Large-scale coal mining is being carried out in Tete province, Mozambique. This area is also being planned to become a large coal fired power production hub serving electricity to neighboring ...countries in southern Africa. Thus, huge amounts of coal will be burned, resulting in the generation of a large quantity of coal ash. High concentrations of hazardous elements are often released from coal and coal ash causing negative impacts to human health and the environment. Therefore, it is important to understand the possibility of hazardous elements leaching. Aqueous batch leaching experiments under ambient conditions were conducted using six coal samples and their ash. Most of the coal leached very low concentrations of hazardous elements. However, an absence of carbonate minerals gave rise to higher acidity levels. This resulted in elevated leaching concentrations of manganese and iron, regardless of their contents. Burning coal resulted in higher contents of hazardous elements in the ash. However, leaching concentrations of most of the elements from the ash samples were still lower than the environmental standards. Chromium and manganese were enriched in slightly acidic leachates regardless of their contents while higher arsenic than the permitted level was leached from the ash containing the highest arsenic content that generated neutral pH leachate. These findings highlight a possibility of hazardous elements contamination from Mozambican coal and coal ash. Therefore, the storage of coal and disposal of coal wastes and ash in Tete Province should be done carefully and monitored to avoid the contamination in the region.
•Leaching properties of hazardous elements from coal and coal ash are different.•Coal ash has higher leachability than its parent coal.•Leachate with lower pH promotes the mobility of some hazardous elements.•There is a possibility of hazardous element contamination from coal and coal ash.
•Coal mining activities are being carried out in Moatize district, Tete province, Mozambique.•The impact of coal mining on the surrounding environment were evaluated.•Surface water and groundwater ...were contaminated with As, Cr, Cu, Ni, Mn and Pb.•As, Cd, Cr, Mn and Pb release from the surrounding surface soils and river sediments exceeded environmental standards.
Water, soils, and sediments contaminated with hazardous elements are of increasing concern because they greatly affect human health and ecological systems. In Mozambique, coal mining and processing operations are important industries; however, they could potentially contaminate the surrounding environment. This study investigates contamination of surface soils, river sediments, river water and groundwater around coal mines in Moatize district, Tete province, Mozambique. Three water pollution indices, water quality index (WQI), heavy metal evaluation index (HEI) and heavy metal pollution index (HPI) and five soil/sediment pollution indices, enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), contamination degree (CD) and pollution load index (PLI) were used to assess the levels of contamination in the area. All water samples were found to be “uncontaminated” to “moderately contaminated” with hazardous metals. The heavy metal concentrations found in waters varied from: As (0.3–10.9 µg/L), Ba (9.8–69.6 µg/L), Cr (2.1–60.2 µg/L), Cu (1.7–62.3 μg /L), Ni (1.2–71.9 μg /L), Mn (5.9–58.1 µg/L), Pb (1.3–10.8 μg /L) and Zn (2.1–40.2 µg/L). Most of these values exceeded the drinking water standards set by WHO. Meanwhile, surface soils and sediments from Moatize and Murrongoze Rivers were “highly polluted” (PLI = 1.11–1.85). Leaching experiments of soil and sediments suggest that hazardous elements from soils and sediments were strongly affected by the type of leaching solution (deionized 18 MΩ cm water and 1M HCl) and several of them were highly bio-accessible that could pose serious ecological and health risks in the area.
