Aeolian sand sample from Tengger desert, located in the southern part of Inner Mongolia (China) was characterized for major elemental composition and mineralogy by EPMA, XRF and XRD methods. The objective of this research was to provide data which would be a guide to aid future beneficiation of this sand, especially for the economic exploitation of feldspar and quartz which have a wide range of applications in various industries like plastic, paint, ceramics and glass industries. The elemental analysis of the sample was carried out by X-ray fluorescence spectrometer and chemical analysis while the minerals present were identified by an X-ray diffraction analyzer. The sand was discovered to contain basically SiO 2 (82.43%), Al 2O 3 (7.68%), Na 2O + K 2O (4.37%) and TiO 2 and Fe 2O 3 as the main impurities. It was also discovered that grinding of the sand is required to enhance the liberation of the minerals and the separation methods recommended are magnetic separation and flotation. It was therefore concluded that aeolian sand is a suitable source of quartz and feldspar for use in the industry.
Aeolian sands are finely to relatively medium grained, uniformly graded materials deposited in huge amounts by wind, mostly in deserts [
In addition, the associated minerals were also identified as it is of great importance in case the deposit needs to be processed. This is because different industries give certain specifications on the maximum impurity percentage contamination to be acceptable in the raw materials. For instance, iron contamination must be below 0.15% in feldspar as a raw material in the manufacture of ceramics [
In order to satisfactorily characterize the samples, different approaches were used. The EPMA technique which is a non-destructive method was one of the methods used. It is a widely used technique where the solid specimens are bombarded with a focused electron beam and the emitted X-rays analyzed to determine the composition, concentration and distribution of the elements in the specimen [
Experimental study samples were collected from the Inner Mongolia Tengger Desert open-pit mine using the sample points method. 2200 kilograms of ore from 15 sub-sample points were packed in 45 bags and used in the Mineral Processing Engineering laboratory in Wuhan University of Technology for the various tests and studies. The sample information of each sample point is shown in
Point serial number | Distance (km) | Number of bags (bags) | Gap(km) |
---|---|---|---|
1 | 30 | 3 | 0 |
2 | 31 | 3 | 1 |
3 | 32 | 3 | 2 |
4 | 34 | 3 | 4 |
5 | 35 | 3 | 5 |
6 | 37 | 3 | 7 |
7 | 38 | 3 | 8 |
8 | 39 | 3 | 9 |
9 | 40 | 3 | 10 |
10 | 41 | 3 | 11 |
11 | 42 | 3 | 12 |
12 | 44 | 3 | 14 |
13 | 45 | 3 | 15 |
14 | 51 | 3 | 21 |
15 | 53 | 3 | 23 |
In order to understand the sample characteristics of each sample point, the samples were thoroughly mixed separately, and test samples prepared for further analysis. Subsequent test samples were prepared by mixing representative samples from the 15 points for laboratory mineral identification and the various laboratory tests.
Particle size analysis is usually significant in evaluating the performance of a grinding circuit [
The elemental analysis of the sample was carried out by X-ray fluorescence spectrometer and chemical analysis while the minerals present were identified by an X-ray diffraction analyzer to determine whether the main minerals in the deposit, such as feldspar, had sufficient content to be used for different uses such as the ceramic industries [
A representative sample of the ore of minus 2 mm in size was mixed with epoxy resin to prepare a polished thin section. An optical microscope (Olympus BX51 model) was then used to observe and determine the minerals present as well as their dissemination sizes.
A comprehensive main and trace elements ore data, as well as detailed optical mineralogy, petrographic examination and mineral composition data was carried out using an electron microprobe analyzer (EMPA) [
Sieve test and laser sizing particle analysis techniques (
The sample appears to be yellow-brown/light yellow to grayish-white in colour
Aperture size (mm) | Mesh number | TG-1 (%) | TG-4 (%) | TG-7 (%) | TG-10 (%) | TG-13 (%) | TG-15 (%) |
---|---|---|---|---|---|---|---|
+0.45 | +40 | Small amount | 0.55 | Small amount | Small amount | 0.55 | Small amount |
−0.45 + 0.30 | −40 + 60 | 1.40 | 21.44 | 8.44 | 1.74 | 18.45 | 11.25 |
−0.30 + 0.20 | −60 + 80 | 16.29 | 23.19 | 36.28 | 15.13 | 19.20 | 24.31 |
−0.20 + 0.15 | −80 + 100 | 31.19 | 17.04 | 23.02 | 28.12 | 16.84 | 23.80 |
−0.15 + 0.125 | −100 + 120 | 39.41 | 26.04 | 23.37 | 42.81 | 27.32 | 28.34 |
−0.125 + 0.074 | −120 + 200 | 11.31 | 10.69 | 8.29 | 11.70 | 16.44 | 11.60 |
−0.074 | −200 | 0.40 | 1.05 | 0.60 | 0.50 | 1.20 | 0.71 |
Note: “small amount” in
Sample | D10 (μm) | D50 (μm) | D90 (μm) |
---|---|---|---|
TG1 | 133.9 | 216.0 | 355.3 |
TG4 | 138.6 | 261.7 | 517.7 |
TG7 | 138.5 | 253.5 | 479.9 |
TG10 | 119.2 | 198.7 | 337.8 |
TG13 | 132.1 | 253.4 | 512.3 |
TG15 | 138.5 | 258.7 | 508.0 |
Average | 133.5 | 240.3 | 451.8 |
under naked eyes and has a grainy texture. From microscopic observations, the main metal minerals include pyrite, magnetite and ilmenite. Mainly, the transparent minerals are quartz, potassium feldspar, plagioclase, sand cuttings, sericite and epidote. The sample chemical analysis results of typical elements in TG samples are shown in
From the analysis results of the typical elements, it was shown that except for the grades of K2O, Na2O and K2O + Na2O in sample point 7, the grades of the other points gradually decreased from the 1st point to the 15th point. The trend was opposite in the grade of SiO2 and the percentage content of SiO2 remained above 81% in all samples. The arithmetic mean grade of K2O and Na2O in the TG samples tested was 2.02% and 1.752% respectively. The total average grade of K2O + Na2O was 3.77% and the average value of SiO2 content was 82.33%.
X-rays obtained from XRF analysis of the Tengger aeolian sand mixed sample (TS sample) were analyzed and the results were as tabulated in
Sample code | Distance(km) | SiO2 | K2O | Na2O | K2O + Na2O |
---|---|---|---|---|---|
TG-1 | 30 | 81.10 | 2.468 | 1.913 | 4.381 |
TG-4 | 34 | 83.52 | 2.583 | 1.627 | 4.210 |
TG-7 | 38 | 81.90 | 2.645 | 1.915 | 4.561 |
TG-10 | 41 | 81.39 | 1.605 | 1.909 | 3.513 |
TG-13 | 45 | 82.07 | 1.570 | 1.616 | 3.186 |
TG-15 | 53 | 83.99 | 1.234 | 1.534 | 2.768 |
Average | 40.17 | 82.33 | 2.018 | 1.752 | 3.770 |
be comprehensively recovered as quartz and feldspar respectively. Apart from the high percentage of SiO2, Na2O, K2O and Al2O3, it was also detected that the sample is composed of 1.7% Fe2O3 content which is an unwanted impurity in feldspar due to its colouring properties especially in the manufacture of high-class colourless glass that should contain a maximum of 0.1% Fe2O3 although up to 0.3% is acceptable [
The X-ray diffraction analysis (XRD) of the sample was as illustrated in XRD pattern as shown in
Chemical composition | Percentage (%) |
---|---|
K2O | 2.449 |
Na2O | 1.920 |
SiO2 | 81.669 |
Al2O3 | 8.931 |
Fe2O3 | 1.700 |
TiO2 | 0.196 |
CaO | 0.830 |
MgO | 0.905 |
SO3 | 0.017 |
P2O5 | 0.048 |
Rb2O | 0.008 |
SrO | 0.022 |
ZrO2 | 0.014 |
BaO | 0.069 |
LOI | 1.222 |
Note: The sample was tested after drying at 105˚C for 2 hours.
mineralogy of the TG samples were found to be quartz (SiO2), potassium feldspar (K-feldspar) or orthoclase (KAlSi3O8), oblique minerals such as plagioclase or albite (NaAlSi3O8) and feldspar sanidine (KAlSi3O8). Some impurity minerals had trace contents and could not be reflected in the XRD analysis.
Chemical analysis (
Quartz, mainly occurring as SiO2, is the dominant mineral by estimation and is one of the minerals to be recovered from aeolian sands. By optical microscopy, it is about 46%, irregular granular (shown in
Component | K2O | Na2O | K2O + Na2O | SiO2 | Al2O3 | Fe2O3 | TFe | CaO | MgO |
---|---|---|---|---|---|---|---|---|---|
Content/% | 2.385 | 1.982 | 4.367 | 82.43 | 7.68 | 1.73 | 1.16 | 1.97 | 2.20 |
Feldspar is also one of the minerals that can be recovered economically from aeolian sands. It mainly occurs in two forms which include potassium feldspar and plagioclase.
Potassium feldspar (Kfs) accounts for about 26% in the microscopic observations and it occurs as irregular granules which are sub-circular, having a medium to fine sand structure with a visible stripped lattice (as shown in
and
Plagioclase (Pl) is about 20% observed as irregular granules, sub-circular, medium-fine sand structure, partly coarse sand structure, visible cleavage and polycrystalline crystal structure (
Magnetite and ilmenite are the main gangue minerals present in the Tengger desert aeolian sand ore. Both are present in small amounts and have irregular granular shapes. Magnetite (Mt) has an approximate particle size of between 0.002 - 0.1 mm (
Limonite (Lm), amphibole (Hbl), chlorite (Chl) and tourmaline (Tur) as well as pyrite (Py) (
Through observations and identification under the microscope, the main forms
of K2O and Na2O were determined to be potassium feldspar (Kfs) and plagioclase (Pl) minerals respectively. The concentration of potassium feldspar and sodium feldspar varied in different microzones (as noted in
Spectrum | K | Na | Si | Al | O | Ti | Fe | Ca | Total |
---|---|---|---|---|---|---|---|---|---|
1 | 17.2 | 1.2 | 43.45 | 12.09 | 26.06 | 0 | 0 | 100.00 | |
2 | 0.34 | 9.85 | 47.49 | 13.96 | 28.36 | 0 | 0 | 100.00 | |
3 | 18.23 | 0.64 | 43.78 | 12.06 | 25.30 | 0 | 0 | 100.00 | |
4 | 1.37 | 8.95 | 48.15 | 13.77 | 27.77 | 0 | 0 | 100.00 | |
5 | 14.07 | 2.49 | 43.86 | 12.97 | 26.25 | 0.37 | 0 | 100.00 | |
6 | 16.02 | 1.82 | 43.37 | 12.43 | 26.36 | 0 | 0 | 100.00 | |
7 | 1.55 | 8.18 | 48.52 | 14.34 | 27.42 | 0 | 0 | 100.00 | |
8 | 16.96 | 1.46 | 43.39 | 12.35 | 25.84 | 0 | 0 | 100.00 | |
9 | 6.95 | 6.41 | 45.08 | 12.99 | 28.32 | 0 | 0 | 0.25 | 100.00 |
10 | 16.09 | 1.76 | 44.07 | 12.14 | 25.94 | 0 | 0 | 100.00 | |
11 | 2.48 | 8.94 | 47.36 | 13.04 | 28.17 | 0 | 0 | 100.00 | |
12 | 2.41 | 8.90 | 46.84 | 13.33 | 28.53 | 0 | 0 | 100.00 | |
13 | 3.62 | 8.53 | 46.83 | 13.27 | 27.74 | 0 | 0 | 100.00 | |
Maximum | 18.23 | 9.85 | 48.52 | 14.34 | 28.53 | ||||
Minimum | 0.34 | 0.64 | 43.37 | 12.06 | 25.30 | ||||
Average | 9.02 | 5.32 | 45.55 | 12.98 | 27.08 |
also varied significantly for sodium with the highest being 9.85% and the lowest being only 0.64%. The microzone X-ray energy spectrum composition of a typical K-feldspar mineral is shown in
It can be seen from
Spectrum | K | Na | Si | Al | O | Fe | Ti | Ca | Mg | Total |
---|---|---|---|---|---|---|---|---|---|---|
1 | 0 | 0 | 68.93 | 0 | 31.07 | 0 | 0 | 100.00 | ||
2 | 6.62 | 0 | 33.71 | 19.48 | 27.31 | 5.76 | 4.71 | 0.23 | 2.18 | 100.00 |
3 | 0 | 0 | 69.52 | 0 | 30.48 | 0 | 0 | 100.00 | ||
4 | 0 | 0 | 68.98 | 0 | 31.02 | 0 | 0 | 100.00 | ||
5 | 0 | 0 | 67.82 | 0 | 32.18 | 0 | 0 | 100.00 | ||
6 | 8.78 | 0 | 54.17 | 14.65 | 12.95 | 6.02 | 2.34 | 1.08 | 100.00 | |
7 | 0 | 0 | 68.37 | 0 | 31.63 | 0 | 0 | 100.00 | ||
8 | 0.38 | 0 | 69.34 | 1.04 | 28.79 | 0 | 0.45 | 100.00 | ||
9 | 5.10 | 0 | 46.38 | 13.34 | 21.79 | 8.85 | 1.44 | 0.42 | 2.67 | 100.00 |
10 | 4.51 | 0 | 47.74 | 12.68 | 21.70 | 9.34 | 1.05 | 0.49 | 2.49 | 100.00 |
11 | 0 | 0 | 68.20 | 0 | 31.80 | 0 | 0 | 100.00 | ||
12 | 0 | 0 | 68.58 | 0 | 31.42 | 0 | 0 | 100.00 | ||
Maximum | 8.78 | 0 | 69.52 | 19.48 | 32.18 | 9.34 | 4.71 | 0.49 | 2.67 | |
Minimum | 0 | 0 | 33.71 | 0 | 12.95 | 0 | 0 | 0.23 | 1.08 | |
Average | 2.12 | 0.00 | 60.98 | 5.10 | 27.68 | 2.50 | 0.83 | 0.38 | 2.11 |
Microscopic observations showed that there were iron impurities in form of magnetite, hematite and ilmenite in the aeolian sands (
Since feldspar and quartz have been identified as the main economically valuable minerals, impurities including mica, titanium and iron minerals must be removed in order to suit ceramic and glass industry specification where they are mainly used. In relation to the above impurities and gangue minerals, the most suitable flowsheet for beneficiation could involve grinding, desliming and classification, then magnetic separation and flotation separations. The main methods of flotation for separating quartz and feldspar include the HF, non-fluoride and non-collector approaches. The HF method of quartz-feldspar separation where hydrofluoric acid is used as an activator for feldspar and primary amines used as collectors at a of pH 2-3 is the most well-known [
Spectrum | K | Na | Si | Al | O | Fe | V | Mg | Total |
---|---|---|---|---|---|---|---|---|---|
1 | 0 | 0 | 0 | 0 | 10.83 | 88.6 | 0.57 | 100.00 | |
2 | 0 | 0 | 0.80 | 6.96 | 8.99 | 82.58 | 0.66 | 100.00 | |
3 | 0 | 0 | 0 | 0 | 10.71 | 89.29 | 100.00 | ||
4 | 0 | 0 | 0 | 4.79 | 10.89 | 83.27 | 1.05 | 100.00 | |
5 | 0 | 0 | 0.61 | 2.18 | 8.20 | 88.28 | 0.73 | 100.00 | |
6 | 0.26 | 0 | 0.65 | 4.79 | 14.21 | 79.52 | 0.56 | 100.00 | |
7 | 0 | 0 | 0 | 0.55 | 10.84 | 88.03 | 0.57 | 100.00 | |
8 | 0 | 0 | 0.64 | 6.12 | 6.75 | 86.48 | 100.00 | ||
9 | 0 | 0 | 0 | 0 | 10.73 | 88.69 | 0.58 | 100.00 | |
10 | 0 | 0 | 0.76 | 6.25 | 9.81 | 83.18 | 100.00 | ||
11 | 0 | 0 | 0.90 | 12.50 | 6.64 | 77.00 | 100.00 | ||
Maximum | 0.26 | 0 | 0.90 | 12.50 | 14.21 | 89.29 | 0.73 | 1.05 | |
Minimum | 0 | 0 | 0 | 0 | 6.64 | 77.00 | 0.56 | 1.05 | |
Average | 0.02 | 0.00 | 0.40 | 4.01 | 9.87 | 84.99 | 0.61 | 1.05 |
but their content is significantly low.
There are vast aeolian sand resources in China. The results obtained from this study show that Tengger desert aeolian sands can be a suitable source of quartz and feldspar for industrial applications. The useful recoverable feldspar mineral component in the sample contains 2.385% K2O and 1.982% Na2O according to chemical analysis results. Quartz occurs as SiO2 which is about 82.43%, being the most abundant mineral. All the other minerals accounted for about 10%, but no other mineral could be recovered economically and hence they were treated as impurities. Chemical and mineralogical analyses confirmed the suitability of the deposit to be processed economically to separate the gangue minerals, which are mostly metallic and/or magnetic, to obtain high purity quartz and feldspar. The impurity minerals containing iron are mainly magnetite, hematite, pyrite, ilmenite and limonite.
From the microscopic observations, EMPA and micro-area spectral composition analysis, the mineral types in the sample are relatively simple and are mainly potassium feldspar, plagioclase and quartz with small amounts of sand, clay, sericite, ilmenite and other minerals. Potassium feldspar particle size ranges from 0.01 to 0.7 mm, with plagioclase having a particle size of 0.01 - 0.8 mm, and the quartz particle size is 0.01 - 0.7 mm. Most of the impurity metal minerals are fine-grained. Since some of the gangue minerals are embedded on the target minerals, mostly feldspar, a proper and suitable grinding process will be necessary to liberate the minerals after which magnetic separation can be used to remove the magnetic impurities. Flotation can then be used to separate the feldspar and quartz minerals due to the difference in their zeta potential when treated under various flotation reagents. Therefore, future research could be determining how this ore can be beneficiated economically by use of magnetic separation and flotation methods, the suitable equipment, conditions and parameters involved.
The authors gratefully acknowledge financial support by the State Natural Science Foundation of China (No. 51874219) and the National Thirteenth-Five Years Key Research and Development Program of China (No. 2017YFC0703202).
The authors declare no conflicts of interest regarding the publication of this paper.
Nzuki, B., Luo, L.Q., Zhou, P.F., Niyonzima, C. and Tu, X. (2019) Mineralogical Characterization of Aeolian Sands from Inner Mongolia, China. Journal of Minerals and Materials Characterization and Engineering, 7, 81-102. https://doi.org/10.4236/jmmce.2019.73007