Ecological Risk Assessment of Heavy Metal Occurrences in the Coal-Fired Furnace Bottom Slags of Power Plants

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This study explored the ecological risks related to bulk resource utilization of industrial solid waste slag from the Yuanyanghu Power Plant in the Ningdong Energy and Chemical Industry Base. Scanning electron microscopy, energy spectrum analysis, and X-ray diffraction were used to characterize and analyze the physical and chemical properties of the slag. The total amount, effective forms, and different occurrence forms of six heavy metals, including lead (Pb), chromium (Cr), nickel (Ni), copper (Cu), cadmium (Cd), and arsenic (As), were determined. The ecological and environmental risks of the heavy metals in the power plant slag were comprehensively evaluated using the potential ecological risk index method and risk assessment coding (RAC) method. The results show that: (1) The slag exhibited a porous microstructure characterized by high concentrations of calcium (36.27%). The mineral composition of the furnace bottom slag was mainly mullite and quartz, and the contents of available potassium and organic matter were abundant. (2) The total concentrations of the six heavy metals in the furnace bottom slag did not exceed the screening value for soil pollution risk in agricultural land. Pb, Cd, Cr, As, and Ni in the slag mainly existed in the form of residue (F5), with Ni and As in the exchangeable state (F1), accounting for 28.05% and 25.49%, respectively. (3) The potential ecological risk index method indicates that the total RI index of the six elements in the slag is at level II, with a moderate ecological hazard level. Among all the metals, Cd and As contribute most to ecological risk. The RAC evaluation results indicate that Ni and As have moderate risk, Cd, Cu, and Cr have low risk, and Pb is risk-free. Based on a comprehensive evaluation, Cd, Ni, and As elements in slag are the main potential pollutants. In large-scale resource utilization, it is necessary to monitor and strengthen ecological risk prevention and control regularly.

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