The Bureau of Mines investigated the separation of aluminum from copper dump leaching liquors using a supported liquid membrane. Aluminum was selectively transported through porous polypropylene impregnated with di (2-ethylhexyl) phosphoric acid in an aliphatic diluent. The effects of variables, such as solution composition, temperature, and extractant concentrations, were measured using a three-level fractional factorial experimental design. Experimental results were used to derive equations for predicting transport rates for aluminum, iron, and copper. The major variables influencing aluminum transport were solution temperature, feed solution ph, aluminum concentration in the feed solution, and extractant concentration. Copper and iron transport rates were almost zero when aluminum transport rates were high. Measured aluminum transport rates under the best conditions of 55 deg. C, ph 3.0, 16 G/l al3+, and 65 pct extractant solution confirmed the predicted value of 210 ug/(cm2.H). Transport rates for iron and copper were less than 5 ug/(cm2.H) under these conditions.