Recovery of water and acid from leach solutions using direct contact membrane distillation

This paper describes for the first time the use of direct contact membrane distillation (DCMD) for acid and water recovery from a real leach solution generated by a hydrometallurgical plant. The leach solutions considered contained H₂SO₄ or HCl. In all tests the temperature of the feed solution was kept at 60 °C. The test work showed that fluxes were within the range of 18–33 kg/m²/h and 15–35 kg/m²/h for the H₂SO₄ and HCl systems, respectively. In the H₂SO₄ leach system, the final concentration of free acid in the sample solution increased on the concentrate side of the DCMD system from 1.04 M up to 4.60 M. The sulfate separation efficiency was over 99.9% and overall water recovery exceeded 80%. In the HCl leach system, HCl vapour passed through the membrane from the feed side to the permeate. The concentration of HCl captured in the permeate was about 1.10 M leaving behind only 0.41 M in the feed from the initial concentration of 2.13 M. In all the experiments, salt rejection was >99.9%. DCMD is clearly viable for high recovery of high quality water and concentrated H₂SO₄ from spent sulfuric acid leach solution where solvent extraction could then be applied to recover the sulfuric acid and metals. While HCl can be recovered for reuse using only DCMD.