Effects of mechanical activation on alumina extraction from alunite ore and its thermal behaviour

Abstract

The decomposition and acid leaching has been investigated of alunite ore activated mechanically by grinding in a planetary ball mill in air atmosphere for 0, 15, 45 and 90 min. The mechanical activation appears to decrease dehydration and desulphation temperatures for alunite ore, owing to amorphisation and structural disorders in alunite as examined by XRD, TG and DTA. The highest alumina extraction values from the non-activated alunite ore were ∼6% by leaching in 1M H2SO4 solution for 30 min without calcination and ∼50% after calcination at 600°C for 1 h, followed by acid leaching under the same conditions. By comparison, for direct acid leaching of mechanically activated alunite ore without calcination, alumina extraction values were ∼12, 40 and 56% for mechanically activated alunites for 15, 45 and 90 min respectively. These values were ∼78, 84 and 89% for mechanically activated samples (15, 45 and 90 min respectively) after calcination at 600°C for 1 h and leaching in 1M H2SO4 solution at room temperature for 30 min.