redox-induced mobilisation and speciation in polluted gold mine sites in tropical climates largely remains unknown. Here, we investigated the impact of changes in soil redox potential (EH) (−54 mV to +429 mV) on mobilisation of As and its dominant species in an abandoned spoil (total As = 4283 mg/kg) using an automated biogeochemical microcosm set-up. Arsenic mobilisation increased (85–137 mg/L) at moderately reducing conditions (−54 mV to + 200 mV)), while its reduced (6–35 mg/L) under oxic conditions (+200 to +400 mV). This indicates the high risk of As potential loss under reducing conditions. The mobilisation of As was governed by the redox chemistry of Fe. XANES and EXAFS analyses showed that sorbed-As(V)-goethite, sorbed-As(III)-ferrihydrite, scorodite and arsenopyrite were the predominant As species in the mine spoil. As(V) dominated at oxic conditions and As(III) predominated at moderately reducing conditions, which may be attributed to either inability of arsenate bacteria to reduce As or incomplete reduction. Lower Fe/As molar ratios during moderately reducing conditions show that the mine spoil may migrate As to watercourses during flooding, which may increase the hazardous effects of this toxic element. Therefore, encouraging aerobic conditions may mitigate As release and potential loss from the mine field. © 2022 Elsevier B.V.
Subjects
Flooding; Gold mining; Hazardous effects; Mobilization; Toxic elements
Other Subjects
Economic geology; Gold mines; Hazards; Molar concentration; Molar ratio; Redox reactions; Arsenic(III); Floodings; Gold mining; Hazardous effects; Mine spoil; Mobilisation; Oxic conditions; Potential loss; Reducing conditions; Toxic elements; Floods; arsenic; ferric hydroxide; organic carbon; arsenate; arsenopyrite; flooding; gold mine; hazardous waste; mobilization; oxic conditions; redox potential; spoil heap; toxic substance; Article; automation; biogeochemical cycle; contamination; flooding; gold mining; hazardous waste; microcosm; mobilization; oxidation reduction reaction; pH; quality control
Type
journal article