Ion exchange resins
Ion exchange resins are +/- 0.60 mm diameter polymer beads made of polystyrene or polyacrylate on which a positively charged molecule (functional group) has been grafted to provide them with ion exchange properties for the purpose of fluid purification (mainly liquid). The ion exchange resins can exchange cation or anion species Depending on the type functional group.
Standard Strong Base Anion (SBA)resins (Chromates removal – Resinex™ A-4
When heavy metals are present as anionic complexes like chromate (Cr˅ˡ⁺), then Resinex™ A-4, a strong base anion, can be used with a comparable efficiency as chelating resins. The positively charged functional group of the resin is a quaternary trimethylamine which holds chloride as counterion. There is an ion exchange reaction between the ionic element to remove (impurity) and chloride, due to a greater affinity of the functional group for the impurity than for chloride.
Selective Strong Base Anion (Perchlorates removal – Resinex™ -PR-1)
The positively charged functional group of the selective strong base anion resin is a quaternary amino group with a longer alkyl chain than standard this of a strong base anion (SBA). This functional group exhibits a very high affinity for oxyanions as perchlorate which are also exchanged with the chloride counterion. The macroporous structure of the polymer enhances the element selectivity by forming channels inside the bead in which certain ions cannot penetrate.
Chelating resins (heavy metals removal – Resinex™ CH-23, Resinex™)
Certain heavy metals can be removed using chelating resins that work on the principle of complexation. The functional group of the resin is a ligand which forms complexes with the element to be removed from the solution (transition metals).
Resinex™ chelating resins can remove heavy metals as cations in water down to ppt level. Resinex™ chelating resins hold special functional groups called ligands which form strong complexes with heavy metals. The two Resinex™ chelating products use for heavy metals removal in groundwater remediation are Resinex™ CH-23 (when no mercury is present) and Resinex™ CH-80 (when mercury is present).
The very high selectivity of these resins for heavy metals as cations generally leads to an extremely high operating capacity. Typically, chelating resins operate at an average flow rate of 10 BV/h (BV = Bed Volume of resin) or a superficial contact time of 6 minutes. Thus, an industrial filter that contains 2000 litres of Resinex™ CH-23 or CH-80 is able to treat 20 m³/h of water flow with a capacity of several months of 24/24h operation. The graph on the right shows the typical treated volume of groundwater water achieved by Resinex™ CH-23 versus the total heavy metal’s contamination.
Jacobi Services adapt the mobile filter range type AquaFlow™ with a top wedge wired screen to prevent channelling in the Resinex™ resin bed in order to optimise the performance of the system.
Resinex™ CH-23 removes also efficiently cobalt, cadmium and copper in their elementary cationic form.
The selectivity order of Resinex™ CH-23 is:
Cu²⁺ > UO₂²⁺ > VO²⁺ > Hg²⁺ > Pb²⁺ > Ni²⁺ > Zn²⁺ > Cd²⁺ > Co²⁺ > Fe²⁺ > Be²⁺> Mn²⁺> Ca²⁺> Mg²⁺> Sr²⁺> > Ba2²⁺
The selectivity order of Resinex™ CH-80 is:
Hg²⁺ > Ag⁺ > Cu²⁺ > Pb²⁺ > Cd²⁺ > Ni²⁺ > Co²⁺ > Fe²⁺ > Ca²⁺ > Na⁺.
Chemisorption (PFCs removal, Resinex™ TPX-4510)
A weakly base resin such as Resinex™ TPX-4510 has a tertiary amine in its free base form as its functional group. The pollutant capture requires the quaternisation of the amino group by the water acidity (H⁺). One can therefore consider this reaction as a chemisorption involving strong ionic forces since no real ion exchange occurs between the solid matrix (resin bead) and the liquid phase (water to treat). The polymer structure, upon its porosity also plays a role in the selective attraction of pollutants by excluding species upon their steric hindrance.