טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGeffen Nitzan
SubjectBoron Removal from Water by Complexation to Polyol
Compounds
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Carlos Dosoretz


Abstract

Boron is an important micronutrient for plants, animals and humans, although the range between deficiency and excess is narrow (e.g., 0.3-0.5 ppm in citrus).

In aqueous environments it is normally present mostly as boric acid and sometimes as borate ions according to the following dissociation reaction:

B(OH)3 + H2O -> B(OH)4- + H+   , pKa=9.25.

Boron is not removed during conventional wastewater treatment procedures and during sea water desalination by reverse osmosis its concentration decreases to only 0.9-1.8 ppm after one stage. Boric acid/borate reacts with chemical compounds containing multiple hydroxyls groups (polyols), such as mannitol, generating anionic complexes at the natural pH of water according to the net complexation reaction, as follows:

B(OH)3+2C6O6H14 -> BC12O12H24+ H2O + H+  , pKa=4.1.

The long term objective of this research is to study the complexation of boric acid/borate with mannitol integrated with membrane desalination systems as a possible substitute for the existing technologies.

Membrane separation experiments were performed in a bench scale filtration unit equipped with a 200 Dalton nanofiltration membrane sheet.

The addition of mannitol (at 1:5 molar ratios) to 10 ppm boron solution increased the rejection at high ph. The addition of polyol and buffer in 40 ppm boron solution improved boron rejection significantly (> 90%).

The influence of increasing pH and buffers on the rejection efficiency was studied by the NMR and by theoretical calculations and is probably due to the increase of the reactants concentration. Finding the conditions affecting complete complexation in neutral pH will enable effective control on this process.