U(VI) removal from diluted aqueous systems by sorption–flotation

Influencing factors

Flotation pH

The pH is extremely important because it determines the charge, the structure, and the concentration of U(VI) species in dilute aqueous systems (Fig. 1). The U(VI) species were calculated using Phreeqc Interactive 3.2.2 software and llnl.dat database considering only the simple aqueous solution of Na₄[UO₂(CO₃)₃] containing 0.042 mM U(VI) (10 mg·L⁻¹ U(VI)), respectively (main concentration of experimental samples). The pH ranged from 2 to 12 to cover all the types of natural waters, such as highly acidic ones from acid mining drainage and those from the uranium mining industry. The ionic strength was determined by the software.

Species calculations were performed taking into account the simple aqueous system containing only the simple chemical substance without any addition of salts to ensure a constant ionic strength. Ionic strength was calculated by the software. The sum of molar fractions was 1, considering all the species involved. Species with very small molar fractions were not displayed.

The curves obtained for [U(VI)] = 0.042 mM are in agreement with literature⁵⁹. According to the calculated data displayed in Fig. 1, the probable U(VI) species occurring in the pH range 7.0–9.5 are: (a) hydroxide complexes—UO₂(OH)₂, [UO₂(OH)₃]⁻, [(UO₂)₃(OH)₇]⁻, and carbonate complexes—UO₂CO₃, [UO₂(CO₃)₂]⁻², [UO₂(CO₃)₃]⁻⁴ and [(UO₂)₂CO₃(OH)₃]⁻ in agreement with literature^53,59. The U(VI) hydroxide—and carbonate species were separately plotted, due to the different fraction ratios.

Figure 2 were showed the sorbent Fe(III) species calculated by Phreeqc Interactive 3.2.2 software and llnl.dat database.

It is observed from Fig. 2 that Fe₂O₃·nH₂O is formed in the pH range between 7.0–9.0, identical to that of [(UO₂)₂CO₃(OH)₃]⁻ and UO₂(OH)₂. Therefore, as a result, there is a competition between these species. Their formation respects the ascending order of solubility product (K_sp) K_{sp, Fe(OH)3} = 4 · 10^–38 < K_{sp, UO2(OH)2} = 1.1 · 10^–22 < K_{sp, UO2CO3} = 1.8 · 10^–12 < K_{sp, FeCO3} = 10^–10.5^60,61.

The influence of pH on removal efficiency has been studied on sorption / precipitate flotation by the function %R = f(pH) (Fig. 3).

The U(VI) samples (200 mL) of 10 mg·L⁻¹ U(VI) were contacted with Fe (III) solution at molar ratio [U(VI)]: [Fe (III)] = 1: 100, which was determined by preliminary tests⁶² under constant stirring (250 RPM) for 30 min to generate the sorbent in situ (Fe₂O₃·nH₂O). The pH adjustment was performed in the pH range 7.0–9.5 corresponding to the maximum sorbent amount (Fig. 4). After adjusting the pH, the sample was contacted with the surfactant (NaOL) at the molar ratio [NaOL]: [U(VI)] = 1:1^51,63, transferred to the flotation cell and diluted in a dilution ratio V_sample: V_water : = 3 : 1 with distilled water under pressure, as described above. Residual concentrations of U(VI) were analysed.

The best U(VI) removal efficiencies (%R > 98%) very close in values were obtained at pH range 7.5–9.5, which may be explained by the physicochemical interactions of U(VI) species studied by sorption and/or precipitation with sorbent species generated in situ: [Fe (OH)₂] ⁺, Fe (OH)₃ and [Fe (OH)₄]⁻ plotted in Fig. 2. Wang et al.⁶⁴ have demonstrated that the sorbent’s surface charge is influenced by aging⁶⁵ by its concentration and the zeta potential of the sorbents generated in situ is positive at pH around 8, then becomes negative⁶⁶.

U(VI) : sorbent dose, [U(VI)]: [Fe(III)]

The sorbent dose is important for the highly efficient removal of U(VI) species from diluted aqueous systems by sorption / flotation, the possible interactions being physical (sorption) or chemical (co-precipitation). The optimum amount of sorbent is a minimum of solid waste, but a maximum of adsorbent support that ensures maximum efficiency.

The different molar ratios [U(VI)]: [Fe(III)] ranging between 1: 5 and 1: 100 were provided using known volumes of 0.1 M and 0.01 M FeCl₃ solutions. The pH adjustments in the range 7.5–9.5 were made using 0.1 M and 0.01 M NaOH solutions. The studies were performed for the pH values 8.5, 9.0, and 9.5 (pH of real mine waters). Surfactant’s concentration used was the same for all these experiments to provide the best solid phase separation. Figure 4a, b show the obtained results for the residual concentrations of U(VI) and Fe (III) and the recovery efficiency.

Lower molar ratios [U(VI)] : [Fe(III)] between 1:5 and 1:25 were not adequate because U(VI) concentrations exceed the legal limit at the international level⁶⁷. The sorbent—contaminant contact surface was not efficient for the removal of U(VI) according to the legislation in force.

The molar ratio [U(VI)]: [Fe (III)] = 1:75 and pH = 8.75, 9.0 and 9.5 corresponds to a maximum efficiency of U(VI) and Fe(III) removal, %R = 99.96% (C_U(VI) = 0.0044 mg·L⁻¹ and C_Fe(III) = 0.01 mg·L⁻¹ as mean value).

Molar ratio, [U(VI)]: [NaOL]

In the precipitate flotation, the surfactant consumption is substoichiometric molar ratio. However, the concentration is important because floatability should increase in terms of concentrations below the critical micellar concentration of the surfactant⁶⁸.

To provide the best separation of the sorbent loaded with U(VI), it is necessary to determine the optimal amount of NaOL, which increases the solid phase’s hydrophobicity and floatability due to its long C-chain⁶³. Aqueous sodium oleate species are pH-dependent, therefore the same pH values were provided to run the experiments.

According to^51,63 the chemical equilibria that should be considered between the oleate species are:

$$ {text{RH}}_{s} mathop leftrightarrow limits^{{K_{1} }} {text{RH}}_{aq} quad {text{pK}}_{{mathbf{1}}} = {7}.{6}0 $$

(2)

$$ {text{RH}}_{{{text{aq}}}} mathop leftrightarrow limits^{{{mathbf{K}}_{2} }} {text{R}}^{ – } + {text{H}}^{ + } quad {text{K}}_{{2}} = {4}.{95} $$

(3)

$$ {text{RH}}_{{{text{aq}}}} + {text{R}}^{ – } mathop leftrightarrow limits^{{{text{K}}_{3} }} {text{R}}_{2} {text{H}}^{ – } quad {text{pK}}_{{3}} = – {4}.{95} $$

(4)

$$ 2{text{R}}^{ – } mathop leftrightarrow limits^{{{text{K}}_{4} }} {text{R}}_{2}^{2 – } quad {text{pK}}_{{4}} = – {4}.00 $$

(5)

$$ {text{R}}_{2} {text{H}}^{ – } + {text{Na}}^{ + } mathop leftrightarrow limits^{{{text{K}}_{5} }} {text{R}}_{2} {text{HNa}}quad left( {{text{precipitate}}} right);{text{pK}}_{{5}} = – {9}.{35} $$

(6)

where: RH is oleic acid; R⁻ is oleate ion; R₂H⁻ is acid-soap complex; R₂HNa is acid-soap salt and R₂²⁻ is oleate dimer, respectively.

The results of the experiments are showed in Fig. 5.

The results shown in Fig. 5 suggest that the most reliable molar ratio is [U(VI)] : [NaOL] = 1 : 1 × 10^–2.

Contact time U(VI) with Fe (III) and NaOL

The contact time includes both the time required to prepare the sorbent in situ and the time of pH adjustment; the determined working pH value of 8.75 was in accordance with the literature data^24,25,69 regarding the formation of the Fe₂O₃ ∙ n H₂O precipitate within the limits 7.0–9.5 as shown in Fig. 2. %R values as a function of contact time are shown in Fig. 6.

It can be observed that after 30 min the removal efficiency (%R) reaches the maximum value of 99.96. An additional increase in contact time determines no variation in removal efficiency (%R = 99.96). Therefore, the chosen contact time was 30 min because any other higher value it is not justified.

Stirring rate

This factor is important in the sorption stage of U(VI) on the sorbent. High stirring velocities determine smaller sizes of sorbent flake and the decrease of the U(VI) removal efficiency.

Figure 7 points out that 250 RPM is the best stirring rate to get U(VI) and Fe (III) removal efficiencies > 98%.

The air pressure (p) in the pressurized water recipient

The air pressure in the pressurized water recipient of flotation cell ensures the formation of homogeneous bubbles capable of taking up the solid sorbent loaded with U(VI) and to ensure sufficient ascending force for the loaded sorbent to concentrate on the top of the flotation cell column. Therefore, a low air pressure does not ensure these conditions and favours the reverse process of depositing the loaded sorbent at the bottom of the flotation cell column^48,49. Higher air pressure values produce turbulence with a negative impact on the stability of aggregate bubble-loaded sorbent.

The results obtained and displayed in Fig. 8 suggests that the best working value of the air pressure is p = 4·10⁵ N·m⁻², when the removal efficiency is maximum: %R_U(VI) = 99.96 and %R_Fe(III) = 99.95%, respectively.

The U(VI) concentration

The variation of the concentration of contaminants has an important impact on the separation efficiency because it determines the consumption of reagents and the volume of loaded sorbent.

As such, when the concentration reaches high values, it increases the weight of the loaded sorbent and decreases the floatability of solid phase.

Figure 9 shows the effect of U(VI) concentration increase on the removal efficiency. Increases to 99.96% and then decreases slightly to concentrations greater than 20 mg·L⁻¹.

Optimum parameters

The optimal parameters (at maximum removal efficiency, %R) in order of the stages of the Sorption / Flotation process are:

U(VI) concentration 10 mg L⁻¹;
Flotation pH range 7.5–9.5;
U(VI) : sorbent dose, [U(VI)] : [Fe(III)] = 1: 75;
Contact time U(VI) with Fe(III) = 25 min.;
Stirring rate = 250 RPM;
Molar ratio [U(VI)]: [NaOL] = 1: 1 × 10^–2;
Contact time U(VI) with Fe(III) and NaOL = 5 min.;
Air pressure, p = 4 × 10⁵ N m⁻²;
Flotation time = 5 min.

The accompanying heavy metals ions’ interference

Seven samples (V_sample = 200 mL) were prepared in which U(VI), Cu (II), Cr (VI), and Mo (VI) were introduced 10 mg·L⁻¹ each, were subjected to sorption / precipitate flotation under the optimal values of the previously established working parameters in order to observe the interactions between all ionic species. The results suggest that, in the multi-component solution, Cu(II) and Fe(III) precipitate, and U(VI) could be sorbed and/or precipitated. The Mo (VI) and Cr (VI) species can also be sorbed on Fe₂O₃ ∙ n H₂O generated in situ.

In the case of Cu (II), the obtained results suggest that at working pH = 8.75 it precipitates as Cu(OH)₂^49,70,71,72.

The precipitates’ formation takes place in the order from the lowest to the most soluble product, i.e. Fe(OH)₃ (K_sp = 2.79 × 10^–39) < UO₂(OH)₂ (K_sp = 1.1 × 10^–20) < UO₂CO₃ (K_sp = 1.8 × 10^–12) < CuCO₃ (K_sp = 1.4 × 10^–10)^{49,60,61,70,71,72}, according to the previously stated principle (3.1.1).

The main speciation of Cr(VI) at working pH = 8.75 is CrO₄²⁻ according to the literature^73,74.

In the case of Mo (VI) species, the researchers pointed out that the probable main speciation is MoO₄²⁻ with a maximum concentration value at pH = 7, when the concentrations of the other two, H₂MoO₄ and HMoO₄⁻, are very low⁷⁵.

Figure 10 shows the influence of the accompanying ions on U(VI) removal by sorption / precipitate flotation. It can be observed that, when Cu (II) and Mo (VI) species accompany U(VI) in bicomponent systems, the sorption U(VI) is not influenced by them unlike the case of Cr (VI), which decreases the removal efficiency of U(VI).

It can also be observed that following the sorption / precipitate flotation process, the removal efficiency of U(VI) from these studied aqueous systems is very high (%R > 99) considering that in solution the residual concentration of U(VI) has values in range 0.1–1.9 µg·L⁻¹ which are much lower than the maximum permitted legal limit concentration (0.02 mg·L⁻¹) stipulated by WHO regulations.

Other research studies presenting interactions in the aqueous species of U(VI) and the heavy metals accompanying of sorbent generated in situ have pointed out dominant metallic ionic specioation in the dilute aqueous systems, which are similar to those studied.

Riba et. al. has showed that for a solution with [U(VI)] = 4.2 mM (10 mg·L⁻¹) in contact with 1.2% O_2(g) and 0.017% CO_2(g) for a pH range of 8 to 9 the dominant species are [UO₂(CO₃)₃]⁴⁻ and [UO₂(CO₃)₂]²⁻²⁵.

Wanze et.al. has pointed out for [U(VI)] = 4.2 × 10^–6 M dissolved in 0.01 M NaCl solution in the presence of carbonate [CO₃²⁻] = 1 × 10⁻² M there are the same dominant speciations⁶⁹.

The presence of [MoO₄²⁻] was demonstrated by Mitchell in the system with [Mo (VI)] = 0.3 and 1 mM (3 mg/L and 100 mg/L) at a pH range 2 to 7⁷⁵.

According to Matis and Mavros in a diluted aqueous system containing Cu (II) = 10 mg/L at pH range 8 to10 precipitates Cu(OH)₂³³.

For [Cr (VI)] between 10^–4 and 6 × 10⁻⁴ M in the pH range 1 to 12, the dominant speciation is CrO₄²⁻^74,76.

The results obtained demonstrate the presence of a competition between the metallic ion ionic species present in order to bind to the active surface of the sorbent charge with electric charge⁷⁴. Since the zero sorption point of sorbent changes with increasing amount of Fe₂O₃ ∙ n H₂O⁶⁴, the obtained results suggest that Cu (II) species precipitate and Cr (VI) and Mo (VI) are removed from aqueous solution by sorption. The experimental results point out that it is possible that U(VI) is electrostatically bound to the electrically charged surface of the sorbent as a carbonate complex.

Experimental results prove that the accompanying heavy metals do not significantly influence the separation efficiency.

From the study of inflencing factors correlated with the maximum efficiency of U(VI) separation, it results that the optimal working parameters of U(VI) separation by sorption / precipitate flotation are: pH range 7.0–9.5, stirring rate 250 RPM, contact time 30 min, molar ratio [U(VI)] : [Fe(III)] : [NaOL] = 1 : 75 : 1 × 10^–2, p = 4·10⁵ N·m⁻², dilution ratio V_sample : V_water = 3 : 1, flotation time 5 min, depending on initial concentration range of U(VI) = 1–30 mg·L⁻¹.

The optimum working conditions established for the synthetic aqueous systems were validated on real mine water samples and very good results have been obtained.

The interaction of sorbent with U(VI) and the accompanying heavy metals

Preliminary data on the interaction between U(VI) and sorbent were obtained using the FT-IR spectra analysis of two samples obtained under optimal working conditions for sorption / precipitate flotation Sample 1—Fe₂O₃∙nH₂O and Sample 2—Fe₂O₃∙nH₂O with U(VI) carbonated complex.

Both spectra include the 3400 cm⁻¹ IR band that can be assigned to the stretching modes of H₂O molecules or the coating of hydrogen-bonded surface OH groups, while the 3037 cm⁻¹ IR band is due to the presence of OH stretching mode in α-FeOOH and a corresponding prominent peak H₂O coordinated or adsorbed close to 1620 cm⁻¹⁷⁷.

The U(VI) carbonate complex’s ions fixing on the adsorbent seems to be emphasized by the movement which is observed from 653 cm⁻¹ to 626 cm⁻¹ in Sample 2. The claim appears to be supported by the positive potential value near pH = 8.0 ⁶⁶.

Table 1 presents the characteristic bands attributed to the sublates obtained after the U(VI) separation from Cr(VI), Cu(II), and Mo(VI) by sorption/precipitate flotation.

Table 1 Characteristic bands of sublates obtained after the separation by sorption/precipitate flotation of U(VI) from Cr (VI), Cu(II), and Mo(VI).

All FT-IR spectra with the characteristic bands shown in Table 1 present the following specific peaks:

In the 3000–3650 cm⁻¹ range are attributed to associated and non-associated hydroxyl groups;
In the 1620–1634 cm⁻¹ range attributed to the water adsorbed on the in situ generated Fe₂O₃·nH₂O surface;
The characteristic bands around 1500 cm⁻¹ value attributed to the carbonate ions stretching vibration, which are present for I (Fe(III)) at 1486 cm⁻¹ , for A (Fe(III) + U(VI)) at 1521 cm-1, for B(Fe(III) + U(VI) + Cr(VI)) at 1542 cm⁻¹, for C(Fe(III) + U(VI) + Cu(II)) at 1512 cm⁻¹, for E(Fe(III) + U(VI) + Mo(VI)) at 1518 cm⁻¹, for D (Fe(III) + U(VI) + Cr(VI) + Cu (II)) with shoulder at 1519 cm⁻¹, for F(Fe(III) + U(VI) + Cr(VI) + Mo(VI)) with shoulder at 1540 cm⁻¹, for G(Fe(III) + U(VI) + Cu(II) + Mo(VI)) with shoulder at 1526 cm⁻¹ and for H(Fe(III) + U(VI) + Cr(VI) + Cu(II) + Mo(VI)) at 1512 cm⁻¹;
The characteristic bands around 1400 cm⁻¹ value may be attributed to the deformation vibration bond of FeOOH and they are present in all samples except sample I (Fe(III)) suggesting that U(VI), Cr(VI), and Mo(VI) might be bonded on the sorbent surface and that Cu(II) might be precipitated as copper carbonate at the working pH;
The characteristic bands at 703 cm⁻¹ attributed ν_Fe-O is present in A (Fe (III) + U(VI)) and B (Fe (III) + U(VI) + Cr (VI)) samples and seems to suggest the possibility of U(VI) bonding on the in situ generated sorbent;
The characteristic bands at 682 cm⁻¹, 647 cm⁻¹, and 612 cm⁻¹ attributed to δ_Fe-O from sample I (Fe (III)) seem to point out the available active sites’ existence for U(VI) and accompanying elements ions bonding;
The band characteristic to the complex [(UO₂)₂(OH)²]²⁺ + CO₃²⁻ appears only in the systems : C(Fe(III) + U(VI) + Cu(II)) at 683 cm⁻¹; E(Fe(III) + U(VI) + Mo(VI)) at 690 cm⁻¹ and F(Fe(III) + U(VI) + Cr(VI) + Mo(VI)) at 683 cm⁻¹;
The bands δ_Fe−O and ν_Fe−O are also shifted towards lower values indicating that chemisorption might be possible at this level as well.

The FT-IR spectra analysis suggests that there is a possibility for the [(UO₂)₂(OH)₂]²⁺CO₃²⁻ complex’s formation considering that the reaction kinetics is of pseudo-second-order involving the chemisorption. At the same time at the working pH, Cu (II) can precipitate, and Cr (VI) and Mo (VI) to be adsorbed on the Fe (III) oxyhydroxide ^50,74.

Table 2 shows the sublates’ thermal analysis’ results obtained after the separation by sorption/precipitate flotation of U(VI) from Cr (VI), Cu (II), and Mo (VI).

Table 2 The thermal analysis of sublates obtained after the separation by sorption/precipitate flotation of U(VI) from Cr (VI), Cu (II), and Mo (VI).

The analysis of TG/DTG/DTA curves shows the sublates’ non-iso-thermal degrading process in the air atmosphere in the case of the bi-, three- and tetra component systems. The samples were subjected to three successive decomposing and water loss processes (Table 2).

The first endothermal process (20–120 °C) points out moisture’s complete loss. The analysed samples present similar moisture. The weight losses in this stage are about Δm₁ = 4.57–6.21% at the maximum temperatures within the range 97.1–109.3 °C.

The samples seem to be stable within the temperature range of 120–250 °C. Then the second decomposition process follows, which is exothermal (250–350 °C) and represents the main degrading stage with the weight loss Δm₂ = 6.14–8.07% at the maximum temperatures within the ranges 273.0–281.0 °C and 304.1–347.5 °C, respectively.

At higher temperatures (350–900 °C) the last exothermal process of thermal-oxidative decomposition of non-volatile products was obtained in the second degrading stage.

In all cases for the temperatures ranging within 513.7–620.9 °C the similar residual weights Δm₃ = 1.35–2.06% point out the studied metallic ions’ oxides’ mixtures’ occurrence.

Reproducibility and optimal parameters validation on real mine water samples

Reproducibility of U(VI) removal by sorption/precipitate flotation

Previously determined sorption/precipitate flotation technique optimal parameters were examined on 10 identical sample solutions (C_o = 10 mg/L) corresponding to two different molar ratios ([U(VI)] : [Fe (III)] : [NaOL] = 1 : 75 : 1 × 10^–2 and 1 : 100 : 1 × 10^–2), respectively, to calculate the U(VI) removal reproducibility by Student method (Table 3).

Table 3 Reproducibility of U(VI) removal by sorption/precipitate flotation.

Optimal parameters validation on real mine water samples

The mine water samples (MW1-MW3) were collected from a former uranium mining site in the Banat region and their chemical composition is shown in Table 4. They were processed according to the proposed flowsheet (Fig. 12) with and without pH adjustment respectively. The pH was adjusted with 0.1 M HCl solution to the working value of 8.75.

Table 4 Chemical composition of real water samples (mg·L⁻¹).

It was observed that the U(VI) removal efficiency was higher after pH adjustment, so that the sorption flotation was very efficient (Fig. 11).

Figure 12 summarizes a proposed technological processing diagram (flowsheet) of the multi-contaminated aqueous system by sorption flotation.

In case the samples were processed without pH adjustment the separation efficiencies were 96.6% for sample MW1 and 97.2 for MW2 and MW3 samples, respectively (Fig. 13).

In case the samples were processed with pH adjustment at pH = 8.75 with 0.1 M HCl solution %R_U(VI) > 99 was obtained for MW1C–MW3C samples (Fig. 13).

One can note that U(VI) removal efficiency was higher for the pH-adjusted samples than for the others, confirming the optimal values of the previously studied parameters.

The generated solid waste may be stored or recycled as a U(VI) secondary source for the manufacture of nuclear fuel.

The optimal parameters validation of tandem process immobilization on NMS-flotation on real water samples was performed in two variants:

a.

Without pH adjustment and sorbent addition: The real water samples with the chemical composition shown in Table 4 (300 mL) MW1–MW3 were pre-treated with 0.15 g NMS and were contacted for 30 min under 250 RPM stirring. The solid phase was separated by decantation. To the resulting liquid phase, MW1i–MW3i, the appropriate amount of 0.25 × 10⁻³ M NaOL solution was added and flotated without pH adjustment and without addition of FeCl₃ 0.1 M because the Fe²⁺ and Fe³⁺ supplied by the NMS in the filtered solution was used as an adsorption support. After flotation, the water samples MW1f.–MW3f. were obtained (Fig. 14).
b.

With pH adjustment and sorbent addition: The real water samples with the chemical composition shown in Table 4 (300 mL) MW1–MW3 were pre-treated with 0.15 g NMS for 30 min under 250 RPM stirring. The solid phase was separated by decantation. To the resulting liquid phase, MW1i–MW3i, the pH was adjusted using 0.1 M FeCl₃ solution to avoid the addition of the foreign ion, the appropriate amount of 0.25 × 10⁻³ M NaOL solution was added and after flotation samples, MW1c–MW3c were obtained (Fig. 15).

Figure 13 shows the U(VI) residual content after immobilization and flotation of real water samples.

Two separation schemes’ versions, which use both U(VI) removal methods, have resulted as follows: one without pH adjustment and without in situ generation of Fe₂O₃·nH₂O (Fig. 14) and another one with pH adjustment and with in situ Fe₂O₃·nH₂O generated (Fig. 15).

The obtained results on the real water samples suggest that U(VI) separation by sorption/precipitate flotation may be used either as a single method or as an additional stage in the case when Fe⁰-based nanomaterials are used in situ.

Source link

U(VI) removal from diluted aqueous systems by sorption–flotation

Influencing factors

Flotation pH

U(VI) : sorbent dose, [U(VI)]: [Fe(III)]

Molar ratio, [U(VI)]: [NaOL]

Contact time U(VI) with Fe (III) and NaOL

Stirring rate

The air pressure (p) in the pressurized water recipient

The U(VI) concentration

Optimum parameters

The accompanying heavy metals ions’ interference

The interaction of sorbent with U(VI) and the accompanying heavy metals

Reproducibility and optimal parameters validation on real mine water samples

Reproducibility of U(VI) removal by sorption/precipitate flotation

Optimal parameters validation on real mine water samples

US Schools Clash With Parents Over Bans on Student Cellphones

CDC reports early flu increases and higher activity levels | News

Spectacular Lightning Seen on Stormy Evening in New Mexico – Yahoo Canada Shine On

8 top-selling Alkaline Water Purifiers in India (2023) – Economic Times

8 top-selling Alkaline Water Purifiers in India (2023) – The Economic Times

Bear spotted in northern New Mexico – Yahoo Canada Shine On

Shopping cart