A Product Diffusion Model for the Extraction of Cerium and Yttrium from Magnetic Coal Fly Ash Using Citric Acid Solution

Abstract

The recovery of rare earth elements from coal-related materials, primarily fly ash, has become an emerging topic for the past few years. The availability of fly ash as solid waste from coal combustion and its low radionuclide concentrations benefit its utilization as an alternative source of rare earth elements. Using organic substances like citric acid to extract the elements further helps the environmental aspect. The maximum recovery value of cerium and yttrium was determined by reacting magnetic fly ash of 5 grams with 0.5 M of a citric acid solution with an S/L ratio of 10 for 24 hours at various temperatures. A mathematical model is also suggested to elucidate the leaching phenomenon better. The mechanistic model is developed based on the metal complex's diffusion through the ash layer. The results show that the leaching capacity of either cerium or yttrium rises along with the temperature. The maximum recovery value for leaching at 363 K is 40.21% and 54.90% for cerium and yttrium, respectively. The product diffusion model presents befitting graphs to the experimental data quite well. The effective diffusion coefficient (De) for both cerium and yttrium rises exponentially with extraction temperature. It is found that the value of De's increases from the order of 10 -10 at 298 K to 10 -8 cm 2 /s at 363 K. The diffusion activation energy for cerium and yttrium complexes appears to be 62.5 kJ/mole and 58.4 kJ/mole, respectively.

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