Kinetics of leaching of alumina from discarded high alumina refractory bricks

Abstract

The effects of the process variables on the kinetics of leaching of alumina from discarded high alumina refractory bricks were studied. Sample was powdered and different Sile fractions were obtained using a standard sieve shaker. The phases present in the sample were identified through X-Ray diffraction technique. The phases found in the samples are corundum (a-AhOl), periclase (MgO), maghemite (y-fe:(Ol), spienel (MgAI:(O.), graphite (C), silimanite (AbOJ.Si02). Compositional analysis has been conducted for different size fractions and a smali variation in the amount of components in different size fractions was observed. Fe:zOl content in the discarded brick was more than that in the fresh unused brick. Variables such as powder size of source material, concentration of ieaching reagent, temperature and time of leaching were seiected for study. leaching experiments were conducted in a 500 ml round bottom flask attached with a retlux condenser and the heating device was a mantle heater. Powder size of -40+70 mesh, -70+100 mesh, 100+140 mesh, -140+200 mesh and -200+270 mesh was taken for study. Of them 200+270 mesh showed better extraction. NaOH of 3 M, 4 M, 4.5 M and 5 M concentration was used to leach the sample. Of them 5 M NaOH caused better extraction. The reaction order determined was 1.7. Effect of temperature was studied by taking the temperature of 40"C, 50"C, 65"C, 75"C and 85"C with a tluctulrtion of ~3°C. More extraction of alwninum was obtained at 85"C. Activation energy determined by differential approach was 39.12 KJ/mol or 9.314 KCaVmol. After leaching with all the optimum variables i.e. with -200+270 mesh, 5 M NaOH, solid-liquid mtio of 1:5 at 8SoC up to 4 hour it was evident that there would be no further considerable extraction. The optimum variables for leaching of discarded high alumina refractory bricks were, - 200+270 mesh powder, S M NaOH, 85°C, leaching time of 4 hOOf