Teua lugha:
ST vifaa & Teknolojia LLC (STET) tribo-electrostatic belt separator is ideally suited for beneficiating very fine (<1µm) kwa coarse kiasi (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). Zaidi ya hayo, 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 Utangulizi
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% of the Earth’s crust, 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].
The primary starting material for aluminum refining is bauxite, the world’s main commercial source of aluminum [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)) and diaspore (α-AlO(OH)) (Jedwali 1), and is usually mixed with the two iron oxides goethite (FeO(OH)) na 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].
Jedwali 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 |
Bauxite deposits are spread worldwide, mostly occurring in tropical or subtropical regions [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 (i.e., 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. Hatimaye, 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. The loss of expensive caustic soda (NaOH) and the generation of red mud are both related to the quality of bauxite used in the refining process. In general, the lower the Al_2 O_3 content of bauxite, the larger the volume of red mud that will be generated, as the non-Al_2 O_3 phases are rejected as red mud. Zaidi ya hayo, the higher the kaolinite or reactive silica content of bauxite, the more red mud will be generated [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, occasionally as low as 30-50% Al_2 O_3. Because the desired product is a high purity
Al_2 O_3, the remaining oxides in the bauxite (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. In general, the lower quality the bauxite (i.e., lower Al_2 O_3 content) the more red mud that is generated per ton of alumina product. Zaidi ya hayo, even some Al_2 O_3 bearing minerals, notably kaolinite, produce undesirable side reactions during the refining process and lead to an increase in red mud generation, as well as a loss of expensive caustic soda chemical, a large variable cost in the bauxite refining process [3,6,8].
Red mud or ARR represents a large and on-going challenge for the aluminum industry [12-14]. Red mud contains significant residual caustic chemical leftover from the refining process, and is highly alkaline, often with a pH of 10 – 13 [15]. It is generated in large volumes worldwide – according to the USGS, estimated global alumina production was 121 million tons in 2016 [16]. This resulted in an estimated 150 million tons of red mud generated during the same period [4]. Despite ongoing research, red mud currently has few commercially viable paths to beneficial re-use. It is estimated that very little of red mud is beneficially re-used worldwide [13-14]. Badala yake, the red mud is pumped from the alumina refinery into storage impoundments or landfills, where it is stored and monitored at large cost [3]. Basi, 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, the quality of the reserves that can be economically accessed is declining [1,3]. For refiners, who are in the business of processing bauxite to make alumina, and eventually aluminum metal, this is a challenge with both financial and environmental implications
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. Utengano unaweza kisha kupatikana kutumia kutumika nje umeme shamba.
Mbinu ina itatumika viwandani katika free-fall wima aina vitenganishi. Katika free-fall vitenganishi, chembe kwanza kupata malipo, 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 kwa 0.1 mm [19-20]. One of the most promising new developments in dry mineral separations is the tribo-electrostatic belt separator. Teknolojia hii ameleta chembe ukubwa mbalimbali kwa chembe mazuri kuliko teknolojia ya utengano ya kawaida ya electrostatic, katika masafa ambapo tu ujenge imekuwa mafanikio katika siku za nyuma.
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, wakati nyenzo zilizo na uhusiano wa chini wa elektroni hutoza chanya.
ST vifaa & Teknolojia (STET) tribo-electrostatic belt separator offers a novel beneficiation route to pre-concentrate bauxite ores. The STET dry separation process offers bauxite producers or bauxite refiners an opportunity to perform pre-Bayer-process upgrading of bauxite ore to improve the quality. This approach has many benefits, Ikijumuisha: Reduction in operating cost of refinery due to lower consumption of caustic soda by reducing input reactive silica; savings in energy during refining due to lower volume of inert oxides (FE2O3, TiO2, Non-reactive SiO2) entering with bauxite; smaller mass flow of bauxite to refinery and therefore less energy requirement to heat and pressurize; reduction in red mud generation volume (i.e., red mud to alumina ratio) by removing reactive silica and inert oxide; na, 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. Aidha, 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. Unlike red mud, tailings from a dry electrostatic process contain no chemicals and do not represent a long-term environmental storage liability. Unlike red mud, dry by-products/tailings from a bauxite pre-processing operation can be utilized in cement manufacture as there is no requirement to remove the sodium, which is detrimental to cement manufacture. 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. Ya haya, 7 different samples were
Jedwali 2. Result of chemical analysis bauxite samples.
2.2 Methods
Majaribio yalifanywa kwa kutumia benchi-kiwango cha wa-electrotuli ukanda, hereafter referred as ‘benchtop separator’. Bench-scale testing is the first phase of a three-phase technology implementation process (Tazama Jedwali 3) including bench-scale evaluation, upimaji wa majaribio na utekelezaji wa kibiashara.
Kitenganishi cha benchtop ni kutumika kwa ajili ya uchunguzi kwa ajili ya ushahidi ya kumshutumu tribo electrostatic na kuamua kama nyenzo ni mgombea mzuri kwa ajili ya electrostatic beneficiation. Tofauti kuu kati ya kila kipande cha vifaa ni iliyotolewa katika jedwali 3. Wakati vifaa kutumika katika kila awamu hutofautiana kwa ukubwa, kanuni ya uendeshaji kimsingi ni sawa.
Jedwali 3. Mchakato wa utekelezaji wa awamu tatu kwa kutumia teknolojia ya mgawanyiko wa STET-electrotuli
| Awamu | Used for: | Electrode Length cm | Aina ya mchakato |
|---|---|---|---|
| 1- Bench Scale Evaluation | Qualitative Evaluation | 250 | Bechi |
| 2- Kipimo cha majaribio Upimaji | Quantitative evaluation | 610 | Bechi |
| 3- Commercial Scale Implementation | Commercial Production | 610 | Endelevu |
Kama inaweza kuonekana katika jedwali 3, tofauti kuu kati ya benchtop separator na kiwango cha majaribio na watoaji wa kibiashara-wadogo ni kwamba urefu wa benchtop separator ni takriban 0.4 mara urefu wa vipimo vya majaribio na kiwango cha kibiashara. Kama ufanisi wa mgawanyiko ni kazi ya urefu wa uchaguzi wa wakipanda, uchunguzi wa kiwango cha benchi hauwezi kutumika kama mbadala kwa ajili ya kupima majaribio ya mtihani. Pilot-scale testing is necessary to determine the extent of the separation that the STET process can achieve, na kuamua kama STET mchakato unaweza kukutana bidhaa malengo chini kutokana na viwango vya kilishi. Badala yake, Kitenganishi benchtop hutumiwa na utawala wa nje vifaa vya mgombea ni uwezekano wa kuonyesha kujitenga yoyote muhimu katika kiwango cha kipimo cha majaribio. Matokeo kupatikana kwenye benchi wadogo itakuwa yasiyo na optimized, na utengano aliona ni chini ya ambayo ingekuwa aliona kwenye kitenganishi kibiashara na ukubwa wa STET.
Testing at the pilot plant is necessary prior to commercial scale deployment, however, testing at the bench-scale is encouraged as the first phase of the implementation process for any given material. Aidha, in cases in which material availability is limited, the benchtop separator provides a useful tool for the screening of potential successful projects (i.e., projects in which customer and industry quality targets can be met using STET technology).
2.2.1 STET ya wa-Electrotuli ukanda
Katika kitenganishi ukanda tribo electrostatic (Kielelezo 1 na Kielelezo 2), nyenzo ni kulishwa katika Mwanya mwembamba 0.9 – 1.5 cm kati ya mbili sambamba ndizi na electrodes. Chembe ni za kiumeme zinazoshtakiwa na mawasiliano ya mchanganyiko. Kwa mfano, in the case of a bauxite sample which main constituents are gibssite, kaolinite and quartz mineral particles, washtakiwa chanya (gibssite) and the negatively charged (kaolinite and quartz) ni kuvutia kwa electrodes kinyume. Chembe ni kisha kufagiliwa na kuendelea kusonga wazi-matundu ukanda na kuwasilishwa katika maelekezo kinyume. Ukanda husonga chembe karibu na kila uchaguzi wakipanda kuelekea mwisho wa mgawanyiko. Shamba la umeme linahitaji tu kusonga chembe sehemu ndogo ya sentimita ili kuhamisha chembe kutoka kushoto-kusonga kwenye mkondo wa kulia. 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. Kasi ya ukanda wa juu pia inawezesha njia za juu sana, hadi 40 tani kwa saa kwenye kitenganishi kimoja. Kwa kudhibiti vigezo mbalimbali vya mchakato, kifaa inaruhusu kwa ajili ya optimization ya daraja la madini na kufufua.
Kielelezo 1. Schematic ya triboelectric ukanda separator
Sanifu kitenganishi ni rahisi. Ukanda na rollers kuhusishwa ni sehemu tu ya kusonga. Ya electrodes ni stationary na linajumuisha ya vifaa na muda mrefu ipasavyo. Ukanda wa ni alifanya ya plastiki vifaa vya. Kitenganishi electrode urefu ni takriban 6 mita za (20 futi.) na upana 1.25 mita za (4 futi.) kwa vitengo vya kibiashara Kilingo kamili. Matumizi ya nguvu ni chini ya 2 kilowati kwa tani moja ya vifaa vya kusindika na wengi wa nguvu zinazotumiwa na motors mbili kuendesha ukanda wa.
Kielelezo 2. Maelezo ya eneo la kujitenga
Mchakato ni kavu kabisa, inahitaji Hakuna vifaa vya ziada na inazalisha uzalishaji hakuna taka maji au hewa. For mineral separations the separator provides a technology to reduce water usage, kupanua Hifadhi ya maisha na/au kupona na reprocess tailings.
Mkusanyiko wa mfumo inaruhusu kubadilika katika miundo ya ufungaji. Wa-electroo wa ukanda wa, teknolojia ya utengano ni imara na viwandani kuthibitika na mara ya kwanza kutumika viwandani kwa usindikaji wa makaa ya mawe mwako kuruka Ash katika 1997. Teknolojia ni bora katika kutenganisha chembe Carbon kutoka mwako kamili ya makaa ya mawe, kutoka Glassy aluminosilicate madini chembe katika Ash kuruka. Teknolojia imekuwa muhimu katika kuwezesha utoaji wa madini-tajiri kuruka Ash kama mbadala ya saruji katika uzalishaji halisi.
Tangu 1995, juu ya 20 tani milioni ya bidhaa kuruka Ash wamekuwa kusindika na watet na ambao umewekwa katika USA. Historia ya viwanda ya kuruka majivu kujitenga ni waliotajwa katika Jedwali 4.
Katika usindikaji wa madini, teknolojia ya mgawanyiko wa ukanda wa kelectric imetumika kutenganisha vifaa mbalimbali ikiwa ni pamoja na calkutaja/Quartz, Ulanga/magnesite, na barite/Quartz.
Kielelezo 3. Commercial tribo-electrostatic belt separator
Jedwali 4. Viwanda maombi ya ya makundi ya.
| Matumizi / Kituo cha nishati | Mahali | Start of commercial operations | Facility details |
|---|---|---|---|
| Duke nishati – Roxboro Station | Kaskazini mwa Carolina | 1997 | 2 Vitenganishi |
| Nishati ya talen- Brandon fukwe | Maryland USA | 1999 | 2 Vitenganishi |
| Scotland nguvu- Longannet Station | Scotland | 2002 | 1 Kitenganishi |
| Ni. Johns mto Power Park | Florida | 2003 | 2 Vitenganishi |
| Kusini Mississippi Electric Power-R. D. Kesho | Mississippi USA | 2005 | 1 Kitenganishi |
| Mpya Brunswick nguvu-Belledune | Mpya Brunswick Canada | 2005 | 1 Kitenganishi |
| RSISI npower-Didcot stesheni | Uingereza | 2005 | 1 Kitenganishi |
| Talen nishati-Brunner kisiwa Station | Pennsylvania Marekani | 2006 | 2 Vitenganishi |
| Tampa Electric-Big bend stesheni | Florida | 2008 | 3 Vitenganishi |
| RSISI npower-Aberthaw stesheni | Wales Uingereza | 2008 | 1 Kitenganishi |
| EDF nishati-Magharibi Burton stesheni | Uingereza | 2008 | 1 Kitenganishi |
| ZGP (Lafarge saruji/Ciech Janikosoda JV) | Polandi | 2010 | 1 Kitenganishi |
| Korea Kusini- Yeongheung | Korea Kusini | 2014 | 1 Kitenganishi |
| PGNiG Termika-Sierkirki | Polandi | 2018 | 1 Kitenganishi |
| Taiheiyo saruji kampuni-Chichibu | Japani | 2018 | 1 Kitenganishi |
| Armstrong kuruka Ash- Saruji ya tai | Philippines | 2019 | 1 Kitenganishi |
| Korea Kusini- Samcheonpo | Korea Kusini | 2019 | 1 Kitenganishi |
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 (i.e., Kulisha, E1 and E2) WA, 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, Wilaya ya kaolinite, 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, Wilaya ya kaolinite, gibbsite, Quartz, anatase, and rutile being detected. An amorphous phase was also detected in S1 and S4 and ranged from approximately 1 kwa 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
Jedwali 5. XRD analysis of feed samples.
Jedwali 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. Zaidi ya hayo, the other major elements of Fe2O3, SiO2 and TiO2 demonstrated significant movement in most cases. For all samples, the movement of loss on ignition (WA) 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. Takwimu 5 na 6 show selectivity of mineral phases to the bauxite-rich product for trihydrate and monohydrate samples, kwa mtiririko huo. 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 (i.e., 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 (Kielelezo 5). For all monohydrate high-temperature samples (i.e., 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 (Kielelezo 6).
Kielelezo 5. Selectivity of mineral phases to product.
Kielelezo 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 (Kielelezo 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 (Kielelezo 8). This is meaningful as it represents an equivalent reduction in mass flow of bauxite that needs to be fed to the Bayer process.
Kielelezo 7. Reactive SiO2 per unit of Available Al2O3
Kielelezo 8. Bauxite to Alumina ratio.
3.3 Discussion
The experimental data demonstrates that the STET separator increased available Al2O3 while simultaneously reducing SiO_2 content. Kielelezo 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. Kielelezo 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. Hata hivyo, 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 (See Figure 10). This analysis does not consider potential savings from reducing import or logistics costs of bauxite, which may further enhance the project return.
Kielelezo 10. Benefits of Reactive Silica Reduction and Available Alumina increase.
4.0 Conclusions
In summary, dry processing with the STET separator offers opportunities to generate value for bauxite producers and refiners. The pre-processing of bauxite prior to refining will reduce chemical costs, lower the volume of red mud generated and minimize process upsets. 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. Aidha, the STET process is a fully commercialized technology in minerals processing, and therefore does not require the development of new technology.
Marejeo
1. Bergsdal, Håvard, Anders H. Strømman, and Edgar G. Hertwich (2004), “The aluminium industry-environment, technology and production”.
2. Das, Subodh K., and Weimin Yin (2007), “The worldwide aluminum economy: The current state of the industry” JOM 59.11, Pp. 57-63.
3. Vincent G. Hill & Errol D. Sehnke (2006), “Bauxite”, in Industrial Minerals & Rocks: Commodities, Markets, and Uses, Society for Mining, Metallurgy and Exploration Inc., Englewood, CO, Pp. 227-261.
4. Evans, Ken (2016), “The history, challenges, and new developments in the management and use of bauxite residue”, Journal of Sustainable Metallurgy 2.4, Pp. 316-331
5. Gendron, Robin S., Mats Ingulstad, and Espen Storli (2013), “Aluminum ore: the political economy of the global bauxite industry”, UBC Press.
6. Hose, H. R. (2016), “Bauxite mineralogy”, Essential Readings in Light Metals, Springer, Cham, Pp. 21-29.
7. Authier-Martin, Monique, et al. (2001),”The mineralogy of bauxite for producing smelter-grade alumina”, JOM 53.12, Pp. 36-40.
8. Hill, Mstari. G., and R. J. Robson (2016), “The classification of bauxites from the Bayer plant standpoint”, Essential Readings in Light Metals, Springer, Cham, Pp. 30-36.
9. Songqing, Gu (2016). “Chinese Bauxite and Its Influences on Alumina Production in China”, Essential Readings in Light Metals, Springer, Cham, Pp. 43-47.
10. Habashi, Fathi (2016) “A Hundred Years of the Bayer Process for Alumina Production” Essential Readings in Light Metals, Springer, Cham, Pp. 85-93.
11. Adamson, A. N., E. J. Bloore, and A. R. Carr (2016) “Basic principles of Bayer process design”, Essential Readings in Light Metals, Springer, Cham, Pp. 100-117.
12. Anich, Ivan, et al. (2016), “The Alumina Technology Roadmap”, Essential Readings in Light Metals. Springer, Cham, Pp. 94-99.
13. Liu, Wanchao, et al. (2014), “Environmental assessment, management and utilization of red mud in China”, Jarida la uzalishaji safi 84, Pp. 606-610.
14. Evans, Ken (2016), “The history, challenges, and new developments in the management and use of bauxite residue”, Journal of Sustainable Metallurgy 2.4, Pp. 316-331.
15. Liu, Yong, Chuxia Lin, and Yonggui Wu (2007), “Characterization of red mud derived from a combined Bayer Process and bauxite calcination method”, Journal of Hazardous materials 146.1-2, Pp. 255-261.
16. Marekani. Kijiolojia utafiti (Kituo) (2018), “Bauxite and Alumina”, in Bauxite and Alumina Statistics and information.
17. Paramguru, R. K., P. C. Rath, and V. N. Misra (2004), “Trends in red mud utilization–a review”, Mineral Processing & Extractive Metall. Rev. 2, Pp. 1-29.
18. Manouchehri, H, Hanumantha Roa, K, & Forssberg, K (2000), “Review of Electrical Separation Methods, Sehemu 1: Vipengele vya msingi, Madini & Metallurgical Processing”, vol. 17, La. 1, pp 23–36.
19. Manouchehri, H, Hanumantha Roa, K, & Forssberg, K (2000), “Review of Electrical Separation Methods, Sehemu 2: Mazingatio ya Vitendo, Madini & Metallurgical Processing”, vol. 17, La. 1, pp 139–166.
20. Ralston O. (1961), Electrostatic Separation of Mixed Granular Solids, Elsevier Publishing Company, out of print.
