Effect of formaldehyde on Cu(Ⅱ) removal from synthetic complexed solutions by ion exchange

摘要

The effect of formaldehyde (HCHO) on the ion exchange of Cu(Ⅱ) from an equimolar EDTA (ethylenediaminetet-raacetic acid, H_4L) solution with a strong-base Amberlite IRA-400 resin was studied. Experiments were conducted as a function of the initial concentration of Cu(Ⅱ) (0.5-10 mM), solution pH (1.0-6.0), HCHO concentration (0-6 vol%), and temperature (15-35℃). It was shown that the amount of exchange of Cu(Ⅱ), which exists in the form of complexed anions CuL~(2-), increased with increasing solution pH and reached a plateau at an equilibrium pH (pH_e) of 3.5. However, the amount of exchange decreased with increasing HCHO concentration up to 3 vol% but then slightly decreased with a further increase in HCHO concentration. Such effect of added HCHO was determined by the following two factors: the competitive exchange of HCOO~- anions and the enhanced exchange of Cu(Ⅰ) in the form of complexed anions CuL~(3-). The exchange isotherm obtained at a fixed pH_e could be well described by the Langmuir equation. The isosteric enthalpy change for the present ion exchange process was also evaluated and discussed.