Immobilization of Metal Hexacyanoferrate Ion-Exchangers for the Synthesis of Metal Ion Sorbents--A Mini-Review

Metal hexacyanoferrates are very efficient sorbents for the recovery of alkali and base metal ions (including radionuclides such as Cs). Generally produced by the direct reaction of metal salts with potassium hexacyanoferrate (the precursors), they are characterized by ion-exchange and structural properties that make then particularly selective for Cs(I), Rb(I) and Tl(I) recovery (based on their hydrated ionic radius consistent with the size of the ion-exchanger cage), though they can bind also base metals. The major drawback of these materials is associated to their nanometer or micrometer size that makes them difficult to recover in large-size continuous systems. For this reason many techniques have been designed for immobilizing these ion-exchangers in suitable matrices that can be organic (mainly polymers and biopolymers) or inorganic (mineral supports), carbon-based matrices. This immobilization may proceed by in situ synthesis or by entrapment/encapsulation. This mini-review reports some examples of hybrid materials synthesized for the immobilization of metal hexacyanoferrate, the different conditionings of these composite materials and, briefly, the parameters to take into account for their optimal design and facilitated use.

Ultrafine sodium titanate nanowires with extraordinary Sr ion-exchange properties

Ultrafine sodium titanate nanowires are produced from TiAl alloy precursors via a nonthermal process where Al leaching and Ti oxidation occur simultaneously in an alkaline medium. The obtained nanowires demonstrate a layered crystal structure with a diameter of a few nanometers and exhibit remarkable Sr ion-exchange properties.

Comparison of The Sorption Kinetics of Lead(II) and Zinc(II) on Titanium Phosphate Ion-Exchanger

The treatment of heavy metal-contaminated wastewater is an important action to reduce the negative impacts of industrial wastes on water bodies. This work focuses on the application of a low-cost titanium (IV) phosphate sorbent of TiO(OH)H₂PO₄·2H₂O chemical composition toward lead and zinc ions depending on their concentration and the temperature of the solution. The kinetic studies showed that the values of the rate of intraparticle diffusion and the effective diffusion coefficients for Zn²⁺ were considerably higher than those for Pb²⁺. To explain the difference between the sorption kinetics rates for Pb²⁺ and Zn²⁺, the effective radius and dehydration degree of the adsorbed ions were calculated. The sorbent capability of the lead and zinc ion removal and its excellent efficiency in the presence of a high concentration of calcium ions were demonstrated using simulated mine water. Due to the fast kinetics and the high exchange capacity of titanium phosphate toward divalent ions, this sorbent can be considered as a promising material for the concentration and immobilization of heavy metals into the phosphate matrix.