In Situ Accelerated Carbon Mineralization for Synergistic Immobilization and Recovery of Hexavalent Chromium Oxyanions from Coal Ash Leachates

High Resolution Image Download MS PowerPoint Slide Coal ash, a substantial global solid waste stream, offers considerable potential for diverse industrial applications. However, its widespread utility is significantly constrained by the high leachability of hazardous elements, most notably hexavalent chromium (Cr(VI)). This study introduces a novel carbonation-based process designed for the effective immobilization and recovery of Cr(VI) present in coal ash leachate. The chemical interactions among Ca 2+, Cr(VI), and CO 3 2– were initially elucidated through thermodynamic simulations. To optimize the experimental parameters for maximum Cr(VI) immobilization, key variables including temperature, CaO dosage, and CO 2 flow rate were systematically investigated. It was determined that solution pH (∼8.5) exerted a significant influence on Cr(VI) mobility. Under the optimized conditions of 20 °C (temperature), 7 g (CaO dosage), and 50 mL/min (CO 2 flow rate), a maximum Cr(VI) immobilization efficiency of 87% was achieved. Subsequent to complete carbonation until constancy of pH is achieved, a Cr(VI) recovery percentage of 82% was recorded. Advanced characterization techniques, including X-ray Fluorescence (XRF) and Scanning Electron Microscopy (SEM), in conjunction with thermodynamic modeling and experimental validation, collectively revealed the mechanisms governing Cr(VI) immobilization and recovery. These analyses confirmed Cr(VI) species adsorption onto, and substitution within, the calcium carbonate crystalline structures. This study demonstrates a novel technique for the immobilization and recovery of Cr(VI) from coal ash leachate, thereby offering a sustainable and eco-friendly solution for its safe management.