IRON CONTROL BY IMPROVED DIGESTION TECHNOLOGY
K. Solymar, K., Zoldi, J. and Ferenczi, T.
The different variants of control filtration and the precipitation before or after control filtration are used actually for iron control. Another actual way, namely the improved digestion technology using catalytic additives to convert goethite into hematite and to recrystallize the minerals is discussed here.
The digestion technology using iron-hydrogarnet catalyst was introduced in the Hungarian alumina plants in 1979-80. By means of this technology the Fe2O3 content in the liquor to precipitation decreased from 25-15 mg/l down to 10-15 mg/l without control filtration, resulting constantly in Fe2O3 content less than 0.025 % in metal grade alumina.
The Fe2O3 content of the pregnant liquor can be decreased further, below 10 mg/l by control filtration using calcium-aluminate filter bed in order to decrease Fe2O3 content of alumina to 0.015 % corresponding to the market demand.
The special chemicals for iron removal have also a good potential.