Inclusion, occlusion and adsorption of rare earth elements from chloride media onto barite-gypsum composite

In this study, a synthetic BaSO4·CaSO4 composite was prepared by co-precipitation technique, characterised and examined for REE sorption. The sorption parameters were; pH = 4, equilibrium time = 20 min, temperature = 303 K, and REE liquor volume to composite mass ratio of 0.2:1 L g−1. The sorption reaction was controlled by pseudo 2nd order kinetic mechanism and Langmuir adsorption isotherm with an adsorption capacity of 168.63 mg g−1. 90.14% of REE (III) was desorbed using 1 mol L−1 HNO3. The process was endothermic and spontaneous. Accordingly, 1:1 barite-gypsum (natural ingredient for BaSO4·CaSO4), with 136 mg g−1 loading capacity, was used for REEs extraction.


Introduction
Rare earth elements REEs are elements of the 4f sub-level, consisting of 15 elements, besides scandium and yttrium, although they belong to the first and second transition elements [1]. Because REEs are widely used in many important fields, such as magnetic, optical, and electrical properties, scientists are working to extract and separate REEs from their ores. REEs have nearly identical atomic radii in the range of 0.87 to 1.25 A°, which is the controlling factor for their similarity in chemical and physical properties, making individual separation difficult and costly [2]. REEs are located in all types of rocks: igneous, sedimentary, and metamorphic rocks [3]. Nevertheless, the main REE resources are monazite (one of the black sand ingredients), bastnaesite, parisit, euxenit, loparit, xenotime [4], and phosphate. In Egypt, the main REE resource is monazite, which is extensively ascertained at the northern cost of the Mediterranean Sea but limited to the southern coast of the Red Sea [5]. Many chemical methods have been used to separate REEs from their ores or leach liquors, including precipitation [6], solvent extraction [7], ion-exchange [8], adsorption [9], liquid emulsion membrane [10,11], and ion inclusion membrane [12]. Generally, precipitation methods (through double-sulfate or HF or oxalic acid as a precipitate) are probably applied at REE concentrations of more than 10%, whereas solvent extraction methods are performed at concentrations of > 2000 mg L −1 . Finally, ion-exchange and adsorption methods are preferred at concentrations of 1000 mg L −1 [13][14][15][16][17][18][19][20]. The sorption process is the transfer of adsorbate ions from an aqueous solution to the adsorbent (solid phase) across the boundary between the two phases. Recently, adsorption has been extensively used in scientific research and industrial applications for multiple purposes, including separation of valuable elements and compounds, purifications, and removal of heavy metals and pollutants [21][22][23][24]. Ion-exchange is mainly chemisorptions in nature due to the exchange of ions between the liquid and solid phases. In addition, the chemical energy before ionic exchange is higher than that after the exchange process, whereas the adsorption process includes two types of sorption: chemisorptions and physisorption [25]. REEs adsorptions are complemented by many adsorbents that vary in performance, uptake, pH range, and selectivity. Many adsorbents have been utilised for REE separations, including ores (clay minerals, kaolinite, soil, and halloysite) [26][27][28], hyper composites (β-cyclodextrin and silica doped with PC88A [29], composite (graphene oxide-tris (4-aminophenyl) amine) [30], polymer composite P(AA-co-AM/PJM-T) 1 3 [31], metal-organic framework (novel DGA-functionalized metal organic frameworks) [32], zeolite (zeolitic imidazolate frameworks) [33], biomass (Phosphorylated Hydrogel (Algal Biomass PEI) [34], and lignocelluloses biomass based on banana waste) [35] and waste material (phosphogypsum) [15]. Authors [36][37][38] investigated the possibility of extracting REEs through the recycling of low value waste streams such as bauxite residue, mine tailings, PG, slag and waste waters. However, there is no study of the separation of REEs from their ores by barite-gypsum composite.
Barite (barium sulphate; BaSO 4 ) is an important inorganic compound used in painting, coating, plastics and pharmaceuticals fibre. The efficient removal of Ra(II) using BaSO 4 ·SrO 4 by co-precipitation of Ra-Ba-SO 4 attributed to the rapid BaSO 4 nucleation rate [39], closer ionic radii of Ra(II) with Ba(II) and experimental studies revealed that divalent cations (i.e., Mg(II), Ca(II), Sr(II) and Ba(II)) have significantly higher impact on radium removal by barite than monovalent cations.
Herein, authors decided to examine synthetic BaSO 4 ·CaSO 4 to separate REEs from the acidic chloride leach liquor of monazite mineral (150 meshes) and apply the optimum conditions for REE separation from monazite by synthetic BaSO 4 ·CaSO 4 onto natural 1:1 barite-gypsum composite.
This paper included the preparation of synthetic (BaSO 4 ·CaSO 4 ) composite by co-precipitation of barium sulphate and calcium sulphate (the main constituents for barite and gypsum) for the separation of REEs from acidic chloride leach liquor of monazite mineral (150 meshes). The characterization of the prepared composite was carried out by FT-IR, XRD, DTA, SEM, particle size analysis, and pore size distribution. All adsorption and desorption behaviours were well studied, in addition to adsorption isotherms, adsorption kinetics, adsorption mechanisms, and even regeneration and reusability. It is well expected that the prepared adsorbent (mixed sulphate) has extremely high resistance to all mineral acid attacks based on the anionic radical (sulphate), which is never replaced with any anionic radial of the other mineral acids, besides the low solubility product of calcium and barium sulphate. Finally, the optimised adsorption conditions were applied to barite-gypsum composite as a cheap sorbent prepared from natural ores. Eventually, this work conducted a novel bio-adsorbent that has high work ability, including high resistance to extreme acidic conditions and reusability.

Preparation of REE solutions
In a 50 cc solution of concentrated HCl acid, REEs hydroxide cake, (obtained from monazite digestion), was carefully dissolved in an 85 °C water bath [31]. Different REE concentrations were created for each batch experiment trial by diluting the stock standard solution, which had an initial concentration of 2000 mg L −1 .

Instruments
The active functional groups in the BaSO 4 ·CaSO 4 composite were identified using a Bomen Miclson FT-IR spectrophotometer, model MB157 from Canada. Shimadzu x-ray diffraction (XRD); model XD-Dl, Kyoto, Japan, with a diffraction angle (2θ) range of 4-70°, was used to identify the crystalline phase structure. The Japanese DTA-TGA-50 maintains thermal stability at a constant rate of 5 °C/min from room temperature to 650 °C. The particle morphology was investigated using a JEOL JSM-5400 (SEM, FEI Quanta FEG-250, and EDX) for SEM and EDX mapping. The poresize chromatech 9320, USA, was used to determine the pore size distribution and its corresponding porosity. The UVspectrophotometer (SP-8001) and the Inductive Coupled Plasma Optical Emission Spectrometer (Prodig Axial high dispersion ICP-OES model, USA) were used to measure the concentration of rare earth ions. However, the concentration of calcium ions was measured by an atomic absorption spectrophotometer (Buck Scientific, VGP 210).

Sorption studies
The sorption technique was employed to extract REE (III) ions from monazite ore. Batch studies were conducted to inspect the sorption performance of REE onto  Equation (3) gives the sorption efficiency (%) of REE (III) at each time interval [41].
Adsorbed amount q (mg g −1 ) is calculated using Eq. (4) [41]: where, q denotes the sorbed amount (mg g −1 ). The initial and final concentrations of the REE (III) are denoted by C i and C f , respectively. The weight of the BaSO 4 ·CaSO 4 (g) is denoted by m. (g), where V denotes the volume of solution (L).
Equation (5) gives the distribution coefficient K d [42] Kinetic modelling Using kinetic modelling and selecting the appropriate one for the sorption reaction, the mechanism of the sorption reaction could be proposed. This study employs four kinetics models: pseudo first order, pseudo second order, the Elovich model, and the intra-particle diffusion model.

Pseudo first order and pseudo second order models
Equations (6) and (7) give the linear equations of pseudofirst order equation [41] and pseudo second order [43], respectively.
where q e and q t are the sorbed amounts of REE (III) at equilibrium time and any time t, respectively, k 1 (min −1 ) and k 2 (g mg −1 ) express the rate constants of pseudo first order and pseudo second order, respectively.

Intra-particle diffusion model
Equation (9) [44] is used to apply the intra-particle diffusion model.
where k id represents the rate constant of intra-particle diffusion (mg g −1 min −1/2 ) and C represents the intercept.

Langmuir and Freundlich model
Langmuir isothermes model examined using linear form Eq. (10) where Q o is the Langmuir adsorption capacity (mg g −1 ), b is the constant related to ∆G o (b α e −ΔGRT ), and C e is the equilibrium metal ion concentration. The separation factor R L could be calculated using Eq. (11) C o denotes the initial adsorbate concentration (mg g −1 ). Adsorption is unfavourable when R L > 1, linear when R L = 1, favourable when R L = 1, and irreversible when R L = 0.
While the linear regression for the Freundlich model is given by Eq. (12) where K f is the Freundlich constant and n is the adsorption capacity and intensity.

Halsey model
The Halsey model applied using Eq. (13) [47] where k H and n are the Halsey isotherm constant and exponent, respectively. This model applied for multilayer adsorption and heterogonous nature of the adsorbent.

Temkin model
The linear regression of Temkin is given by Eq. (14) [48] where: is related to the maximum binding energy, b T is said to be the adsorption heat.

Desorption studies
The loaded BaSO 4 ·CaSO 4 by REE was desorbed in several desorbing agents for an hour. The mixture was filtrate to separate the BaSO 4 ·CaSO 4 .composite from the liquid phase, and then the concentration of REE ions measured. The desorption efficiency % was calculated using Eq. (15): where C aq is assigned to the concentration of REE within the aqueous phase C s is that the concentration of REE within the BaSO 4 ·CaSO 4 .

Result and discussion
Characteristics f the adsorbent FTIR analysis Figure 1 showed the characteristics peaks for the present functional groups of BaSO 4 ·CaSO 4 composite and after loading with REE (III). The observed wave numbers weree 3610, 3552 and 1622 cm −1 corresponding to stretching band of water molecule. Theses hydroxyls ion increased the Ca (II) exchange with REE (III) [49]. While in loaded BaSO 4 ·CaSO 4 composite the peaks at 1146, 1084 and 983 cm −1 in BaSO 4 ·CaSO 4 assigned to symmetrical vibration of SO 4 2− were shifted to 1128, 1075 and 982 cm −1 . However, due to deformation structure after REE (III) loading. The band at 2135 cm −1 corresponded to the sulphuroxygen stretching vibration is changed to the bending vibration of SO 4 2− and shifted to 2064 cm −1 . The two peaks at 2925, 2855 cm −1 related to the symmetric and asymmetric vibration of SO 4 2− [50].  [51]. However, the grey agglomerated particles referred to spherical particles of CaSO 4 [52]. Figure 2b showed rough surface and REEs adhered to the surface of the composite as indicated by arrows. Figure 2c represented the difference in fine particle [53] size of BaSO 4 ·CaSO 4 composite (500 < particle size < 1300 nm) before and after sorption. The particle size of BaSO 4 ·CaSO 4 composite increases after sorption process, which may be attributed to the agglomeration of the particles or to sorption of REE(III). The EDX mapping of BaSO 4 ·CaSO 4 composite after sorption was represented in  Figure 3 depicts the thermal stability of BaSO 4. CaSO 4 composite. The prepared composite shows great thermal stability. As shown in Fig. 3, the total weight loss up to 700 °C was 3.93%, accompanied by three endothermic peaks at 132 °C, 205 °C, and 340 °C. The first endothermic peak is due to loss of physically adsorbed water, with a weight loss 3.51%. While the second and third endothermic peaks were at 205 °C and 340 °C with a total weight loss 0.42% due to removal of the structural water from BaSO 4 and CaSO 4 [54].

Surface measurements
The surface parameters of the BaSO 4 ·CaSO 4 composite can be seen at Table 1. The total pore area increase due to the roughness of the surface increases after REE (III) sorption [55]. However, the average pore diameter decreased due to packing of REE (III) ions on the inner wall of pore in the sorption process, resulting in a decrease in the total pore volume. The bulk density expresses the volume of the BaSO 4 ·CaSO 4 composite and closed pores. While the apparent density expresses the volume of the BaSO 4 ·CaSO 4 composite, closed pores and open pores, comparing the two densities for BaSO 4 ·CaSO 4 composite before sorption and after sorption, it is clear that, the open pores decreases after sorption process and a prediction for intra-particle diffusion mechanism fitting is considered.  The maximum sorption capacity was found to be at pH 4. At pH 5, it was noticed that an increase of sorption capacity, but these increase owing to the formation of several hydroxides of REE (III) [56]. This result was confirmed by precipitation curve Fig. 5b. However, Shukla et al. [57] reported that the decrease in pH value below pH 2.5 caused an increase in the solubility of CaSO 4 due to higher hydration of ions. Therefore, pH 4 selected as an optimum pH for the experimental batch sorption reaction. Figure 6 investigated that the time impact on the sorption reaction. The reaction between REE (III) and BaSO 4 ·CaSO 4 composite firstly was rapid due to the increased number of available vacant sites [58]. It then became slower till it reached the equilibrium at 20 min due to slower mass transfer from the bulk of the solution to the surface of the composite as the concentration of REE (III) decrease [59]. After

Concentration impact
The impact of initial metal concentration had a great influence on the sorption reaction. Figure 7 depicted the sorption efficiency and the sorbed amount as a function of initial concentration. It was observed that at lower initial concentration of 100 mg L −1 ; the sorption efficiency and sorbed amount were 94.92% and 18.98 mg L −1 , respectively. While, at higher initial concentration of 2000 mg L −1 , the sorption efficiency and sorbed amount were 34.41% and 137.64 mg L −1 , respectively. This behaviour was explained by the available free active sites at lower initial concentration [60], while an increase in initial REE(III) concentration implies that REE(III) ions were present in the mixture and hence more ions were attached to same quantity of the active sites of BaSO 4 ·CaSO 4 composite in addition to the increase in the driving force for the movement of the REE(III) ions from the mixture to the composite surface and, in this case, higher concentration would result in sorbent surface saturation [61].

Temperature impact
The temperature effected the sorption reaction due to its relationship with the kinetic energy of metal ions in the solution [59]. Figure 8 investigated the temperature as a function of the sorbed amount (q e ) and distribution coefficient (K d ). The temperature impact was studied at a temperature range of 30-50 °C. It was shown that as the temperature increased, both of the sorbed amount and distribution coefficient increased due to the increase in kinetic energy i.e. the increase of the accessibility of REE (III) onto active sites of BaSO 4 ·CaSO 4 composite pointed to the endothermic nature of the sorption process. The sorbed amounts of REE (III) onto BaSO 4 ·CaSO 4 composite were 140, 163.38 and 180.37 mg g −1 at 30, 40, and 50 °C, respectively. After these ratios any extra increase leaded to a decrease in sorption efficiency and sorbed amount. This is because there are enough vacant active sites available for binding till the 0.2 V/m ratios and by increasing the V/m ratios the REE (III) ions increased but the active sites did not. [62].

Kinetic Modelling
With the aid of Eqs. (4-6), the kinetic modelling was inspected; pseudo-1 st -order, pseudo-2nd-order, intra particle diffusion model and Elvoich model. S.1 a, b, c, and d showed the linear regression of the applied models of REE(III) sorption onto BaSO 4 ·CaSO 4 composite, and Table 2 listed its estimated parameters. It is evident that the value of the R 2 for the pseudo-2nd -order and pseudo 1st order is higher and closer to one. The values of the calculated capacity of the sorbed metal ions at equilibrium q e(cal.)   . in all respect. The sorption reaction mechanism is suggested to follow a pseudo-2nd-order mechanism by comparing the estimated q e(cal.) and observed q e (exp.) values. This comparison also predicted a chemisorptions reaction [63].
The intercept (S.1c) ascribed to the thickness of the surface during interparticle-diffusion model evaluation revealed the participation of the surface adsorption in the rate-determining step. The larger the intercept, the more is its participation to the sorption reaction. The intra-particle diffusion model taken through three steps. The 1 st step, which occurred within the first two minutes, represents the diffusion of metal ions from the solution to the surface of the BaSO 4 ·CaSO 4 composite. The second stage (from 3 to 15 min) was designed to simulate the gradual sorption of REE (III) on the surface onto BaSO 4 ·CaSO 4 composite may be the rate-determining step. The third stage (extended from 20 to 120 min) is the equilibrium saturation. The sorption reaction mechanism was controlled by multi-diffusion step.
The high correlation factor R 2 of Elvoich indicated that the sorption reaction was controlled by chemisorption mechanism with a confirmation to pseudo 2nd order fitting as the value of β (desorption constant) was very small compared to α (adsorption constant) [64].

Adsorption isotherm
To examine the fitting model to sorption reaction, Eqs. (10)(11)(12)(13)(14) were used. The parameters of the applied models were listed in Table 3. While S.2. a, b, c, and d depict the plots for the applied model; Langmuir, Freundlich, Halsey, and Temkin, respectively. The order of increase of correction factor was Langmuir > Halsey > Freundlich > Temkin. This order reflected the suitability of Langmuir model in describing the sorption of REE (III) onto BaSO 4 ·CaSO 4 composite. The sorption process was favourable because R L = 0.0654, i.e. 0 < R L < 1.
Freundlich data results in Table 3 showed values of K f and 1/n are 10.45 mg g −1 and 0.4161 (n = 2.403), respectively; the sorption was considered to be favourable because the freundlich exponent values of n were in the range (2-10) [65].
S.2. reflected a relatively good agreement of Halsey to the adsorption data with R 2 = 0.96 than the Freundlich isotherm; this result confirmed the heterogeneous nature of BaSO 4 ·CaSO 4 composite [65]. Applying Temkin isotherm model, R 2 = 0.92 and this model was not fit well to the equilibrium data compared to the Langmuir, Freundlich and Halsey. The calculated parameters A T (1.005 L g −1 ) was the equilibrium binding constant, which indicates the maximum bonding energy; b T (176.534 kJ mol −1 ) is the constant related to the heat of adsorption [66].

Thermodynamic studies
In S.3, a plot of ln K d against 1/T for the sorption of REE (III) onto a combination of BaSO 4 ·CaSO 4 was shown. The parameters for thermodynamic studies were presented in Table 4. The free energy change ∆G o obtained during the adsorption reaction at temperatures of 303, 313, and 323 K indicated that the adsorption of REE (III) onto BaSO 4 ·CaSO 4 composite was spontaneous and favourable. Additionally, increase in negative values of ∆G o as temperature increased indicates greater driving force for binding of rare earth ions. The endothermic nature of the sorption process was confirmed by the positive value of ∆H o . The positive value of ∆S o was an evident for the affinity of REE (III) sorption onto BaSO 4 ·CaSO 4 composite due to the increase in randomness at the solid-solution interface during the adsorption process.

Desorption studies
Desorption experiments had been conducted to evaluate the ability of BaSO 4 ·CaSO 4 composite to release REE (III) ions using a variety of desorbing agents, including HNO 3 , H 2 SO 4 , Citric acid, and distilled water. Figure 10a showed that the HNO 3 was the optimum desorbing agent for REE (III) sorbed onto BaSO 4 ·CaSO 4 with a Desorption efficiency 90.135%. The effect of increasing concentration of HNO 3 on the desorbing efficiency (Fig. 10b) implied that the desorbing efficiency increased with the increase in nitric acid concentration up to 1 mol L −1 . However, above 1 mol L −1 concentration of HNO 3 , the desorbing efficiency was not changed. The difference in desorbing efficiency of HNO 3 , H 2 SO 4 and citric acid owing to the difference in acid strength where the order of increase of K a is H 2 SO 4 > HNO 3 > citric acid > H 2 O. However, an exception of the desorbing efficiency of HNO 3 is higher than that using H 2 SO 4 due to the presence of SO 4 2− ions and common ion effect with BaSO 4 ·CaSO 4 leads to decrease the desorption of REE(III). In case of using distilled water as desorbing agent, the desorption efficiency was zero due to precipitation of REE (III) as RE (OH) 3

Mechanism of sorption reaction
The mechanism of the sorption reaction was suggested to perform through three possible mechanisms as shown in Fig. 11; inclusion, occlusion, and adsorption. Inclusion was the process of replacing the main metal (Ba (II) or Ca (II)) in the crystalline structure with a REEs metal. Occlusion occurs when REEs are physically trapped between the layers of a growing mineral (i.e., BaSO 4 or CaSO 4 ), as evidenced by surface measurements and a decrease in porosity. Adsorption occurred at the surface when REEs were physically or chemically bound to the outer layer of BaSO 4 ·CaSO 4 [68]. The surface of BaSO 4 ·CaSO 4 composite was not electroneutral like the bulk of the composite due to the active surface SO 4 2− groups form incomplete coordination spheres, [68,69]. Such a negatively charged surface has the potential to attract positively charged REE (III) ions from the liquor of monazite from surrounding solution, resulting in the formation of an electrical double layer (EDL) around The suggested mechanism could also be evaluated by measuring the concentration of Ca(II) released in the solution by ion exchange. This exchange related to high charge density that will favour the exchange with Ca(II) within BaSO 4 ·CaSO 4 layers [70]. Table 5 includes the initial and final concentrations of Ca(II) and REE(III) in the solution after sorption of REE(III) onto BaSO 4 ·CaSO 4 composite.
The LRE ions (light rare earth ions) have similar ionic radii to Ca (II) leads to high incorporation extent of LRE ions than HRE ions [71]. However, the charge difference between rare earth ions and Ca(II) limits the extent of the solid state substitution [71] where the Ca(II) released in solution was 488 mg L −1 ; i.e. 19.52% of Ca(II) was substituted by rare earth ions [72].

Reusability
The efficiency of the BaSO 4 ·CaSO 4 composite was evaluated by regeneration and recycling of BaSO 4 ·CaSO 4 composite through (Adsorption-desorption-Adsorption) cycle. The desorbing agent was 1 mol L −1 HNO 3 . The Sorbed amount of BaSO 4 ·CaSO 4 composite decreased after the first cycle from 140 to 103.4 mg g −1 . From the second cycle to fifth cycle, the sorption capacity was nearly 103 mg g −1 and not changed. i.e., the reusability of BaSO 4 ·CaSO 4 composite was 73.9%; this confirmed the suggested mechanism and nearly 74% of sorption was carried out by occlusion and adsorption. Figure 12 depicts the Adsorption-desorption-Adsorption cycles of BaSO 4 ·CaSO 4 composite for adsorption of REE (III) using 1 mol L −1 HNO 3 .

Sorption of REE (III) onto barite-gypsum composite
1:1 (wt/wt) Barite-gypsum composite (the natural ingredients for BaSO 4 ·CaSO 4 composite) was prepared by a physical mixing technique where barite and gypsum were crushed using an agate mortar, then thermally treated at 300 °C for 2 h with a rate of 5 °C min −1 . Then, the resulting mixture was grounded again before being used as an adsorbent. The previous sorption experimental results pointed to the efficient possibility of the use of barite. Gypsum composite in sorption of REE (III) digested solution. Table 6 illustrated the sorbed amounts of REE (III) on barite, gypsum, and barite-gypsum composite at the optimum conditional parameter determined during the previous experiments.

Conclusion
A synthetic BaSO 4 ·CaSO 4 composite was successfully prepared via the co-precipitation technique. Characterisation of BaSO 4 ·CaSO 4 composite was performed by FT-IR, XRD, DTA, SEM, particle size analysis, and pore size distribution. Adsorption of REEs elements from acidic aqueous solutions was examined using BaSO 4 ·CaSO 4 composite. The best adsorption parameters at 303 K of REEs ions were  volume to composite mass ratio 0.2:1 L g −1 , pH = 4, initial concentration of REE sorbent; 1100 mg g −1 , and 20 min contact time. Kinetic and isotherm models were applied. The results indicated that, pseudo 2nd order model was more fitted. The adsorption mechanism was checked for Langmuir, Freundlich, Hasely, and Temkin isotherm models. Maximum adsorption capacity of rare earth ions onto the prepared BaSO 4 ·CaSO 4 composite was 168.63 mg g −1 . Thermodynamic studies showed the extent of adsorption capacity increases with temperature, i.e., the sorption reaction was endothermic and spontaneous. Desorption of REE (III) was performed using 1 mol L −1 HNO 3 with a desorption efficiency of 90.135%. The reusability of the BaSO 4 ·CaSO 4 composite was 73.9% for five successive adsorption -desorption-adsorptions cycles. The studied experimental results showed that we can use 1:1 (wt/wt) barite-gypsum composite; as natural ingredient for BaSO 4 ·CaSO 4 composite; for REE (III) sorption, barite-gypsum composite were prepared by physical mixing and thermally treated at 300 oC for 2 h as a host and cheap sorbent for rare earth ions. The amount of REE (III) that has been sorbed onto the barite-gypsum composite was 136 mg g −1 .

Author contributions
All authors contributed to the study conception and design, Material preparation, data collection and analysis. All authors read and approved the final manuscript.
Funding Open access funding provided by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB). The authors received no financial support for the research, authorship, andor publication of this article.
Data Availability All the data used for this work are publicly available.

Conflict of interest
The authors declare that they have no conflict of interest.
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Human and animals Not applicable.
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