Mechanical activation of pyrophyllite ore for aluminum extraction by acidic leaching

A pyrophyllite [Al2Si4O10(OH)(2)] ore as an alternative source for alumina (Al2O3) was intensively milled for mechanical activation to increase aluminum extraction by acid leaching method. For this purpose, unmilled and milled ore samples were compared to reveal the changes caused by intensive milling. The samples were also leached in HCl solutions to determine whether mechanical activation increased the alumina extraction or not. The milling considerably disrupted XRD peak intensities of the clay minerals found in the ore, except quartz. After milling just for 30 min, peaks of the minerals were not distinguished, suggesting that all are amorphous. Dehydroxylation of the minerals in the unmilled ore was realized to occur at lower temperature ranges and energy consumed for dehydroxylation significantly reduced with prolonged milling. While aluminum recovery by leaching of the unmilled ore was about 12%, it increased to 73.09% as a result of milling the ore for 50 min. It was concluded that as the milling time is extended, energy needed to undergo dehydroxylation due to amorphization continues to decrease and aluminum recovery reaches higher values, suggesting that the clay minerals in the ore can be converted to mechanically activated state.