Jianping Gong,Shaochun Hou,Tao Xu,Yongzhi Zhao,Jun Li
The traditional rare earth extraction process generates a large amount of radioactive waste or alkaline wastewater, which has become an important constraint to rare earth production in recent years. In this study, the differences in solubility between rare earth sulfates and phosphoric acid and the high selectivity of tributyl phosphate (TBP) for phosphoric acid were exploited. The preliminary separation of phosphorus from rare earths was achieved in three stages of counter-current leaching under the low liquid-to-solid (L/S) ratio of 1:1, 323 K, with 98% of P while 2% of rare earth oxide (REO) entering into the solution. Subsequently, the dissolved phosphorus was selectively extracted by TBP. In total, 81% of P was extracted by five-stage cross-flow extraction under the organic-to-aqueous (O/A) ratio of 5:1, 298 K, leaving rare earths (REEs) in the raffinate. The extraction mechanism of low-concentration phosphoric acid in this system was investigated by Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopies. Finally, the residual solid phase of the counter-current leaching process was leached with dilute sulfuric acid to recover the rare earths, and 97% of the REO was recovered to the solution. The whole process realizes the separation and extraction of rare earth and phosphorus resources, reduces the production of radioactive waste, and provides the possibility of green production of rare earths.
The solid–liquid phase behavior of the NaF–Na3PO4–H2O ternary system and its binary subsystems NaF–H2O and Na3PO4–H2O at 308.15, 323.15, and 348.15 K has been measured by the isothermal dissolution equilibrium (IDE) method. Compared with the measured solid–liquid phase behavior data, the previously reported results have been evaluated and the unreasonability has been discussed. The phase diagrams at the investigated temperatures for this ternary system are drawn according to the measured solid–liquid phase behavior and the corresponding wet solid and liquid-wet solid–solid lines. From the phase diagrams, it is found that at a given temperature, there are three types of equilibrium solid phases, NaF(s), double salt 2Na3PO4·NaF·19H2O(s), and Na3PO4·12H2O(s) in the ternary system. Accordingly, there are two cosaturated points for NaF(s) and double salt 2Na3PO4·NaF·19H2O(s), double salt 2Na3PO4·NaF·19H2O(s) and Na3PO4·12H2O(s), respectively. The comparison of phase diagrams at different temperatures suggests that, with the rise of temperature, the double salt crystal region became a little bit larger, and correspondingly, the crystal regions of pure salt (NaF(s) and Na3PO4·12H2O(s)) became smaller, which is not beneficial to the separation of fluoride and phosphate. This indicates that the fluoride and phosphate separation process should be at lower temperatures.
Xudong Zheng,Wen Sun,Ning Wei,Tingting Bian,Yi Zhang,Lingli Li,Yuzhe Zhang,Zhongyu Li,Hongxiang Ou
Phosphorus and nitrogen flow to water leads to eutrophication and depletion of reserves. Bionic-inspired tannin modification is proposed for preparing a tannin-modified La–Zn(4,4′-dipy)(OAc) 2 /bacterial cellulose composite membrane for simultaneous adsorption of total phosphorus and ammonia nitrogen in water. Its physical and chemical properties were characterized by XRD , SEM , FT-IR, TGA and other characterization methods. La–Zn(4,4′-dipy)(OAc) 2 nanomaterial achieved effective adhesion on the tannin-modified bacterial cellulose membrane. Adsorption experiments showed that the composite membrane could both adsorb total phosphorus and ammonia nitrogen, and adsorption capacity of ammonia nitrogen was better than that of total phosphorus. The maximum adsorption capacities of ammonia nitrogen and total phosphorus were 482.35 mg/g and 374.71 mg/g. In the binary solution, the adsorption capacity of the composite membrane to ammonia nitrogen and total phosphorus decreased, but the adsorption capacity to phosphorus decreased slightly. Results of adsorption experiments showed that the adsorption process of nitrogen and phosphorus by the composite membrane belonged to single-layer adsorption, and the calculation results of the kinetic equation were in accordance with the quasi-second-order, and the adsorption equilibrium of the composite membrane was reached within 360 min. In short, the composite membrane had a better adsorption and separation effect both on ammonia nitrogen and total phosphorus.
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