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SEkipman T & Teknoloji, LLC (STET) a te devlope yon separasyon senti électrostatique tribo de sistèm ki founi endistri mineral otomatik a yon mwayen pou byen materyèl beneficiate ak yon teknoloji chèch nèt. E lòt pratik électrostatique separasyon sonje bagay limite nan matyè pi konsekan pase 75µm nan gwosè, la séparation triboelectric senti bon aux pou separasyon trè byen (<1μm) modere (300μm) particles with very high throughput. The triboelectric belt separator technology has been used to separate a wide range of materials including coal combustion fly ash, calcite/quartz, talc/magnésite, barite/quartz, and feldspar/quartz. Separation results are presented describing the tribo-charging behavior for bauxite minerals.
Yon ti rale
Mank de dwa ak dlo frè vin yon gwo faktè ki afekte faisabilité de min pwojè atravè lemond. Rapò a Hubert Fleming, ansyen direktè mondyal pou dlo kale, "Tout min site nan mond lan ki te swa te rete, ni te ralanti sou ane ki sot pase a, li te, nan prèske 100% nan ka yo, yon rezilta dlo, either directly or indirectly”.1 Dry mineral processing methods offer a solution to this looming problem.
Metòd chèch tankou électrostatique separasyon elimine bezwen pou dlo frè, epi yo ofri potansyèl pou yo ka diminye depans. 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 pou 0.1 mm.3,4 One of the most promising new developments in dry mineral separations is the tribo-electrostatic belt separator. Teknoloji sa a te pwolonje ranje gwosè renn pou lèt matyè pase konvasyon separasyon électrostatique teknoloji, nan de konba kote flottaison sèlman te gen siksè nan tan lontan.
Tribo-Electrostatic Belt Separation
Nan séparateur senti tribo électrostatique a (Figi 1 and Figure 2), materyèl nouri nan la mèg gap 0.9 - 1.5 cm ant de paralèl) électrodes. Matyè yo triboelectrically yo akize interparticle kontak. Pa ekzanp, in the Case of chabon combustion vole saran, yon melanj de kabòn matyè ak matyè mineral, kabon ki pozitivman chaje ak mineral negativman chaje yo atire elektwod opoze a. Patikil yo Le sa a, bale moute pa yon senti kontinyel ki ap deplase louvri-mesh ak travese nan direksyon opoze. Kouwa a deplase matyè adjasan pou chak lektwòd anvè toupatou bò la séparation. Jaden elektrik la bezwen selman deplase patikil yo yon ti fraksyon nan yon santimet pou avanse pou pi yon patikil ki soti nan yon kouran goch-deplase nan yon kouran ki ap deplase dwat. 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. Gwo vitès senti anwo nan syèl la tou permet débits trè wo, jiska 40 tòn pa è sou yon moun ki pa marye séparateur. Pa okipe kay yo plizyè karakteristik pwosesis, tankou senti vitès, bay manje pwen, elektwod ak pousantaj manje, aparey la pwodui ba kabon vole sann nan sa ki nan kabon 2 % ± 0.5% achte manje nan kabon 4% pou fini 30%.
Konsepsyon an se separateur se relativman senp. Kouwa ak asosye woulèt se sèl kalite manm. Électrodes èstasyone ak reyalize yon materyèl ki fè a se sa dirab. Se senti a te fe nan materyel plastik. Longe a separateur elektwod se apepre 6 met (20 .) e laje a 1.25 met (4 .) pou inite komesyal konple. Konsomasyon nan pouvwa a pi piti pase 2 Kilowatè tòn pa materyèl ki te trete ak pi fò nan pouvwa consommée pa de motè mete senti a.
Pwosè a chèch nèt, mande pou pa gen materyel adisyonel ak pwodui pa gen dlo deche oswa emisyon le. Nan ka a nan kabon soti nan vole sann separasyon, materyel yo refe konsiste de vole sann diminye nan kontni kabon nan nivo apwopriye pou itilize kom yon admixture pozzolanik nan konkre, ak yon fraksyon kabon segonde ki ka boule nan plant la génération elektrisite. Itilize nan toulede kouran pwodwi bay yon 100% solisyon vole sann dispozisyon pwoblem. 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. Yon machin ki fèt pou travay 40 tòn pa lè se apeprè 9.1 met (30 .) lontan, 1.7 met (5.5 .) lajè ak 3.2 met (10.5 .) anwo nan syèl la. Mande balans plant lan menm se sistèm pou tansmèt chèch materyèl ki soti lakay la séparation. Caractère nan sistèm nan ki pèmèt pou fleksibilite nan konplo enstalasyon.
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, nan patikil mineral aliminyom glassyal nan sann lan vole. Teknoloji a te enstrimantal nan pemet resikle nan mineral-rich la vole sann kom yon ranplasman siman nan pwodiksyon konkre. Depi 1995, sou 20,000,000 tonnes of fly ash has been processed by the 19 tribo-electrostatic belt separators installed in the USA, Kanada, RETIRE, Poloy, and South Korea. The industrial history of fly ash separation is listed in Tab 1.
Tab 1. Industrial application of tribo-electrostatic belt separation for fly ash
| Itilite / estasyon elektrik | Kote yo ye | Start of commercial operations | Facility details |
|---|---|---|---|
| Duke Eneji - Roxboro Estasyon | North Carolina USA | 1997 | 2 Separateur yo |
| Talen Energy- Brandon Shores | Maryland USA | 1999 | 2 Separateur yo |
| Pouvwa ekose- estasyon longannet | Scotland UK | 2002 | 1 Separateur |
| Jacksonville Elektrik-St. Johns River Power Park | Florid USA | 2003 | 2 Separateur yo |
| South Mississippi Electric Power -R.D. Demen | Mississippi USA | 2005 | 1 Separateur |
| Nouvo Brunswick pouvwa-Belledune | Nouvo Brunswick Kanada | 2005 | 1 Separateur |
| Estasyon RWE-Didcot | Anglete UK | 2005 | 1 Separateur |
| Talen Energy-Brunner Island Station | Penso | 2006 | 2 Separateur yo |
| Tampa elektrik-gwo pliye estasyon | Florid USA | 2008 | 3 Separateur yo two-pass scavenging |
| RWE npower-Aberthaw Estasyon | Wales UK | 2008 | 1 Separateur |
| EDF Eneji-West Burton estasyon | Anglete UK | 2008 | 1 Separateur |
| ZGP (Lafarge Cement /Ciech Janikosoda JV) | Poloy | 2010 | 1 Separateur |
| Pouvwa Sidès Kore di- Yeongheung | Kore di sid | 2014 | 1 Separateur |
| PGNiG Termika-Sierkirki | Poloy | 2018 | 1 Separateur |
| Taiheiyo Cement Company-Chichibu | Japon | 2018 | 1 Separateur |
| Armstrong Fly Ash- Eagle Cement | Philippines | Scheduled 2019 | 1 Separateur |
| Pouvwa Sidès Kore di- Samcheonpo | Kore di sid | Scheduled 2019 | 1 Separateur |
Tribo-Electrostatic Separation of Bauxite Minerals
Sen ekipman & Teknoloji (STET) performed bench scale dry tribo-electrostatic separation testing on multiple samples of bauxite minerals. The samples are listed below in Tab 2.
Tab 2. Properties of bauxite samples tested by STET
| Description | Desired Product & Goals | |
|---|---|---|
| Echantiyon 1 | ROM Bauxite | Al2O3 recovery Reduce SiO2, Fe2O3, TiO2 |
| Echantiyon 2 | PLK (Partially Lateritized Khondalite) | Al2O3 recovery Reduce SiO2, Fe2O3, TiO2 |
| Echantiyon 3 | Red Mud | Fe2O3 recovery Reduce SiO2, Al2O3, TiO2 |
| Echantiyon 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 Tab 3.
Tab 3. Chemical properties of bauxite samples tested by STET
| Al2O3 wt.% | Fe2O3 wt.% | SiO2 wt.% | SiO2 wt.% | LOI wt.% | |
|---|---|---|---|---|---|
| Echantiyon 1 | 43.7 | 25.9 | 3.9 | 2.3 | 23.6 |
| Echantiyon 2 | 34.9 | 19.4 | 28.5 | 2.1 | 14.7 |
| Echantiyon 3 | 19.0 | 52.1 | 6.7 | 4.9 | 11.1 |
| Echantiyon 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 Tab 4.
Tab 4. Particle size of bauxite samples tested by STET
| D10 mikron | D50 mikron | D90 mikron | D90 mikron |
|
|---|---|---|---|---|
| Echantiyon 1 | 2 | 19 | 73 | 118 |
| Echantiyon 2 | 2 | 45 | 575 | 898 |
| Echantiyon 3 | 1 | 27 | 212 | 325 |
| Echantiyon 4 | 1 | 7 | 59 | 93 |
Samples were separated using the STET benchtop separator. La séparation benchtop ki itilize pou elijib pou evidans, dezyem prèv électrostatique tribo chaje ak pou detèmine si yon materyèl ki se yon bon kandida pou électrostatique 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 fwa longe pilot-echel ak inite echel komesyal yo. Kom efikasite nan separateur se yon fonksyon nan longe a elektwod, tes bank-echel pa ka itilize kom yon ranplasan pou tes pilot-echel. Tes pilot-echel ki nesese pou detemine mezi separasyon an ki pwosesis STET la kapab reyalize, epi pou detemine si pwosesis STET kapab satisfe objektif pwodwi yo anba pousantaj manje yo. Olye de sa, separateur banchtop la itilize pou regle materyel kandida ki pa fasil pou demontre nenpot separasyon enpotan nan nivo pilot-echel la. Rezilta yo jwenn sou echel la ban-yo pral ki pa optimisé, epi separasyon an obseve se mwens pase sa ki ta dwe obseve sou yon separate gwose STET gwose STET.
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. epi tou, the other major elements of Fe2O3, SiO2 and TiO2 demonstrated significant movement in most cases. In Sample 1, Echantiyon 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 Figi 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 Tab 5.
Tab 5. Summary of tribocharging behaviour for major elements. POS = charged positive, NEG = charged negative.
| Al2O3 | Fe2O3 | Sio2 | TiO2 | LOI | |
|---|---|---|---|---|---|
| Echantiyon 1 | POS | NEG | NEG | NEG | POS |
| Echantiyon 2 | NEG | POS | NEG | N/A | N/A |
| Echantiyon 3 | POS | NEG | N/A | NEG | POS |
| Echantiyon 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. epi tou, 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. epi tou, 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 Tab 6.
Tab 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. |
Conclusion
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. epi tou, 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.
Referans
1. Blin, P I & Dion-Ortega, YON (2013) E seche, Magazin CIM, vol. 8, Non. 4, pp. 48-51.
2. Manouchehri, H, Hanumantha Roa, SOUFRI, & Forssberg, SOUFRI (2000), Revi tout metòd separasyon elèktrik, Pati 1: Aspè fondamantal yo, Inewo & Métallurgiques otomatik, vol. 17, Non. 1 pp 23–36.
3. Manouchehri, H, Hanumantha Roa, SOUFRI, & Forssberg, SOUFRI (2000), Revi tout metòd separasyon elèktrik, Pati 2: Considérations pwatik, Inewo & Métallurgiques otomatik, vol. 17, Non. 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.
