The technical viability for utilizing Jebel Kurun phosphate reserve in Sudan for the production of a fertilizer grade phosphoric acid is assessed. Statistical analysis has been carried for 56 samples. Phosphate rock has been classified into three main types and then the number of samples representing each type has been identified. Average values for phosphorus pentoxide is 19% and for uranium is 81.47 ppm. The most abundant elements are silicon, aluminum, phosphorus, calcium and iron. Aluminophosphate ore (CaO% ≤ 12%, Al 2O 3% ≥ 20%, P 2O 5% ≥ 18%) is represented by 55.36% of sampled phosphate rock. This type can be used to produce phosphoric acid when P 2O 5 > 30%. Apatite rock including aluminophosphate CaO% ≥ 25%, Al 2O 3% ≤ 10%, P 2O 5% ≥ 20%, 12% ≤ SiO 2 ≤ 35% is represented by 1.79% of sampled phosphate rock, this type can be used to produce phosphoric acid when it can meet the requirements of (CaO% ≥ 30%, Al 2O 3% ≤ 7%, P 2O 5% ≥ 25%, SiO 2% ≤ 30%). Silica ore including phosphorus (SiO 2% ≥ 40%, P 2O 5% ≤ 10%) is represented by 16.07% of sampled phosphate rock and Iron ore including phosphorus (Fe 2O 3% ≥ 20%, P 2O 5% ≤ 10%) is represented by 5.36% of samples. Both types cannot be used to produce phosphoric acid. The statistical distribution of P 2O 5 in the size fractions for a core drilled samples is required.
The only major phosphate rock reserves found up to now in the Sudan are the deposits discovered in 1983 during exploration work by geologists of the German Geological Group in the neighborhood of Jebel Kurun (
This phosphate occurrence with minor base metal and uranium content forms a low elongated hill rising to about 25 meters above the surrounding plain. The hill extends for about 500 meter in a WSW-ENE direction and its width increases from about 100 meters in the west to 200 meters in the east [
A preliminary resource estimate at Kurun indicates 1.68 million tonnes of phosphate ore grading 20% P2O5, which amounts to about 336,000 tonnes of P2O5. The depth is calculated to the base of the hills (12 m in the west and 20 m in the east), but the true depth of the phosphate mineralization is not known [
K. Brinkmann (1985) [
The arithmetic average of the chemical analysis of the 52 samples gave 20.1% P2O5, in tests with formic acids. Soluble phosphates were proved to be less than 20% of total phosphates, and the visible phosphate reserves of the sampled portion of Jebel Kurun down to the elevation of the plain were estimated at 336,000 ton of P2O5 [
The sampled area covered about 32,000 m2 i.e. 200 × 50 = 10,000 m2 in the west plus 275 × 80 = 22,000 m2 in the east. The average elevation above the plain was taken at 12 meters in the west and 20 meters in the east. The average phosphate content is 20% P2O5 and the specific gravity = 3 ton/m3. The limits of the phosphate mineralization were not determined laterally and in depth and therefore an increase in the amount of the reserves is possible [
Geological Research Authorities of the Sudan expect the continuation of phosphate towards the depth; therefore they expect a total reserve of phosphate may reach 81 million tons with average content of 20% P2O5 [
Brinkman in 1986 [
Twelve selected samples from Jebel Kurun phosphate―bearing rocks were analyzed by X-ray diffraction method and were found to contains the following minerals (
Giad industrial group (Sudan) reported the analysis results in 2017 for two samples (
No | Name | Formula | Color |
---|---|---|---|
1 | Crandallite | CaAl3H[(OH)6(PO4)2]∙H2O | Yellow |
2 | Woodhouseite | CaAl3[(OH)6(SO4)(PO4)] | Yellow |
3 | Wavellite | Al3[(OH)3(PO4)2]∙5H2O | Green |
4 | Turguoise | CuAl6[(OH)6(PO4)4∙4H2O | Blue |
5 | Apatite | Ca5[(F,Cl,OH) (PO4)3] | |
6 | Variscite | Al(PO4)∙2H2O | Grey |
No | Grains distribution | Unit | LOT KR-AP | LOT KR-Al |
---|---|---|---|---|
1 | part > 1 mm | % | 0.23 | 1.24 |
2 | part [900 µm - 1 mm] | % | 0.73 | 1.08 |
3 | part [500 µm - 900 µm] | % | 10.53 | 14.54 |
4 | part [400 µm - 500 µm] | % | 4.16 | 7.24 |
5 | part [300 µm - 400 µm] | % | 15.64 | 10.26 |
6 | part [200 µm - 300 µm] | % | 37.28 | 16.09 |
7 | part [100 µm - 200 µm] | % | 23.96 | 28.95 |
8 | part [20 µm - 100 µm] | % | 7.47 | 20.60 |
9 | part < 20 µm | % | 0.00 | 0.00 |
The analytical results indicate the following observations:
• A very high content of alumina in the rock.
• Most of the phosphate present as fluorapatite, that has an excellent digestibility in hydrochloric acid.
LOT KR-AP | LOT KR-Al | ||||
---|---|---|---|---|---|
Analysis | Units | Values | |||
P2O5 | % | 30.56 | 22.25 | ||
CaO | % | 26.44 | 7.76 | ||
SiO2 | % | 7.17 | 8.66 | ||
Al2O3 | % | 18.55 | 31.18 | ||
Fe2O3 | % | 0.60 | 0.96 | ||
MgO | % | 0.03 | 0.02 | ||
Na2O | % | 0.05 | 0.03 | ||
K2O | % | 0.16 | 0.10 | ||
Fluor | % | 1.15 | 0.91 | ||
Ag | mg/kg | <5 | <5 | ||
As | mg/kg | <25 | <25 | ||
Ba | mg/kg | 518 | 1413 | ||
Bi | mg/kg | <10 | <10 | ||
Cd | mg/kg | 21.5 | 4.7 | ||
Co | mg/kg | 2.04 | 12.5 | ||
Cr | mg/kg | 37 | 52 | ||
Cu | mg/kg | 241 | 2339 | ||
Hg | mg/kg | <10 | <10 | ||
Li | mg/kg | 1.39 | 1.74 | ||
Mn | mg/kg | 501 | 140 | ||
Mo | mg/kg | 10.14 | 10.29 | ||
Ni | mg/kg | 22.44 | 45.55 | ||
Pb | mg/kg | <10 | <10 | ||
Se | mg/kg | <10 | <10 | ||
Sr | mg/kg | 5003 | 13,772 | ||
V | mg/kg | 2382 | 5113 | ||
Zn | mg/kg | 1827 | 3508 | ||
• Sand is present as quartz.
• Alumina and phosphate are present as Crandallite: CaAl3(OH)6(PO3(O0.5(OH)0.5))2.
• Assess the technical viability for the utilization of Jebel Kurun phosphate rock to produce phosphoric acid for fertilizer usage.
• Classification of J. Kurun phosphate rock and identification of types suitable for the production of phosphoric acid.
• Identification of the chemical characteristics and behavior of Jebel Kurun phosphate rock.
Surface samples were collected (
Samples were analyzed by using X-ray fluorescence spectrometry (XRF) after grinding, homogenizing and pelletizing process. The concentration of the detected elements was calculated from the measured net intensity of the corresponding fluorescent X-rays combined with elemental sensitivity factor and the coefficient of absorption in the residual matrix of the specimen through iteration procedure [
Statistical analysis for the collected samples were carried on by using Microsoft Office Excel software program to calculate the average value, maximum value, minimum value, variance and correlation coefficient between tested elements and P2O5 concentration.
Correlation coefficient strength between each element and P2O5 concentration was divided into seven classes: No correlation, very weak, weak, moderate, strong, very strong and perfect correlation
Giad Industrial Group in Sudan, studied the analysis report with a conventional technology supplier and classified Kurun mining area phosphate rock into three main types (
1) The first type: Phosphate rock including Lucinite or aluminophosphate ore
• Main component content:
CaO% ≤ 12%, Al2O3% ≥ 20%, P2O5% ≥ 18%
2) The second type: Apatite rock including aluminophosphate
• Main component content:
CaO% ≥ 25%, Al2O3% ≤ 10%, P2O5% ≥ 20%, 12% ≤ SiO2 ≤ 35%
3) The third type: Silica ore including phosphorus or iron ore including phosphorus
• Main component content:
SiO2% ≥ 40%, P2O5% ≤ 10%
Or
Fe2O3% ≥ 20%, P2O5% ≤ 10%
The reserve portion that could be utilized to produce phosphoric acid by conventional processes has been estimated by identifying the number of samples representing type one and type two by using Microsoft Office Excel.
The statistical analysis results (
It is important to remember that the correlation coefficient between two variables is a measure of their linear relationship and that a value of r = 0 implies a lack of linearity and not a lack of association. a value of r equal to +1 implies a perfect linear relationship with a positive slope, while a value of r equal to −1 results from a perfect linear relationship with a negative slope [
Uranium in Jebel Kurun area has an average value of 81.47 ppm (
A research published by the Journal of the Argentine Chemical Society [
Item | SiO2 | Al2O3 | CaO | Cr2O3 | Fe2O3 | K2O | MgO | MnO | Na2O | P2O5 |
---|---|---|---|---|---|---|---|---|---|---|
% | % | % | % | % | % | % | % | % | % | |
Average | 23.42 | 22.64 | 9.70 | 0.01 | 6.08 | 0.32 | 0.19 | 0.20 | 0.18 | 19.00 |
Maximum | 96.04 | 43.2 | 36.63 | 0.07 | 71.10 | 4.26 | 0.70 | 5.51 | 0.68 | 32.94 |
Minimum | 1.88 | 0.51 | <0.01 | <0.001 | 0.26 | <0.01 | <0.01 | <0.001 | 0.02 | 0.13 |
Standard Deviation | 23.58 | 11.60 | 8.83 | 0.01 | 12.31 | 0.56 | 0.14 | 0.88 | 0.13 | 9.05 |
Correlation Coefficient | −0.82 | 0.66 | 0.54 | −0.14 | −0.49 | −0.27 | −0.02 | −0.38 | −0.12 | 1 |
TiO2 | LOI | Ba | Ce | Dy | Er | Eu | Ga | Gd | Hf | |
---|---|---|---|---|---|---|---|---|---|---|
% | 1000˚C | ppm | ppm | ppm | ppm | ppm | ppm | Ppm | ppm | |
Average | 0.12 | 14.56 | 1535.97 | 19.48 | 4.70 | 8.51 | 1.14 | 3.75 | 3.94 | 2.43 |
Maximum | 1.13 | 23.89 | 11534.1 | 177.7 | 15.2 | 23.8 | 5.7 | 24.7 | 15.8 | 9 |
Minimum | <0.01 | 0.76 | 47.2 | 1.1 | 0.2 | 0.1 | <0.1 | 0.7 | 0.1 | <1 |
Standard Deviation | 0.19 | 5.89 | 1917.74 | 25.70 | 3.56 | 6.17 | 1.14 | 3.56 | 3.74 | NA |
Correlation Coefficient | −0.22 | 0.63 | 0.00 | −0.28 | −0.14 | 0.22 | −0.23 | −0.33 | −0.24 | NA |
La | Lu | Nb | Nd | Pr | Rb | Sc | Sm | Sn | Sr | |
---|---|---|---|---|---|---|---|---|---|---|
ppm | ppm | ppm | ppm | ppm | ppm | ppm | ppm | ppm | ppm | |
Average | 12.37 | 4.76 | 2.84 | 12.76 | 2.96 | 6.22 | 11.18 | 3.03 | NA | 6069.55 |
Maximum | 84.6 | 19.9 | 22.5 | 89.4 | 22.4 | 115.6 | 64 | 16.5 | 52 | 15605.7 |
Minimum | <0.5 | <0.1 | <0.5 | <0.5 | 0.1 | <0.5 | <1 | <0.1 | <1 | 32.4 |
Standard Deviation | 13.42 | 4.32 | 3.58 | 14.78 | 3.49 | 15.38 | 11.61 | 3.32 | NA | 4901.3 |
Correlation Coefficient | −0.27 | 0.44 | 0.04 | −0.30 | −0.31 | −0.33 | 0.14 | −0.29 | NA | 0.44 |
Ta | Tb | Th | Tm | U | V | W | Y | Yb | Zr | |
---|---|---|---|---|---|---|---|---|---|---|
ppm | ppm | ppm | ppm | ppm | ppm | ppm | ppm | ppm | ppm | |
Average | 0.23 | 0.69 | 1.03 | 2.22 | 81.47 | 3768.82 | 6.49 | 110.16 | 20.23 | 29.68 |
Maximum | 1.1 | 2.5 | 11.7 | 8 | 208.3 | 13620 | 130.4 | 308.1 | 86.3 | 308 |
Minimum | <0.1 | <0.1 | <0.1 | <0.1 | 1.2 | 66 | <0.5 | 1.5 | 0.1 | 4 |
Standard Deviation | 0.214 | 0.59 | 1.80 | 1.90 | 53.89 | 2703.00 | 18.09 | 76.84 | 18.75 | 41.21 |
Correlation Coefficient | −0.06 | −0.20 | −0.41 | 0.32 | 0.16 | 0.61 | −0.31 | 0.23 | 0.37 | -0.37 |
Component | Positive | Strength | Negative | Component |
---|---|---|---|---|
Ba | r = 0 | No correlation | r = 0 | ----------- |
Er, Nb, Sc, U, Y | 0 < r < 0.25 | Very weak | −0.25 < r < 0 | Cr2O3, MgO, Na2O, TiO2, Dy, Eu, Gd, Ta, Tb |
Ce, Ga, Lu, Sr, Tm, W, Yb, U < 60 PPM | 0.25 < r < 0.5 | Weak | −0.5 | Fe2O3, K2O, MnO, La, Nd, Pr, Rb, Sm, Th, Zr |
Al2O3, CaO, LOI 1000˚C, V | 0.5 < r < 0.75 | Moderate | −0.75 < r < −0.5 | ------------ |
----------- | 0.75 < r < 0.9 | Strong | −0.9 < r < −0.75 | SiO2 |
------------ | 0.9 < r < 1 | Very Strong | −1 < r < −0.9 | ----------- |
P2O5 | 1 | Perfect Correlation | −1 | --------- |
in phosphate ore samples from Kurun area (r = +0.58), which contain 56.63 mg/kg uranium in average. The chemical analysis of phosphate ore samples indicated that in the case of phosphate samples that contain low uranium concentration, there is a strong positive correlation between uranium content and P2O5%, but if uranium concentration increases over 60 mg/kg, no correlation exits.
Samples with P2O5 content higher than 15% and an average uranium content 88.93 ppm, indicate a weak negative correlation (-0.37) between P2O5 and uranium, and represent 78.57% of phosphate samples. Accordingly uranium would not be expected to be of economic interest, considering that samples that have P2O5 content lower than 15% and average uranium content 54.13 ppm exhibited a moderate positive correlation 0.61 between uranium and P2O5 and represent 21.43% of total samples.
Statistical analysis for trace elements (Tables 5-7 & Figures 8-11) indicates the mean values and correlation coefficient with phosphorous pentoxide.
Giad Industrial Group in Sudan admitted that the effective reserves for the type 1 and type 2 (
• Phosphorus pentoxide P2O5 has an average value of 19%; the most abundant major elements for the studied phosphate rock are silicon, aluminum, phosphorus, calcium and iron. Strong negative correlation (-0.82) is between phosphorus pentoxide and silicon dioxide.
• Samples with P2O5 content higher than 15% and average uranium content 88.93 ppm, indicate negative correlation (-0.37) between P2O5 and uranium; they represent 78.57% of phosphate samples, and accordingly uranium would not be expected to be of economic interest, considering that samples
No | Phosphate ore Type | Number of Samples | Comments |
---|---|---|---|
Type one | Phosphate rock including Lucinite or aluminophosphate ore CaO% ≤ 12%, Al2O3% ≥ 20%, P2O5% ≥ 18% | 31 | Should be beneficiated before producing phosphoric acid. Can be used to produce phosphoric acid by chemical method when the content of P2O5 is more than 30%. Two samples have a P2O5 content higher than 30% The technical processes are complicated and the costs of production are high. |
Type two | Apatite rock including aluminophosphate CaO% ≥ 25%, Al2O3% ≤ 10%, P2O5% ≥ 20%, 12% ≤ SiO2 ≤ 35% | 1 | Can be used to produce qualified concentrated phosphate rock by floatation method when it can meet the requirement (CaO% ≥ 30%, Al2O3% ≤ 7%, P2O5% ≥ 25%, SiO2% ≤ 30%). The technical processes are simple and the costs of production are reasonable. |
Type three | Silica ore including phosphorus SiO2% ≥ 40%, P2O5% ≤ 10% | 9 | Cannot be used to produce phosphoric acid |
Iron ore including phosphorus Fe2O3% ≥ 20%, P2O5% ≤ 10% | 3 | Cannot be used to produce phosphoric acid | |
Other | -------------- | 12 | ------------------------------- |
Total Number of Samples | 56 |
that have P2O5 content lower than 15% and average uranium content 54.13 ppm expressed a positive correlation (0.61) between uranium and P2O5 and they represent 21.43% of total samples.
• Aluminophosphate ore (CaO% ≤ 12%, Al2O3% ≥ 20%, P2O5% ≥ 18%) is represented by 55.36% of sampled phosphate rock; this type can be used to produce phosphoric acid when P2O5 > 30%.
• Apatite rock including aluminophosphate CaO% ≥ 25%, Al2O3% ≤ 10%, P2O5% ≥ 20%, 12% ≤ SiO2 ≤ 35% is represented by 1.79% of sampled phosphate rock; this type can be used to produce phosphoric acid when it can meet the requirement (CaO% ≥ 30%, Al2O3% ≤ 7%, P2O5% ≥ 25%, SiO2% ≤ 30%).
• Silica ore including phosphorus (SiO2% ≥ 40%, P2O5% ≤ 10%) is represented by 16.07% of sampled phosphate rock, Iron ore including phosphorus (Fe2O3% ≥ 20%, P2O5% ≤ 10%) is represented by 5.36% of samples phosphate rock, and both types cannot be used to produce phosphoric acid.
• Study the statistical distribution of P2O5 in the size fractions of the mined and crushed rock is recommended and using a diamond drill for sampling deposits in order to calculate the reserve by grade.
I would first like to thank my thesis advisor Prof. Kamil M. Wagialla of the Chemical Engineering Department/Faculty of Engineering at University of Khartoum. I would also like to thank my colleagues in Giad Industrial Group (Sudan), Geological Research Authority―(Sudan), Arab Fertilizer Association (Egypt), Ecophos Technologies (Belgium) and Norinco Company (China) for their support and valuable inputs.
The authors declare no conflicts of interest regarding the publication of this paper.
Elmahdi, M.E. and Wagialla, K.M. (2018) Jebel Kurun Phosphate Rock Characteristics and Technical Viability to Produce Phosphoric Acid. Journal of Minerals and Materials Characterization and Engineering, 6, 555-567. https://doi.org/10.4236/jmmce.2018.65040