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Tratamiento terciario: intercambio iónico

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Purpose

  • Removal of ions, hardness, specific cations or anions
  • Concentration of cations and anions

Principle

Both during the production of process water as well as during the purification of industrial waste water, it is sometimes necessary to remove some (or substantially all) ions from the water. This is possible with a separation technique such as ion exchange. With this technique very low residual concentrations of ions in the treated water can be obtained.

As the name describes during this process ions from the treated water are exchanged to harmless counter-ions such as Na, H, Cl- or OH-. Determined by the choice of the material selected the exchange can be done selective or not selective. Once the capacity of the ion exchanger is saturated it is regenerated with a concentrated solution of counterions. The ion resin is brought back to its original state whereby the separated regeneration liquid contains the desorbed load.

Applications

  • Softening or demineralization of process water
  • Extraction of heavy metals from waste water
  • Recovery of precious metals, or catalysts from wastewater
  • Recovery of acids or bases from rinse waters
  • Purification of products

Configurations

An ion exchanger consists essentially of one or more pressure vessels filled with ion exchange material. This can be a synthetic resin, or a mineral such as zeolite or alumina. A whole range of materials is available for various applications. If the feed water contains suspended solids then a preceding filtration technique is advised to prevent clogging.

Example of realization

Sand filter followed by cation and anion filter

Operational costs

To determine the operationals cost one not only has to consider the initial investment but also the cost of chemicals needed for regeneration of the columns as well as the replacement of the ion exchanger itself. For these reasons ion exchanger often only get used in waste water treatment for effluent polishing or if reuse is feasible. Reverse osmosis is increasingly seen as an alternative for demineralization of water.

Approach Trevi

Trevi will first examine whether any savings can be realized through resource restriction. This allowed Trevi to install ion exchangers at companies to achieve a closed loop system in certain industrial processes, thus saving water and chemicals. If further source restriction is not possible ion-exchange can also be used to remove small concentrations of metals from the waste water prior to the discharge point.