No abstract

No abstract

No abstract

No abstract

Ion exchange is widely used for the recovery and separation of metals from process and waste streams in chemical process industries. The effect of added complexing anions such as EDTA, NTA, and citrate on the cation exchange of Cu 2+ and Zn 2+ with strong-acid Purolite NRW100 resin was studied at 298 K, with the metals in solution in excess over the complexing anions. Experiments were performed as a function of solution pH (1.0-6.0), concentration of metals (4.5-22.5 mol/m 3 ), and concentration ratio of complexing anions to metals (0-1). It was shown that the rate of metal exchange decreased when the complexing anions were present. The addition of EDTA and NTA decreased the amount of metal exchange throughout the entire pH range studied, but it was the case for the citrate system only at high pH (>4). In the absence of complexing anions, the Langmuir equation could be used to correlate the exchange isotherms at a given pH on a macroscopic basis. However, a proposed chemical model that takes into account possible solid-liquid exchange reactions and solution chemistry could be used to describe the metal exchange equilibria in the presence of complexing anions.

No abstract

Experimental studies on the cation-exchange separation of three pairs of divalent metal ions (Zn/Cu, Co/Cu, and Ni/Cu) from water in the presence of water-soluble ligands were made at 298 K. Four ligands including ethylenediaminetetraacetic acid, nitrilotriacetic acid, iminodiacetic acid, and citrate were selected. Experiments were performed as a function of the solution pH (1.0−6.0) and the concentration ratio of the ligand to total metals (0−1). It was shown that the exchange selectivity was enhanced when the anionic ligands were present. The extent of enhancement strongly depended on the solution pH but was not completely related to the metal-complexing affinity of the ligands. A parameter, based on the combinations of the overall formation constants of the ligands with two metals, was thus proposed to correlate the exchange selectivity obtained under various sets of metal pairs and anionic ligands. This correlation allowed selection of a suitable type or amount of the anionic ligands for effective separation of a given pair of heavy metals.

No abstract