Radiation removal of lead and cadmium complexed with ethylenediamine tetraacetic ACID from aqueous solutions

The removal of lead (100 mg/L) and cadmium (27 mg/L) complexed with ethylenediamine tetraacetic acid (EDTA) in presence of different scavengers has been investigated. The experiments show that in acidic solutions, the EDTA complexed lead may be reduced at a dose of 40 kGy up to 97% without the addition of typical OH radical scavengers such as Na(K) formate. The addition of OH radical scavengers as 1×10⁻³ mol/L HCOOK, 2×10⁻³ mol/L carbonate or 2×10⁻³ mol/L bicarbonate (wide range of pH) results in no further improvement. The bubbling of the solution with nitrogen or oxygen also exhibits no positive effect. On the contrary, saturation with nitrous oxide in the presence of scavengers has a modest positive influence, whereas in the system which is scavenger-free, high negative effect (30 %) was observed. The presence of nitrate (e _aq ⁻ scavenger) appears to be important for an effective reduction of complexed lead. The efficient removal of cadmium complexed with EDTA proceeds up to 96 % at a dose of 40 kGy with an addition of 5×10⁻³ mol/L of carbonate as the OH radical scavenger and simultaneously pH buffer (pH 10.5). After irradiation, the cadmium is present in the final form of CdCO₃.