Environmental Hazard Assessment of Storage Conditions of Wastes from Mining and Processing of Arsenopyrite Minerals

Le Thu Thuy1, *, Tran Hong Con2, Nguyen Trong Hiep3, Vu Thi Minh Chau3, Le Minh Tuan4, Do Hoang Linh2

1 Hanoi University of Natural Resources and Environment, Hanoi, Vietnam

2 Hanoi University of Science, Vietnam National University, Hanoi, Vietnam

3 Southern Branch of Joint Vietnam-Russia Tropical Science and Technology Research Center, Ho Chi Minh, Vietnam

4 Institute of science and technology for energy and environment, Vietnam Academy of Science and Technology, Ho Chi Minh, Vietnam

* e-mail: ltthuy.mt@hunre.edu.vn

Abstract

Arsenopyrite is a common mineral of the sulphide class, belonging to minerals of hydrothermal genesis. On anthropogenic dumps, arsenopyrite is exposed to weathering agents and releases arsenic into the environment. In areas, where Cu, Pb, Zn minerals are mined, arsenic contamination of the environment is a serious problem. The results of this study show that arsenopyrite ores are capable of releasing arsenic and heavy metals during weathering on dumps under seepage and flooding conditions. The paper presents the results of a laboratory experiment on a developed simulation model of substance change in ore mine dumps under two conditions: seepage (modelling open ore dumps through which rainwater seeps) and flooding (modelling ore dumps stored in flooded lowland areas). The modelling conditions were consistent with the real ones. The ratio of arsenopyrite and sand was 1:20. The duration of the experiment was 60 days, which allowed determining arsenic in different chemistries. During the experiment under water seepage conditions, pH decreased and redox potential varied from 5 to 50 mV. With decreasing pH, release of metals and arsenic into the environment increased over time. Once pH reached values characterising an acidic environment (2.0–4.5), weathering markedly accelerated. Under conditions of excess water with high dissolved oxygen content, metals released faster. When pH was between 5.5 and 6.0, the rate of metal release decreased. When the ore was oxidised, iron in the divalent form Fe(II) slowly oxidised to Fe(III) at the pH value above. Under these conditions, Fe(III) was hydrolysed in the column. Thus, the released arsenic was adsorbed on Fe(III) and the resulting iron hydroxide Fe(OH)3 coated the ore particles. Due to the reduced contact of the waste ore with the aqueous medium, the arsenic concentration continued to decrease. Under both seepage and flooding conditions, As(III) dominated As(V) in the flow exiting the ore column. As(III) can be highly toxic to the environment, therefore care should be taken to ensure that conditions are provided for its conversion to less toxic As(V).

Keywords

arsenic pollution, arsenic transformation, arsenopyrite, ore mining, toxic waste, industrial waste, anthropogenic pollution

Acknowledgments

We express our sincere gratitude to the Hanoi University of Natural Resources and Environment, Hanoi University of Science, the Southern Branch of the Joint Russian-Vietnamese Tropical Research and Technology Centre and the Institute of Environmental Technology, Vietnam Academy of Science and Technology, which created the conditions for the study and helped the research team in its implementation.

For citation

Le Thu Thuy, Tran Hong Con, Nguyen Trong Hiep, Vu Thi Minh Chau, Le Minh Tuan and Do Hoang Linh, 2024. Environmental Hazard Assessment of Storage Conditions of Wastes from Mining and Processing of Arsenopyrite Minerals. Ecological Safety of Coastal and Shelf Zones of Sea, (2), pp. 107–121.

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