Application of Ion Exchange Resins

Exchange reaction at cation exchanger in regeneration:

R^Cat-NH4 + HNO3 ↔ R^Cat-H + NH4NO3

One core element of the Fertarex® process thereby is the use of pre-cooled concentrated nitric acid (55% HNO3). The acid strips the ammonium from the cation exchanger and at the same time converts the functional group back into the so called H-form, which is then ready to be loaded in the next cycle. The spent regenerant solution draining from the resin will contain 80g/L (8%) NH4NO3, along with a certain excess of HNO3 in the richest fraction. In parallel the anion exchanger is regenerated, for which a solution of 15% ammonia is used. The regeneration of the exhausted anion exchanger works according to the following equation:

Exchange reaction at anion exchanger in regeneration:

R^An-NO3 + NH4OH ↔ R^An-OH + NH4NO3

Thereby the ammonia solution strips the nitrate from the resin and transforms it into the OH-form (R^An-OH), which is then ready to be used in the next cycle. Also the spent regenerant of the anion exchanger contains 80 to 100g/L (8-10%) ammonium nitrate and in addition a large excess of ammonia (NH3).

The basic principle of the Fertarex^® process is – in addition to later elaborations – to combine these two spent regenerant solutions into one and to balance the excess of ammonia by further addition of nitric acid. Thereby an 18% to 25% ammonia nitrate solution is obtained that can be fed back into the fertilizer production.

The process principle described above is simplified. In practice the effluents from the ion exchangers produced during their regeneration are separated into fractions and used in a specific way. The purpose of these additional steps is to produce an ammonia nitrate solution with the highest possible concentration and to avoid secondary wastewater.

a) The first and fourth fraction derived from the regenerant is fed back into the wastewater storage tank. It contains only small amounts of ammonia nitrate.

b) The second fraction that contains 90-95% of eluted NH4NO3 and around 50% to 60% of excess chemicals (HNO3 or NH3) is neutralized, concentrated (e.g. by evaporation) and sent back into the fertilizer production.

c) The third fraction that contains 40 to 45% of the excess of the regenerant chemicals (HNO3 or NH3) is used to completely exhaust the anion exchanger or – after saturation with NH3 – is used to prepare a new batch of regenerant solution for the regeneration of the anion exchanger.

To contact ion exchange resins with concentrated nitric acid can be dangerous because this acid is a strong oxidant and improper handling can result in an exothermic reaction. The other hazard connected to this process is through the potential for impurities to enter into the final product. Organic impurities would give rise to the formation of the instable ammonium nitrite (NH4NO2) that can initiate an explosion of the product. Therefore it is very essential that the ion exchange resins used for the process are clean and do not leak organic material.

The Fertarex^® process works on the well accepted principle of the application of ion exchangers in water demineralization. The process preferentially makes use of ion exchange resins of the Lewatit^® brand offering high quality standards to assure safe operation. Multiple engineering features are integrated into the process to accomplish challenging targets as there are:

a) high economic efficiency requirements

b) safety constraints.

In the expectation that environmental limits as a trend are getting stricter, fertilizer producers all around the world will be forced to intensify their activities to protect the environment. This technology offers a cost effective and economically advantageous method for doing so. Additionally, producers of porous ammonium nitrate for explosives in Russia, Ukraine, India, Pakistan, Eastern Europe, Australia and China may also benefit from this process technology.