Performance appraisal of foam separation technology for removal of Co(II)-EDTA complexes intercalated into in-situ formed Mg-Al layered double hydroxide from radioactive liquid waste

- Flotation of CoEDTA2− intercalated into in-situ formed Mg-Al LDH was studied.
- Combination of coprecipitation/foam separation efficiently removed CoEDTA2− by SLS.
- High removal percentage, 99%, and high volume reduction, ∼200, are obtained.
- CoEDTA-LDH was efficiently floated from radioactive liquid waste within a minute.
- The removal mechanism of CoEDTA2− by coprecipitation/foam separation was proposed.

Combination of coprecipitation and foam separation is suggested in this study as a new strategy for removal of CoEDTA2− complexes from aqueous solutions. This strategy is based on intercalation of these complexes into Mg-Al LDH colloidal particles, in-situ formed by coprecipitation process, and the subsequent separation of these particles by foam separation. The effect of the solution pH on the removal efficiency of CoEDTA2− is studied in the pH range of 4-12 using sodium lauryl sulfate (SLS) and cetyltrimethylammonium bromide (CTAB) as anionic and cationic collectors, respectively. The results show that SLS is better than CTAB for the present study. The influence of [Mg(II)]/[Al(III)] molar, from 0.5 to 3, showed that CoEDTA2− is better removed at a ratio of 2. The impact of foam separation parameters, SLS and ethanol concentrations, on removal of CoEDTA2− intercalated into Mg-Al LDH is evaluated. The data demonstrated that both parameters played a significant role. The effect of various competitive anions on the removal efficiency of CoEDTA2− is studied and their deleterious effect is followed the order NO3− < Cl− < SO42− < CO32−. The efficiency of the present process is confirmed by its application for removal of CoEDTA2− from radioactive liquid waste where removal percentage more than 99% is achieved. The removal mechanism of the studied complex is also proposed. The efficiency of coprecipitation/foam separation process is further confirmed by comparing the data obtained for CoEDTA2− from radioactive liquid waste (flotation% > 99%, volume reduction = 192 and flotation time = 1 min) with those reported for removal of metal-EDTA complexes using other treatment processes.

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