Long-term leaching characterization and geochemical modeling of chromium released from AOD slag

The long-term leaching of chromium from AOD slag was analyzed by column percolation test (CEN/TS 14405). According to the analytical result, the eluate of the AOD slag exhibited alkaline and reductive property. Chromium released from the AOD slag was primarily presented as trivalent chromium (Cr(III)). The eluate exhibited low hexavalent chromium (Cr(VI)) concentration. As the L/S ratio increased to 115 L kg^-1, the accumulated release quantity of Cr(III) and total chromium per AOD slag mass reached 1549.68 and 1613.67 μg kg^-1, respectively. The long-term leaching toxicity of chromium from the AOD slag was noticeable. Besides, a long-term geochemical model was built with PHREEQC software to assess the evolution of pH and chromium concentration in the eluate. The simulated pH and chromium concentrations were well consistent with those of the column percolation experiment. The result suggested that the geochemical model for chromium leaching prediction applies to the assessment of the eco-risk of AOD slag during the long-term leaching. The concentration of trivalent chromium presenting as Cr(OH)₄^- for instability of Cr(III) hydroxide in the alkaline eluate was regulated by the dissolution of the primary phase Cr₂O₃.