The results of the development of the industrial diffusion dialysis technology and the unit based on it for mixed acid recovery from titanium metal processing have been considered. Mixed acid can be selectively separated from the spent liquor contained mainly HNO3, HF and titanium ions by diffusion dialysis using a new series of anion exchange membranes. The results showed that this separation is seriously affected by the membrane water content and ion exchange capacity (IEC). Some titanium complex anion (TiF6)(2-) give rise to the difficulty in separation so that the best separation efficiency does not occur at the cases of high water content and IEC of membranes. By controlling the membrane preparation conditions (bromination content and position), a desired membrane for this system has been obtained with both relatively high acid recovery ratio and acid/titanium selectivity.Economic estimation was conducted based on an industrial diffusion dialyser with 499 sheets of 1600 mm x 800 mm membrane and the practical runs parameters: process quantity 2400 m(3) per year, total acid recovery ratio 85%. The results showed that the investment could be recovered within 5 months. After 5 years' run, one such dialyser can bring about CN$ 4.3 million profits besides the significant environmental benefits. (C) 2003 Elsevier B.V. All rights reserved.