Detoxification-Oriented Carbonate Leaching of Selenium and Tellurium from Lead-Rich Fly Ash: Experimental and Kinetic Analysis

Copper anodic slime is commonly smelted with lead to enhance silver and gold recovery, leading to the generation of a lead-rich fly ash containing significant amounts of selenium and tellurium, which poses serious environmental and health risks. This study aims to evaluate sodium carbonate (Na2CO3) leaching as a benign pre-treatment method to partially remove selenium and tellurium while stabilizing lead through carbonate formation. With detoxification as the primary goal, the study employed a central composite design (CCD) in Design-Expert software to investigate the effects of Na2CO3 concentration, temperature, solid-to-liquid ratio, and time on the dissolution of selenium and tellurium. The results demonstrated selenium recovery rates of up to 53.9% and tellurium recovery rates reaching approximately 33.9%. Scanning electron microscopy revealed the presence of semi-spherical and elongated particles, with lead carbonate forming preferentially on particle surfaces during the leaching process. Energy-dispersive spectroscopy confirmed the transformation of lead sulfate phases to lead carbonate, which limited the dissolution of selenium and tellurium. Kinetic evaluations indicated that selenium leaching was governed by mixed control mechanisms, including surface reactions and diffusion, while tellurium dissolution exhibited erratic kinetic behavior. Thermodynamic assessments indicated that lead stabilization occurs as cerussite (PbCO3), enhancing environmental safety.