الفهرس 
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Abstract
REEs are precious sources, which can be widely applied in many fields, the world today has hugely benefited from the different applications of rare earth elements (REEs) to most high-tech devices. Thus, many efforts were multiplied to find efficient methods for their preconcentration, separation and determination. Therefore, recovery and separation of REEs from aqueous phase could supplement the demand of REEs. There are many separation methods available, however, they have disadvantages. Recently, adsorption has been studied and the results are quite encouraging and different amounts of adsorbents have been tested.
In this thesis, the main objective was to develop and synthesize a new adsorbents in solid phase extraction method (SPE), that can be use for extraction and separation of RE ions from aqueous phase and apply these adsorbents for preconcentrate of ultratrace RE ions from Egyptian monazite ores prior to their determination by ICP- based techniques. Among all RE ions, we chose La3+, Nd3+, Gd3+ and Y3+ to study their adsorptive abilities. For this purpose, superparamagnetic iron oxide nanoparticles functionalized by L-cysteine (Cys-SPIONs) and graphene oxide nanosheets (GO) were tested as nanoadsorbent materials in SPE technique.
The present work was carried out in four main chapters;
Chapter (1):
This chapter include an introduction and short notes covering the background of lanthanides, their various applications, their properties, their distribution in minerals, the abundance of monazite ore in Egypt, the separation methods of REEs and their applications.
Moreover this chapter contains an introduction covering the background of nanotechnology, nano-structured materials types and their environmental application for extraction of REEs. Furthermore, this chapter focused on talking about magnetic nanoparticles, graphene oxides nanosheets and different synthesis methods, surface functionalization and their characterization. Finally, a literature review covering the works that were done in the past to the present in fields of lanthanides extraction, separation and determination.
Chapter (2):
This chapter represent the different experimental procedures which were followed in the present work and include the materials used in the present work, description for the instrument used in the analysis and extraction of lanthanides elements, the experimental procedures that were followed and finally, this chapter includes the elemental analysis for monazite mineral that used in this work.
Chapter (3):
This chapter focused on using superparamagnetic iron oxide nanoparticles functionalized by L-cysteine (Cys-SPIONs) as solid phase (nanoadsorbent) for extraction of RE3+ ≈ La3+, Nd3+, Gd3+ and Y3+ ions from aqueous solution and applied this adsorbent for extraction of RE3+ from monazite sample solution. This chapter included the results obtained and their interpretation. Chapter 3 was divided into main three parts as follow:
Part (1):
Bare iron oxide magnetic nanoparticles were prepared by chemical co-precipitation method and the surface of the magnetic particles underwent subsequent modification with L-cysteine to form Cys-SPIONs. The particles were characterized using TEM, BET, XRD, FTIR, EDX, TGA and zeta potential measurements. The results showed that the Cys-SPIONs are of nanometer size with a mean diameter of 10 nm without the observation of aggregation . The Cys-SPIONs were stable in solution and could be easily separated from aqueous solution using a magnetic separation method. FTIR Spectroscopy, TGA and zeta potential measurements proved the attachment of L-cysteine on the particle surface. These surface functionalized magnetic nanoparticles can be used as a tool for the extraction of REEs from different sources.
Part (2):
A batch technique was adopted to investigate the removal efficiency of Cys-SPIONs toward La3+, Nd3+, Gd3+ and Y3+ ions under various environmental conditions. The kinetic process of La3+, Nd3+, Gd3+ and Y3+ ions sorption on Cys-SPIONs reached equilibrium within < 15 min. The kinetic behavior fitted with pseudo- second-order model well and influence on the adsorption rate. The fast sorption kinetics and high sorption amount were attributed to the plentiful surface sites provided by the surface-coated L-cysteine. The Cys-SPIONs was able to remove ∼88, 96.5, 98 and 92 % of La3+, Nd3+, Gd3+ and Y3+ ions, respectively in aqueous solution at pH = 7. The sorption isotherm agreed well with the Langmuir model, having a maximum sorption capacity qmax ∼ 57, 85.5, 98 and 73 (mg/g) of La3+, Nd3+, Gd3+ and Y3+ ions, respectively. The adsorption rate of studied rare earth ions follow this order: Gd3+ > Nd3+> Y3+> La3+. In the other hand, the desorption behavior of RE3+ on the Cys-SPIONs surface suggests that Cys-SPIONs can be reused after treated with 0.5 M HNO3 solution and recovery % of RE3+ was (≥ 96%). The RE3+ sorption was not affected by the presence of divalent cations of calcium, magnesium, and nickel ions due to Cys-SPIONs strong tendency to form stable complexation with trivalent lanthanide.
The obvious sorption−desorption hysteresis suggested that the removal of RE3+ ions was dominated by inner-sphere surface complexation. Good selective separation of Nd3+ relative to La3+ and Y3+ were 4.3 and 2.8, respectively but didn’t have separation of Nd3+ relative to Gd3+ due to similarity between them in electronegativity and ionic radius. Finally, Cys-SPIONs is excellent nanoadsorbent for extraction and recovery of REEs due to it have been advantages of both the possibility of magnetic retrieval and a high selectivity for REEs extraction and could open application for this adsorbent to extraction of REEs from different natural sources as Egyptian monazite minerals as we discuss in next part.
Part (3):
Monazite ores are the second most important source of the world supply of REEs and thorium as associated metals, generally contain ~ 55–65 wt.% rare earth oxides (REO). The high grade Egyptian monazite sand (97%) contains more than 71% LREO. Therefore, This part adept a process for selective extraction of RE3+ ions from the monazite nitric liquor, generated after several chemical treatment process for Egyptian black sand monazite mineral, applying solid phase extraction technique.
The influence of several variables such as contact time between phases, initial concentration of the started solution, temperature and its pH were investigated. After the mineral thorium content separation, the results indicated the possibility of extraction efficiency of RE3+ ions from nitric acid media containing a mixture of rare earth group by using Cys-SPIONs as nanoadsorbent in SPE technique. Cys-MNPs achieve high removal efficiency 96.7, 99.3, 96.5 and 87 % for La3+, Nd3+, Gd3+ and Y3+, respectively at pH = 6 in 15 min. Adsorption kinetic studies follow a pseudo-second order model suggesting that the rate-limiting step is chemisorption. Maximum adsorption capacity qmax ≈ 71.5, 145.5, 64.5 and 13.6 mg/g of the La3+, Nd3+, Gd3+ and Y3+ ions, respectively. It was better descried by Langmuir isotherm model, and the relative order of qmax values Nd3+> La3+ > Gd3+ > Y3+. The affinity adsorption order of RE3+ ions in monazite sample solution were changed compared to the adsorption order in case of the same metal ions adsorption on the surface of the same adsorbents in synthetic aqueous solution because. This fact can be attributed to presence of another metal ions in the monazite sample solution, which will effect on the competitive between RE3+ ions on the surface of Cys-SPIONs (c.f. Table 2.2).
High desorption efficiency was obtained and 85–90% recovery of RE3+ ions was achieved by using 0.1 M HNO3. The coexisting mono and divalent electrolyte ions such as Na2+ and Ca2+ in monazite solution had no significant competition effects on the selective adsorption of RE3+ as a group by Cys-SPIONs. Cys-SPIONs is achieving good selective separation for Nd3+ ions from La3+ as LREEs (SF=6.3), Nd3+ from Gd3+ as MREEs (SF = 5.63) and higher separation factor for Nd3+ from Y3+ as HREEs (SF=23.8).
In this chapter, we proved that the Cys-SPIONs is excellent adsorbent to achieve selective extraction, preconcentration and separation of REEs in Solid phase extraction method, whether from synthetic aqueous solution or mineral samples.
Chapter (4):
This chapter focused on using graphene oxide nanosheets (GO) as solid phase (nanoadsorbent) for extraction of RE3+ ≈ La3+, Nd3+, Gd3+ and Y3+ ions from aqueous solution and applied this adsorbent for extraction of RE3+ from monazite sample solution. This chapter included the results obtained and their interpretation, and it was divided into three parts.
Part (1):
Graphene oxide nanosheets have attracted multidisciplinary attention due to their unique physicochemical properties. Herein, graphene oxide nanosheets were synthesized from graphite using a modified Hummers method and were characterized by using TEM, SEM, UV–Visible, Raman spectrum, DLS, FT-IR, EDX, TGA and zeta potential measurements. The obtained results show that the superior water dispersibility of GO is not just because of the presence of a larger concentration of ionizable oxygen functionalities but also because of the chemical nature of these functionalities.
Part (2):
In this part, we have showed that the synthesized GO exhibits good extraction % performance for La3+, Nd3+, Gd3+ and Y3+. The adsorption process was completed within 30 min at pH = 6, which might be attributed to the electrostatic interaction between rare earth ions RE3+ and oxygenic functional groups on GO surface. The maximum adsorption capacity of La3+, Nd3+, Gd3+ and Y3+ on GO surface could be obtained using the nonlinear Langmuir model achieving 85.7, 188.6, 225.5 and 135.7 (mg/g), respectively. The sorption of RE3+ ions on the graphene oxide nanosheets was strongly dependent on pH and independent of the ionic strength, indicating that the sorption was mainly dominated by inner-sphere surface complexation rather than by outer-sphere surface complexation or ion exchange. The kinetic studies showed that the experimental data fits well to the pseudo-second order model, suggesting that chemisorption process is the rate-limiting step. The La3+, Nd3+, Gd3+ and Y3+ saturated GO surface suspension can be recovered up to ≈ 99% by using HNO3 solution (0.1 M). All above results indicate that GO is a suitable adsorbent for selective adsorption of trivalent rare earth ions. Nd3+ could be selectively separated from the mixed Nd3+/La3+(SF=2.3) and Nd3+/Y3+ (SF=1.7) solutions and couldn’t achieved separation between Nd3+/Gd3+ over the whole pH range. The selective adsorption and desorption of RE3+ experiments forecasted that GO nanosheets would be a good candidate for their potential industrial application.
Part (3):
In this section, we have investigated GO nanosheets as adsorbents for the extraction of RE3+ ions from monazite sample solution in solid phase technique. Go nanosheets achieved high removal efficiency 94, 98.5, 92 and 85 % for La3+, Nd3+, Gd3+ and Y3+, respectively, at pH = 6 in 30 min. Batch adsorption results showed that GO nanosheets had perfect affinity towards La3+, Nd3+, Gd3+ and Y3+ much better than other metal ions and the maximum adsorption capacity estimated from Langmuir model was 96, 218, 41.5 and 20 (mg/g), respectively, at pH = 5 and at room temperature. It was better descried by Langmuir isotherm model, and the relative order of qmax values Nd3+> La3+ > Gd3+ > Y3+. The adsorption kinetic and equilibrium data were fitted to the pseudo-second-order model. The RE3+-saturated GO nanosheets could be recovery by 0.1 M HNO3(R%= 65-75). The selectivity of the GO nanosheets toward pairs of Nd3+/lanthanide ions was investigated and noted that the separation factor increases rapidly of the Nd3+ ions from La3+ as LREEs (SF=4.8), Nd3+ from Gd3+ as MREEs (SF = 5.6) and higher separation factor for Nd3+ from Y3+ as HREEs (SF=12.5). Therefore, Go nanosheets is promoted and improve the preliminary production of light lanthanide elements with considerably high recovery.
Considering the simple synthesis procedure, low cost, high removal efficiency, environmental friendliness, easy separation, and excellent stability, it is expected that Cys-SPIONs more than GO nanosheets can be potentially used for the high-efficient preconcentration and solidification of trivalent lanthanides/actinides in geological repositories and nuclear waste management. Keeping in mind the heterogeneity and complexity of the real water environment, additional investigations are on going, to further verify the performances of Cys-SPIONs and GO nanosheets toward actual radioactive waste disposal.