Abstract: After leaching the alkali residue calcined by a nuclear fuel component company,the refractory alkali residue with uranium content greater than 1.00% was obtained,which did not meet the expected requirements of the treatment.In order to maximize the leaching and recovery of uranium,the refractory alkali residue was leached by means of sulfuric acid mixing and maturation intensification.The effects of maturation temperature,concentrated sulfuric acid dosage,maturation time and particle size of refractory alkali residue on uranium leaching rate were studied emphatically.The optimum conditions of maturation with concentrated sulfuric acid are as follows:the particle size of -0.013 mm for the refractory alkali residue,maturation temperature of 150 ℃,maturation time of 5 h,concentration of concentrated sulfuric acid of 75 mL.Under these conditions,the measured leaching rate of uranium in terms of slag could reach 89.98%,and the uranium content of refractory alkali residue decreases from 1.940% to less than 0.33%.The main phases of refractory alkali slag are silicon dioxide and ferric oxide,in which uranium exists in the form of uranium trioxide.Sulfuric acid mixing can destroy the coating structure of iron oxide in the refractory alkali residue and leach the coated uranium.

Key words: refractory alkali residue, mixed acid maturation, intensified leaching, uranium leaching rate in terms of slag