Rapid Stabilization of Aluminum Dross Ash By Fluidized Bed Steam Treatment

Aluminum dross ash, a difficult-to-recycle waste generated in the aluminum industry, has been mostly disposed of. Aluminum dross ash contains aluminum nitride to form ammonia in the disposal, so that stabilization treatment has been needed to remove nitrogen. The most common stabilization treatment is a wet process in which aluminum dross ash is immersed in water to remove nitrogen as ammonium ion into the solution. While this process has low initial cost, it also has a problems like generation of a large amount of ammonia-containing waste water and long processing in several days order.

The authors have been proposed a new dry treatment for aluminum dross ash stabilization by fluidized bed steam processing. A laboratory scale fluidized bed was prepared to demonstrate the denitrification characteristics of actual aluminum dross ash in steam fluidization. In the experiments, aluminum dross ash was mixed with silica sand to achieve the smooth fluidization.

The effects of treatment temperature and steam concentration were confirmed at 110, 150, 170 and 200 °C and in 30, 40, 60 vol%. From the experiments with the superficial gas velocity of around 2 u_mf, it was found that reaction temperature of 150 °C and steam concentration of 40% were appropriate for nitrogen removal from aluminum dross ash. In the appropriate temperature and vapor pressure, the nitrogen removal rate gradually decreased and eventually became zero in the fixed bed, whereas the nitrogen removal was continued without a significant decline of the reaction rate in the fluidized bed.

Those phenomena were probably caused by aluminum oxide layer formed on the surface of aluminum nitride acting as an inhibitor of the reaction. In fluidized bed, the oxide layer could be updated by particle collision, so that the steam treatment by a fluidized bed is promising for aluminum dross stabilization.