Studies on the separation of silver(I) microquantities from macroquantities of salts of other elements on selective ion-exchangers

Comments on the Letter to the Editor written by S. Allahyari et al. concerning the paper “A comparative study of chelating and cationic ion exchange resins for the removal of palladium(II) complexes from acidic chloride media”

“…In the former case after 72 h of phases contact time the gas was educed and the ion exchange resin changed colour becoming brown (probably nitric oxide was produced) whereas in the latter one the destruction of Lewatit TP-214 takes place after passing the solution in the amount of 15 bed volumes. In the case of HCl [2], HCl-NaCl [1], H 2 SO 4 , NH 4 OH [11] solutions similar observation was not made. Additionally, in the papers [1][2][3][4][5][6][7][8][9][10][11][12] neither of the authors observed and mentioned the ion exchange resin functional groups degradation in the HCl -noble metal system.…”

“…In the case of HCl [2], HCl-NaCl [1], H 2 SO 4 , NH 4 OH [11] solutions similar observation was not made. Additionally, in the papers [1][2][3][4][5][6][7][8][9][10][11][12] neither of the authors observed and mentioned the ion exchange resin functional groups degradation in the HCl -noble metal system. Moreover, this resin is applied on a large scale which indicates that its groups must be stable to be efficient.…”

“…In all cases the recovery was nearly quantitative even for 8 M HCl. It is true that the degradation of the functional thiourea groups is possible but it was found in the case of palladium(II) removal [4] and silver(I) removal [11] from the solutions of the following compositions: 0.1-0.9 M HCl-0.9-0.1 M HNO 3 -Pd(II) and HNO 3 -Ag(I) (with the increase in the nitric acid concentration to 5 M, the ion exchanger destruction is violent) [11]. In the former case after 72 h of phases contact time the gas was educed and the ion exchange resin changed colour becoming brown (probably nitric oxide was produced) whereas in the latter one the destruction of Lewatit TP-214 takes place after passing the solution in the amount of 15 bed volumes.…”

Comparison of the Batch and Breakthrough Properties of Stable and Plain Alginate Microcapsules with a Chelating Resin and an Ion Exchanger in Ag+ Adsorption

“…The adsorption of Ag + by Lewatite occurs via an irreversible reaction of the thiourea ligand and the Ag + receptor. On the other hand, the uptake of Ag + by 200 CT is reversible and 200 CT retains its ionic identity during the reaction.…”

“…Most of the initial chelating resins were weak Lewis acids and, therefore, were ineffective in acidic solutions. Later, new resins that contained weakly basic functional groups (e.g., thiourea) were synthesized that were able to preserve their selectivity in the extreme acidic conditions. – Unfortunately, this modification created a new drawback, which was the formidable elution of the saturated resins . Another general shortfall of the chelating resins is their slow kinetics, which necessitates a large resin inventory and expensive capital and fixed costs.…”