Investigation on process optimization and kinetics for leaching of rare earth elements from red mud using citric acid

The relevance for a circular economy has been brought to light by the overuse of natural resources, especially when it comes to recovering valuable materials from secondary sources to support important technologies like renewable energy. Rare earth elements (REEs), which are indispensable for several cutting-edge applications, are found in considerable quantities in red mud, one of these sources. Target element speciation and thorough waste characterization are necessary for the effective recovery of REEs. Using citric acid as an environmentally benign leachant, this work aims to optimize the leaching parameters and comprehend the kinetics of REE extraction from red mud. The impact of leachant content, reaction temperature, and leaching time on REE leaching efficiency was assessed using a central composite design (CCD) in the context of response surface methodology (RSM). With a leaching efficiency of 90.16%, the ideal parameters were found to be 2 mol/L citric acid, 343 K, and 240 min. With an activation energy of 25.10 kJ/mol, kinetic study using a shrinking sphere model demonstrated that the leaching process is controlled by a diffusion-controlled mechanism. The findings show that citric acid could potentially be used to recover high REEs under moderate circumstances, offering a sustainable and effective way to recover key elements from red mud. This strategy improves the supply chain for valuable resources and encourages the effectiveness of resources.