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Because of its low whiteness, complex composition, radioactivity and high impurity percentage, the usage of phosphogypsum (PG) resources is limited. A theoretical foundation for upgrading and bleaching PG can be obtained by researching the presence and status of impurities in the material and its symbiotic connection with gypsum. This paper makes use of an automatic mineral phase analyzer, optical microscope, XRF, XRD and SEM-EDS. After analyzing the chemical makeup of PG, phase composition and particle size composition, the distribution law and symbiotic interaction between impurities and gypsum in various particle sizes were discovered. Using a flotation test, the process mineralogy analysis results were confirmed. According to the XRF and XRD study results, the primary impurity elements in PG are Si, P and F. Si is more abundant in PG that is between +850 μm and −37.5 μm in size. The concentrations of gypsum and quartz in PG are 82.59% and 8.73%, respectively, according to the results of XRD and process mineralogy. The monomer dissociation degree of the gypsum mineral phase is as high as 90.47%. Gibbsite and pyrite are the primary causes of the low whiteness of PG and are clearly related to the quartz mineral phase. The coupling process of "flotation + pickling" produced purified PG with a purity of 95.35%, whiteness of 70.76% and SiO2 content of 2.73%. The quality met the first-class index standards of PG in GB/T23456-2018. [ABSTRACT FROM AUTHOR]

Bauxite residue is a hazardous solid waste produced in the alumina production process and has also become a significant rare earth resource. The extraction behaviors of La, Ce, Sc and Y solubilized in the phosphoric acidic leachate of bauxite residue were investigated in this study with di-(2-ethylhexyl) phosphoric acid as the extractant. With a relatively low concentration of 2% at an aqueous solution pH of 1.5, 90% Sc and 98% Y were extracted by di-(2-ethylhexyl) phosphoric acid. Less than 5% La and Ce and impurities of Fe, Al, Ti and Ca were extracted in this situation. As the concentration of di-(2-ethylhexyl) phosphoric acid increased to 20%, almost all the Sc and Y were extracted and the extraction ratios of La and Ce were 87% and 95%, respectively. A good separation of REEs against impurities was simultaneously obtained in the solvent extraction process and their separation coefficients were much higher than 1. A stepwise extraction process was proposed and established to extract Sc/Y and La/Ce sequentially from the phosphoric acidic leachate. It was further revealed that the Sc and Y in the acidic leachate were extracted by di-(2-ethylhexyl) phosphoric acid through an ion exchange process, and that the extraction of La and Ce was due to an antagonistic process where both an ion exchange reaction and a solvation reaction occurred. [ABSTRACT FROM AUTHOR]

Currently, the primary method for leaching rare earth ores is through in situ leaching. This approach involves contact between clay minerals and liquids, which can lead to the potential swelling of clay minerals with water, triggering natural disasters such as landslides. The main purpose of this study is to select the suitable anti-swelling solution for Hunan Jianghua ionic rare earth ore. According to the ore composition analysis, 88 wt% of Hunan Jianghua ionic rare earth ore is composed of halloysite clay mineral. Therefore, halloysite clay mineral is used to investigate its anti-swelling behavior in order to provide a reference for future research on the selection of raw ore swelling inhibitors. In this study, the traditional leaching agent, MgSO4 solution, was used as the solvent along with two additional compounds, CH3COOK and KCl, which were prepared in different concentrations to form a new composite swelling inhibitor solution to observe their effect on the swelling rate of halloysite clay mineral. At the same time, the seepage velocity of halloysite clay mineral with different anti-swelling solutions is studied. The results indicate that the optimal concentration in the CH3COOK + MgSO4 solution system is 0.05 mol/dm3. At this concentration, the swelling rate is 5.129%, the inhibition rate is 20.08%, and the seepage velocity rate is 12.51 × 10−3 cm/min, respectively. In KCl + MgSO4 solution, the swelling rate is 4.868%, the inhibition rate is 24.15% and the seepage velocity rate is 13.23 × 10−3 cm/min at the concentration of 0.02 mol/dm3, which is the optimum concentration. In addition, FTIR and TG studies have further demonstrated the mechanism by which these two composite bulking inhibitors inhibit the swelling of halloysite clay mineral. [ABSTRACT FROM AUTHOR]

In order to reveal the influence of ammonium salts on the rare earth leaching process of weathered crust elution-deposited rare earth ores, ammonium acetate, ammonium chloride, and ammonium sulfate were used as leaching agents. The effects of the leaching agent on the rare earth leaching efficiency and the expansion, dissolution, and transformation behavior of clay minerals in the rare earth leaching process were studied. The results showed that rare earth leaching efficiency followed the order ammonium acetate > ammonium chloride > ammonium sulfate, with values of 90.60%, 85.96%, and 84.12%, respectively. The swelling ratio of clay mineral followed the order ammonium acetate < ammonium chloride < ammonium sulfate; the clay mineral swelling ratio was 2.09% when ammonium acetate was the leaching agent. Thermogravimetric analysis showed that the interlayer water content was the lowest when ammonium acetate was used as the leaching agent. Under the conditions of different leaching agents, the clay mineral contents changed from illite and halloysite to smectite and kaolinite. When ammonium acetate was used as the leaching agent, the relative conversion of illite was 1.49%, and that of smectite was only 0.17%. SEM analysis showed that the clay minerals expanded and dissolved obviously when ammonium chloride and ammonium sulfate were used as the leaching agents. Meanwhile, the clay mineral layered structure was relatively complete when ammonium acetate was used as the leaching agent. Therefore, when ammonium acetate was used as the leaching agent, it had the least effect on the swelling, dissolution, and transformation of clay minerals. This can provide a theoretical basis for the safe production of weathered crust elution-deposited rare earth ore, and for the screening of green and efficient leaching agents. [ABSTRACT FROM AUTHOR]

A ternary-structured photocatalyst of graphite carbon nitride quantum dot sensitized TiO2 nanotubes (g-CNQDs/TNTs) on SiO2 photonic crystals (PCs) was fabricated successfully to achieve higher photodegradation efficiency of dyes in wastewater. Hydrothermal compositing conditions of g-CNQDs/TNTs were optimized to be 160 °C for 20 h and with a loading ratio of 1 : 8 of g-CNQDs to TNTs. In addition, the effect of the photonic bandgap (PBG) of PCs on the photocatalytic activity was investigated. When the PBG of PCs was located near the absorption peak of g-CNQDs at 464 nm, the photodegradation performance of g-CNQDs/TNTs and g-CNQDs/TNTs/PCs was 2.14 times and 3.76 times higher than that of pristine TNTs, respectively. The synergistic effect of quantum dots and PCs contributes to suppressing the recombination of photo-generated carriers and enhancing light harvesting. This work provides a pathway for efficient pollutant degradation on multi-synergistic photocatalysts by constructing a ternary-structure. [ABSTRACT FROM AUTHOR]