Journal of Nuclear and Radiochemical Sciences, Vol. 18, pp. 16-23, 2018

ArticlesAlkaline leaching of uranium from El-Sibaiya East Phosphorite in the presence of sodium
peroxide
El-Sayed A. Manaaa, b, Sameh H. Negmb, Mahmoud O. Abd El-Magiedb,*aChemistry Department, College of Applied Medical Science, Taif University, KSA
Nuclear Materials Authority, El Maadi, Cairo, EgyptbReceived June 11, 2018; Accepted September 13, 2018; Published online October 3, 2018
Chemical, mineralogical and radiometric investigation studies were executed on a representative phosphorite
sample collected from El-Sibaiya East area to evaluate its suitability for the alkaline leaching of its uranium content. The uranium alkaline leaching was carried out in three phases using Na 2CO3 and a mixture of Na 2CO3/NaHCO3 with/without an oxidant (Na2O2). Factors include; Na2CO3, NaHCO3, Na2O2 concentrations; digestion
temperature, reaction time and ore fineness were studied and optimized. The results pointed to that the bestleaching efficiency of uranium (83.2%) was conducted using the mixture solution of Na2CO3/NaHCO3 (0.5M) in
the presence of 2.5% Na2O2 (w/w). The other conditions affected the leaching process were studied and optimized
as 80 oC (leaching temperature), 3h (leaching time), 44μm (ore grain size) and a solid/liquid ratio of 2/25. The
leached uranium was recovered by precipitation using NaOH solution where the precipitated product was definedby the XRD as sodium diuranate (Na2U2O7) of high purity.

1. Introduction
The phosphate rocks refer to those ores containing apatite
and/or francolite (carbonate-fluorapatite) minerals as the main
constituents [1]. Generally, the phosphate rock contains, atleast 24% P 2 O 5, less than 3% Fe 2 O3 with CaO: P 2 O 5 ratio
ranges between 3:1 and 3.5:1 [2]. Phosphate rocks of sedimentary origin typically have 30-35% P2O5 whereas those of igneous or igin contain marginally higher P 2 O 5 (35- 40%).
Uranium, REEs, gypsum, vanadium, and f luorides are byproducts resulted from milling of the phosphate rocks [3, 4].
T he Eg y pt ia n phos ph at e de p osit s a r e pa r t of t he
Mediterranean phosphate province that extends from Morocco
to Turkey and belong to the late Cretaceous-Palaeogene age [5,6]. They locate over a band between latitude 24° and 27° N inthree main belts which are, from north to south, the northernbelt extends from Baharia Oasis to Sinai, the central belt is
confined to the area of the Red Sea coast (from Safaga to
Quseir), Nile valley (between Kharaga and Dakkla chooses)[5, 7, 8]. The second belt is the one of high economic potentiality to which the area of this study belongs.
The uranium concentration in Egyptian phosphate varies
from location to another, but in general, within range of 5 to
200 ppm as U(IV) and U(VI) depends on the mode of thephosphate deposit formation and its age. Hexavalent uranium
species are adsorbed on the phosphate grains surface or fixedon phosphate ore to form secondary uranium minerals.
Uranium (IV)/(VI) ratio is highly variable but the most abundant form is uranium (IV) [9]. Many researchers attributed
that, to the might, the early diagenetic formation of marine
phosphate in a reductive environment, uranium (IV) diffuses
from the water into sediments.
About 80000 ton of uranium is encountered in the Egyptian
phosphate based on the estimated reserves of the phosphatethat exceed three billion metric tons, and the calculated average of the uranium content is about 0.001% [10]. About 90%*Corresponding author. mahmoud_nma@yahoo.com

of phosphate rocks are being used in fertilizers manufacturingwhile the remaining part is being utilized in the phosphoricacid manufacture, detergents, chemicals, insecticides and infood industries [11, 12]. Trace amounts of the uranium content
transfer to the manufactured phosphate fertilizers hence to theagriculture soils that impose a potential risk to the humanhealth in the long run. Accordingly, several researchers interested in the removal of uranium from the phosphate rocks
prior to their processing or even from the contaminated soils
using the leaching and/or adsorption techniques [13-16].
Chemically, the main methods used for uranium leachingfrom phosphate samples are the acidic and alkaline processes
include hydrometallurgy or pyrometallurgy techniques [17].
The acidic leaching compared to alkaline have advantages
include; more effective especially with hard ores, low temperature and time-consuming [18]. Sulfuric acid is the commonlyused due to the high solubility of the produced uranyl sulfate
complexes [19, 20]. When the gangue materials contain highsilica or fluorine minerals, sulfuric acid leaching is preferred,because of its costs less than alkaline leaching beside dissolve
uranium minerals more rapidly. During the acidic treatmentof phosphate samples using H 2SO4 about 80-90% of the uranium content is leached [21, 22].
In spite of the acidic methods are widely used for uranium
leaching, but the alkaline technique is more appropriate especially when the ores have high carbonate content like calcite,
dolomite, iron minerals and carbonate hydroxylapatite which
made the acidic leaching is more expensive [23, 24]. In addition, the alkali materials are not significantly reacting with silicate and alumino-silicate minerals, which commonly present
in the ores [25]. Moreover, the alkaline leaching has otheradvantages than the acidic are includes the higher selectivity,
lower corrosively and low wastes discharge.
The present work delivered two targets. The first is of environmental importance and represented in minimizing theuranium content in the phosphate ores (before their manufacturing to fertilizers and other products) using the alkalineleaching technique by a mixture of Na2CO3/NaHCO3 (0.5M) in© 2018 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 10/03/2018

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J. Nucl. Radiochem. Sci., Vol. 18, 2018

the presence of Na 2O2 as an oxidant to enhance the uranium
leaching efficiency. The second is of strategic importancethrough the recovery of the leached uranium by its precipitation from the leach liquor using sodium hydroxide solution.
The investigated phosphorite sample was collected as a representative sample from El-Sibaiya East area, East Nile valley,
Egypt.
2. Experimental
2.1. Materials and Methods. El-Sibaiya east phosphorite
sample after grinding was subjected to wet chemical analysis.
The chemical reagents used either in the chemical analysis of
the phosphorite representative sample or in the leaching experiments were of the analar grade. The elemental standard solutions which used for calibration were prepared by dissolving
the adequate weigh of the proper chemical reagents in theexact volumes of the de-ionized water. A uranium stock solution containing 1000 mg/L of U(VI) was prepared by dissolving 1.782 g of uranyl acetate in 1% nitric acid solution anddiluting to 1000 mL.
The major elemental analysis composition was determinedin the oxide forms except for the fluorine content. P2O5, SiO2,
Al 2O3 and TiO2 concentrations were estimated spectrophotometrically [26] using UNICAM UV2-100 spectrophotometer.
Oxides concentration, include CaO, Fe2O3, and MgO, wasdefined by the traditional titration method [27] while Na 2O
and K 2O concentrations were determined photometricallyusing JENWAY PFP7 flame photometer. Moisture content insoil samples was measured by weighing out 2g of the powdered sample and then heating in drying cabinet at 105 °C for
3h until constant weight is obtained. The loss in weight is considered as moisture loss (H 2O content). The above sample,
minus its moisture content, is further heated for 3hours at 550600 °C in a drying cabinet until constant weight is obtained
the difference in weight between the sample heated at 105 °C
and 550 - 600 °C gives the total organic matter in the sample.
Original water presents (H 2O+) is measured by igniting 2g of
the powdered sample at 1000 °C in a porcelain crucible. The
difference in weight of the sample at the two temperatures(500 °C and 1000 °C) gives the original water present.
The radiometric concentration of U, Th and Ra was measured by the laboratory γ-spectrometry technique using theMulti-Channel Gamma Spectrometer with NaI (Tl) detector
which holds in the Nuclear Materials Authority, Egypt. All
the samples, after crushing to the relevant size, were carefully
quartered and put into covered plastic vessels (212.6 cm 3 involume) then tightly sealed by adhesive tapes. The sealed vessels were covered well by thin aluminum foil to prevent escaping of the accumulating Ra-222 gas then were left for 30 days
before the measuring process. Uranium, thorium (in theirequivalent forms eU and eTh) and radon were measured andexpressed in the ppm unit.
Additionally, uranium was also measured by the wet chemical technique that can identify the concentration of both theold and recent uranium. The exactly weighted one gram ofeach sample was well ground to less than 0.063 mm (- 200mesh) in size, then was attacked by a mixture of concentrated
acids (HF, HClO 4 and HCl) with aggressive heating till thecomplete dryness. The extra acid attack was applied to assure
the full digestion of the solid samples. After cooling and complete dissolution in the distilled water, the concentration of
uranium was measured colorimetrically with the chemical
reagent “Arsenazo III” using the UV/VIS spectrophotometer[28].
On the other hand, the total REEs concentration and thetrace element concentrations were measured using UNICAM
969 AAS. The mineralogical investigations were carried out
for a whole rock phosphorite sample using Philips X-ray gen-

Abd El-Magied et al.
erator model PW 3710/31 diffractometer with automatic sample changer model PW1775 and supported by the remarks
obtained from the IR analysis. All the employed instruments
are in Nuclear Materials Authority, Katameya, Cairo, Egypt.
2.2. The alkaline leaching of uranium from the El-Sibaiyaphosphorite. The alkaline leaching of uranium from the
El-Sibaiya phosphorite was tested using the Na 2 CO3 andNaHCO3 in the solution form. It is worth to point that theleaching process was performed in three different phases; thefirst phase included using Na2CO3 only as leaching agent; thesecond tested the leaching efficiency of Na 2CO3 in the presence of Na2O2 as oxidant; the third phase involved using a mixture of Na 2 CO 3 and NaHCO 3 as leaching solution in thepresence of Na2O2.
The leaching experiments in the three phases were performed in 250 ml glass flask equipped with a water-cooled
condenser to minimize the solution loss by heating. The
leaching process was carried out using a thermostatic hotplate
provided with a magnetic stirrer at 450 rpm stirring speed.
The other leaching conditions were fixed during the threephases. After completion of each leaching experiment, theobtained slurry was cooled and filtrated then the uranium concentration was measured in the filtrate and its leaching efficiency was calculated by the ratio of dissolved uranium in thefiltrate against its content in the solid phosphorite. The different factors affecting the leaching process include; Na2CO3 concentration, Na 2 CO 3/ore phase ratio, Na 2 O 2 and NaHCO 3
addition, reaction time, temperature and ore fineness, werestudied and optimized.
The uranium leaching efficiency using 0.5M Na2CO3 solution was tested under the effect of variable solution/sample
ratio (5/1 to 20/1 ml/g), while other conditions were fixed constant (74 μm, 90 °C and 4h).
Under the same conditions of ore grain-size (74 μm) andreaction temperature, a mixture of 0.5M Na 2CO3 and 0.5M
NaHCO3 was used for uranium leaching in presence andabsence of Na2O2 under different solution/sample ratios.
The effect of leaching temperature on uranium leachingfrom the phosphate ore was investigated in the range of 25 to
100 °C. The other leaching condition were ore grain-size(74 μm), Na2CO3-NaHCO3 solution (0.5M), Na2O2 (2.5% w/w),
solution/solid ratio (25/2) and 4h leaching time.
To study the effect of ore grain size on the uranium leachingefficiency, the phosphate rock was ground then sieved using
sieves of gradual size. The alkaline leaching process was performed with various ore grain sizes ranged from 105 to 44 μm.
the other applied conditions were Na 2CO3-NaHCO3 solution(0.5M), 80 °C, Na 2O2 (2.5% w/w), solution/solid ratio (25/2)
and 3h leaching time. All the experiments were performed in
duplicates with experimental error ± 0.5-2 %.
3. Results and Discussion
3.1. General geology. The Campanian-Maastrichtian phosphate deposits in Egypt nominated as the Duwi Formation(Fig. 1). The Duwi Formation in the Nile Valley region was
divided into Mahamid Member (Lower Member), Sibaiya
Member and Adayma Member (Upper Member) [29]. This
Formation is mainly composed of phosphate beds intercalatedwith shale, marl, oyster-limestone and chert bands. These
phosphate beds are named A, B, and C from base to top. The
horizon (A) represents the high economic phosphorite bed inall studied sections where it has the largest thickness and thehigh phosphorus content. The horizons (B) and (C) didn’t consider economic phosphorite beds because they varied in the
thickness from 10 to 30 cm and have low phosphorus content.
3.2. Mineralogical, chemical and radioactivity charac-

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Alkaline leaching of uranium from El-Sibaiya East Phosphorite in the

18

Counts/s

Figure 1. Photograph, Lithostratigraphic composite succession and location of Duwi Formation exposed in El-Sibaiya East area.

V:Apatite
Q:Quartz

10

20

30

40

50

X:Calcite
O:Gypsum

60 

Figure 2. X-ray diffraction pattern of El-Sibaiya phosphorite.

terization. Before the alkaline leaching process, it was necessary to define the important mineralogical components thatencountered the uranium as well as the rock chemical composition to verify the validity of the alkaline leaching to thesecomponents. Also, it was an essential issue to determine theradio-element content in the used ore.
3.2.1. The mineralogical composition of El-Sibaiya phosphorite. The output of the X-ray diffraction analysis (2.792.80 Å, 2.69-2.70Å, and 2.62-2.63 Å) pointed to the presenceof francolite (as the major phosphate mineral), calcite, gypsum, and quartz (Fig. 2). Most of the uranium content in thephosphorite is almost encountered in the francolite because of
the open nature of its crystal lattice; the francolite (carbonate
f luorapatite) usually exhibits varied chemical composition[30].
Moreover, the IR analysis provides several remarks that
supported XRD results. The IR spectrum (Fig. 3) indicatedthat the peak at 1042.7 cm -1 ref lects the distortion of CO32which resulted from loses an electron due to the effect of uranium and thorium radiation in the used sample. The band of3426.1 cm-1 refers to the substitution of a considerable amountof –OH group for –F in francolite mineral. On the other hand,

4000

3000

2000
Wave number [cm-1]

517.8
469.1

875.2

1042.71425.9

606.2
571.8

1799.2

799.0
712.1

2368.82338.73426.12515.1

Abd El-Magied et al.

2981.02924.82873.03674.33648.6

J. Nucl. Radiochem. Sci., Vol. 18, 2018

Transmittance [%]

19

1000

400

Figure 3. IR spectrum of El-Sibaiya phosphorite.

the broadband at 3426.1 cm -1 resulted from the molecularwater adsorbed by francolite while broad bands at 1425.9 and712.1 cm-1 refer to the calcite mineral appearance [31]. The
moderate sharp adsorption bands 517.8, 606.2, 712.1 and 799
cm-1 reflect the presence of quartz mineral.
3.2.2. The chemical analysis of El-Sibaiya phosphorite.
The achievable data from the chemical analysis (Table 1) indicated that there are two essential groups of major elements; thefirst locate predominantly within the apatite lattice (CaO,
P2O5, F and CO2) while the second usually locates outside thephosphate grain, either of detrital origin (SiO2, Al2O3, K 2O andTiO2) or by weathering (Fe2O3 and MgO). Trace elements
within the apatite lattice generally associated with detrital
minerals and organic matter. Generally, the high concentration of alkali metals (Ca and Mg), as well as the presence ofhigh content of the carbonate hydro apatite, encourages thealkaline leaching technique rather than the acidic leaching.
3.2.3. The radioactivity of El-Sibaiya phosphorite. The
radiometric measured eU, eTh and Ra are listed in Table 2.
The recorded uranium concentration either radiometrically(eU, 100.2 ppm) or chemically (145.1 ppm) intimately matcheswith the values assigned for the worldwide phosphorite. An
indicative remark regarding the addition of recent uranium isconducted from the ratio of the chemically measured uranium/
radiometrically measured uranium [32]. The D-factor (U/eU),
is equal to the ratio of the chemically determined uranium/
radiometrically measured uranium, indicates the addition or
removal of uranium. The value of D-factor of El-Sibaiya East
Phosphorite sample is more than unity (1.45), it is clear thatchemical uranium is higher than the radiometric uranium inthe sample, which reflects disequilibrium due to the additionof uranium. Such recent uranium is more reasonable to be in
the hexavalent form (U6+) and adsorbed on the phosphorite
grains surface rather than its admission into the crystal latticeof the rock-forming minerals [9]. Usually, this kind of theadsorbed uranium is easily leached either by alkaline or acidic
solutions. However, the value of the above-mentioned ratio
does not indicate a highly significant addition process. The
values of the total loss of ignition (L.O.I) at different temperature indicates that the studied sample has high carbonate content.
3.3. The alkaline leaching by Na 2CO 3 . Generally thealkaline process relies on formation of highly soluble uranium(VI) tri-carbonate [UO2(CO3)3]4- or uranium (VI) di-carbonate[UO2(CO3)2]2- species as elucidated in the Pourbaix diagram,which visualize the stability of uranium species in the alkaline
solution depending on the solution Eh and pH [33, 34]. The

TABLE 1: Major and trace elements content in El-Sibaiyaphosphorite
Major elements
Element oxide %
%
24.62
P2O5
CaO
39.64
15.11
SiO2
2.31
Fe2O3
MgO
3.61
Na2O
1.07
1.12
Al2O3
0.15
TiO2
0.13
K 2O
F
2.21
110 °C0.48
550 °C
2.45
1050 °C
5.81
Total loss of ignition
8.74

Trace elements
Element
ppm
U
145.1
Ʃ REEs
244.4
Th
4.1
Sr
1742
Ba
620
Zn
139
Cr
135
Mn
132
V
60
Y
51
Rb
25
Zr
15
Cu
15
Ni
10

TABLE 2: Equivalent uranium contents of El-Sibaiyaphosphorite sample
Radioactive metaleU (ppm)eTh (ppm)
Ra (ppm)eTh/eUeU/eThContent
100.2
4.1
129.1
0.1
25.0

different factors affecting the leaching of uranium from
El-Sibaiya East Phosphorite using alkaline solutions were
investigated to conure the effects these several controlling factors in the leaching process. The results (Fig. 4) pointed to thelimited capability of the Na2CO3 solution in leaching the uranium content from the phosphate sample.
The uranium leaching efficiency increased from 4.1 to13.2% by increasing the solution/ore ratio from 5/1 to 12.5/1.
Then decrease with the higher ratio. In the same context, theleaching experiments were performed using 1M Na 2 CO3instead of 0.5 M Na 2CO3 as a leach solution under the sameleaching conditions. The conducted results showed that no
noticeable difference results obtained, so the optimum Na2CO3

J. Nucl. Radiochem. Sci., Vol. 18, 2018

Alkaline leaching of uranium from El-Sibaiya East Phosphorite in the
Carbonate

20

Carbonate/Oxidant

20

Carbonate/Bicarbonate/Oxidante

15

Uranium leaching (%)

Uranium leaching (%)

100

10
5

75

50

25

0
0

5

10

15

20

25

0
0

Na 2CO 3/ Phosphorite sample (mL/ g)

5

10

15

20

25

Leaching solution/Phosphorite sample (mL/g)

Figure 4. Effect of Na 2CO3 solution/sample ratio upon uranium
leaching from El-Sibaiya phosphorite.

Figure 6. Effect of Na2CO3/phosphate rock on uranium leaching in
the presence and absence of Na2O2 oxidant and NaHCO3 species.

Uranium leaching (%)

70
leaching was accelerated from 42.6 to 56.4 % as the solution/
sample increased from 5/1 to 12.5/1. Increasing the alkali
solution/sample ratio to 20/1 was accompanied by slightdecreasing in the uranium leachability (52.1%). This decreasing is likely ascribed to forming of sodium hydroxide according to the following equations:

60
50
40
30

∆

20

Na2O2(s) + 2H2O(L) → 2NaOH(aq) + H2O2(aq)↑

(3)

10

Na2O2(s) + H2O(L) → 2NaOH(aq) +1
O2(g)↑
2

(4)

∆

0
0

5

10

15

20

25

Figure 5. Effect of Na 2CO3 solution/sample ratio in presence ofNa2O2 as oxidant on uranium leaching from phosphate rock.

concent ration used for u raniu m leaching was 0.5 M.
Generally, the uranium leaching by should behave according
to the following equation:(1)

The low uranium leaching efficiency using Na2CO3 solution
could be described by one or more reasons. The first reason
may back to the dominant of U4+ in the phosphate sample
while the above equation reveals that the Na 2CO3 reacts with
U6+ species only. The second plausible reason might due to theprecipitation of leached uranium as sodium diuranate due tothe chemical reaction between the generated sodium hydroxide and the formed uranium carbonate species according to thefollowing equation:
2Na4UO2(CO3)3(aq) + 6NaOH(aq)→ Na2U2O7(ppt)↓ + 6Na2CO3(aq) + 3H2O(aq)

(5)

2−

UO2(aq) + 6CO 3(aq) + O2(g) + 2H2O(L)4−−→ 2UO2(CO3) 3 (aq) + 4OH (aq)

Na 2CO 3/ Phosphorite sample (mL/ g)

UO3(S) + 3Na2CO3(aq) + H2O(L)→ Na4[UO2(CO3)3](aq) + 2NaOH(aq)2UO2(aq) + O2(g) → 2UO3(aq)(2)

3.3.1. The alkaline leaching by Na2CO3 in presence of anoxidant. To overcome the effect of U4+ content on the leachingprocess, the previous experiments were carried out but in presence of sodium peroxide (Na 2O2) as an oxidant (2.5% Na2O2/ore). Sodium peroxide as oxidant chosen due to two reasons;the first is its high oxidation potential while the second reason
is avoiding introducing other metal species than Na+ into theleach liquor.
The obtained results (Fig. 5) indicated that the uranium(6)

Accordingly, some of the uranium content not leached by
the used solutions besides the formed soluble uranium carbonate species might be precipitated as Na2U2O7 as a result of eq
2, so the oxidant percent should be adjusted in addition thegenerated OH- species should be removed. The role of Na2O2oxidant is oxidized U4+ (un-leachable form) to U6+ (leachableform) using the liberated oxygen or hydrogen peroxide during
the vigorous reaction of Na2O2 with H2O.
3.3.2. The alkaline leaching by Na2CO3 / NaHCO3 solution. To avoid the negative uranium leaching effect due to theformed NaOH in the two previous phases, the alkaline leaching was examined by a mixture of Na2CO3 and NaHCO3 in thepresence of Na2O2 as the oxidant. The results (Fig. 6) pointed
to increasing the uranium leaching efficiency from 54.6 to81.4% as increasing the leaching solution/sample ratio from
5/1 to 12.5/1. Above the leaching solution/sample ratio of
12.5/1, there was no significant increase in the uranium leachability. The leaching-enhancing by the added NaHCO3 can be
explained by Eq 7, which also shows the reaction of NaHCO3
with the formed NaOH in the leaching medium, hence, preventthe re-precipitation of some soluble uranium carbonate species
as sodium diuranate.
NaHCO3(aq) + NaOH(aq) → Na2CO3(aq) + H2O(aq)(7)

UO3(aq) + Na2CO3(aq) + 2NaHCO3(aq)→ Na4UO2(CO3)3(aq) + H2O(aq)(8)

3.3.3. Effect of leaching temperature. The achievable data
(Fig. 7) revealed a continuous increase in the uranium leachability with the temperature raising and the maximum leaching efficiency was conducted at a temperature of 80 °C. The

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J. Nucl. Radiochem. Sci., Vol. 18, 2018

Abd El-Magied et al.

100
Uranium leaching (%)

Uranium leaching (%)

100

75

50

25

0

75

50

25

0
0

25

50

75

100

0

25

T emperature ( oC)

50

75

100

125

Grain size (μm)
Figure 9. Effect of ore fineness on uranium leaching from phosphaterock using Na2CO3 and NaHCO3 in presence of a Na2O2 oxidant.

Counts/s

Figure 7. Effect of temperature on uranium leaching from phosphaterock using Na2CO3 and NaHCO3 in presence of Na2O2 as oxidant.

100

V Sodium diuranate
PDF_2 (26-973)

Uranium leaching (%)

900

75
625

50

400
225

25
100
25

0
0

2

4

6

8

T ime (h)

10

20

30

40

50



Figure 8. Effect of leaching time on uranium leaching from phosphate rock using Na2CO3 and NaHCO3 in presence of a Na2O2 oxidant.

Figure 10. X-ray diffractogram of the precipitated sodium diuranate(Na2U2O7).

uranium leaching increased from 27.7 to 81.3% as the leachingtemperature increased from 25 to 80 °C. More temperatureelevation (than 80 °C) was not accompanied by any significant
increase in the uranium leachability. Improving the uranium
leachability with temperature increasing might due to increasing of ions mobility under the effect of given energy. Also,
this indicates that the alkaline leaching is an endothermic process.
3.3.4. Effect of leaching time. To evaluate the effect of theleaching time on the uranium leaching from phosphate rock,the leaching experiments were carried out on time ranged
from 1 to 6 h at a temperature of 80 °C. The results (Fig. 8)
illustrated that as the reaction time increased the uranium
leaching increased and the optimum leaching time was foundto be 3h (83.2%).
3.3.5. Effect of ore fineness. Generally; the more ore fineness is the faster the digestion attack [35]. The obtained
results (Fig. 9) displayed increasing of the uranium leachingefficiency with decreasing the ore grain size, while the maximum uranium leaching efficiency 83.2% was recorded at ore
grain sizes of 44 μm and no significant increasing of the uranium leaching with the finer grain sizes. Such behavior is
likely interpreted by increasing the surface area in the finesize that leads to increasing of the available reaction-surface
between the alkaline agents and phosphate ore hence, facilitates the leaching process. However, another reason should beconsidered where the uranium usually tends to concentrate in
the fine-sized grain rather than the coarse ores.
3.4. Uranium precipitation. Uranium recovering from theaqueous leach liquors depends on nature and metals content of
the liquor solution. In the acidic solutions, solvent extraction
or ion exchange techniques are generally applied for metal
recovery rather than the precipitation technique due to the various dissolved metal ions in the solution. On the contrary, due
to the high selectivity of the alkaline process for uranium
leaching, direct precipitation is properly used. In this study,
the leach liquor analysis showed that iron, aluminum, titanium
species, etc., are nearly insoluble using the use of carbonate
solution as found by Lunt et al., [36]. In the obtained leach
liquor very low concentrations of phosphates, aluminates ascarbonates species were investigated.
In this work, uranium precipitation from the carbonate
leach liquor (pH 11.2) was applied using a 25% sodiumhydroxide solution at 50 °C for 6h reaction time at pH 11.5-12.
The uranium precipitation from El-Sibaiya phosphorite alkali
treated solution is presented by eq 9. After concentrating theobtained solution by evaporation, the suspended yellow solution ( fine particles) was kept for 24h and then separated bycentrifugation then gently washed for several times and driedat 100 °C. The obtained sodium diuranate (Na2U2O7) productwas defined by XRD technique (Fig. 10).

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Alkaline leaching of uranium from El-Sibaiya East Phosphorite in the

Grinding

22

El-Sibaiya phosphorite oresieving
0.5M (Na2CO3 + NaHCO3)44μm
4

2 5%w/w/ Na2O2
2.5%w/w

25% NaOH
Leachh liliquorCentrifugationg
Suspended solution

Washing

Yellow precipitation

drying

Filtrate
CO32-

Na2U2O7 ppt.
(yellow cake)
Figure 11. The overall uranium leaching and precipitation flow-sheet

needed in highly purified form.
2[UO2(CO3)3] 4−(aq) + 14NaOH(aq)→ Na2U2O7(ppt)↓ + 3Na2CO3(aq) + 7H2O(aq)(9)

The overall treatments that applied on El-Sibaiya phosphorite to leach and precipitate its uranium content were summarized in a flow-sheet (Fig. 11).
4. Conclusion
El-Sibaiya east phosphorite representative sample was subjected to alkaline leaching for uranium leaching. Many leaching factors include, leaching solutions concentrations,temperature and reaction time and ore fineness were studied
and optimized. Uranium leaching efficiency of 83.2% was
obtained. The obtained leach liquor was treated with 25%
NaOH to precipitate leached uranium species as Na2U2O7 successfully. Referring to this work and the illustrated data, thefollowing points could be concluded:
1. Using the alkaline leaching technique to leach the uranium
from its bearing ores should be chosen based on the oxidation state of the present uranium.
2. The successful alkaline leaching should be carried out inpresence of an oxidant to guarantee the presence of all uranium ions in the hexavalent state form.
3. A mixture of sodium carbonate and sodium bicarbonate has
to be used with the presence of sodium peroxide as an oxidant to conduct the highest U-leaching ratio from El-Sibaiya
east phosphorite
4. Under the proper leaching conditions, the alkaline leachingof uranium is more favorable than the acidic leaching forseveral reasons particularly when the recovered uranium is

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