Foam separation of radio-molybdenum oxyanions (99MoO42−) incorporated into Co(II)/Al(III) layered double hydroxide using anionic surfactant

Foam separation of radio-molybdenum oxyanions (⁹⁹MoO₄²⁻) incorporated into in-situ formed Co(II)/Al(III) layered double hydroxide (LDH) particles was applied for recovery of these anionic species from aqueous solutions. The results showed that Co(II)/Al(III) molar ratios of 2 and 2.5 resulted into not only high recovery values for ⁹⁹MoO₄²⁻ (R > 0.97), but also high decontamination factor (DF = 33 and 36, respectively). Almost complete recovery was achieved for ⁹⁹MoO₄²⁻ coprecipitated with Co(II)/Al(III) LDH in the pH range 9.9–10.5. Ageing time of 5 min was sufficient to completely coprecipitate the concerned anionic species. Sodium dodecyl sulfate (SDS) concentrations in the range 1.5 × 10⁻³ - 3 × 10⁻³ mol/L had the ability to efficiently form hydrophobic ⁹⁹MoO₄^2--Co(II)/Al(III)-LDH particles, where recovery values of about 0.96 were achieved with high DF values. The influence of the coexistence of different foreign anions (Cl⁻, NO₃⁻, HCO₃⁻, CO₃²⁻ and SO₄²⁻) during coprecipitation process of ⁹⁹MoO₄²⁻ and foam separation of the resultant particles was investigated. The suggested strategy in the present study was effectively applied for recovery of ⁹⁹MoO₄²⁻ anions from ground water (R ≈ 0.98 and enrichment ratio (ER ≈ 7172) and radioactive process wastewater (R ≈ 0.96 and ER = 3887). Based on characterization of Co(II)/Al(III) LDH using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) before and after foam separation process using SDS and the obtained data, the recovery mechanism of ⁹⁹MoO₄²⁻ was proposed.