After this the fly ash was leached with hydrochloric acid followed by precipitating the leached liquorwith ammonia hydroxide to get hydroxides of alumina
and iron which are dehydrated at high temperature (1100 °C) to obtain iron and aluminium oxides as a
mixed powder. Leaching of alumina and iron oxides fromfly ash with hydrochloric acid, the effects of four parameters
viz. acid concentration and acid to fly ash ratio, leaching temperature and time were investigated and optimum
conditions were (i) concentration of HCl 6 N, (ii) fly ash (g) to HCl acid (ml) ratio 1:4, (iii) temperature
of leaching 107 °C, and (iv) duration of leaching 5 h. The total recoveries of iron oxide and aluminium oxide
were 63% and 73%, respectively.