Ion exchangers for demineralization, recirculation and selective exchangers

Ion exchangers are used for demineralization, recirculation and selective exchange in industry. What is an ion exchanger resp. ion exchanger resin? Ion exchangers are spherical granules, similar in appearance to sand, which carry out an ion exchange process in an aqueous solution, i.e. they can remove ions and release the ions with which they have previously been exposed, so-called “conditioned”. Depending on the type of ion exchanger resin, the effect is that the aqueous solution, e.g. city water, circulating water or waste water, is purified of the unwanted ions previously contained in it. They are typically contained in blue GRP pressure tanks with PE inliners, so-called ion exchanger cartridges.

The packaging units for ion exchanger resins are usually 25L bags, 1000L = 40 bags on pallets or 1000L big bags. Ion exchanger resins often exist in a gel form for simple applications such as city water desalination and in a macroporous, more reactive form for more complex applications.

The various ion exchanger resins are generally divided into groups that characterize the ion exchangers. Strongly acidic cation exchangers or weakly acidic cation exchangers are used to remove cations from the water. Strongly basic anion exchangers or weakly basic anion exchangers are used to remove anions from the water. There are also so-called “medium-base” exchangers. These are weakly basic anion exchangers that also contain strongly basic anion exchanger groups. A mixture of the strongly acidic and strongly alkaline exchangers is so-called mixed bed resin, as used in a demineralization cartridge, so-called VE-cartridges, for the production of demineralized water. As an ion exchanger is not a filter but a chemical bond, the ion exchanger must generally be preconditioned for the respective application. Common preconditionings for cation exchangers are the H+, Na+, Ca+, K+ or NH4 form, for anion exchangers the OH- or Cl- form or, in the case of weak basic exchangers, additionally the NH3 or protonated ammonium form. Once the available capacity of the ion exchanger resin has been utilized, it can in most cases be reprocessed, so-called regeneration, usually with hydrochloric acid for the cation exchanger and caustic soda for the anion exchanger. In individual cases, regeneration is not (or no longer) possible, e.g. due to age-related signs of wear, especially in the anion exchanger, or foreign contamination (e.g. with mineral oils or cyano complexes on a strongly basic anion exchanger). After the ion exchanger regeneration service, it is activated or preconditioned to the desired form.activation or preconditioning in the desired form takes place. The form of activation depends on the application and transforms the ion exchanger into a reusable form.

Typical suppliers of high quality ion exchanger resin are: Lanxess Lewatit and Purolite.

Strongly acidic cation exchangers such as the Lewatit SP112H ion exchanger resin remove these metals from solutions:

  • Aluminum, Al+++
  • Silver, Ag+
  • Barium, Ba++
  • Calcium, Ca++
  • Cadmium, Cd++
  • Caesium, Cs+
  • Chromium III, Cr+++
  • Cobalt, Co++
  • Copper, Cu++
  • Iron II, III, Fe++, Fe+++
  • Indium, In+++
  • Magnesium, Mg++
  • Manganese, Mn++
  • Nickel, Ni++
  • Lead, Pb++
  • Titanium, TiO++
  • Vanadium, VO++
  • Zinc, Zn++

Strongly acidic cation exchanger resins are also used in metal finishing, especially in the desalination of galvanic rinsing water in the circulation system or when chromic acid is to be recovered from rinsing water. Lewatit SP 112 can also eliminate interfering metal ions from pickling baths and process solutions and clean chromic acid or phosphorus baths. The selectivity series for strongly acidic cation exchangers (sulfonic acid exchangers) is as follows:

Al3+ > Cr3+ > Fe3+ > Ba2+ > Pb2+ > Ca2+ > Ni2+ > Mg2+ > K+ > NH4+ > Na+ > H+

Cation exchangers are suitable for softening, desalination and other special applications.

For example, for softening boiler feed water, condensate or household appliances (dishwasher, washing machine). Cation exchangers are also used in the textile industry to soften sea water and drinking water. Cation exchangers are also ideal for aquariums and aquarium water.

Weakly basic anion exchangers such as Lewatit MP62 remove the following complex-bound (residual) metals from solutions and groundwater:

  • Silver, Ag, cyanide
  • Gold, Au, cyanide and chloride
  • Cadmium, Cd, cyanide and chloride
  • Chromium III, Cr, sulphatic
  • Chromium VI, CrVI
  • Cobalt, Co, cyanide
  • Copper, Cu, cyanide
  • Iron II,III, Fe, cyanide
  • Mercury, Hg, cyanide and chloride
  • Molybdenum (molybdate), MoO4-
  • Nickel, Ni, cyanide
  • Palladium, Pd, chloride
  • Platinum, Pt, chloride and sulphate
  • Rhenium, Re, chloride
  • Uranium, U, sulphatic
  • Vanadium (vanadate), V, VO3-
  • Tungsten (wolframate), W, WO3-
  • Zinc, Zn, cyanide and chloride

The selectivity series for weakly basic anion exchangers (tertiary amine exchanger) is as follows:

OH– >> SO42- > HSO4– > I– > NO3– > Br– > Cl– > F–

Weakly basic anion exchanger resin is suitable for desalination in combination with cation exchanger resins (for example with Lanxess Lewatit MonoPlus S100 / SP 112).

There are also other special applications for weakly basic anion exchanger resin isuch as nitrate removal from water (e.g. using the special resin Lewatit SR7), the recovery of valuable materials (such as chromium, molybdenum and gold) and the removal of iron from concentrated hydrochloric acid. In addition, the anion exchanger resin Lewatit MP 62 in chloride form or another protonated form can also be used in hydrometallurgy for the metal recovery of vanadium, molybdenum and tungsten (separation as complex anions), as well as for the recovery of precious metals from rinsing water and for groundwater remediation by removing chromate and heavy metal cyanide complexes.

The anion exchanger resin Lewatit MP 64/68 as a “medium basic” resin is also suitable for groundwater remediation (removal of chromate and heavy metal cyanide complexes), chlor-alkali electrolysis (removal of mercury from chlor-alkali electrolysis waste water using after the amalgam process). In addition, the anion resin can be used in hydrometallurgy, in particular in the metal recovery of molybdenum, vanadium and tungsten as complex anions as well as the recovery of gold from cyanide leaches and the recovery of chromic acid from rinsing water.

Strongly basic anion exchangers have permanently quaternized ammonium groups and have a lower capacity than weakly basic anion exchangers. In contrast to weakly basic exchanger resins, they can also be used in alkaline media. However, they bind some metal compounds (usually complex anions) so strongly that they can no longer be eluted during regeneration. As a result, certain anions permanently inactivate strongly basic anion exchangers over time. However, lower effluent values are achieved with strongly basic anion exchangers compared to weakly basic anion exchangers, as anions of weak acids can also be removed with SBA resins.

Strongly basic anion exchangers (SBA) such as Lewatit MP500 remove these metals from solutions and thus act as a cation exchanger:

  • Silver, Ag, cyanide (non-regenerable)
  • Arsenic, As, fluoridic
  • Gold, Au, cyanide and chloride (non-regenerable)
  • Cadmium, Cd, cyanide and chloride (non-regenerable)
  • Chromium III, Cr, sulphatic
  • Chromium VI, CrVI
  • Cobalt, Co, cyanide (non-regenerable)
  • Copper, Cu, cyanide (non-regenerable)
  • Iron II,III, Fe, chloridic (special regeneration) and cyanidic [Fe(CN)6]3/4- non-regenerable)
  • Mercury, Hg, cyanide and chloride (HgCN non-regenerable)
  • Molybdenum (molybdate), MoO4-
  • Nickel, Ni, cyanide (non-regenerable)
  • Palladium, Pd, chloride
  • Platinum, Pt, chloride and sulphate
  • Rhenium, Re, chloride
  • Uranium, U, sulphatic
  • Vanadium (vanadate), V, VO3-
  • Tungsten (wolframate), W, WO3-
  • Zinc, Zn, cyanide and chloride (ZnCN non-regenerable)

The selectivity series for strongly basic anion exchangers (quaternary amine exchanger) is for anions (without anion complexes):

SO42- > HSO4– > I– > NO3– > Br– > Cl– > HCO3– > HSiO3– > F– > OH–

In groundwater remediation, strongly basic anion exchangers (possibly also in combination with weakly basic anion exchangers) are used to remove cyano complexes (cations). Free cyan is also bound by the anion exchanger, but only weakly. The selectivity series in this case is for cyano complexes with the following metals:

Co2+ > Hg2+ > Fe2+ > Cu2+ > Ni2+ > Ag+ > Au+ > Cd2+

The weakly acidic selective exchanger resin Lewatit TP 207 or Purolite S930 Plus is a macroporous cation exchanger with chelating iminodiacetic acid groups. This enables the selective binding of heavy metal cations from weakly acidic to weakly basic solutions.

Weakly acidic cation exchangers (SAT) such as Lewatit TP207 remove the following metals from solutions:

  • Aluminum, Al+++
  • Arsenic, As (special process)
  • Silver, Ag+
  • Gold, Au+, chloridic
  • Barium, Ba++
  • Calcium, Ca++
  • Cadmium, Cd++, chloride and cyanide
  • Chromium III, Cr+++, sulphatic
  • Cobalt, Co++
  • Copper, Cu++ (especially from the copper tetraamine complex)
  • Iron II, III, Fe++, Fe+++
  • Mercury, Hg++
  • Indium, In+++
  • Magnesium, Mg++
  • Manganese, Mn++
  • Molybdenum, as molybdate (MoO4-)
  • Nickel, Ni++
  • Lead, Pb++
  • Palladium, Pd+, chloride
  • Platinum, Pt+, chloride/sulfatic
  • Titanium, TiO++
  • Uranium, UO2-, sulphatic and nitratic
  • Vanadium, VO++ and vanadate
  • Tungsten (wolframate), W, WO3-
  • Zinc, Zn++ and chloride

Areas of application for Lewatit TP 207 ion exchanger resin (IDE exchanger) include metal finishing (removal of heavy metal residues from the effluents of continuous and batch detoxification systems by selective ion exchange), the selective removal of dissolved traces of heavy metals from wastewater after hydroxide precipitation (even under high calcium concentrations, so-called selective exchangers), and the recovery of valuable and precious metals from rinsing water (decentralized treatment). In addition, the removal of heavy metal residues from waste water detoxification processes in metal finishing at the last position as a police filter, the extension of the service life of process baths by removing interfering metal ions in the metalworking industry and the elimination of interfering metal ions from pickling baths and process solutions, especially the cleaning of chromic acid and phosphoric acid baths, unless a strongly acidic cation exchanger SAC is more advantageous. Finally, it can be used in hydrometallurgy to separate metal ions from digestion solutions, for example, and in flue gas cleaning to remove residual concentrations of heavy metals from flue gas scrubbing water from waste incineration plants and fossil incineration plants (coal-fired power stations). As a rule, selective exchangers are operated or preconditioned in the mono-Na form or in the Ca form, instead of the production-related delivery form: di-Na form.

The binding of heavy metal ions from neutral waters proceeds in selective exchangers according to the following selectivity series:

Fe3+ > Cu2+ > TiO2+ > VO5+ > UO2+ > VO2+ > Hg2+ > Pb2+ > Sc3+ > Ni2+ > Zn2+ > Co2+ > Co2+ > Cd2+ > Fe2+ > Be2+ > Al3+ > Mn2+ > Ca2+ > Mg2+ > Sr2+ > Ba2+ > Na+ > K+ > Cs+

Finally, Lewatit TP 207 ion exchanger resin can also be used in groundwater remediation for the removal of heavy metals or arsenic, which may require separate activation or doping.

The weakly acidic cation exchanger Lewatit CNP 80 (H) as a carboxylic acid resin, on the other hand, is particularly suitable for decarbonizing cooling water, boiler feed water, household softeners, humidifiers, drinking water (e.g. coffee machines), irrigation water and brewing water. The carboxylic acid resin can also be used for the recovery of metals (e.g. copper, nickel, cadmium, cobalt and zinc) from diluted solutions, for which it must be converted into the salt form.

There are other ion exchanger resins for special applications, e.g. thiourea exchanger resins such as the selective exchanger resin Lewatit TP 214 for removing mercury and precious metals such as silver, gold, palladium and platinum from solutions.

  • Silver, Ag+
  • Gold, Au+, chloride
  • Bismuth, Bi++
  • Copper, Cu++
  • Mercury, Hg++, also chloride
  • Nickel, Ni++
  • Lead, Pb++
  • Palladium, Pd+, chloride
  • Platinum, Pt+, chloride/sulfatic
  • Zinc, Zn++ and chloride
  • Tin, Sn++/++++

Binding to the thiourea exchanger is based on the following selectivity series

Hg2+ > Ag+ > Au+/3+ > Pt2+/4+ > Cu2+ > Pb2+/4+ > Bi2+ > Sn2+ > Zn2+ > Cd2+ > Ni2+

For other applications, there are separate ion exchangers, e.g. with aminomethyl phosphonic acid groups, which are used with special doping or activation, e.g. for fluoride removal in chemical-physical waste water treatment.

Products

Ion exchanger: Strongly acidic cation exchanger Lewatit SP112
Ion exchanger: Strongly basic anion exchanger Lewatit M500
Ion exchanger: Lewatit TP207 weakly acidic selective exchanger

In the ion exchanger resin application VE system with 2 columns or VE cartridge, a strongly acidic cation exchanger (SAC) is generally used as a sulphonic acid exchanger based on styrene-divinylbenzene copolymer in the H+ form, e.g. Lewatit Monoplus SP112H.

The strongly basic anion exchanger (SBA) as a quaternary amine exchanger based on styrene-divinylbenzene copolymer in OH form, e.g. Lewatit Monoplus M500OH. However, the delivery form of this resin is the Cl- form, as the OH- form tends to undergo Hoffman’s amine degradation, producing aliphatic amines that cause a strong fish-like odour.

A mixture of strongly acidic cation exchangers and strongly acidic anion exchangers, so-called mixed bed resin, e.g. Lewatit NM60, is used in the ion exchanger resin application VE cartridges (demineralization cartridges) or polisher mixed bed resin after a reverse osmosis system or EDI. For high-purity VE applications, similar exchanger types are used, but they are more highly cross-linked and therefore more reactive, so-called ultra-pure water resins or UPW resins, such as Amberjet UP6040 instead of the mixed bed resin Lewatit NM60.

In the ion exchange resin application case of selective exchangers, it is usually an iminodiacetic acid exchanger, so-called IDE exchanger, such as the Lewatit TP 207 in the Na+ form, which as a police filter downstream of an industrial wastewater treatment system reduces residual heavy metal contents from the wastewater to the monitoring values required by regulations.

In addition to the applications mentioned, there are also numerous special applications for which ion exchanger resins with special exchanger groups have been developed, such as carboxylic acid exchangers, thiourea exchangers or bispicolyanimine exchangers.

In addition to the active exchanger group and the preconditioning (activation) of the ion exchanger, other parameters such as contact time or flow rate in m/h or bed volume/h (BV/h), temperature and pH value must also be taken into account for the application.

Ion exchanger resins are usually used in pressure housings with pre-filtration, e.g. a multi-layer filter, gravel or sand filter, cartridge or pleated filter. Depending on the contamination of the input water, further purification steps such as activated carbon, scavanger resins for surfactant removal or biological denaturation, e.g. by UV, may also be necessary, e.g. to reduce permanent inactivation of the resins by mineral oils or to prevent biological contamination. In selective exchangers, pH adjustment can help to maintain function and optimize capacity.

Depending on the application, ion exchanger resins can be used directly from the delivery container or require separate activation as part of our ion exchanger regeneration. For this purpose, the resins are removed from the delivery container (25L PE bag or big bag), pre-cleaned if necessary and converted into the desired working form (e.g. Na form, Ca form, K form, NH4 form, Fe3+, Al3+ form or OH-, NH3-, or Cl-form). This process also removes production-related impurities that would otherwise be introduced into the process. Regeneration before use is therefore always recommended.