Extraction of aluminum from a pickling bath with supported liquid membraneextraction

Large amounts of waste are produced yearly in the galvanic and chemical sur face treatment industry. Bath liquids used in the various processes lose th eir function due to contamination. The spent bath liquids have to be replac ed and treated prior to disposal, leading to high costs and a high environm ental burden. In this paper, a proposed solution to the problem is investig ated: the selective removal of the contaminant with supported liquid membra ne extraction. The extraction of aluminum, a contaminant at high concentrat ions, from a pickling bath liquid with hydrofluoric acid and phosphoric aci d as its main components has been carried out with the basic extractants Al amine 308 and Alamine 336 in a flat sheet-supported liquid membrane setup. Aluminum transport rates were obtained in the order of 10(-6)-10(-5) mov(m( 2).s), which are normal values for this technique. The extraction was not c ompletely selective as dissolved phosphorus was coextracted. In all experim ents, 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 precipita tion prevents industrial application of the systems investigated.