Aluminum, floe formation

To improve magnesium reduction, which also improves siHca reduction in cold process softening, sodium aluminate may be used. The sodium aluminate provides hydroxyl ion (OH ) needed for improved magnesium reduction, without increasing calcium hardness in the treated water. In addition, the hydrolysis of sodium aluminate results in the formation of aluminum hydroxide, which aids in floe formation, sludge blanket conditioning, and siHca reduction. 

Zinc also may be produced by electrolysis of zinc sulfate solution. The zinc oxide in the roasted concentrate is leached with sulfuric acid. The oxide is converted to soluble zinc sulfate. Impurity metals, such as iron, copper, cadmium, arsenic, tin, and cobalt are removed by precipitation, floe formation, and other methods. The purified zinc sulfate solution is electrolyzed using aluminum cathodes and lead anodes. Zinc is deposited on the cathode. 

Other authors (7) reported that the Al-type floe is removed better in flotation than in sedimentation. Furthermore, the specific density of aluminum, which is lower than that of iron, is responsible for the better flotation effect. It appears that floe formation in the aluminum system does not provide sufficiently high sedimentation rates, although enough chemicals are available for solid-bubble enmeshment (i.e., good flotation). 

The importance of corrosion product mass transfer was realized first in the early operation of NRU. Here the solubility of the oxide formed on the aluminum fuel sheathing led to the production of a colloidal alumina floe in the heavy water. The mechanism for its formation, means to control it, and the role it played in transporting uranium and fission products released from failed fuel were studied (55, 56). 

---