At this point, the water layer must be separated from the aluminum hydroxide slurry which has settled to the bottom of the tank. The water can be drawn off by valves located at various levels on the tank. Alternatively, the aluminum hydroxide floc can be floated by bubbling air from the bottom of this tank. As the floc reaches the top of the tank, it may be skimmed off and disposed with other solid waste. Acidify the aluminum hydroxide slurry with concentrated sulfuric acid to regenerate aluminum sulfate.
Alum flocculation is superior to that of calcium chloride.
The trivalent ion is, in general, far more effective in this function than divalent ions. In turn, the aluminum trivalent ion is more effective than other common trivalent ions. The savings in oil resulting from an effective program could equal or exceed the cost for the trade waste program. Elimination of oil contamination will prolong coolant life. A review of coolant practices is suggested for prolonged coolant life.