Assessment of sand dunes in Missan Governorate, South-eastern Iraq: Implications for Extraction High Purity Silica

Sand dunes are widely spread in Missan Governorate, South-eastern Iraq in many areas including; Manziliyah, Khazina, Zubadiate, and Chailat. X-ray diffraction (XRD) results of sand samples of sizes 0.063-2 mm, 0.125-0.250mm, and 0.250-0.500mm, revealed that quartz is the main mineral phase, followed by calcite, feldspar and trace of gypsum. Chemically SiO2 is the main oxide in sand of an average 61.36 % while the rest oxides; CaO (14.08%), Al2O3 (6. 76%), Fe2O3 (3.05%), K2O+Na2O (2.30 %) are considered as impurities that could affect the properties of sand. XRD tests indicated the formation of crystalline phase of synthetic silica. XRF showed an increases in SiO2 to 85.37%, while all other oxides (impurities) were reduced to their minimum rate, particularly CaO (1.06 %). Field emission scanning electron microscope (FESEM) and Brunauer-Emmett-Teller (BET) tests indicated the existence of well compiled spherical particles of synthetic silica within the size of 8.55 nm and surface area of 66.51 m2\g. The medium sand size (0.250-0.500mm) is the appropriate size to produce high purity crystalline silica as it contains the greatest percentage of silica and the low percent of impurities compared to other sizes of sand.


Introduction:
Sand dune is an abundant natural material that occurs in many parts of the world [1] The sand dunes have a distinct mineral content, as well as a distinct texture in both size and form of the naturally sorted grains.Many sectors can benefit from these combined properties as a low-cost raw material [2] Sand is one of the important raw materials for many different industries, whether used as a natural form or after make some treatments or improvements in order to be used in other applications [3].Different methods for preparation silica have been applid such as emulsions [4], sol-gel [5], Stöber method [6] hydrothermal, alkaline fusion [7], coprecipitation, and electrocoagulation [8].A type of technology known as the coprecipitation method uses chemicals to create a solute and then wait for the desired precipitate to develop., when compared coprecipitation method to other conventional methods, it is simple method to separate the production at short time and low temperature [9].The equipment utilized is simple and inexpensive allowing for the production of a powder with a specific crystal size..The present study aims to assess the suitability of sand dunes in Missan area, southeastern Iraq as low-cost raw materials to produce high purity crystalline silica using coprecipitation methods.

Materials and Methods
The study area includes the sand dune fields located at the north-east of Missan area, at latitude (32˚ 21' 0''-32 ˚ 36' 00'')N.and longitude (46 ˚53' 00''-47 ˚21' 00'' )E, includes the following stations; Manziliyah, Khazina Zubadiate ,and Chailat, Figure .1,Eleven samples from sand dunes were gathered based on how they dispersed throughout the field.During October 2020, Sand samples were subjected to sieve to sand sizes 0.063-2 mm, 0.250-0.500mm,and 0.125-0.250mm.Raw sand (total, medium, and fine size) have been analysed using X-ray diffraction technique at the Ministry of Science and Technology in Iraq uses PW3830 comprehensive X-ray devices, and chemically employs the X-ray fluoresces (XRF) technique at the University of Baghdad, Iraq.Then, sand samples were grinded by a clean electric agate mortar to 200 mesh [10].For a full day, the powder samples were immersed in 37% of a 2M hydrochloric solution, Figure 2 , Immersion of sand in HCl acid can lessen contaminants in raw material [9] After being filtered and rinsed with distilled water until the pH reaches neutral, the sand is dried at 100°C for two hours.[11].The obtained sand was identified and assessed using XRD and XRF after the immersion process.Next, sand was immersed in 7M NaOH (99%) at 95 °C for 3-4 hours using a magnetic stirrer [11]; [7],Afterward, silicic acid was prepared by add 2M HCl to prepare sodium silicate solution .Ten times, distilled water was used to wash away the NaCl from the silicic acid [7].After filtering, the silicic acid was dried at 110 °C for 2-3 hours.[12].After that, the agglomerated silica are ground in to produce silica powder.XRD was used to identify the silica powder (Figure .3) in order to look into the phase formation.Utilizing the XRF technique, the elemental composition is also assessed.Fourier transform infrared spectrometry (FTIR) Type: FTIR-8400S (SHIMADZU) at University of Basra was apply to detect the synthetic silica functional groups,.Field emission scanning electron microscopy (FESM-EDS) in Tehran University, Iran, was used to demonstrate the morphology and image of crystal form, and Bruner-Emmett-Teller (BET) technique: BEL Prep VAC II type in Tehran University, Iran, was also apply to determine the specific surface area of prepared silica.

3-Results and Discussion 3-1 Reaction Mechanism
Sodium silicate solid is formed by immersion raw sand in sodium hydroxide and heating to a temperature of 95˚C.

3-2-2 Chemical Assessment
The result of XRF analysis of the raw sand is listed in Table 1, Figure 6, It indicates that the predominant oxides, are SiO2, CaO, Al2O3, Fe2O3, and alkali (K2O+Na2O) of 60.81 %, 13.58 %, 6. 81%, 3.05 %, and 2.22 % respectively.While the other oxides tend to be concentrated in the fine sand fractions, except of SiO2 and P2O5 which are abundant in the medium sand fractions.Table 2.These statistics indicate that there is an increase of about 17.04 % of SiO2 content in comparison to its concentrations in raw sand materials (60.81%) after immersion by HCl Table 3 and 4, Figure 7, which clearly indicates the dissolved of some oxides (impurities) as a result of the immersion process especially CaO which reduced by 13.04% from the initial content.

3-3 Characterization of Crystalline Silica 3-3-1 XRD Assessment
XRD results of synthetic silica Figure 8 demonstrates that there is no discernible difference between the examined samples' mineralogical composition and their composition following the immersion process.The new phases formed are crystalline silica.

4-Conclusions
The main conclusions of this study are: 1-The immersion of raw sand materials in HCl is an effective process to dissolved and reduce the impurities especially the CaO.In addition to reduce other oxides to a minimum amount.2-It is possible to extracted crystalline silica form sand dune, the Si-O-Si and Si-O groups of synthetic silica are distinguished by their typical absorption bands of 790.84 cm -1 and 451.36 cm -1 , respectively.3-Agglomerated and spherical crystalline silica particles measuring 7.86 nm were detected by the SEM test, and 66.51 m 2 \ g of specific surface area was revealed by the BET method.4-The percentage of silica in the fine sand size is low and the percentage of impurities is high so it cannot be relied upon to produce high purity silica whereas the medium sand size is the appropriate size to produce high purity crystalline silica.5-Manziliyah sand is the best sand for the synthesis of crystalline silica because of low impurities, followed by zubaidate, Chailat and Khazina sand.6-High purity crystalline silica has been successfully synthesized from four different locations from Missan dune fields, South-eastern of Iraq, including Manziliyah, Khazina, Zubadiate, and Chailat by means of coprecipitation method using NaOH (The percentage of SiO2 in sands of the study area were increased by the coprecipitation method from 60.81% to 85.37% ).

2 Figure 1 .
Figure 1.The study area and sample locations.

Figure 2 :
Figure 2: Diagram for the coprecipitation process of producing synthetic silica from sand dunes.

Figure 3 :
Figure 3: High-purity crystalline silica preparation3-2 Characterization of Raw Sand 3-2-1 XRD AssessmentSamples were scanned at 2-theta (2-60°) using XRD technique, the XRD characterization of the studied sand (total, medium, and fine size) revealed that quartz, is the predominant mineral in sand followed by feldspar, calcite and gypsum, Figure4.XRD data for the sample that immersed in HCl showed the presence of quartz and feldspar only, Figure5.These results indicate that the immersion process is effective to reduce the amount of calcite and gypsum.

Table 2 :
Medium and fine sand size chemical analysis

Table 3 :
Chemical examination of the entire sand particle following immersion

Table 4 :
Chemical examination of medium and, fine sand upon immersion Figure 6: Major oxide average in sand dunes Figure 7: Major oxides after immersion

Table 5 :
Synthetic silica chemical analysis based on the overall size of the sand