Ion-exchange of Pb~(2+), Cu~(2+), Zn~(2+), Cd~(2+), and Ni~(2+) ions from aqueous solution by Lewatit CNP 80

摘要

Removal of trace amounts of heavy metals can be achieved by means of selective ion-exchange processes. The newly developed resins offered a high resin capacity and faster sorption kinetics for the metal ions such as Pb~(2+), Cu~(2+), Zn~(2+), Cd~(2+), and Ni~(2+) ions. In the present study, the removal of Pb~(2+), Cu~(2+), Zn~(2+), Cd~(2+), and Ni~(2+) ions from aqueous solutions was investigated. Experimental investigations were undertaken using the ion-exchange resin Lewatit CNP 80 (weakly acidic) and were compared with Lewatit TP 207 (weakly acidic and chelating). The optimum pH range for the ion-exchange of the above mentioned metal ions on Lewatit CNP 80 and Lewatit TP 207 were 7.0-9.0 and 4.5-5.5, respectively. The influence of pH, contact time, metal concentration and amount of ion-exchanger on the removal process was investigated. For investigations of the exchange equilibrium, different amounts of resin were contacted with a fixed volume of Pb~(2+), Cu~(2+), Zn~(2+), Cd~(2+), and Ni~(2+) ion containing solution. The obtained sorption affinity sequence in the presented work was Ni~(2+) ＞ Cu~(2+) ＞ Cd~(2+) ＞ Zn~(2+) ＞ Pb~(2+). The metal ion concentrations were measured by AAS methods. The distribution coefficient values for metal ions of 10~3 M initial concentration at 0.1 mol/L ionic strength show that the Lewatit CNP 80 was more selective for Ni~(2+), Cu~(2+) than it was for Cd~(2+), Zn~(2+) and Pb~(2+). Langmuir isotherm was applicable to the ion-exchange process and its contents were calculated. The uptake of metal ions by the ion-exchange resins was reversible and thus has good potential for the removal of Pb~(2+), Cu~(2+), Zn~(2+), Cd~(2+), and Ni~(2+) from aqueous solutions. The amount of sorbed metal ion per gram dry were calculated as 4.1, 4.6, 4.7, 4.8, and 4.7mequiv./g dry resin for Pb~(2+), Cu~(2+), Zn~(2+), Cd~(2+), and Ni~(2+), respectively. Selectivity increased in the series: Cd~(2+) ＞ Pb~(2+) ＞ Cu~(2+) ＞ Ni~(2+) ＞ Zn~(2+). The results obtained showed that Lewatit CNP 80 weakly acidic resin had shown better performance than Lewatit TP 207 resin for the removal of metals. The change of the ionic strength of the solution exerts a slight influence on the removal of Pb~(2+), Cu~(2+), Zn~(2+), Cd~(2+), and Ni~(2+). The presence of low ionic strength or low concentration of NaNC＞3 does not have a significant effect on the ion-exchange of these metals by the resins. We conclude that Lewatit CNP 80 can be used for the efficient removal of Pb~(2+), Cu~(2+), Zn~(2+), Cd~(2+), and Ni~(2+) from aqueous solutions.