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Peralatan ST & Teknologi LLC (STET) pemisah tali pinggang tribo-electrostatic is ideally suited for beneficiating very fine (<1µm) kepada sederhana coarse (500µm) mineral particles, with very high throughput. Experimental findings demonstrated the capability of the STET separator to beneficiate bauxite samples by increasing available alumina while simultaneously reducing reactive and total silica. STET technology is presented as a method to upgrade and pre-concentrate bauxite deposits for use in alumina production. Dry processing with the STET separator will result in a reduction in operating costs of refinery due to lower consumption of caustic soda, savings in energy due to lower volume of inert oxides and a reduction in volume of alumina refinery residues (ARR or red mud). sebagai tambahan, the STET technology may offer alumina refiners other benefits including increased quarry reserves, extension of red mud disposal site life, and extended operating life of existing bauxite mines by improving quarry utilization and maximizing recovery. The water-free and chemical-free by-product produced by the STET process is usable for manufacture of cement in high volumes without pre-treatment, in contrast to red mud which has limited beneficial reuse.
1.0 Pengenalan
Aluminum production is of central importance for the mining and metallurgy industry and fundamental for a variety of industries [1-2]. While aluminum is the most common metallic element found on earth, in total about 8% kerak Bumi, as an element it is reactive and therefore does not occur naturally [3]. Hence, aluminum-rich ore needs to be refined to produce alumina and aluminum, resulting in significant generation of residues [4]. As the quality of bauxite deposits globally decline, the generation of residue increases, posing challenges to the alumina and aluminum-making industry in terms of processing costs, costs of disposal and the impact on the environment [3].
Bahan permulaan utama untuk penapisan aluminium adalah bauksit, sumber komersial utama dunia aluminium [5]. Bauxite is an enriched aluminum hydroxide sedimentary rock, produced from the laterization and weathering of rocks rich in iron oxides, aluminum oxides, or both commonly containing quartz and clays like kaolin [3,6]. Bauxite rocks consists mostly of the aluminum minerals gibbsite (Al(Oh)3), boehmite (γ-AlO(Oh)) dan diaspore (α-AlO(Oh)) (Jadual 1), and is usually mixed with the two iron oxides goethite (FeO(Oh)) dan hematite (Fe2O3), the aluminum clay mineral kaolinite, small amounts of anatase and/or titania (TiO2), ilmenite (FeTiO3) and other impurities in minor or trace amounts [3,6,7].
The terms trihydrate and monohydrate are commonly used by industry to differentiate various types of bauxite. Bauxite that is totally or nearly all gibbsite bearing is called a trihydrate ore; if boehmite or diaspore are the dominant minerals it is referred to as monohydrate ore [3]. Mixtures of gibbsite and boehmite are common in all types of bauxites, boehmite and diaspore less common, and gibbsite and diaspore rare. Each type of bauxite ore presents its own challenges in terms of mineral processing and beneficiation for the generation of alumina [7,8].
Jadual 1. Chemical composition of Gibbsite, Boehmite and Diaspore [3].
| Chemical Composition | Gibbsite AL(Oh)3 or Al2O3.3H2O | Boehmite ALO(Oh) or Al2O3.H2O | Diaspore ALO(Oh) or Al2O3.H2O |
|---|---|---|---|
| Al2O3 wt% | 65.35 | 84.97 | 84.98 |
| (Oh) wt% | 34.65 | 15.03 | 15.02 |
Deposit Baxite tersebar di seluruh dunia, kebanyakannya berlaku di kawasan tropika atau subtropika [8]. Bauxite mining of both metallurgical and non-metallurgical grade ores is analogous to the mining of other industrial minerals. Normally, the beneficiation or treatment of bauxite is limited to crushing, sieving, washing, and drying of the crude ore [3]. Flotation has been employed for the upgrading of certain low-grade bauxite ores, however it has not proven highly selective at rejecting kaolinite, a major source of reactive silica especially in trihydrate bauxites [9].
The bulk of bauxite produced in the world is used as feed for manufacturing of alumina via the Bayer process, a wet-chemical caustic-leach method in which the Al_2 O_3 is dissolved out of the bauxite rock by using a caustic soda rich solution at elevated temperature and pressure [3,10,11]. Subsequently, the bulk of alumina is utilized as feed for the production of aluminum metal via the Hall-Héroult process, which involves electrolytic reduction of alumina in a bath of cryolite (Na3AlF6). It takes about 4-6 tons of dried bauxite to produce 2 t of alumina, which in turns yields 1 t of aluminum metal [3,11].
The Bayer process is initiated by mixing washed and finely ground bauxite with the leach solution. The resulting slurry containing 40-50% solids is then pressurized and heated with steam. At this step some of the alumina is dissolved and forms soluble sodium aluminate (NaAlO2), but due to the presence of reactive silica, a complex sodium aluminum silicate also precipitates which represents a loss of both alumina and soda. The resulting slurry is washed, and the residue generated (Iaitu., red mud) is decanted. Sodium aluminate is then precipitated out as aluminum trihydrate (Al(Oh)3) through a seeding process. The resulting caustic soda solution is recirculated into the leach solution. Akhirnya, the filtered and washed solid alumina trihydrate is fired or calcined to produce alumina [3,11].
Leaching temperatures may range from 105°C to 290°C and corresponding pressures range from 390 kPa to 1500 kPa. Lower temperatures ranges are used for bauxite in which nearly all the available alumina is present as gibbsite. The higher temperatures are required to digedepositsst bauxite having a large percentage of boehmite and diaspore. At temperatures of 140°C or less only gibbsite and kaolin groups are soluble in the caustic soda liquor and therefore such temperature is preferred for the processing of trihydrate alumina . At temperatures greater than 180°C alumina present as trihydrate and monohydrate are recoverable in solution and both clays and free quartz become reactive [3]. Operating conditions such as temperature, pressure and reagent dosage are influenced by the type of bauxite and therefore each alumina refinery is tailored to a specific type of bauxite ore. Kehilangan soda kaustik mahal (NaOH) and the generation of red mud are both related to the quality of bauxite used in the refining process. Secara umum, the lower the Al_2 O_3 content of bauxite, lebih besar jumlah lumpur merah yang akan dijana, as the non-Al_2 O_3 phases are rejected as red mud. sebagai tambahan, the higher the kaolinite or reactive silica content of bauxite, lebih banyak lumpur merah akan dijana [3,8].
High-grade bauxite contains up to 61% Al_2 O_3, and many operating bauxite deposits -typically referred as non-metallurgical grade- are well below this, kadang-kadang serendah 30-50% Al_2 O_3. Because the desired product is a high purity
Al_2 O_3, baki oksida di baitulit (Fe2O3, SiO2, TiO2, organic material) are separated from the Al_2 O_3 and rejected as alumina refinery residues (ARR) or red mud via the Bayer process. Secara umum, kualiti ba bauxite yang lebih rendah (Iaitu., lower Al_2 O_3 content) the more red mud that is generated per ton of alumina product. sebagai tambahan, even some Al_2 O_3 bearing minerals, terutamanya kaolinite, produce undesirable side reactions during the refining process and lead to an increase in red mud generation, serta kehilangan bahan kimia soda kaustik yang mahal, kos pembolehubah besar dalam proses penapisan baja [3,6,8].
Lumpur merah atau ARR mewakili cabaran besar dan berterusan untuk industri aluminium [12-14]. Lumpur merah mengandungi sisa bahan kimia kausa yang ketara dari proses penapisan, dan sangat alkali, selalunya dengan pH 10 – 13 [15]. It is generated in large volumes worldwide – according to the USGS, anggaran pengeluaran alumina global 121 juta tan dalam 2016 [16]. This resulted in an estimated 150 juta tan lumpur merah yang dihasilkan dalam tempoh yang sama [4]. Walaupun penyelidikan berterusan, lumpur merah pada masa ini mempunyai beberapa laluan yang berdaya maju secara komersial untuk kegunaan semula yang bermanfaat. Dianggarkan bahawa sangat sedikit lumpur merah dinaikkan semula di seluruh dunia [13-14]. Sebaliknya, the red mud is pumped from the alumina refinery into storage impoundments or landfills, di mana ia disimpan dan dipantau dengan kos yang besar [3]. Oleh itu, both an economic and environmental argument can be made for improving the quality of bauxite prior to refining, in particular if such improvement can be done through low-energy physical separation techniques.
While proven reserves of bauxite are expected to last for many years, kualiti rizab yang boleh diakses secara ekonomi semakin menurun [1,3]. Untuk penapis, yang berada dalam perniagaan pemprosesan bauksit untuk membuat alumina, dan akhirnya logam aluminium, ini adalah satu cabaran dengan implikasi kewangan dan alam sekitar
Dry methods such as electrostatic separation may be of interest of the bauxite industry for the pre-concentration of bauxite prior to the Bayer process. Electrostatic separation methods that utilize contact, or tribo-electric, charging is particularity interesting because of their potential to separate a wide variety of mixtures containing conductive, insulating, and semi-conductive particles. Tribo-electric charging occurs when discrete, dissimilar particles collide with one another, or with a third surface, resulting in a surface charge difference between the two particle types. The sign and magnitude of the charge difference depends partly on the difference in electron affinity (or work function) between the particle types. Separation can then be achieved using an externally applied electric field.
The technique has been utilized industrially in vertical free-fall type separators. In free-fall separators, the particles first acquire charge, then fall by gravity through a device with opposing electrodes that apply a strong electric field to deflect the trajectory of the particles according to sign and magnitude of their surface charge [18]. Free-fall separators can be effective for coarse particles but are not effective at handling particles finer than about 0.075 untuk 0.1 mm [19-20]. One of the most promising new developments in dry mineral separations is the tribo-electrostatic belt separator. Teknologi ini telah memperluaskan julat saiz zarah kepada zarah yang lebih halus daripada teknologi pemisahan elektrostatik konvensional, ke dalam julat di mana hanya pengapungan telah berjaya pada masa lalu.
Tribo-electrostatic separation utilizes electrical charge differences between materials produced by surface contact or triboelectric charging. In simplistic ways, when two materials are in contact, the material with a higher affinity for electros gains electrons thus changes negative, manakala bahan dengan caj pertalian elektron yang lebih rendah positif.
Peralatan ST & Teknologi (STET) tribo-electrostatic belt separator offers a novel beneficiation route to pre-concentrate bauxite ores. Proses pemisahan kering STET menawarkan pengeluar bauksit atau penapisan bauksit peluang untuk melakukan peningkatan pra-Bayer bijih bauxite untuk meningkatkan kualiti. Pendekatan ini mempunyai banyak faedah, Termasuk: Pengurangan kos operasi kilang penapisan disebabkan penggunaan soda kaustik yang lebih rendah dengan mengurangkan input sedlika reaktif; savings in energy during refining due to lower volume of inert oxides (Fe2O3, TiO2, Non-reactive SiO2) memasuki dengan bacelah; smaller mass flow of bauxite to refinery and therefore less energy requirement to heat and pressurize; reduction in red mud generation volume (Iaitu., lumpur merah kepada nisbah alumina) by removing reactive silica and inert oxide; Dan, tighter control over input bauxite quality which reduces process upsets and allows refiners to target ideal reactive silica level to maximize impurity rejection. Improved quality control over bauxite feed to refinery also maximizes uptime and productivity. Selain itu, reduction in red mud volume translates into less treatment and disposal costs and better utilization of existing landfills.
The preprocessing of bauxite ore prior to the Bayer process may offer significant advantages in terms of processing and sales of tailings. Tidak seperti lumpur merah, ekor dari proses elektrostatik kering tidak mengandungi bahan kimia dan tidak mewakili liabiliti penyimpanan alam sekitar jangka panjang. Tidak seperti lumpur merah, produk/ekor kering dari operasi pra-pemprosesan bauksit boleh digunakan dalam pembuatan simen kerana tiada keperluan untuk membuang natrium, yang memudaratkan pembuatan simen. In fact – bauxite is already a common raw material for Portland cement manufacturing. Extending operating life of existing bauxite mines may also be reached by improving quarry utilization and maximizing recovery.
2.0 Experimental
2.1 Materials
STET conducted pre-feasibility studies in over 15 different bauxite samples from different locations around the world using a bench-scale separator. Daripada ini, 7 different samples were
Jadual 2. Result of chemical analysis bauxite samples.
2.2 Methods
Experiments were conducted using a bench-scale tribo-electrostatic belt separator, hereafter referred as ‘benchtop separator’. Bench-scale testing is the first phase of a three-phase technology implementation process (Lihat Jadual 3) including bench-scale evaluation, pilot-scale testing and commercial-scale implementation.
The benchtop separator is used for screening for evidence of tribo-electrostatic charging and to determine if a material is a good candidate for electrostatic beneficiation. The main differences between each piece of equipment are presented in Table 3. While the equipment used within each phase differs in size, the operation principle is fundamentally the same.
Jadual 3. Three-phase implementation process using STET tribo-electrostatic belt separator technology
| Phase | Used for: | Electrode Length cm | Type of Process |
|---|---|---|---|
| 1- Bench Scale Evaluation | Qualitative Evaluation | 250 | Batch |
| 2- Pilot Scale Ujian | Quantitative evaluation | 610 | Batch |
| 3- Commercial Scale Implementation | Commercial Production | 610 | Continuous |
As can be seen in Table 3, the main difference between the benchtop separator and pilot-scale and commercial-scale separators is that the length of the benchtop separator is approximately 0.4 times the length of pilot-scale and commercial-scale units. As the separator efficiency is a function of the electrode length, bench-scale testing cannot be used as a substitute for pilot-scale testing. Pilot-scale testing is necessary to determine the extent of the separation that the STET process can achieve, and to determine if STET process can meet the product targets under given feed rates. Sebaliknya, the benchtop separator is used to rule out candidate materials that are unlikely to demonstrate any significant separation at the pilot-scale level. Results obtained on the bench-scale will be non-optimized, and the separation observed is less than which would be observed on a commercial sized STET separator.
Testing at the pilot plant is necessary prior to commercial scale deployment, Walau bagaimanapun, testing at the bench-scale is encouraged as the first phase of the implementation process for any given material. Lebih-lebih lagi, in cases in which material availability is limited, the benchtop separator provides a useful tool for the screening of potential successful projects (Iaitu., projects in which customer and industry quality targets can be met using STET technology).
2.2.1 STET Triboelectrostatic Belt Separator
In the tribo-electrostatic belt separator (Rajah 1 and Figure 2), bahan diberi makan ke dalam jurang nipis 0.9 – 1.5 cm between two parallel planar electrodes. Zarah-zarah dicaj secara triboelektik oleh kenalan interparticle. Sebagai contoh, in the case of a bauxite sample which main constituents are gibssite, kaolinite and quartz mineral particles, the positively charged (gibssite) and the negatively charged (kaolinite and quartz) are attracted to opposite electrodes. Zarah-zarah kemudian disapu oleh tali pinggang terbuka yang berterusan dan disampaikan ke arah yang bertentangan. Tali pinggang menggerakkan zarah bersebelahan setiap elektrod ke arah hujung bertentangan pemisah. Medan elektrik hanya perlu menggerakkan zarah pecahan kecil sentimeter untuk menggerakkan zarah dari kiri bergerak ke aliran yang bergerak kanan. The counter current flow of the separating particles and continual triboelectric charging by particle collisions provides for a multi-stage separation and results in excellent purity and recovery in a single-pass unit. Kelajuan tali pinggang yang tinggi juga membolehkan kendandahan yang sangat tinggi, selewat-lewatnya 40 tonnes per hour on a single separator. Dengan mengawal pelbagai parameter proses, the device allows for optimization of mineral grade and recovery.
Rajah 1. Skema pemisah tali pinggang triboelektrik
Reka bentuk pemisah agak mudah. Tali pinggang dan penggelek yang berkaitan adalah satu-satunya bahagian yang bergerak. Elektrod-elektrod adalah alat tulis dan terdiri daripada bahan tahan lama yang sesuai. Tali pinggang diperbuat daripada bahan plastik. Pemisah elektrod panjang adalah kira-kira 6 meter (20 Ka.) dan lebar 1.25 meter (4 Ka.) bagi unit-unit komersil saiz penuh. The power consumption is less than 2 kilowatt-hour per tonne of material processed with most of the power consumed by two motors driving the belt.
Rajah 2. Terperinci zon pengasingan
Proses ini sama sekali Kering, memerlukan bahan-bahan tambahan yang tiada dan menghasilkan tiada sisa pelepasan air atau udara. For mineral separations the separator provides a technology to reduce water usage, extend reserve life and/or recover and reprocess tailings.
Kekopatan sistem membolehkan fleksibiliti dalam reka bentuk pemasangan. The tribo-electrostatic belt separation technology is robust and industrially proven and was first applied industrially to the processing of coal combustion fly ash in 1997. The technology is effective in separating carbon particles from the incomplete combustion of coal, daripada zarah mineral aluminosilicate sayu pada Abu Terbang. Teknologi ini memainkan peranan penting dalam membolehkan kitar semula abu terbang kaya mineral sebagai pengganti simen dalam pengeluaran konkrit.
Sejak 1995, over 20 million tonnes of product fly ash have been processed by the STET separators installed in the USA. Sejarah perindustrian pemisahan abu terbang disenaraikan dalam Jadual 4.
In minerals processing, the triboelectric belt separator technology has been used to separate a wide range of materials including calcite/quartz, ENCHANTEUR di samping bedak/magnesite, dan barite/kuarza.
Rajah 3. Commercial tribo-electrostatic belt separator
Jadual 4. Industrial application of tribo-electrostatic belt separation for fly ash.
| Utiliti / stesen janakuasa | Lokasi | Start of commercial operations | Facility details |
|---|---|---|---|
| Duke tenaga – Stesen Roxboro | North Carolina Amerika Syarikat | 1997 | 2 Pemisah |
| Talen tenaga- Brandon Shores | Maryland Amerika Syarikat | 1999 | 2 Pemisah |
| Kuasa Scotland- Stesen Longannet | Scotland UK | 2002 | 1 Pemisah |
| Jacksonville Electric-St. Johns River Power Park | Florida Amerika Syarikat | 2003 | 2 Pemisah |
| South Mississippi Electric Power -R.D. Morrow | Mississippi Amerika Syarikat | 2005 | 1 Pemisah |
| Brunswick Baru Power-Belledune | Baru Brunswick Kanada | 2005 | 1 Pemisah |
| Stesen RWE npower-Didcot | England UK | 2005 | 1 Pemisah |
| Talen Energy-Brunner Island Station | Pennsylvania Amerika Syarikat | 2006 | 2 Pemisah |
| Stesen Selekoh Elektrik-Besaran Tampa | Florida Amerika Syarikat | 2008 | 3 Pemisah |
| Stesen RWE npower-Aberthaw | Wales UK | 2008 | 1 Pemisah |
| Stesen Burton EDF Energy-West Burton | England UK | 2008 | 1 Pemisah |
| ZGP (Lafarge Cement /Ciech Janikosoda JV) | Poland | 2010 | 1 Pemisah |
| Kuasa Korea Tenggara- Yeongheung | Korea Selatan | 2014 | 1 Pemisah |
| PGNiG Termika-Sierkirki | Poland | 2018 | 1 Pemisah |
| Taiheiyo Cement Company-Chichibu | Japan | 2018 | 1 Pemisah |
| Armstrong Fly Ash- Eagle Cement | Philippines | 2019 | 1 Pemisah |
| Kuasa Korea Tenggara- Samcheonpo | Korea Selatan | 2019 | 1 Pemisah |
2.2.2 Bench-scale testing
Standard process trials were performed around the specific goal to increase Al_2 O_3 concentration and to reduce the concentration of gangue minerals. Tests were conducted on the benchtop separator under batch conditions, with testing performed in duplicate to simulate steady state, and ensure that any possible carryover effect from the previous condition was not considered. Prior to each test, a small feed sub-sample was collected (designated as ‘Feed’). Upon setting all operation variables, the material was fed into the benchtop separator using an electric vibratory feeder through the center of the benchtop separator. Samples were collected at the end of each experiment and the weights of product end 1 (designated as ‘E1’) and product end 2 (designated as ‘E2’) were determined using a legal-for-trade counting scale. For bauxite samples, ‘E2’ corresponds to the bauxite-rich product. For each set of sub-samples (Iaitu., Suapan, E1 and E2) LOI, main oxides composition by XRF, reactive silica and available alumina was determined. XRD characterization was performed on selected sub-samples.
3.0 Results and Discussion
3.1. Samples Mineralogy
Results of the quantitative XRD analyses for feed samples are included in Table 5. The majority of the samples were primarily composed of gibbsite and varying amounts of goethite, hematite, kaolinit, and quartz. Ilmenite and anatase were also evident in minor amounts in the majority of the samples.
There was a change in the mineral composition for S6 and S7 as these feed samples were primarily composed of diaspore with minor amounts of calcite, hematite, goethite, boehmite, kaolinit, gibbsite, quartz, anatase, and rutile being detected. An amorphous phase was also detected in S1 and S4 and ranged from approximately 1 untuk 2 percent. This was probably due to either the presence of a smectite mineral, or non-crystalline material. Since this material could not be directly measured, results for these samples should be considered approximate.
3.2 Bench-scale experiments
A series of test runs were performed on each mineral sample aimed at maximizing Al2O3 and decreasing SiO_2 content. Species concentrating to the bauxite-rich product will be indicative of positive charging behavior. Results are shown in Table 6
Jadual 5. XRD analysis of feed samples.
Jadual 6. Summary Results.
Testing with the STET benchtop separator demonstrated significant movement of Al2O3 for all samples. Separation of Al2O3 was observed for S1-5 which were mainly gibbsite, and also for S6-7 which were mainly diaspore. sebagai tambahan, the other major elements of Fe2O3, SiO2 and TiO2 demonstrated significant movement in most cases. For all samples, the movement of loss on ignition (LOI) followed movement of Al2O3. In terms of reactive silica and available alumina, for S1-5 which are nearly all gibbsite (aluminum trihydrate) values should be considered at 145°C while for S6-7 for which the dominant mineral is diaspore (aluminum monohydrate) values should be assessed at 235°C. For all samples testing with the STET benchtop separator demonstrated a substantial increase in available alumina and a significant reduction in reactive silica to product for both trihydrate and monohydrate bauxite samples. Movement of major mineral species was also observed and is graphically shown below in Figure 4.
In terms of mineralogy, STET benchtop separator demonstrated concentration of the alumina bearing species gibbsite and diaspore to the bauxite-rich product while simultaneously rejecting other gangue species. Angka 5 Dan 6 show selectivity of mineral phases to the bauxite-rich product for trihydrate and monohydrate samples, respectively. Selectivity was calculated as the difference between the mass deportment to product for each mineral species and the overall mass recovery to product. A positive selectivity is indicative of mineral concentration to the bauxite-rich product, and of an overall positive charging behavior. Contrary, a negative selectivity value is indicative of concentration to the bauxite-lean coproduct, and of an overall negative charging behavior.
For all trihydrate low-temperature samples (Iaitu., S1, S2 and S4) kaolinite exhibited a negative charging behavior and concentrated to the bauxite-lean co-product while gibbsite concentrated to the bauxite-rich product (Rajah 5). For all monohydrate high-temperature samples (Iaitu., S6 and S7) both reactive silica bearing minerals, kaolinite and quartz, exhibited a negative charging behavior. For the latter, diaspore and boehmite reported to the bauxite-rich product and exhibited a positive charging behavior (Rajah 6).
Rajah 5. Selectivity of mineral phases to product.
Rajah 6. Selectivity of mineral phases to product.
Measurements of available alumina and reactive silica demonstrate substantial movement. For low temperature bauxites (S1-S5), the amount of reactive silica present per unit of available alumina was reduced from 10-50% on a relative basis (Rajah 7). A similar reduction was observed in the high temperature bauxites (S6-S7) as can be seen in Figure 7.
The bauxite to alumina ratio was calculated as the inverse of the available alumina. The bauxite to alumina ratio was decreased by between 8 – 26% in relative terms for all samples tested (Rajah 8). This is meaningful as it represents an equivalent reduction in mass flow of bauxite that needs to be fed to the Bayer process.
Rajah 7. Reactive SiO2 per unit of Available Al2O3
Rajah 8. Bauxite to Alumina ratio.
3.3 Perbincangan
The experimental data demonstrates that the STET separator increased available Al2O3 while simultaneously reducing SiO_2 content. Rajah 9 presents a conceptual diagram of the expected benefits associated to the reduction of reactive silica and the increase of available alumina prior to the Bayer Process. The authors calculate that the financial benefit to an alumina refiner would be in the range of $15-30 USD per ton of alumina product. This reflects avoided cost from caustic soda lost to de-silicaton product (DSP), energy savings from reducing the input of bauxite to the refinery, reduction in red mud generation and a small revenue stream generated from selling the low-grade bauxite by-product to cement producers. Rajah 9 outlines the expected benefits of implementing STET triboelectrostatic technology as a mean to pre-concentrate bauxite ore prior the Bayer process.
Installation of the STET separation process for bauxite pre-processing could be performed either at the alumina refinery or the bauxite mine itself. Walau bagaimanapun, the STET process requires dry grinding of the bauxite ores prior to separation, to liberate the gangue, therefore the logistics of grinding and processing the bauxite at the refinery may be more straightforward.
As one option – the dry bauxite would be ground using well-established dry grinding technology, for example a vertical roller mill or impact mill. The finely ground bauxite would be separated by the STET process, with the high-alumina bauxite product sent to the alumina refinery. The installation of dry grinding would allow for the elimination of wet grinding traditionally used during the Bayer process. It is assumed that the operating cost of dry grinding would be roughly comparable to the operating cost of wet grinding, especially considering the wet grinding performed today is performed on a highly alkaline mixture, leading to considerable maintenance costs.
The dry low-grade bauxite co-product (tailings) from the separation process would be sold to cement manufacture as an alumina source. Bauxite is commonly added to cement manufacture, and the dry co-product, unlike red mud, does not contain sodium which would prevent its use in cement manufacture. This provides the refinery with a method of valorizing material that would otherwise exit the refining process as red mud, and would require long term storage, representing a cost.
An operating cost calculation performed by the authors estimates a project benefit of $27 USD per ton of alumina, with the major impacts achieved through reduction in caustic soda, reduction in red mud, valorization of the co-product and fuel savings due to lower volume of bauxite to the refinery. Therefore an 800,000 ton per year refinery could expect a financial benefit of $21 M USD per year (Lihat Rajah 10). This analysis does not consider potential savings from reducing import or logistics costs of bauxite, which may further enhance the project return.
Rajah 10. Benefits of Reactive Silica Reduction and Available Alumina increase.
4.0 Kesimpulan
Secara ringkasnya, pemprosesan kering dengan pemisah STET menawarkan peluang untuk menjana nilai bagi pengeluar dan penapisan baja. Pra-pemprosesan bacelin sebelum penapisan akan mengurangkan kos kimia, menurunkan jumlah lumpur merah yang dihasilkan dan meminimumkan kecewa proses. STET technology could allow bauxite processors to turn non-metallurgical grade into metallurgical grade bauxite – which could reduce need for imported bauxite and/or extend exiting quarry resource life. STET process could also be implemented to generate higher quality non-metallurgical grade and metallurgical grade bauxite, and cement grade bauxite by-products prior to the Bayer process.
The STET process requires little pre-treatment of the mineral and operates at high capacity – up to 40 tones per hour. Energy consumption is less than 2 kilowatt-hours per ton of material processed. Lebih-lebih lagi, the STET process is a fully commercialized technology in minerals processing, and therefore does not require the development of new technology.
Rujukan
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