Separation of Hydrochloric Acid and Oxalic Acid from Rare Earth Oxalic Acid Precipitation Mother Liquor by Electrodialysis.

In this study, the hydrochloric acid from rare earth oxalic acid precipitation mother liquor was separated by electrodialysis (ED) with different anion exchange membranes, including selective anion exchange membrane (SAEM), polymer alloy anion exchange membrane (PAAEM), and homogenous anion exchange membrane (HAEM). In addition to actual wastewater, nine types of simulated solutions with different concentrations of hydrochloric acid and oxalic acid were used in the experiments. The results indicated that the hydrochloric acid could be separated effectively by electrodialysis with SAEM from simulated and real rare earth oxalic acid precipitation mother liquor under the operating voltage 15 V and ampere 2.2 A, in which the hydrochloric acid obtained in the concentrate chamber of ED is of higher purity (>91.5%) generally. It was found that the separation effect of the two acids was related to the concentrations and molar ratios of hydrochloric acid and oxalic acid contained in their mixtures. The SEM images and ESD-mapping analyses indicated that membrane fouling appeared on the surface of ACS and CSE at the diluted side of the ED membrane stack when electrodialysis was used to treat the real rare earth oxalic acid precipitation mother liquor. Fe, Yb, Al, and Dy were found in the CSE membrane section, and organic compounds containing carbon and sulfur were attached to the surface of the ACS. The results also indicated that the real rare earth precipitation mother liquor needed to be pretreated before the separation of hydrochloric acid and oxalic acid by electrodialysis.

Constructing an Amino-reinforced amidoxime swelling layer on a Polyacrylonitrile surface for enhanced uranium adsorption from seawater.

Polyacrylonitrile (PAN)-based materials have been studied for decades as uranium (U(VI)) adsorbents, because the further products of abundant nitrile groups, amidoxime (AO) groups, show great affinity for U(VI) ions. However, excessive amidoximation could cause the shrinkage of PAN fibers, resulting in decreased adsorption performance. Hence, an amino-reinforced amidoxime (ARAO) swelling layer was constructed on the PAN fiber surface (PAN-NH2-AO) by modification of the strongly hydrophilic amino group to prevent shrinkage. The molecular chains in the ARAO swelling layer would be swelled due to the adsorption of a large amount of water. Simultaneously, U(Ⅵ) ions can penetrate into the ARAO swelling layer with water molecules and coordinate with amino or AO groups, leading to increased adsorption performance. PAN-NH2-AO exhibited maximum U(VI) and water adsorption capacities of 492.61 mg g-1 and 20.32 g g-1 at 25 â„ƒ with a swelling ratio of 20.73%, respectively. The adsorption capacity of PAN-NH2-AO was 0.312 mg g-1 after a 91-day immersion in Yellow Sea, China. The study of the adsorption thermodynamics and kinetics of PAN-NH2-AO showed that the adsorption process was spontaneous homogeneous chemical adsorption. This paper proposes a novel method to obstruct amidoximation induced shrinkage and to maximize the potential application of PAN-based materials.

Swollen-layer constructed with polyamine on the surface of nano-polyacrylonitrile cloth used for extract uranium from seawater.

In this study, a swelling layer was constructed on the surface of the nano-polyacrylonitrile (PAN) fiber fabric prepared by electrospinning to enrich uranium (U (VI)) adsorption from seawater. The constructed swelling layer composes of a polyethyleneimine (PEI) containing a huge amount of amino groups and imino groups with strong hydrophilicity. The molecular chain swelled in an aqueous solution by forming a swelling layer on the PAN surface. In addition, p-aminobenzenesulfonic acid (SA) was used as the side chain end group grafted on the PAN surface, the benzene ring as the side chain can hinder the rotation of the PEI chain, thereby increasing the rigidity. The increasing of the rigidity leads to stretch the conformation of the PEI molecular chain, increasing the probability of collision with U (VI), which is beneficial for adsorption. The adsorption capacity of the prepared adsorbent in the adsorption experiment reached 215.25 mg g-1, and the adsorption capacity in the 8 ppm spiked simulated seawater reached 144.5 mg g-1. The adsorption mechanism of U (VI) was analyzed by XPS. The sulfonic acid group in SA as the terminal group and amino group in the swelling layer formed a coordination structure with U (VI). The swelling layer constructed on the surface of polyacrylonitrile fibers is used to effectively extract uranium from seawater.

Construction of gel-like swollen-layer on Polyacrylonitrile Surface and Its Swelling Behavior and Uranium Adsorption Properties.

In this study, a hyperbranched chelated hydrophilic swollen-layer was constructed on the surface of polyacrylonitrile (PAN) fiber with amino trimethylene phosphoric acid (ATMP) as a terminal group, which applied as an adsorbent for seawater uranium U(VI) extraction. This shows that U(VI) enter the gel-like swollen-layer to form a more complex body structure. The molecular chain conformational extension in the swollen-layer reduces the resistance of the uranyl ion to enter the swollen-layer, which is conducive to the adsorption behavior. The adsorption performance on the U(VI) by the adsorption experiment were found to be consistent with the Langmuir isotherm adsorption model and the pseudo-second-order kinetics, indicating that the adsorption of U(VI) by this material is uniform single-layer chemical adsorption. Ion competition experiments and cyclic adsorption experiments verify the practical application potential of the materials. In the dynamic simulation of seawater adsorption experiments, the adsorption capacity of the adsorbent reached 7.4 mg/g. Studies on the adsorption mechanism have found that a large number of hydroxyl groups in the swollen-layer and ATMP as an end machine have a chelation effect on U(VI).