Uranium solution-mineral equilibria at low temperatures with applications to sedimentary ore deposits

To adsorb and recover uranium(VI) from seawater, an improved macroporous fibrous polymeric adsorbent containing amidoxime chelating functional group (FPAO) was synthesized by irradiation-induced graft polymerization utilizing methacrylic acid (MAA) as a hydrophilic monomer. The adsorption mechanism of U(VI) on FPAO adsorbent was investigated in a wide pH range by the method of the thermodynamics. It was found that the pH value at different conditions had significant effect on the adsorption of U(VI) on FPAO adsorbent. The adsorption ability of FPAO for U(VI) increased from pH 2.0 to pH 6.0 and decreased from pH 6.0 to pH 9.0. U(VI) was effectively adsorbed by FPAO adsorbent at around pH 6.0. The predominant composition of resulting the mononuclear complex was determined as UO 2 2R–C(NO)NH 2 by investigating the effect of the concentrations of U(VI), FPAO, H + and Cl − on the adsorption reaction. The adsorption equilibrium equation of U(VI) on FPAO adsorbent was expressed as UO 2 (OH) + (aq)  + 2R–C(NOH)NH 2(fp)  ↔ UO 2 2R–C(NO)NH 2(fp)  + H + (aq) +H 2 O. The overall adsorption equilibrium constant was calculated to be K ad =7.08×10 7 M −1 at ionic strength of 0.1 M at 25 °C. A monolayer molecule adsorption mechanism between U(VI) and FPAO was also determined by examining the relationships between the adsorbed amount of U(VI) and contact time.

The adsorption mechanism of uranium(VI) from seawater on a macroporous fibrous polymeric adsorbent containing amidoxime chelating functional group

Electrochemical, complexation, and electronic properties of uranyl(VI) and -(V) carbonato complexes in an aqueous Na2CO3 solution have been investigated to define the appropriate conditions for preparing pure uranyl(V) samples and to understand the difference in coordination character between UO22+ and UO2+. Cyclic voltammetry using three different working electrodes of platinum, gold, and glassy carbon has suggested that the electrochemical reaction of uranyl(VI) carbonate species proceeds quasi-reversibly. Electrolysis of UO22+ has been performed in Na2CO3 solutions of more than 0.8 M with a limited pH range of 11.7 < pH < 12.0 using a platinum mesh electrode. It produces a high purity of the uranyl(V) carbonate solution, which has been confirmed to be stable for at least 2 weeks in a sealed glass cuvette. Extended X-ray absorption fine structure (EXAFS) measurements revealed the structural arrangement of uranyl(VI) and -(V) tricarbonato complexes, [UO2(CO3)3]n- [n = 4 for uranyl(VI), 5 for uranyl(V)]. ...

Comparative Study of Uranyl(VI) and -(V) Carbonato Complexes in an Aqueous Solution

The influence of pH value on the adsorption of U(VI) towards a novel, macroporous fibrous polymeric adsorbent containing amidoxime chelating functional group (MFPA) was investigated. It was found that the adsorption of MFPA for U(VI) strongly relied on the pH value in aqueous phase. U(VI) showed no adsorption below pH 1.0 and low adsorption in a pH range of 2.0 to 7.0, respectively. The adsorption of U(VI) onto MFPA increased significantly from pH 7.0 to 8.0 and then decreased evidently in excess of pH 8.0. As the pH value was 8.5 especially greater than 9.0, a colloid precipitate appeared because of the formation of UO 2 (OH) 2 . The optimum adsorption pH value in experiment was hence determined to the pH 8.0, which is close to that of seawater. The complex composition between U(VI) and amidoxime chelating functional group in a pH range of 7.0 to 8.0 was determined as UO 2  · 2R–C(NO)NH 2 by investigating the effect of the concentrations of U(VI), MFPA, and hydrogen ion on the adsorption of U(VI), i.e., one U(VI) could react with two amidoxime chelating functional groups. The corresponding adsorption equilibrium equation was expressed as follows: UO 2 ( OH ) ( aq ) + + 2 R C ( NOH ) NH 2 ( ads ) ↔ UO 2 · 2 R C ( NO ) NH 2 ( ads ) + H ( aq ) + + H 2 O The overall adsorption equilibrium constant was calculated to be K ad  = 5.66 × 10 2 M −1 at ionic strength of 0.1 M at 25 °C. Furthermore, a monolayer molecule adsorption mechanism between U(VI) and MFPA was discussed by examining the relationships between the amount of U(VI) adsorbed and contact time.

pH Effect on the uranium adsorption from seawater by a macroporous fibrous polymeric material containing amidoxime chelating functional group

This work aims at the investigation of nano-Mg(OH)2 as a promising adsorbent for uranium recovery from water. Systematic analysis including the uranium adsorption isotherm, the kinetics and the thermodynamics of adsorption of low concentrations of uranyl tricarbonate (0.1–20 mg L−1) by nano-Mg(OH)2 was carried out. The results showed a spontaneous and exothermic uranium adsorption process by Mg(OH)2, which could be well described with pseudo second order kinetics. Surface site calculation and zeta potential measurement further demonstrated that UO2(CO3)34− was a monolayer adsorbed onto nano-Mg(OH)2 by electrostatic forces. Accordingly, the adsorption behavior met the conditions of the Langmuir isotherm. Moreover, in most of the reported literature, nano-Mg(OH)2 had a higher UO2(CO3)34− adsorption affinity b, which implied a higher adsorption amount at equilibrium in a dilute adsorbate system. The significance of the adsorption affinity b for choosing and designing adsorbents with respect to low concentration of resources/pollutants treatment has also been assessed.

A study of the potential application of nano-Mg(OH)2 in adsorbing low concentrations of uranyl tricarbonate from water

Equilibria in uranyl carbonate systems—II: The overall stability constant of UO2(CO3)22− and the third formation constant of and the third formation constant of UO2(CO3)34−

Joseph P. Scanlan

Papers

Equilibria in uranyl carbonate systems—II: The overall stability constant of UO2(CO3)22− and the third formation constant of and the third formation constant of UO2(CO3)34−