Magnesium bicarbonate,prepared by the carbonation of magnesium hydroxide slurry,was used as a novel saponifier to eliminate the ammonia nitrogen pollution in the rare earth extraction separation process.The effect of impurity ions introduced by system on the carbonation reaction of magnesium hydroxide was studied in the work.The results showed that the presence of Ca2+ could lead to side reactions so as to reduce the conversion rate of magnesium hydroxide,and a small number of rare earth ions would have great influence on the carbonation reaction.What's more,there was no influence on carbonation reaction with the low concentration of Na+or Mg2+,the conversion rate of magnesium hydroxide could reach above 96%.This paper showed a practical theory which could provide scientific guidance for the preparation of novel saponifier in rare earth extraction separation process.
A novel Ce(Ⅳ) ion-selective polyvinyl chloride(PVC) membrane electrode based on HDEHP and HEH/EHP as ionophore was successfully prepared. The factors affecting the response of Ce(Ⅳ) ion were investigated, such as membrane composition, internal solution, concentration of SO_4^(2–), and acidity in test solution. The best performance was obtained using the membrane with PVC:DBP:HDEHP:HEH/EHP:OA mass ratio of 75:175:5:5:5. The proposed electrode exhibited a Nernstian slope of 30.44 mV/decade for Ce(Ⅳ) ion over a linear concentration range of 1×10^(–5)–1×10^(–1) mol/L with the detection limit of 9.0×10^(-6) mol/L. The electrode showed stable response within the SO_4^(2–) concentration range of 0.1–1 mol/L and the acidity range of 0.25–1.2 mol/L H+. The proposed electrode showed high selectivity for Ce(Ⅳ) over a wide variety of interfering ions and a fast response time. It was used as an indicator in the potentiometric titration of Ce(Ⅳ) solution with H_2O_2 solution, and could also be used for the determination of Ce(Ⅳ) in real Ce(Ⅳ)-containing aqueous samples.
Magnetic separation of iron in rare-earth tailings was achieved by magnetizing roast process with coal as reductant. Effects of the temperature, carbon to oxygen ratio, and cooling type on magnetic susceptibility and composition of rare-earth tailings were investigated. The results show that roast conditions with the temperature of 650 °C, carbon to oxygen ratio of 3.85, and holding time of 2.5 h are in favor of reduction of Fe_2O_3 to Fe_3O_4 when the roasted rare-earth tailings is cooled along with furnace. Under these roast conditions, magnetic susceptibility of rare-earth tailings is 2.36 that is very close to theoretical value(2.33). However, magnetic separation results of iron in rare-earth tailings cooled along with furnace are not satisfactory. Through comparing magnetic separation results of iron in rare-earth tailings cooled by different ways, it is found that water cooling is more favored of magnetic separation of iron in the roasted rare-earth tailings than furnace cooling and air cooling. Grade and recovery of iron in concentrate from rare-earth tailings cooled by water are 45.00%-49.00% and 65.00%-77.50%, respectively.
Solvent extraction has been the most widely used technique for rare earths separation. In this study, thermodynamics and kinetics of lutetium extraction with HEH(EHP) in hydrochloric acid medium were investigated. The extraction mechanism and the relevant parameters were determined by experiment research which can guide the practical extraction process. The data indicated that chloride ion had no effect on lutetium extraction, the rate constant increased when stirring speed was enhanced. Effects of temperature, HEH(EHP) concentration, acidity, and chloride concentration were also studied. Thickness of the diffusion film was also calculated to be 4.66×10^(–3) cm at 150 r/min.
In view of the problem of ammonia-nitrogen wastewater pollution in rare earths extraction and separation, the novel saponification agent of organic phase, which is magnesium bicarbonate solution, was prepared with the natural rich and cheap dolomite as raw material through carbonation process. The behavior and purification of main impurities ions in the carbonation process as well as the application effect of the novel saponification agent in the extraction and separation was researched. The results showed that the concentration of Fe, Al, Si impurities ions was less than 5 ppm in the saponification agent through the development of effective removal technology, respectively. When the novel saponification agent was used in the extraction and separation, magnesium utilization rate was more than 95%, and rare earths extraction rate above 99.5% has achieved. Therefore, the technology could replace ammonia-water to saponify the organic phase in rare earth extraction and separation process.
