Diffusion dialysis is driven by concentration gradients, and the entire unit is composed of diffusion dialysis membranes, liquid distribution plates, reinforcing plates, and liquid flow plate frames, etc., forming a certain number of structural units from a set number of membranes. Each unit is separated into a dialysis chamber (A) and a diffusion chamber (B) by an anion homogeneous membrane. When waste acid solution and receiving liquid (pure water) are introduced on either side of the anion homogeneous membrane, the concentration of free acid and its salts on the waste acid side is significantly higher than on the water side. Due to the presence of a concentration gradient, free acid and salts in the waste acid tend to渗透 into chamber B, but the membrane is selectively permeable and does not allow each ion to pass with equal probability. Firstly, the anion membrane skeleton carries a positive charge, attracting hydrated ions with a negative charge and repelling those with a positive charge in the solution. Therefore, under the influence of concentration gradients, anions on the waste acid side are attracted and smoothly pass through the membrane pores to the water side. Simultaneously, in accordance with the requirement of electrical neutrality, positively charged ions are also carried along. Since the hydrated radius of H+ is smaller and the charge is less, while the hydrated ion radius of metal salts is larger and they are more highly charged, H+ will preferentially pass through the membrane. This separates the acid from the waste liquid. Due to the countercurrent operation, at the waste liquid outlet, the concentration of free acid in the acid chamber is greatly reduced due to diffusion, but it is still higher than the concentration of free acid in the incoming water. Additionally, during the actual membrane production, the water content and pore size of the membrane can be controlled by substituting side groups.