The effect of process parameters on boric acid transport during the electrodialytic desalination of aqueous solutions containing selected salts

摘要

The separation of boric acid from salts by electrodialytic (ED) desalination has previously been presented. In this process, the boric acid species are retained in the diluate solution, whereas their accompanying salts are removed in the concentrate solution. By this approach, boron can be recovered in the subsequent steps, free from contaminating salts. In the present work, the effects of the ED process parameters on the boric acid transport rate from the diluate have been investigated. The effects of the boric acid concentration in the diluate, membrane type, ion type transferred across the membrane and electric current density were discussed. The boron flux across the membrane was observed to strongly depend on the initial diluate boron concentration as well as the electric current density. The cations migrating across the cation-exchange membranes were found to cause a statistically significant decrease in the boron flux across the membranes in the following order: K~+>Na~+>Ca~(2+)>Mg~(2+). The anions transported across the anion-exchange membranes affected the boron flux in the following order: SO4~(2-) >NO3~-≈Cl~-. Tentative explanations for the observed boron fluxes were given.