Study on the Speciation and Leaching of Chromium in Calcium-Free Sintering of Newly Returned Chrome Slag

This investigation delves into the chromium occurrence within new slag derived from chromium salt processing in a chemical plant. The slag's chromium is predominantly in a reduced state, with hexavalent chromium being largely present in a residual state. The mineralogy of the new slag is characterized by four primary minerals: magnesite (categorized into dense and colloidal forms), hematite, soluble salts, and silicates. Chromium is chiefly associated with chromite, magnesite, and silicate minerals, comprising approximately 61.03% of the total (represented as Cr₂O₃). Temperature had the most significant effect on the leaching efficiency of hexavalent chromium, followed by pH and humidity. Kinetic assessments reveal that the leaching process follows a first-order reaction model, with an activation energy of 10.76 kJ/mol, indicating that internal diffusion is the governing step in the leaching mechanism.