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The adsorption mechanism of salicyl hydroxamic acid (SHA, C7H7O3N) on rare earth minerals was investigated using two complementary methods: precipitation studies and modelling. Precipitation studies showed that SHA adsorption occurs through a displacement of the hydroxide ion at the surface in an ion exchange mechanism, leading to surface precipita...
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... are actually quite abundant in the Earth's crust. As can be seen in Figure 1, cerium, for example is as plentiful as copper, and copper is quite abundant (Haxel et. al., 2002). ...
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... can be seen on the graph below and the four others in Appendix B, the buffer region leading to equivalence point is perturbed. Figure 15 shows the titration of water in the absence of SHA. In this case, the waster was adjusted to pH 13.5 with NaOH, boiled, and then cooled under a vacuum to prevent CO2 dissolution. ...
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... analyze the titration curve in Figure 15, it is noted that a strong base (NaOH) is being titrated against a strong acid (HCl). It can be seen that the equivalence point is exactly at 7, without any blemish that could be caused by dissolved carbon dioxide (carbonic acid). ...
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... has a huge relevance in explaining the results obtained from adsorption experiments and rationalizing the plots obtained using StabCal. It can be considered that below pH 12.3, as seen on Figure 17, predominantly neutral aqueous SHAH species exists; thus its adsorption by ion exchange actually leads to the formation of water: í µí± í µí± í µí± í µí± í µí± í µí± -í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± + í µí±í µí±í µí±í µí±í µí°´í µí°´í µí±í µí± ⇔ í µí± í µí± í µí± í µí± í µí± í µí± -í µí±í µí±í µí±í µí±í µí°´í µí°´íµí°´í µí±í µí±í µí±í µí±í µí±í µí± + í µí±í µí± 2 í µí±í µí± ...
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... the data obtained, more accurate predominance StabCal diagrams can be calculated. Using Ce2(CO3)3 as an example, Figure 19 was calculated with thermodynamic data (i.e., including SHAH). Although differences are subtle, there are differences predominantly observed by the slight change in Ce2(CO3)3 solubility between 7 and 8. Otherwise, the diagrams are essentially the same. ...
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... do this, SHA is assumed to occupy a rectangular form when it lies horizontally with a projected area of 7.53Å by 5.26Å and, when it adsorbs vertically, with a projected area of 5.26 Å by 2.42Å. Figure 21 below illustrates the packing of SHA to form a monolayer. In Figures 19, 20 and 21, the atoms in black are carbons, in red are oxygens, in white are hydrogens, and in blue is nitrogen. ...
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... 21 below illustrates the packing of SHA to form a monolayer. In Figures 19, 20 and 21, the atoms in black are carbons, in red are oxygens, in white are hydrogens, and in blue is nitrogen. The distances indicated in the figure legends are those measured between the atoms highlighted with light yellow circles. ...
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... distances indicated in the figure legends are those measured between the atoms highlighted with light yellow circles. The horizontal adsorption is modeled by considering the distance in Figure 20 as the length (7.53 Å between the yellow highlighted atoms) and the distance in Figure 21 as the width. ...
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... the vertical adsorption uses Figure 21 and Figure 23 as length and width, respectively. ...
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... for vertical, horizontal latitudinal and horizontal longitudinal are shown in Figure 30, Figure 31 and Figure 32, respectively. ...
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... precipitation is to therefore to be expected. By comparison, Figure 41 shows SHA adsorbing horizontally and suggests that the adsorption at one site will sterically hinder adsorption at other sites; however, two sites will be masked and three sites will not be. All five of these unoccupied sites will lead to surface precipitation but will be hindered at the two masked sites. ...
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... are actually quite abundant in the Earth's crust. As can be seen in Figure 1, cerium, for example is as plentiful as copper, and copper is quite abundant (Haxel et. al., 2002). ...
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... can be seen on the graph below and the four others in Appendix B, the buffer region leading to equivalence point is perturbed. Figure 15 shows the titration of water in the absence of SHA. In this case, the waster was adjusted to pH 13.5 with NaOH, boiled, and then cooled under a vacuum to prevent CO2 dissolution. ...
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... analyze the titration curve in Figure 15, it is noted that a strong base (NaOH) is being titrated against a strong acid (HCl). It can be seen that the equivalence point is exactly at 7, without any blemish that could be caused by dissolved carbon dioxide (carbonic acid). ...
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... has a huge relevance in explaining the results obtained from adsorption experiments and rationalizing the plots obtained using StabCal. It can be considered that below pH 12.3, as seen on Figure 17, predominantly neutral aqueous SHAH species exists; thus its adsorption by ion exchange actually leads to the formation of water: í µí± í µí± í µí± í µí± í µí± í µí± -í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± + í µí±í µí±í µí±í µí±í µí°´í µí°´í µí±í µí± ⇔ í µí± í µí± í µí± í µí± í µí± í µí± -í µí±í µí±í µí±í µí±í µí°´í µí°´íµí°´í µí±í µí±í µí±í µí±í µí±í µí± + í µí±í µí± 2 í µí±í µí± ...
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... the data obtained, more accurate predominance StabCal diagrams can be calculated. Using Ce2(CO3)3 as an example, Figure 19 was calculated with thermodynamic data (i.e., including SHAH). Although differences are subtle, there are differences predominantly observed by the slight change in Ce2(CO3)3 solubility between 7 and 8. Otherwise, the diagrams are essentially the same. ...
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... do this, SHA is assumed to occupy a rectangular form when it lies horizontally with a projected area of 7.53Å by 5.26Å and, when it adsorbs vertically, with a projected area of 5.26 Å by 2.42Å. Figure 21 below illustrates the packing of SHA to form a monolayer. In Figures 19, 20 and 21, the atoms in black are carbons, in red are oxygens, in white are hydrogens, and in blue is nitrogen. ...
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... 21 below illustrates the packing of SHA to form a monolayer. In Figures 19, 20 and 21, the atoms in black are carbons, in red are oxygens, in white are hydrogens, and in blue is nitrogen. The distances indicated in the figure legends are those measured between the atoms highlighted with light yellow circles. ...
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... distances indicated in the figure legends are those measured between the atoms highlighted with light yellow circles. The horizontal adsorption is modeled by considering the distance in Figure 20 as the length (7.53 Å between the yellow highlighted atoms) and the distance in Figure 21 as the width. ...
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... the vertical adsorption uses Figure 21 and Figure 23 as length and width, respectively. ...
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... for vertical, horizontal latitudinal and horizontal longitudinal are shown in Figure 30, Figure 31 and Figure 32, respectively. ...
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... precipitation is to therefore to be expected. By comparison, Figure 41 shows SHA adsorbing horizontally and suggests that the adsorption at one site will sterically hinder adsorption at other sites; however, two sites will be masked and three sites will not be. All five of these unoccupied sites will lead to surface precipitation but will be hindered at the two masked sites. ...
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... are actually quite abundant in the Earth's crust. As can be seen in Figure 1, cerium, for example is as plentiful as copper, and copper is quite abundant (Haxel et. al., 2002). ...
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... can be seen on the graph below and the four others in Appendix B, the buffer region leading to equivalence point is perturbed. Figure 15 shows the titration of water in the absence of SHA. In this case, the waster was adjusted to pH 13.5 with NaOH, boiled, and then cooled under a vacuum to prevent CO2 dissolution. ...
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... analyze the titration curve in Figure 15, it is noted that a strong base (NaOH) is being titrated against a strong acid (HCl). It can be seen that the equivalence point is exactly at 7, without any blemish that could be caused by dissolved carbon dioxide (carbonic acid). ...
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... has a huge relevance in explaining the results obtained from adsorption experiments and rationalizing the plots obtained using StabCal. It can be considered that below pH 12.3, as seen on Figure 17, predominantly neutral aqueous SHAH species exists; thus its adsorption by ion exchange actually leads to the formation of water: í µí± í µí± í µí± í µí± í µí± í µí± -í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± + í µí±í µí±í µí±í µí±í µí°´í µí°´í µí±í µí± ⇔ í µí± í µí± í µí± í µí± í µí± í µí± -í µí±í µí±í µí±í µí±í µí°´í µí°´íµí°´í µí±í µí±í µí±í µí±í µí±í µí± + í µí±í µí± 2 í µí±í µí± ...
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... the data obtained, more accurate predominance StabCal diagrams can be calculated. Using Ce2(CO3)3 as an example, Figure 19 was calculated with thermodynamic data (i.e., including SHAH). Although differences are subtle, there are differences predominantly observed by the slight change in Ce2(CO3)3 solubility between 7 and 8. Otherwise, the diagrams are essentially the same. ...
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... do this, SHA is assumed to occupy a rectangular form when it lies horizontally with a projected area of 7.53Å by 5.26Å and, when it adsorbs vertically, with a projected area of 5.26 Å by 2.42Å. Figure 21 below illustrates the packing of SHA to form a monolayer. In Figures 19, 20 and 21, the atoms in black are carbons, in red are oxygens, in white are hydrogens, and in blue is nitrogen. ...
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... 21 below illustrates the packing of SHA to form a monolayer. In Figures 19, 20 and 21, the atoms in black are carbons, in red are oxygens, in white are hydrogens, and in blue is nitrogen. The distances indicated in the figure legends are those measured between the atoms highlighted with light yellow circles. ...
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... distances indicated in the figure legends are those measured between the atoms highlighted with light yellow circles. The horizontal adsorption is modeled by considering the distance in Figure 20 as the length (7.53 Å between the yellow highlighted atoms) and the distance in Figure 21 as the width. ...
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... the vertical adsorption uses Figure 21 and Figure 23 as length and width, respectively. ...
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... for vertical, horizontal latitudinal and horizontal longitudinal are shown in Figure 30, Figure 31 and Figure 32, respectively. ...
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... precipitation is to therefore to be expected. By comparison, Figure 41 shows SHA adsorbing horizontally and suggests that the adsorption at one site will sterically hinder adsorption at other sites; however, two sites will be masked and three sites will not be. All five of these unoccupied sites will lead to surface precipitation but will be hindered at the two masked sites. ...
Citations
... They concluded that even more selective collectors were needed [10] . Hence, collectors, such as salicylhydroxamic acid (SHA), have recently been examined [11][12][13][14] . It was collectively concluded from these studies that LC and CN played critical roles [2,4] . ...
... Thus, with respect to REEs, H2O5 and SHA are likely to bond with REM surfaces by reacting through these oxygens, leading to either a chemisorbed or surface precipitated collector or a combination of the two. A mechanism has been presented along these lines [2,4,[11][12][13][14] and is the subject of continuing investigations [15,16] . ...
Flotation is the most common beneficiation process used for separating minerals, but for rare earth minerals (REMs), performance can suffer due to the dilute nature of the rare earth elements. Furthermore, the REMs tend to possess smaller grain sizes, making the use of traditional flotation cells difficult if total liberation is needed. Consequently, improved efficiencies are needed for extracting REMs from various sources. For these systems, hydroxamic acids are commonly used as flotation collectors. Two such hydroxamic collectors were studied in this work: salicylhydroxamic acid (SHA) and N,3-dihydroxy-2-naphthamide (H2O5). Because there is no documented synthesis route for H2O5, several synthesis approaches were examined. Furthermore, because there is no information on H2O5, important structural and characteristic data was gathered regarding its (1) preferred structural isomer as a Cu2+ complex and (2) electrostatic potential values of the possible dentate groups in different tautomeric forms, thereby allowing H2O5 to be compared to SHA, particularly regarding flotation behavior. Hydrogen nuclear magnetic resonance (H-NMR), Laser Raman Spectroscopy (LRS), and predominantly Fourier-Transform Infrared (FT-IR) spectroscopy showed that both SHA and H2O5 preferred to be keto tautomers when uncomplexed; however, once chelated to Cu2+ ions, the collectors adopted enol forms. Molecular modeling using Spartan software showed an increase in the electrostatic potential of the possible dentate groups in both molecules for the enol form. H2O5 also resulted in an increased recovery by flotation of REMs of about 23% compared to SHA at similar reagent dosages.
... LREEs on the periodic table array from lanthanum (La) to gadolinium (Gd) and HREEs from terbium (Tb) to lutetium (Lu) plus Sc and Y which are also considered HREEs because of their comparable chemical and physical properties. In recent times, pending the source, REEs have been grouped to include Sm to Dy as the middle rare earth elements (MREEs) [4]. ...
Rare earth elements (REEs) are strategic materials of extreme importance to both military and civil applications. REEs are mined and processed because of their criticality. End of life rare earth metals are recycled for efficient use of natural resources and also to ensure supply of these critical raw materials. By using hydro- or pyro-metallurgical approaches, REEs can be processed from mined ore or recycled from magnets and other materials as rare earth oxides, fluorides and chlorides. Typically, rare earth oxides are dissolved in a molten halide bath, converted to metal by electrolysis at elevated temperatures, and then recovered as a liquid upon tapping and, later, as a solid upon casting and cooling. This research focuses on advanced separations which differences in physical and chemical properties of the molten bath are taken advantage of to yield effective recovery of neodymium metal. To achieve the neodymium metal recovery, a unique approach using novel potential (E)-pO2- diagrams coupled with cyclic voltammetry (CV) and electrowinning (EW) was employed. Another aspect includes the use of a novel hydrometallurgical method to recycle neodymium magnets to produce neodymium fluoride so it could also become a feedstock to the molten bath considered in this work.
... Similar results of this example case were obtained for studies of SHA adsorbing on Nd 2 O 3 and other REOs at pH 8-11 and was the subject of three theses. [34][35][36] ...
Adsorption of salicyl hydroxamic acid (SHA) on neodymium oxide (Nd2O3) surfaces was studied at different SHA concentrations. The adsorbed surfaces were examined using X-Ray Diffraction (XRD) and Laser Raman Spectroscopy (LRS). XRD results show that the oxide remains intact until stoichiometric amounts equivalent to Nd(SHA)3 were exceeded. At lower concentrations, the behavior appeared to be an ion exchange of SHA with hydroxide as well as carbonates and chlorides. Results are attributed to a monolayer of chemisorbed SHA at low concentrations and multilayers of surface precipitated Nd(SHA)3 at higher concentrations. LRS corroborated these findings. Peaks from the C-H stretching band and C = N vibration bands were identified and areas under the peaks were quantified. Formation of the hydroxamate compound was ascertained from the C = N bands around 1597 cm−1. It was concluded that chelation occurs through chemical bonding of SHA with surface Nd confirming chemisorption and with trivalent Nd confirming surface precipitation. Thermodynamic calculations in the form of solubility speciation diagrams suggest that chemisorption predominates at moderate pH between 6 and 9 and surface precipitation predominates at higher pH between 9 and 12. Adsorption isotherms were determined for the monolayer and found to yield free energy values between physisorption and chemisorption but, due to the reaction being ion exchange, it was concluded to be chemisorption.
Keywords: Chemisorption, ion exchange, salicyl hydroxamic acid, chelation, surface precipitation, neodymium oxide
... After this time, the REP at the lower pH conditions shows SHA desorbing, a phenomenon that is attributed to surface carbonation due to the equilibrium of carbonate (CO3 2-) with carbon dioxide (CO2) as testing was conducted in open air. Sime (2018) suggested that SHA adsorption likely was attributed to an ion exchange mechanism that lead to chemisorption and or surface precipitation. His crystal lattice models also suggest SHA would adsorb both ways at REP surfaces. ...
... Results suggest surface precipitation occurs but could be after some chemisorption occurs. Sime (2018) showed through crystal lattice calculations that this was likely. ...
... Like La-REP, SHA appears to desorb and is likely caused by surface carbonation. Sime (2018) modeled SHA adsorption at Eu-REP and suggested it would be mostly chemisorption but, because a complete monolayer could not be established, surface precipitation likely occurred. ...
Adsorption behavior of the anionic collector salicyl hydroxamic acid (SHA) on a group of selected rare earth phosphates (REPs) was studied by means of experimental methods and modeling software. These REPs were then compared to rare earth carbonates (RECs) and rare earth oxides (REOs) to develop a trend. A suite of rare earth elements (REE) were studied that included light (LREE) and middle (MREE). Results for heavy (HREE) were inferred. Synthetic phosphate, oxide and carbonate powders of the rare earth elements Lanthanum (La), Cerium (Ce), Europium (Eu) and Dysprosium (Dy) were tested for these studies. Dysprosium phosphate was the only REE that was synthesized in the lab for further testing. The studies were conducted at a range of pH levels to mimic commercial flotation processes and to optimize recovery parameters involving the collector SHA. Differences in adsorption behavior between LREE, and MREE as well as HREE are attributed to solution chemistry, coordination number and REEionic diameter. SHA adsorption follows an ion-exchange process that leads to chemisorbed or surface precipitated states, depending on atomic spacing and pH level. These effects are strongly attributed to lanthanide contraction.
The lanthanides are more commonly referred to as rare earth elements (REEs). Approximately 250 rare earth minerals (REMs) are known but vary in their composition as solid solutions. Because REEs have similar properties, REMs are usually separated from invaluable gangue into a single bulk concentrate. Flotation is almost universally the method of choice. Flotation is a complex process that works based on differences in hydrophobicity, involving a plethora of variables that enhance those differences with the goal of improving the grade and recovery of the REMs reporting to the concentrate.
In this regard, flotation is briefly reviewed from reagent, machine, and flowsheet design perspectives with application to REMs. It is stressed that REM flotation depends on REE coordination number and cation size, typically requiring the need for collector blends. A case study is then presented to illustrate the importance of depressants. This was accomplished by examining their role on the first-order rate constant in kinetic modeling. Four novel depressants were identified and a parametric design of experiments was conducted. The study looked at the type of depressant and the dosage of collector to generate a statistically significant model using a three-compartmental kinetic approach. Not only were grade and recovery examined but so was the response of the first-order rate constant to changing experimental conditions.
