Water Treatment

Boron Removal

Boron is an essential trace nutrient, but if found in levels higher than 0.3 mg/L it can be very damaging to agricultural crops when present in irrigation water. It is also a known teratogen, causing potential damage to human reproduction. Boron is usually found at low levels, averaging <5 mg/L, and often comes from detergents via water treatment plants.

Boron is found predominately as boric acid. Its removal is complicated by the fact that its predominant species is in two forms, as displayed in the equation below:

B(OH)3 + OH- ---> B(OH)4 -

The chemistry of boron selective ion exchange is such that it will remove boric acid in either form and therefore operate successfully at a range of pH values. No pH correction is required and there is no increase in scaling potential.

Boron-specific ion exchange resins have a very specific functional group which makes a very stable complex with boric acid. This complex formation is not pure ion exchange, and therefore does not require the boric acid to be ionized in the water. Because this complexing resin is so specific, it removes only boric acid from water and has no significant effect on the concentration of other ions.

During the regeneration stage of boron ion exchange, a conjugate acid is formed prior to elution. In this state, the resin is slow at capturing boron and the ion exchange procedure is inefficient. To return the resin to its free base state for adsorption, an alkaline regeneration step is used following the acid resin regeneration. The resin is then rinsed prior to absorption.

The ion exchange system has benefits of low power consumption and waste volumes of less than 1%. A typical ION-IX boron removal process can be broken up into 5 distinctive zones with all zones operating continuously. There are generally 30 vessels in total of which at any one time, 22 are in the adsorption zone, 3 are in regeneration, 2 are regeneration rinse, 1 is in neutralization and 2 are in final rinse.

Ion exchange is the most appropriate technology to remove boron selectively from desalinated seawater. Reverse osmosis, necessary to reduce the salinity of seawater down to drinking water levels, can be combined with selective ion exchange.

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