Reclamation of Aluminum Finishing Sludges

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The reclamation of aluminum-anodizing sludges produced as a result of finishing extruded architectural aluminum using etching and anodizing processes was studied by Georgia Tech Research Corporation. Two sequential phases focused on (1) enhanced dewatering of aluminum-anodizing sludges with recessed-chamber filter presses and (2) acidic extraction of dewatered aluminum-anodizing sludges to produce commercial-strength solutions of aluminum sulfate, i.e., liquid alum. A high-pressure (14 to 15 bar) and a diaphragm filter press were effective in dewatering aluminum anodizing sludges to cake solids contents of 27% to 29% and 25% to 31%, respectively. These values were well above the 21 % value required to justify pursuit of direct acidic extraction of aluminum. Commercial-strength solutions of aluminum sulfate with concentrations of 8% as AI2Oa were produced using conventional-neutralization, segregated-neutralization, etch-recovery sludge cakes. The trace metal contents of the alum products were, in general, typical of commercial products.

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