Removal of boric acid, monoborate and boron complexes with polyols by reverse osmosis membranes

• The effects of RO membrane type on boron species rejection were evaluated.
• The species considered were: boric acid, monoborate and complexes with polyols.
• The rejection efficiency was found to be predetermined by boric acid transport.
• Boric acid rejection decreased as follows: SW-30 > BW-30 > TW-30 > XLE.

The effects of reverse osmosis (RO) membrane type on the rejection efficiency of boric acid, monoborate and boron complexes with d-mannitol, sodium d-gluconate and N-methyl d-glucamine was revealed. The membranes examined included: XLE, TW-30, BW-30 and SW-30, supplied by DOW™ FILMTEC™. The mass transport coefficients: permeability and reflection coefficient were determined for each species in boric acid–polyol aqueous system. The influence of the membrane type upon these coefficients was evaluated and quantitative, comparative analysis of the efficacy of boron rejection at varying permeate flux, the feedwater boron content, the alcohol/boron molar ratio and the pH was conducted. It was found that boron rejection in the above systems was determined by the extent of boric acid transport, even when boric acid constituted only a minor component of the feedwater. At high permeate flux the effectiveness in boric acid rejection decreased in the following descending membrane order: SW-30 > BW-30 > TW-30 > XLE. The results presented here enable the selection of the best membrane, the most suitable operating conditions for boron separation by RO in the presence or absence of polyols, and for quantitative prediction of the efficiency of boron removal with various RO membranes.