Experimental and theoretical study of nanofiltration of weak electrolytes: SO42-/HSO4-/H+ system

In this study, experimental data on the sulphuric acid rejection for pH values from 1 to 3 have been obtained with an aromatic poly(piperazine)amide membrane (NF270) at various trans-membrane pressures. The results were modelled by a novel version of the Solution-Electro-Diffusion model taking into account equilibrium reactions, and a general (quasi)analytical solution was obtained for the transport of weak electrolytes of arbitrary valence type. The equilibrium weak acid reaction made the total sulphate (SO42−/HSO4−) rejection decrease strongly as the fraction of single-charged hydrogen sulphate (HSO4−) in the feed increased. From the modelling procedure, permeances to H+, HSO4− and SO42− over the studied pH range were determined.