Dewis iaith:
Haniaethol
ST Equipment & Technoleg, 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, the triboelectric belt separator is ideally suited for separation of very fine (<1μm) i gymedrol fras (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, cyfrifir/cwartz, TALC/magnesite, barite/chwarts, and feldspar/quartz. Separation results are presented describing the tribo-charging behavior for bauxite minerals.
Cyflwyniad
Mae'r diffyg mynediad i ddwr ffres yn dod yn ffactor pwysig sy'n effeithio ar ddichonoldeb prosiectau cloddio ledled y byd. Yn ôl Hubert Fleming, cyn gyfarwyddwr byd-eang Hatch Water, "O'r holl brosiectau glofaol yn y byd sydd naill ai wedi cael eu hatal neu eu arafu dros y flwyddyn ddiwethaf, mae wedi bod yn, ym mron 100% o'r achosion, ganlyniad i ddŵr, either directly or indirectly”.1 Dry mineral processing methods offer a solution to this looming problem.
Bydd dulliau sych fel gwahanu electrostatig yn dileu'r angen am ddŵr ffres, a chynnig y potensial i leihau costau. Electric separation methods that utilize contact, neu dribo-Electric, charging are particularity interesting because of their potential to separate a wide variety of mixtures containing conductive, Inswleiddio, a gronynnau lled ddargludol.
Tribo-Mae gwefru trydan yn digwydd pan fydd arwahanol, gronynnau annhebyg yn gwrthdaro â'i gilydd, neu gyda thrydydd arwyneb, gan arwain at wahaniaeth yn y tâl arwyneb rhwng y ddau fath o ronyn. Mae arwydd a maint y gwahaniaeth tâl yn dibynnu'n rhannol ar y gwahaniaeth mewn affinedd electron (neu swyddogaeth waith) rhwng y mathau gronynnau. Gellir gwahanu wedyn drwy ddefnyddio maes trydan a gymhwysir yn allanol.
Mae'r dechneg wedi'i defnyddio'n ddiwydiannol mewn gwahanyddion math fertigol am ddim. Mewn gwahanyddion di-dâl, y gronynnau i'w prynu'n gyntaf, 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 i 0.1 mm.3,4 One of the most promising new developments in dry mineral separations is the tribo-electrostatic belt separator. Mae'r dechnoleg hon wedi ymestyn yr ystod maint gronynnau i mân ronynnau na thechnolegau gwahanu electrostatig confensiynol, mewn i'r ystod lle mae dim ond arnofio wedi bod yn llwyddiannus yn y gorffennol.
Tribo-Electrostatic Belt Separation
Yn y tribo-gwahanydd gwregys electrostatig (Ffigur 1 a ffigur 2), deunydd yn cael ei fwydo i'r bwlch tenau 0.9 – 1.5 cm rhwng dwy electrodau planhigol cyfochrog. Mae'r gronynnau yn cael eu codi'n triboelectrically gan gyswllt rhyngronynnau. Er enghraifft, yn achos lludw anghyfreithlon hylosgi glo, cymysgedd o ronynnau carbon a gronynnau mwynau, mae'r carbon a godir yn gadarnhaol a'r mwynau a godir yn negyddol yn cael eu denu i electrodau gyferbyn. Yna mae'r gronynnau yn cael eu ysgubo i fyny gan lain-rwyllau agored sy'n symud yn barhaus ac yn cael eu cyfleu i gyfeiriadau gyferbyn. Mae'r gwregys yn symud y gronynnau wrth ymyl pob electrod tuag at ben arall y gwahanydd. Mae'r maes trydan angen dim ond symud y gronynnau yn ffracsiwn bach o centimedr i symud gronyn o symud chwith i Nant sy'n symud i'r dde. 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. Mae cyflymder uchel y llain hefyd yn galluogi, hyd at 40 tunnell yr awr ar wahanydd unigol. Drwy reoli paramedrau proses amrywiol, megis cyflymder gwregysau, pwynt porthiant, bwlch electrod a chyfradd porthiant, mae'r ddyfais yn cynhyrchu lludw anghyfreithlon carbon isel ar gynnwys carbon o 2 % ± 0.5% o gywion anghyfreithlon porthiant yn amrywio mewn carbon o 4% i dros 30%.
Mae'r dyluniad gwahanydd yn gymharol syml. Y gwregys a'r rholeri cysylltiedig yw'r unig rannau sy'n symud. Mae'r electrodau yn llonydd ac yn cynnwys deunydd sy'n para'n briodol. Mae'r gwregys wedi ei wneud o ddeunydd plastig. Mae'r darn electrod gwahanydd tua 6 Mesuryddion (20 Troedfedd.) a'r lled 1.25 Mesuryddion (4 Troedfedd.) ar gyfer unedau masnachol maint llawn. Mae'r defnydd o bŵer yn llai na 2 cilowat-awr y dunnell o ddeunydd a brosesir gyda'r rhan fwyaf o'r pŵer a ddefnyddir gan ddau fodur sy'n gyrru'r gwregys.
Mae'r broses yn hollol sych, Nid oes angen unrhyw ddeunyddiau ychwanegol ac nid yw'n cynhyrchu unrhyw ddŵr gwastraff nac allyriadau. Yn achos carbon o wahanu lludw anghyfreithlon, mae'r deunyddiau a adenillir yn cynnwys lludw anghyfreithlon wedi'i leihau mewn cynnwys carbon i lefelau sy'n addas i'w defnyddio fel gymysgedd pozzolaidd mewn concrit, a ffracsiwn carbon uchel y gellir ei losgi yn y gwaith cynhyrchu trydan. Mae defnyddio'r ddwy ffrwd gynnyrch yn darparu 100% ateb i broblemau gwaredu lludw anghyfreithlon. For mineral separations, processing bauxite for example, the separator provides a technology to reduce water usage, ymestyn bywyd wrth gefn a/neu adfer ac ailbrosesu teilchion.
The tribo-electrostatic belt separator is relatively compact. Peiriant sydd wedi'i gynllunio i brosesu 40 tonnes per hour is approximately 9.1 Mesuryddion (30 Troedfedd.) Hir, 1.7 Mesuryddion (5.5 Troedfedd.) eang a 3.2 Mesuryddion (10.5 Troedfedd.) Uchel. Mae'r cydbwysedd gofynnol o blanhigion yn cynnwys systemau i gyfleu deunydd sych i'r gwahanydd ac oddi wrth. Mae crynoder y system yn caniatáu hyblygrwydd mewn dyluniadau gosod.
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. Mae'r dechnoleg yn effeithiol wrth wahanu gronynnau carbon oddi wrth hylosgiad anghyflawn glo, oddi ar y gwydryn'n alwosilicate o ronynnau mwynol yn y Lludw clêr. Mae'r dechnoleg wedi bod yn gyfrwng i alluogi ailgylchu'r lludw pryfed mwynol llawn mwynau i gymryd lle mewn cynhyrchu concrit. Ers 1995, Dros 20,000,000 tonnes of fly ash has been processed by the 19 tribo-electrostatic belt separators installed in the USA, Canada, Du, Gwlad Pwyl, and South Korea. The industrial history of fly ash separation is listed in Tabl 1.
Tabl 1. Cymhwysiad diwydiannol tribo-gwahanu gwregys electrostatig ar gyfer lludw sy'n hedfan
| Cyfleustodau / gorsaf bwer | Lleoliad | Dechrau gweithrediadau masnachol | Manylion y cyfleuster |
|---|---|---|---|
| Ynni Dug – gorsaf Roxboro | Gogledd Carolina UDA | 1997 | 2 Gwahanyddion |
| Ynni talen- Esgidiau Brandon | Maryland UDA | 1999 | 2 Gwahanyddion |
| Scottish Power- Gorsaf longannet | Scotland UK | 2002 | 1 Gwahanydd |
| Jacksonville Electric-St. Mae Parc pŵer afon Johns | Florida UDA | 2003 | 2 Gwahanyddion |
| Pŵer trydan de Mississippi-R. D. Morrow | Mississippi UDA | 2005 | 1 Gwahanydd |
| New Brunswick Power-Belledune | New Brunswick Canada | 2005 | 1 Gwahanydd |
| RWE npower-gorsaf Didcot | England UK | 2005 | 1 Gwahanydd |
| Talen Energy-gorsaf Ynys Brunner | Pennsylvania UDA | 2006 | 2 Gwahanyddion |
| Tampa Electric-gorsaf fawr yn plygu | Florida UDA | 2008 | 3 Gwahanyddion two-pass scavenging |
| RWE npower-gorsaf Aberddawan | Cymru'r DU | 2008 | 1 Gwahanydd |
| EDF Energy-gorsaf Burton-Gorllewin | England UK | 2008 | 1 Gwahanydd |
| ZGP (Lafarge cemeg/Ciech Janikosoda JV) | Gwlad Pwyl | 2010 | 1 Gwahanydd |
| Corea southeast pŵer- Yeongheung | De Corea | 2014 | 1 Gwahanydd |
| Cymorth PGNiG Termika-Sierkirki | Gwlad Pwyl | 2018 | 1 Gwahanydd |
| Cwmni sment taiheiyo-Chichibu | Siapan | 2018 | 1 Gwahanydd |
| Lludw'n hedfan Armstrong- Cewri'r eryr | Philipinau | Scheduled 2019 | 1 Gwahanydd |
| Corea southeast pŵer- Samcheonpo | De Corea | Scheduled 2019 | 1 Gwahanydd |
Tribo-Electrostatic Separation of Bauxite Minerals
Offer sain & Technoleg (STET) performed bench scale dry tribo-electrostatic separation testing on multiple samples of bauxite minerals. The samples are listed below in Tabl 2.
Tabl 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 Tabl 3.
Tabl 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 Tabl 4.
Tabl 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. Defnyddir y gwahanydd pen-uchaf ar gyfer sgrinio am dystiolaeth o godi tâl electrostatig ac i benderfynu a yw deunydd yn ymgeisydd da ar gyfer bywoliaeth electrostatig. 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 gwaith hyd y cyfnod peilot ac unedau ar raddfa fasnachol. Gan fod yr effeithlonrwydd gwahanydd yn ffwythiant o'r hyd electrod, Ni ellir defnyddio profion ar raddfa fainc yn lle profion ar raddfa beilot. Mae profion ar raddfa beilot yn angenrheidiol i benderfynu ar faint y gwahanu y gall y broses STET ei gyflawni, ac i benderfynu a all proses STET gwrdd â thargedau'r cynnyrch o dan gyfraddau porthiant a roddir. Yn lle, Defnyddir gwahanydd'r manben i ddiystyru'r deunyddiau ar gyfer ymgeiswyr sy'n annhebygol o ddangos unrhyw wahaniad arwyddocaol ar lefel y peilot. Bydd y canlyniadau a geir ar raddfa'r fainc yn ddi-optimeiddio, ac mae'r gwahanu a welwyd yn llai nag a fyddai'n cael ei weld ar wahanydd STET maint masnachol.
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. Yn ychwanegol, Mae prif elfennau eraill Fe2O3, SiO2 ac TiO2 dangos symudiad sylweddol yn y rhan fwyaf o achosion. In Sample 1, Sample 3 and Sample 4, y symudiad o golled ar gynnau (LOI) dilyn symudiad Al2O3. The movement of the major elements is shown below in Ffigur 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 Tabl 5.
Tabl 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. Yn ychwanegol, 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. Yn ychwanegol, 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 Tabl 6.
Tabl 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. Yn ychwanegol, Mae prif elfennau eraill 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.
Cyfeiriadau
1. Blin, P & Dion-Orteg, O (2013) Uchel a Sych, Cylchgrawn CIM, Cyfrol. 8, Na. 4, Tudalennau. 48-51.
2. Cymorth manouchehri, H, Cymorth hanumantha mo, K, & Forssberg, K (2000), Adolygiad o Ddulliau Gwahanu Trydanol, Rhan 1: Agweddau sylfaenol, Mwynau & Prosesu Metelegol, Cyfrol. 17, Na. 1 PP 23 – 36.
3. Cymorth manouchehri, H, Cymorth hanumantha mo, K, & Forssberg, K (2000), Adolygiad o Ddulliau Gwahanu Trydanol, Rhan 2: Ystyriaethau ymarferol, Mwynau & Prosesu Metelegol, Cyfrol. 17, Na. 1 PP 139 – 166.
4. Ralston O. (1961) Gwahanu electrostatig o solidau gronynnog cymysg, Elsevier cwmni cyhoeddi, allan o brint.
5. Kogel, Jessica Elzea; Trivedi, Nikhil C; Barker, James M; Krukowski, Stanley T.; Industrial Minerals and Rocks: Nwyddau, Marchnadoedd, and Uses 7th Edition, (2006), Page 237.
