Separation of phosphoric acid from an industrial rinsing water by means of nanofiltration

Separation of phosphoric acid from industrial rinsing water containing dissolved aluminium was evaluated with four commercial flat sheet nanofiltration membranes. The MPF34 (Koch) and Desal-5 DK (GE Osmonics) membranes effectively retained aluminium. The aluminium removal efficiency of the NF membranes was always more than 98% for Desal-5 DK (GE Osmonics) and MPF34 (Koch). The phosphoric acid recovered in the permeate stream was 77% for Desal-5 DK and 56% for MPF34. It is observed from the study that the membranes can successfully be applied for the separation of phosphoric acid from industrial rinsing wastewaters. Membrane stability tests for the Desal-5 DK membrane showed a low decreasing of the aluminium rejection and a significant increasing of permeate flux. The extended Nernst–Planck equation, coupled with steric hindrance, the Donnan equilibrium, dielectric exclusion and chemical speciation, explained the experimental results