Abstract
ABSTRACT Large amounts of waste are produced yearly in the galvanic and chemical surface treatment industry. Bath liquids used in the various processes lose their function due to contamination. The spent bath liquids have to be replaced and treated prior to disposal, leading to high costs and a high environmental burden. In this paper, a proposed solution to the problem is investigated: the selective removal of the contaminant with supported liquid membrane extraction. The extraction of aluminum, a contaminant at high concentrations, from a pickling bath liquid with hydrofluoric acid and phosphoric acid as its main components has been carried out with the basic extractants Alamine 308 and Alamine 336 in a flat sheet-supported liquid membrane setup. Aluminum transport rates were obtained in the order of 10−6−10−5mol/(M2·s), which are normal values for this technique. The extraction was not completely selective as dissolved phosphorus was coextracted. In all experiments, precipitation took place on the surface of the liquid membrane and in the bulk of the strip phase. Increasing the stripping alkalinity from pH = 8 to pH = 13 reduced the amount of precipitation in the bulk of the strip phase but caused a substantial decrease in the aluminum flux. The precipitation prevents industrial application of the systems investigated.
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