Removal of Fluorine from RECl3 in Solution by Adsorption, Ion Exchange and Precipitation

In this paper, methods of effective removal of fluorine from rare earth chloride solution by adsorption, ion exchange and precipitation with lanthanum carbonate or CO2 gas as fluorine-removal agent, respectively, were studied. The relevant parameters studied for fluorine-removal percentage were the effects of the type and dosage of fluorine-removal agent, the injection flow and mode of CO2, the initial concentration of rare earth solution and initial pH value, contact time, temperature and stirring. XRD, SEM and EDS were used to analyze and characterize the filter slag obtained after fluorine removal. SEM and EDS results showed that RECO3(OH) with a porous structure was formed in rare earth chloride solution when lanthanum carbonate was used as fluorine-removal agent, and it had strong selective adsorption for F−. The XRD spectra showed that F− was removed in the form of REFCO3 precipitates, which indicates that the adsorbed F− replaced the OH- group on the surface of RECO3(OH) by ion exchange. The experimental results showed that a fluorine-removal percentage of 99.60% could be obtained under the following conditions: lanthanum carbonate dosage, 8%; initial conc. of rare earths, 240 g/L; initial pH, 1; reaction temperature, 90 °C; reaction time, 2 h. Simultaneously, a fluorine-removal process by CO2 precipitation was explored. In general, RE2(CO3)3 precipitation is generated when CO2 is injected into a rare earth chloride solution. Interestingly, the results of XRD, SEM and EDS showed that the sedimentation slag was composed of REFCO3 and RE2O2CO3. It was inferred that RE2(CO3)3 obtained at the initial reaction stage had a certain adsorption effect on F− in the solution, and then F− replaced CO32− on the surface of RE2(CO3)3 by ion exchange. Therefore, F− was finally removed by the high crystallization of REFCO3 precipitation, and excess RE2(CO3)3 was aged to precipitate RE2O2CO3. The fluorine-removal percentage can reach 98.92% with CO2 precipitation under the following conditions: venturi jet; CO2 injection flow, 1000 L/h; reaction temperature, 70 °C; initial pH, 1; reaction time, 1.5 h; initial conc. of rare earths, 240–300 g/L; without stirring. The above two methods achieve deep removal of fluorine in mixed fluorine-bearing rare earth chloride solution by exchanging different ionic groups. The negative influence of fluorine on subsequent rare earth extraction separation is eliminated. This technology is of great practical significance for the further development of the rare earth metallurgy industry and the protection of the environment.

Evaluating radiation risks and resource opportunities associated with phosphogypsum in the Philippines

Phosphogypsum (PG) accumulates during wet-phosphoric acid production for fertilizers. In the Philippines, PG is partly (40%) utilized to produce gypsum walls and cement. This work assesses the radiological risks and resource opportunities associated with PG stacks in the Philippines. The conducted in situ radiometric survey measured the activity concentrations of 40K, 238U, and 232Th at 270 locations. Besides, another 120 surface samples were collected. Pure PG exceeds the recommended radiation limits, but simple dilution with conventional materials can make PG available as an inexpensive secondary raw material for construction. PG further contains relevant concentrations of rare earths and Y (195 ppm).

Effect of Lanthanum Cerium Cysteine on Cure Characteristics, Mechanical Properties, and Thermooxidative Aging for Natural Rubber

In this work, a novel additive lanthanum cerium cysteine (LC-Cys), with the molecular formula La0.35Ce0.65(Cys)3Cl3·3H2O, was successfully synthesized through complex decomposition reaction of L-Cysteine and chlorinated rare earths. The effects of additive LC-Cys on cure characteristics, mechanical properties, and thermooxidative aging were investigated. LC-Cys as a multifunctional additive was applied to increase the curing rate and reduce the content of zinc oxide in the presence of the sulfur vulcanization system. It was found that the vulcanizates filled with (5ZnO/2LC-Cys) exhibited the highest modulus, which indirectly indicated the high crosslink and stiffness of the vulcanizates. Moreover, the vulcanizates with LC-Cys showed excellent mechanical properties and resistance to thermooxidative aging. Compared to NR composites filled with normal ZnO, LC-Cys even enhanced the mechanical strength and thermooxidative aging properties with 40% lower ZnO addition.