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Phosphatic Resources: A Valuable Wealth of Rare Earths
Published in Abhilash, Ata Akcil, Critical and Rare Earth Elements, 2019
Dhruva Kumar Singh, Vivekanand Kain
Two US patent based on synergistic mixture of D2EHPA + TBP and di-nonyl phenyl phosphoric acid (DNPPA) + TOPO for the recovery of uranium from weak (WPA) as well as strong (MGA) phosphoric acid solutions [10,11]. Significant concentration of rare earths in WPA (Table 17.3) makes it an attractive preposition to include the recovery of rare earths as a by-product of uranium in the second cycle of D2EHPA + TBP process. This will not only improve the economics of overall process but also definitely be a step towards the conservation of natural resources (monazite/xenotime). With D2EHPA, yttrium behaves like heavy rare earths and gets preferentially extracted to most of the rare earths such as La, Ce, Nd, Sm, and Gd. The extraction order of rare earths with D2EHPA is as follows: La < Ce < Pr < Nd < Sm < Eu < Gd < Tb < Dy < Ho < Y< Er < Tm < Yb < Lu. In order to recover rare earths, the patented process was modified by introducing selective scrubbing of rare earths with oxalic acid prior to uranium stripping, and the results were published by D.K. Singh et al. in 2008 [34]. The modified process including recycling of oxalic acid is shown in Figure 17.3. Iron forms soluble complex with oxalic acid by forming ferric oxalate while rare earths get precipitated as oxalate, which upon filtration and ignition yields mixed rare earths rich in heavy rare earths mainly consisting of Y, Er, Yb, etc.
Clay Mineral Catalysis of Redox, Asymmetric, and Enantioselective Reactions
Published in Benny K.G. Theng, Clay Mineral Catalysis of Organic Reactions, 2018
Earlier, Del Castillo et al. (1996) have noted that the hydroxylation of phenol over Ti-PILC is dependent on the type of solvent used. With methanol as a solvent, hydroquinone is the principal product formed, while catechol is preferentially formed in the presence of acetone. Zhou et al. (2014) have identified 4-chlorocatechol and 5-chloro-1,2,4-benzenetriol as intermediates in the catalytic wet peroxide oxidation of 4-chlorophenol (over and Al−Fe-, Al−Cu-, and Al−Fe−Cu-PILC), yielding 2,4-dioxopentanedioic acid and a ferric-oxalate complex as end products in addition to CO2, H2O, and Cl−. We might add that the reaction of phenol with hydroxyl radicals can lead to polymer formation (Voudrias and Reinhard 1987; Birkel et al. 2002), while Fe3+-exchanged montmorillonite can effectively promote the surface oligomerization of phenolic compounds and estrogens (Polubesova et al. 2010; Qin et al. 2015).
Theoretical analysis and experimental Validation of selective oxalate precipitation
Published in Mineral Processing and Extractive Metallurgy, 2022
S. Ghasemi, N. Rafiei, A. Heidarpour
Some modifications in the precipitation step will improve the selectivity in oxalate precipitation. For example, the oxidation state of the multivalent metal cations is affected by the reaction environment. Under an oxidative atmosphere, higher oxidation state species are predominant, while lower oxidation state metal species can be found under an inert or reductive atmosphere. In the case of iron, if is oxidised to under the oxidative atmosphere prior to precipitation, ferric oxalate with much higher solubility (Sinha et al. 2016) than ferrous oxalate will be produced. Therefore, it is likely that iron would not precipitate in the early stages. Controlling the pH (Figure 2) and temperature will also affect the selective precipitation step. Modification of such parameters is the subject of our next research.
Effect of complex iron on the phosphorus absorption by two freshwater algae
Published in Environmental Technology, 2021
Yongting Qiu, Zhihong Wang, Feng Liu, Zekun Wu, Hongwei Chen, Daijun Tang, Junxia Liu
Figure 4 shows the influence of the concentration of complex iron on the P absorption rate of A. flos-aquae. In ferric humate and ammonium ferric citrate group, iron concentration had no significant effect onthe P absorption rate of A. flos-aquae. Only at low concentration, the P absorptivity decreases slightly. In EDTA-Fe group, the P absorption rate of 0.9 mg/L group was faster than that of the other three concentration groups. In the ferric oxalate group, the absorption of phosphorus increased first and then decreased with the increase of iron concentration.
Effect of different kinds of complex iron on the growth of Anabaena flos-aquae
Published in Environmental Technology, 2019
Yongting Qiu, Zhihong Wang, Feng Liu, Junxia Liu, Tao Zhou
In this paper, results showed that the bioavailability of complex iron is related to its complex form. The complex iron has chemical equilibrium in water, and the complexing constants of iron in different complexing states are different. This reveals that the stability of the complexed iron in water is different and further leads to a difference in the absorption of iron. The factors that affected the stability of the chelated iron can be divided into internal and external causes [25]. In this study, the influence of external factors on biomass can be ignored through the strict control of experimental conditions. The internal factors include the central ion (Fe) and the influence of organic reagent molecules. Iron is an excessive metal element whose d electron orbit and f electron orbit are not filled. The complex formed by ionic iron has the property of partial covalent bond that has a similar coordination ability for O and N, and can form a stable complex with organic reagents containing hydroxyl groups. The three organic complexing agents selected in this experiment all contain hydroxyl groups and can form covalent bonds with iron ions. Therefore, the differences in stability are related to the molecular structure of complexing agents. For example, ferric oxalate is a combination of three oxalic acid and two order iron ions (Figure 2(a)). The structure is stable, and iron in the complex is not easily captured by complexing agents secreted by the algae. In the EDTA-Fe group, EDTA is complexed with iron to form a ring structure (Figure 2(b)), and iron is not readily dissociated and absorbed by the algae cells. Chu et al. studied the effect of EDTA and iron on the growth of M. aeruginosa and found that the chelation between EDTA and iron inhibited the uptake of iron by algal cells [26]. The ferric ammonium citrate group also conforms to this law. Because ammonium iron simply replaces hydrogen in the citric acid hydroxyl group to form a complex (Figure 2(c)), iron and ammonium are relatively easily robbed by other strong complexing agents. So, iron from ferric ammonium citrate can also be better used in low concentration. Therefore, the degree of iron absorption by A. flos-aquae is different, resulting in different growth of algae, which is supported by the report of Gress et al. made who indicated that the rate of iron uptake was a function of the chelator strength, with the weakest chelator supporting the highest uptake rate [27]. In this experiment, the iron ions in ferric ammonium citrate were much easily absorbed by A. flos-aquae, followed by EDTA-Fe, and the ferric oxalate showed the least.