Abstract
As part of a program to investigate technology for the extraction of alumina from abundant domestic ores, the Bureau of Mines studied hno3 leaching of calcined Georgia kaolinitic clay. In this investigation, iron impurities were removed from the aluminum nitrate pregnant leach liquor by solvent extraction, and the purified liquor was evaporated to prepare a suitably concentrated crystallizer feed liquor. Aluminum nitrate nonahydrate was crystallized from the liquor to separate the aluminum from undesirable trace elements and excess water. Continuous crystallization at 40 deg c in a pilot plant vacuum evaporative unit was performed for 5 days to observe the effects of impurity buildup under minimum bleed-stream conditions. Liquor feed rate was 26 lb/h and al(no3)3.9H2o (ann) crystal production rate was 17 lb/h. Fe2o3 and cr2o3 were not effectively separated from the crystals, and p2o5, mgo, and k2o impurities must be removed by recrystallization. Other impurties did not excessively contaminate the crystals. Washing the crystals with water or aqueous hno3 gave an equivalent increase in crystal purity levels by displacing mother liquor. Theoretical equations, applicable to any continuous evaporative crystallization of ann, were developed to produce material balances for engineering applications.
