Abstract

In the present work, the water recovery and concentration of H2SO4 and metals from a copper mining effluent by membrane distillation was studied. The performance of the direct contact membrane distillation was analyzed by estimating the water flux, the water recovery, and the concentration factor for acid and metals, taking into account the structural properties of the membrane, transport phenomena, and the most sensitive process parameters, with the objective to determine the feasibility of the process. The results show that, with increasing temperature gradient, the transmembrane flux improves, that the solution concentration has a negligible effect, and that there is a proportional relation between vapor pressure and flux. Considering a feed temperature of 60 degrees C and coolant inlet temperature of 20 degrees C, for the aqueous acid solutions formed by copper sulfate after 5 h, a concentration factor of 1.4 was obtained and, for the synthetic effluents, the concentration factor after 10 h was 1.65 (water recovery of 40%). Of all the membranes tested, a laminated polyvinylidene difluoride (PVDF) membrane with a nominal pore size of 0.2 mu m had the best performance. A model that includes the Pitzer equation to determine the vapor pressure of the solutions was developed to analyze the experimental tests and predict the flux; the model reproduces the experimental data with a maximum deviation of 7%. The feasibility for separation of acid and copper from concentrated mining effluents (rich in copper) by membrane distillation was analyzed through a conceptual process design; this analysis determined that it is possible to recover acid and copper by solvent extraction after three stages of membrane distillation. The total cost estimated (0.739 $.m(-3)) proves that the process is competitive with other desalination methods.