| الملخص | ABSTRACT
A detailed beneficiation study was conducted on samples from Ardhuma quartz sand to provide raw material for silicon production. The beneficiation includes various techniques; vibrating screening (wet&dry), attrition scrubbing and magnetic separation (wet&dry). These techniques were used individually or in combination for the production of quartz sand fulfill the requirements of MG- silicone raw materials.
Quartz sand product assaying (SiO2 99.49, Fe2O3 0.011, Al2O3 0.23, TiO2 0.03, CaO 0.03, MgO <0.01, SO3 0.04, L.O.I 0.09, Na2O 0.03, K2O 0.02 and P2O5 0.01)% was obtained applying beneficiation techniques consisted of autogeneses grinding, dry screening (150µ), attrition scrubbing and wet screening (150µ), The product is satisfied for the raw material of MG-Silicon production.
Keyword: MG-silicon, Silicon industries, Quartz sand, Ardhuma deposit, Autogenouse grinding.
INTRODUCTION
After Oxygen, silicon is the second most abundant element (27.5%) in the lithosphere. It does not occur in elemental form, but only in oxides and silicates. Since the turn of the 20th century, silicon has been produced almost exclusively by carbothermal reduction of silicon dioxide:
SiO2 +2C Si+2CO………… H298 = 695kj
The carbothermal process yields silicon with a purity of 98% (metallurgical-grade silicon, MG-Si). The usual starting materials are chunks of quartzite, coke coal, as well as charcoal and wood chips for good ventilation of charge. To produce 1 ton of silicon, 2.9-3.1 ton of quartz or quartzite, 1.2-1.4 ton coke (gas coke and petroleum coke are required. The purity of the silicon produced depends primarily on the purity of these materials and secondarily on the purity of the graphite electrodes and the furnace lining. The purity of silicon can be increased by using purer starting materials (Zulehner, 2005). Silicon is a life necessity. In 2002, statistics reported by Dow corning company showed that, world production around one million ton of silicones, which is equivalent to 9 billion US Dollars covering 50% silicon oils, 40% silicon rubbers, 10% silicon resins. A rough estimation stated that Iraq, the Arab world and the Middle East import silicones of several hundred million dollars, for the this reason and due to the presences of high reserves of pure silica sand (SiO2>98 %), as well as oil and petrochemical industries in Iraq, silicon and silicones technology become vital for the future national economy (Ibn Sina State Company, 2010).
The grade of quartz raw materials depends on the required grade of the products. Metallurgical – Grade Silicon with 99 % is required a high grade of quartz materials as shown in table (1).
MATERIALS AND METHODS
• Materials: Raw silica sand sample of (50Kg) from Ardhuma location table (2).
• Methods :
1- Single Process:
-Screening (Dry & Wet): Dry screening experiments were conducted using sieves openings of (850, 600 and 150) µm and fractions in the ranges of (-850+150), (-600 +150) and (+150) µ were collected as products. Wet screening experiment was carried out on (150) µ sieve opening (ASTM) using sieve device type (RETSCH).
2- Combined process: In addition to the screening, several techniques were used in combination so as to improve process efficiency. These techniques include:
-Magnetic separation (Dry & Wet): Raw silica sand samples of 100 gm were processed using dry high intensity magnetic separator device type (OUTOTECH), magnetic separation was performed with a magnetic field intensity of about (16.5) Kilogauss. The wet magnetic separation experiment was done on 100 gm of silica sand using wet high intensity magnetic separator device type (CARPCO) with a magnetic field of about (7 Kilogauss), to increase the magnetic field force a small stainless steel balls was used for this purpose and the slurry (25% solid percent ) passed slowly through these balls.
-Attrition Scrubbing: Samples of silica sand were processed using attrition scrubbers type (DENVER). The products were either further processed by magnetic separation or simply passed through 150µ sieve.
-Autogenously grinding: It’s a process where sand allowed for mixing and grinding by itself. This process was applied to improve the screening process through liberating clay fine particles away from sand particles, thus, minimizing the impurities incorporated with the sand.
RESULTS AND DISCUSSION
1-Single Process:
Screening (Dry & Wet): Several experiments were conducted to up-grade the silica sand of Ardhuma using sieves of different pores (850, 600 and 150) µ. The screening process was achieved under dry and wet conditions. As it shown in table (3) screening process has a high contribution to the up-grading of Ardhuma silica sand. Both wet and dry screenings increases the SiO2 contents and decrease the other components, but only in a limited extent. While the samples that were pre-autogenously ground of (+150) µ particle size were contain several components such as (SiO2, Al2O3, CaO, P2O5, SO3, Na2O, K2O and L.O.I) % that are compatible to the requirements of MG-Silicon raw materials. However, when autogenouse grinding was applied, the product has markedly lesser SiO2 content; this is encouraged the applying of this technique in the next experiments.
2-Combined Processes:
Attrition Scrubbing: In order to improve the specifications of the screening products, several experiments were done using a combined technique of screening and attrition scrubbing. It is obvious from the result shown in table (4), that attrition scrubbing (1000 rpm for 1 hr.) was a good mean in improving the efficiency of screening and vice versa. A combination of autogenouse grinded sand of +150µ particle size, followed by attrition scrubbing, obtained a product meets the requirements of the MG-Silicon raw materials. The removal of the fine impurities can be occurred by the action autogenouse grinding and screening, while the iron-contaminants particularly these staining the surface of the sand particles, was highly reduced by high attrition activity.
3- Magnetic Separation
-Dry high intensity magnetic separation
High intensity magnetic separator was used at dry and wet conditions with a magnetic field of about 16 and 7 kilo gauss respectively. Firstly, a set of experiments consisting of dry magnetic separation followed by screening (wet & dry) and/or attrition scrubbing were conducted. The results shown in table (5), pointed out that a combination of autogenously grinding plus dry screening on 150µ sieve in addition to a magnetic separation step could be feasible method for sand up-grading, hence, the product match the requirements of MG-Silicon raw materials. This may due to the sequence of the whole process, where a lot of fine impurities (majorly clay) were removed through autogenouse grinding and screening. While, magnetic separation eliminate as much as possible of iron-contaminants.
-Wet high-intensity magnetic separation.
Another set of experiments were done using wet high-intensity magnetic separation, with a magnetic field of about (7 Kilo Gauss) assisted by small steel balls. The results in table (6) shows clearly that products obtained by combinations including wet magnetic separation have no privilege upon previous methods, furthermore, it is much expensive than the previous methods, considering water and power consumption.
Two major conclusions can be extracted from this experimental work:
1. Attrition scrubbing and magnetic separation, used individually or in combination altogether with screening producing silica sand compatible to the requirement of silicon production raw materials.
2. Autogenouse grinding has a high contribution to the sand up-grading.
REFERENCES
1-Ibn Sina State Company, 2010. Production of silica and silicones from Iraqi silica sand, a paper submitted to the symposium of the production of silicon & silicones from Iraq silica sand.
2-State Company of Mining Industries and Aquatic Insulation, 2011. Physical & chemical requirements for silicon production.
3-Zulehner W., 2005. Silicon (chaps 1-4), Ullmann’s encyclopedia of industrial chemistry, Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim.
Table 1: Chemical composition required for Metallurgical-Grade Silicon production (2).
Component SiO2 Fe¬2O3 Al¬2O3 TiO2 CaO MgO P2O5 SO3 Na2O K2O L.O.I
% 99 min. 0.03 max. 0.5 max. trace 0.1 max. 0.006 max. 0.4 max. 0.5 max. 0.25 max. 0.05 max. 0.2 max.
Table 2: Chemical composition of Ardhuma silica sand.
Chemical Composition SiO2 Fe2O3 Al2O3 CaO TiO2 SO3 L.O.I MgO Na2O K2O
% 98.76 0.085 0.48 0.23 0.18 0.07 0.20 0.032 0.03 0.01
Table 3: Chemical composition of products obtained from screening (wet & dry).
Treatment SiO2% Fe2O3% Al2O3% TiO2% CaO% MgO% SO3% Na2O% K2O% P2O5% L.O.I%
-Dry screening (-850+150)µ 98.45 0.083 0.39 0.15 0.25 0.038 - 0.02 0.02 - 0.21
-Dry screening (-600+150)µ 98.45 0.065 0.31 0.12 0.20 0.040 - 0.03 0.02 - 0.12
-Dry screening (+150)µ 98.24 0.039 0.33 0.03 0.19 0.040 - - - - 0.20
-Wet screening (+150)µ 99.15 0.035 0.32 0.07 0.16 0.040 0.06 0.03 0.04 0.01 0.21
-Auto. Grind. & Dry screening (+150)µ 99.21 0.024 0.28 0.03 0.16 0.020 0.07 0.03 0.02 0.01 0.10
-Auto. Grind.& Wet screening (+150)µ 99.21 0.035 0.27 0.07 0.04 0.020 0.07 0.03 0.02 0.01 0.20
Table 4: Chemical composition of products obtained from attrition scrubbing & wet Screening combined experiments.
Treatment SiO2% Fe2O3% Al2O3% TiO2% CaO% MgO% SO3% Na2O% K2O% P2O5% L.O.I%
-Attrition Scrubbing
-Wet Screening (+ 150)µ 99.00 0.03 0.44 0.08 0.05 0.03 0.03 0.03 0.04 0.01 0.16
- Dry screening (-600+150)µ
-Attrition Scrubbing
-Wet Screening (+ 150)µ 99.10 0.027 0.46 0.06 0.05 0.03 0.03 0.03 0.04 0.01 0.16
- Dry screening (+150)µ
-Attrition Scrubbing
-Wet Screening ( +150)µ 99.11 0.027 0.35 0.06 0.04 0.02 0.03 0.02 0.03 0.01 0.16
- Autogenouse grinding
- Dry Screening ( +150)µ
-Attrition Scrubbing
-Wet Screening (+150)µ 99.48 0.011 0.23 0.03 0.03 <0.01 0.04 0.02 0.02 0.01 0.09
-Wet screening (+150)µ
-Attrition Scrubbing
- Wet Screening ( +150)µ 99.49 0.026 0.21 0.06 0.04 0.01 0.03 0.02 0.04 0.01 0.08
Table 5: Chemical composition of products obtained from Dry high intensity magnetic separation, attrition scrubbing, dry & wet screening combined experiments.
Treatment SiO2% Fe2O3% Al2O3% TiO2% CaO% MgO% SO3% Na2O% K2O% P2O5% L.O.I%
-Dry magnetic separation 99.02 0.04 0.5 0.05 0.12 0.01 0.09 0.01 0.08 0.01 0.25
-Dry magnetic separation
-Attrition Scrubbing
- Wet Screening ( +150) µ 99.27 0.03 0.38 0.03 0.04 <0.01 0.07 0.01 0.01 0.01 0.2
-Dry screening (-600+150) µ
-Dry magnetic separation 99.11 0.04 0.44 0.03 0.06 <0.01 0.04 0.01 0.07 0.01 0.22
-Dry screening (+150) µ
-Dry magnetic separation 99.20 0.03 0.41 0.03 0.04 <0.01 0.04 0.01 0.06 0.01 0.2
-Autogenouse Grinding
-Dry screening ( +150) µ
-Dry magnetic separation 99.24 0.02 0.29 0.03 0.04 <0.01 0.04 0.01 0.01 0.01 0.2
-Wet screening (+150)µ
-Dry magnetic separation 99.21 0.03 0.39 0.03 0.04 <0.01 0.04 0.01 0.01 0.01 0.2
- Autogenouse grinding
-Dry magnetic separation
-Attrition Scrubbing
-Wet screening (+150)µ 99.34 0.02 0.24 0.02 0.03 <0.01 0.04 0.01 0.01 0.01 0.12
Table 6: Chemical composition of products obtained from wet high intensity magnetic separation scrubbing& wet screening combined experiments.
Treatment SiO2% Fe2O3% Al2O3% TiO2% CaO% MgO% SO3% Na2O% K2O% P2O5% L.O.I%
-Autogeneses grinding
-Wet magnetic separation
- Wet Screening (+150 ) 99.06 0.04 0.41 0.04 0.12 0.01 0.07 0.01 0.09 0.02 0.20
-Autogeneses grinding
-Dry Screening (+150 )
-Wet magnetic separation 99.08 0.03 0.32 0.04 0.06 0.01 0.06 0.01 0.06 0.01 0.2
- Attrition Scrubbing
-Wet magnetic separation
-Wet Screening (+150 ) 99.13 0.03 0.3 0.03 0.03 <0.01 0.04 0.01 0.01 0.01 0.15 | en_US |
