Vybrat jazyk:
Abstrakt
ST Equipment & Technologie, LLC (STET) has developed a tribo-electrostatic belt separation processing system that provides the mineral processing industry a means to beneficiate fine materials with an entirely dry technology. In contrast to other electrostatic separation processes that are typically limited to particles greater than 75µm in size, Triboelektrický pásový separátor je ideální pro oddělení velmi jemné (<1µm) až středně hrubá (300µm) částice s velmi vysokou propustností. The triboelectric belt separator technology has been used to separate a wide range of materials including coal combustion fly ash, vápenec/quartz, mastek/magnezit, barite/quartz, and feldspar/quartz. Separation results are presented describing the tribo-charging behavior for bauxite minerals.
Úvod
Nedostatečný přístup k čerstvé vodě se stává významným faktorem ovlivňující proveditelnost důlních projektů po celém světě. Podle Hubert Fleming, bývalý ředitel globální pro šrafování vody, "Ze všech důlních projektů ve světě, který přestal nebo se zpomalil v uplynulém roce, už je to, v téměř 100% případů, v důsledku vody, either directly or indirectly”.1 Dry mineral processing methods offer a solution to this looming problem.
Suché metody jako elektrostatické oddělování eliminuje potřebu pitné vody, a nabízí potenciál pro snížení nákladů. Electric separation methods that utilize contact, or tribo-electric, charging are 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.2 Free-fall separators can be effective for coarse particles, but are not effective at handling particles finer than about 0.075 do 0.1 mm.3,4 One of the most promising new developments in dry mineral separations is the tribo-electrostatic belt separator. Tato technologie rozšířila rozsah velikostí částic na jemnější částice než konvenční elektrostatickou separaci technologie, do oblasti, kde byla v minulosti úspěšné pouze flotační.
Tribo-Electrostatic Belt Separation
In the tribo-electrostatic belt separator (Obrázek 1 and Figure 2), materiál je dávkován do tenké mezery 0.9 – 1.5 cm between two parallel planar electrodes. Částice jsou účtovány triboelectrically interparticle kontakt. Například, v případě spalování uhlí popílek, směs uhlíkových částic a minerální částice, kladně nabité uhlíku a záporně nabité minerální jsou přitahovány k protilehlé elektrody. Částice jsou poté zaplaveny souvislou pohybující se pásek s otevřeným oky a dopravené opačným směrem. Pás se pohybuje částice sousedící s každou elektrodu vůči opačných koncích oddělovače. Elektrické pole potřebuje jen posunout částice o malý zlomek centimetru, aby přemístily částici zleva doprava k datovému proudu. The counter current flow of the separating particles and continual triboelectric charging by carbon-mineral collisions provides for a multi-stage separation and results in excellent purity and recovery in a single-pass unit. Vysoký pás rychlost také velmi vysoké síta, až do 40 tun za hodinu na jeden oddělovač. Tím, že řídí různé parametry procesu, například rychlost pásu, kanál bod, Vzdálenost elektrod a posuvu, zařízení produkuje nízkouhlíkových popílek na obsah uhlíku 2 % ± 0.5% od krmných popílků v uhlíku od 4% na více než 30%.
Oddělovač design je relativně jednoduchá. Pás a přidružené válečky jsou jediné pohyblivé. Elektrody jsou stacionární a sestávají z vhodně trvanlivého materiálu. Pás je vyroben z plastu. Délka elektrody oddělovač je přibližně 6 metrů (20 FT.) a šířka 1.25 metrů (4 FT.) pro plnou velikost obchodní jednotky. Spotřeba energie je nižší než 2 kilowatthodin za tunu zpracovaného s většinou energie spotřebované dva motory pohánějící pás materiálu.
Tento proces je zcela suchá, vyžaduje žádné další materiály a neprodukuje žádné odpadní vody nebo vzduchu emise. U uhlíku z popílku separace, Obnovená materiály se skládají z popílku sníženy na úroveň, které jsou vhodné pro použití jako Puzolánový příměsi do betonu v obsahu uhlíku, a zlomek vysokým obsahem uhlíku, které mohou být vypáleny na výrobu rostlinných elektřiny. Využití obou proudů produktu poskytuje 100% řešení problémů likvidace popílek. For mineral separations, processing bauxite for example, the separator provides a technology to reduce water usage, extend reserve life and/or recover and reprocess tailings.
The tribo-electrostatic belt separator is relatively compact. Stroj určený ke zpracování 40 tun za hodinu je přibližně 9.1 metrů (30 FT.) dlouhá, 1.7 metrů (5.5 FT.) široký a 3.2 metrů (10.5 FT.) vysoká. Se skládá ze systémů zprostředkovat suchý materiál z oddělovač a nezbytnou rovnováhu rostlin. Kompaktnost systému umožňuje flexibilitu v provedení instalace.
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 1995. The technology is effective in separating carbon particles from the incomplete combustion of coal, z minerálních částic sklovité hlinitokřemičitanu v popílek. Technologie se stala nápomocnou v tom, že umožňuje recyklovat popílek bohatý na minerální látky jako náhradní cement v konkrétní výrobě. Od 1995, nad 20,000,000 tonnes of fly ash has been processed by the 19 tribo-electrostatic belt separators installed in the USA, Kanada, VELKÁ BRITÁNIE, Polsko, and South Korea. The industrial history of fly ash separation is listed in Tabulka 1.
Tabulka 1. Industrial application of tribo-electrostatic belt separation for fly ash
| Nástroj / elektrárna | Umístění | Start of commercial operations | Facility details |
|---|---|---|---|
| Duke Energy – stanice Roxboro | Severní Karolína, USA | 1997 | 2 Oddělovače |
| Talen energie- Brandon břehy | Maryland USA | 1999 | 2 Oddělovače |
| Scottish Power- Longannet stanice | Velká Británie Skotsko | 2002 | 1 Oddělovač |
| Jacksonville Electric-St. Johns River Power Park | Florida USA | 2003 | 2 Oddělovače |
| South Mississippi Electric Power -R.D. Morrow | Mississippi USA | 2005 | 1 Oddělovač |
| Nový Brunswick Power-Belledune | New Brunswick Kanada | 2005 | 1 Oddělovač |
| Stanice RWE npower-Didcot | Anglie Velká Británie | 2005 | 1 Oddělovač |
| Talen Energy-Brunner Island Station | Pennsylvania USA | 2006 | 2 Oddělovače |
| Vodní stanice Tampa Electric-Velká | Florida USA | 2008 | 3 Oddělovače two-pass scavenging |
| Stanice RWE npower-Aberthaw | Wales, Spojené království | 2008 | 1 Oddělovač |
| Stanice ERF Energy-West Burton | Anglie Velká Británie | 2008 | 1 Oddělovač |
| ZGP (Lafarge Cement /Ciech Janikosoda JV) | Polsko | 2010 | 1 Oddělovač |
| Korea jihovýchodní moc- Yeongheung | Jižní Korea | 2014 | 1 Oddělovač |
| PGNiG Termika-Sierkirki | Polsko | 2018 | 1 Oddělovač |
| Taiheiyo Cement Company-Chichibu | Japonsko | 2018 | 1 Oddělovač |
| Armstrong Fly Ash- Eagle Cement | Filipíny | Scheduled 2019 | 1 Oddělovač |
| Korea jihovýchodní moc- Samcheonpo | Jižní Korea | Scheduled 2019 | 1 Oddělovač |
Tribo-Electrostatic Separation of Bauxite Minerals
St. zařízení & Technologie (STET) performed bench scale dry tribo-electrostatic separation testing on multiple samples of bauxite minerals. The samples are listed below in Tabulka 2.
Tabulka 2. Properties of bauxite samples tested by STET
| Description | Desired Product & Goals | |
|---|---|---|
| Sample 1 | ROM Bauxite | Al2O3 recovery Reduce SiO2, Fe2O3, TiO2 |
| Sample 2 | PLK (Partially Lateritized Khondalite) | Al2O3 recovery Reduce SiO2, Fe2O3, TiO2 |
| Sample 3 | Red Mud | Fe2O3 recovery Reduce SiO2, Al2O3, TiO2 |
| Sample 4 | ROM Bauxite Slimes | Al2O3 recovery Reduce SiO2, Fe2O3, TiO2 |
Chemical composition for all feed and separated product samples was measured by X-Ray Fluorescence (XRF) using a WD-XRF system. The results of the chemical analysis for the feed samples are shown below in Tabulka 3.
Tabulka 3. Chemical properties of bauxite samples tested by STET
| Al2O3 wt.% | Fe2O3 wt.% | SiO2 wt.% | SiO2 wt.% | LOI wt.% | |
|---|---|---|---|---|---|
| Sample 1 | 43.7 | 25.9 | 3.9 | 2.3 | 23.6 |
| Sample 2 | 34.9 | 19.4 | 28.5 | 2.1 | 14.7 |
| Sample 3 | 19.0 | 52.1 | 6.7 | 4.9 | 11.1 |
| Sample 4 | 34.6 | 23.2 | 18.0 | 4.4 | 18.8 |
Particle size was measured by laser particle size measurement using dry pneumatic dispersion. The results for the feed samples are shown below in Tabulka 4.
Tabulka 4. Particle size of bauxite samples tested by STET
| D10 Micron | D50 Micron | D90 Micron | D90 Micron |
|
|---|---|---|---|---|
| Sample 1 | 2 | 19 | 73 | 118 |
| Sample 2 | 2 | 45 | 575 | 898 |
| Sample 3 | 1 | 27 | 212 | 325 |
| Sample 4 | 1 | 7 | 59 | 93 |
Samples were separated using the STET benchtop separator. 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 primary 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. Instead, 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 with the STET benchtop separator demonstrated significant movement of Al2O3 with the majority of the samples tested. In three of the four samples tested by STET, substantial movement of Al2O3 was observed. Navíc, the other major elements of Fe2O3, SiO2 and TiO2 demonstrated significant movement in most cases. In Sample 1, Sample 3 and Sample 4, the movement of loss on ignition (LOI) followed movement of Al2O3. The movement of the major elements is shown below in Obrázek 5.
The STET separator is a physical separation process and selectively separates mineral phases based on tribocharging, a surface phenomenon. The degree to which minerals are susceptible to tribocharging is in some cases able to be predicted via consultation of a triboelectric series, but in the case of complex mineral ores, often in practice must be determined empirically. A summary of the tribocharging properties for the samples tested is shown below in Tabulka 5.
Tabulka 5. Summary of tribocharging behaviour for major elements. POS = charged positive, NEG = charged negative.
| Al2O3 | Fe2O3 | SiO2 | TiO2 | LOI | |
|---|---|---|---|---|---|
| Sample 1 | POS | NEG | NEG | NEG | POS |
| Sample 2 | NEG | POS | NEG | N/A | N/A |
| Sample 3 | POS | NEG | N/A | NEG | POS |
| Sample 4 | POS | N/A | NEG | NEG | POS |
Dry processing with the STET separator offers opportunities to generate value for bauxite and aluminium producers. The utilization of lower grade bauxite deposits may allow for lower mining costs by reducing stripping ratios and by reduced generation of tailings. Navíc, the pre-processing of bauxite ores by dry triboelectrostatic separation may result in improved economics of aluminium refining by supplying higher grades of bauxite to the refining process, or by reducing volumes of red mud generated. Navíc, higher aluminium content in red mud may allow for reprocessing. A summary of ideal characteristics for metallurgical grade bauxite is presented, as well as a summary of the benefit of the STET separator, below in Tabulka 6.
Tabulka 6. Summary of ideal characteristics for metallurgical grade bauxite.5
| Ideal Grade Characteristic | Impact if Inadequate | Observed with STET Separation |
|---|---|---|
| Low “reactive silica” (>1.5% - <3.0%) (kaolinite) | Increases caustic usage, a critical operating cost factor. | Reduction in total silica |
| High extractable alumina | Increases capital and operating costs for mining, processing and mud disposal. | Increase in alumina |
| Low organic carbon | Increases operating costs by reducing plant efficiency. | |
| Low boehmite (<3%) | Precludes low-temperature processing that can increase capital and operating costs. | |
| Low goethite (tolerable in a high-temperature plant or with high hematite) | Slows clarification, lowers product quality and increases alumina loss via mud circuit. | Reduction in total iron |
| Low moisture (can create nuisance dust if too low) | Increases capital costs (larger evaporation facility), fuel consumption, shipping costs. | |
| Iron content (ideally >5%-<15%) | Low iron can lower product quality. High iron dilutes alumina content of bauxite. | Reduction in total iron |
| Low quartz | Increases maintenance costs (pipe wear). Increases caustic usage in high-temperature plants. | Reduction in total silica |
| Low impurities and trace elements | Can lower process efficiency (sulfur, chlorine, calcium) and metal quality (gallium, zinc, vanadium, phosphorus). | |
| Soft and friable | Increases mining and grinding costs. | |
| Dissolves readily | Increases capital (larger digestion equipment) and operating costs. | |
| Low titania | Can increase caustic usage in high-temperature plants. | Reduction in titania |
| Low carbonates | Can require special processing. |
Závěr
Tribo-electrostatic separation was demonstrated as an effective method for generating a high-grade bauxite ore for use in alumina production. Testing with the STET benchtop separator demonstrated significant movement of Al2O3 with the majority of the samples tested. In three of the four samples tested by STET, substantial movement of Al2O3 was observed. Navíc, the other major elements of Fe2O3, SiO2 and TiO2 demonstrated significant separation in most cases. Dry processing with the STET separator offers opportunities to generate value for bauxite and aluminium producers.
Odkazy
1. Blin, P & Dion-Ortega, A (2013) Vysoká a suchá, Časopis CIM, Vol. 8, Ne. 4, PP. 48-51.
2. Manouchehri, H, Hanumantha Roa, K, & Forssberg, K (2000), Přehled metod elektrickéseparace, Část 1: Základní aspekty, Minerály & Hutního zpracování, Vol. 17, Ne. 1 pp 23–36.
3. Manouchehri, H, Hanumantha Roa, K, & Forssberg, K (2000), Přehled metod elektrickéseparace, Část 2: Praktické aspekty, Minerály & Hutního zpracování, Vol. 17, Ne. 1 pp 139–166.
4. Ralston O. (1961) Electrostatic Separation of Mixed Granular Solids, Elsevier Publishing Company, out of print.
5. Kogel, Jessica Elzea; Trivedi, Nikhil C; Barker, James M; Krukowski, Stanley T.; Industrial Minerals and Rocks: Commodities, Markets, and Uses 7th Edition, (2006), Page 237.
