Plėsti programos sausas Triboelectric atsiskirtų mineralinės medžiagos

Expanding Applications in Dry Triboelectric

Separation of Minerals

James D. Bittner, Daiva Petkeviciene. Flynn, Ir Rasa Janušonienė. Hrach

ST įranga & Technologijos UAB, Needham Massachusetts 02494 JUNGTINĖS AMERIKOS VALSTIJOS

Tel: +1‐781‐972‐2300, email: jbittner@titanamerica.com

Abstraktus

ST įranga & Technologijos, UAB (STET) has developed a processing system based on triboelectrostatic belt separation 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) vidutiniškai šiurkštus (300μm) particles with very high throughput. The high efficiency multi‐stage separation through internal charging/recharging and recycle results in far superior separations that can be achieved with a conventional single‐stage free‐ fall triboelectrostatic separator. Triboelektrinio diržo separatoriaus technologija buvo naudojama atskirti įvairias medžiagas, įskaitant stiklinių aliuminio silikatų ir anglies mišinius, kalcitas/kvarcas, talkas /magnezitas, ir baritas /kvarcas. An economic comparison of using the triboelectrostatic belt separation versus conventional flotation for barite / quartz separation illustrates the advantages of dry processing for minerals.

Raktiniai žodžiai: Mineralų, dry separation, barito, triboelectrostatic charging, belt separator, lakieji pelenai

ĮVADAS

The lack of access to fresh water is becoming a major factor affecting the feasibility of mining projects around the world. According to Hubert Fleming, former global director for Hatch Water, “Of all the mining projects in the world that have either been stopped or slowed down over the past year, it has been, in almost 100% of the cases, a result of water, either directly or indirectly” Blin (2013). Dry mineral processing methods offer a solution to this looming problem.

Wet separation methods such as froth flotation require the addition of chemical reagents that must be handled safely and disposed of in an environmentally responsible manner. Inevitably it is not possible to operate with 100% water recycle, requiring disposal of at least of portion of the process water, likely containing trace amounts of chemical reagents.

Dry methods such as electrostatic separation will eliminate the need for fresh water, and offer the potential to reduce costs. One of the most promising new developments in dry mineral separations is the triboelectrostatic belt separator. Ši technologija išplėtė dalelių dydžio diapazoną iki smulkesnių dalelių nei įprastos elektrostatinio atskyrimo technologijos, į diapazoną, kuriame praeityje buvo sėkminga tik flotacija.

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Paveikslas 2. Išsami informacija apie atskyrimo zoną

Šis procesas yra visiškai sausas, nereikalauja jokių papildomų medžiagų ir negamina jokių nuotekų ar oro teršalų. In the case of carbon from fly ash separations, the recovered materials consist of fly ash reduced in carbon content to levels suitable for use as a pozzolanic admixture in concrete, and a high carbon fraction which can be burned at the electricity generating plant. Abiejų produktų srautų panaudojimas suteikia tam 100% pelenų šalinimo problemų sprendimas.

The triboelectrostatic belt separator is relatively compact. Mašina, skirta apdoroti 40 tonos per valandą yra maždaug 9.1 matuokliai (30 Ft) ilgas, 1.7 matuokliai (5.5 metrų.) platus ir 3.2 matuokliai (10.5 metrų.) didelis. The required balance of plant consists of systems to convey dry material to and from the separator. Sistemos kompaktiškumas leidžia lanksčiai projektuoti montavimo dizainą.

Paveikslas 3. Commercial triboelectrostatic belt separator

Comparison to other electrostatic separation processes

The triboelectrostatic belt separation technology greatly expands the range of materials that can be beneficiated by electrostatic processes. The most commonly used electrostatic processes rely on differences in the electrical conductivity of the materials to be separated. Šiuose procesuose, medžiaga turi liestis su įžemintu būgnu arba plokštele paprastai po to, kai medžiagos dalelės yra neigiamai įkrautos jonizuojančiosios koronos išsiskyrimo. Laidiosios medžiagos greitai praras savo įkrovą ir bus išmestos iš būgno. The non‐conductive material continues to be attracted to the drum since the

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charge will dissipate more slowly and will fall or be brushed from the drum after separation from the conducting material. These processes are limited in capacity due to the required contact of every particle to the drum or plate. The effectiveness of these contact charging processes are also limited to particles of about 100 μm or greater in size due to both the need to contact the grounded plate and the required particle flow dynamics. Įvairių dydžių dalelės taip pat turės skirtingą srauto dinamiką dėl inercinio poveikio ir sukels pablogėjusį atskyrimą. Ši diagrama (Paveikslas 4) iliustruoja pagrindinius šio tipo separatoriaus bruožus.

Paveikslas 4. Drum electrostatic separator “Elder (2003)"

Triboelektrostatiniai atskyrimai neapsiriboja laidžių / non‐conductive materials but depend on the well known phenomenon of charge transfer by frictional contact of materials with dissimilar surface chemistry. Šis reiškinys jau dešimtmečius naudojamas "laisvo kritimo" atskyrimo procesuose. Toks procesas pavaizduotas 5. Dalelių mišinio komponentai pirmiausia sukuria skirtingus krūviai, susilietus su metaliniu paviršiumi, or by particle to particle contact in a fluidized bed feeding device. As the particles fall through the electric field in the electrode zone, kiekvienos dalelės trajektorija nukreipiama į priešingos krūvio elektrodą. Po tam tikro atstumo, surinkimo dėžės naudojamos srautams atskirti. Tipiniai įrenginiai reikalauja kelių skyriklio etapų su vidutinio tankio frakcijos perdirbimu. Kai kurie prietaisai naudoja pastovų dujų srautą, kad padėtų perduoti daleles per elektrodo zoną.

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Paveikslas 5. "Laisvo kritimo" triboelektrostatinis separatorius

Šio tipo laisvo kritimo separatorius taip pat turi medžiagos dalelių dydžio apribojimus, kuriuos galima apdoroti. Srautas elektrodų zonoje turi būti kontroliuojamas, kad būtų kuo mažiau turbulencijos, kad būtų išvengta atskyrimo "tepimo". Smulkių dalelių trajektoriją labiau veikia turbulencija, nes smulkių dalelių aerodinaminės tempimo jėgos yra daug didesnės nei gravitacinės ir elektrostatinės jėgos. The very fine particles will also tend to collect on the electrode surfaces and must be removed by some method. Dalelės, mažesnės nei 75 μm cannot be effectively separated.

Another limitation is that the particle loading within the electrode zone must be low to prevent space charge effects, kurios riboja apdorojimo normą. Passing material through the electrode zone inherently results in a single‐stage separation, since there is no possibility for re‐charging of particles. Todėl, multi‐stage systems are required for improving the degree of separation including re‐charging of the material by subsequent contact with a charging device. Dėl to atsirandančios įrangos tūris ir sudėtingumas atitinkamai didėja.

In contrast to the other available electrostatic separation processes, the triboelectrostatic belt separator is ideally suited for separation of very fine (<1 μm) vidutiniškai šiurkštus (300μm) materials with very high throughputs. The triboelectric particle charging is effective for a wide range of materials and only requires particle – particle contact. Maži tarpai, high electric field, skaitiklis srov, vigorous particle‐particle agitation and self‐cleaning action of the belt on the electrodes are the critical features of the separator. The high efficiency multi‐stage separation through charging / recharging and internal recycle results in far superior separations and is effective on fine materials that cannot be separated at all by the conventional techniques.

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APPLICATIONS OF TRIBOELECTROSTATIC BELT SEPARATION

Lakieji pelenai

The triboelectrostatic belt separation technology was first applied industrially to the processing of coal combustion fly ash in 1995. For the fly ash application, the technology has been effective in separating carbon particles from the incomplete combustion of coal, iš stiklinių aliuminio mineralų dalelių lakiosiose pelenuose. The technology has been instrumental in enabling recycle of the mineral‐rich flyash as a cement replacement in concrete production. Nuo 1995, 19 triboelectrostatic belt separators have been operating in the USA, Kanada, JUNGTINĖ KARALYSTĖ, and Poland, processing over 1,000,000 tonnes of fly ash annually. The technology is now also in Asia with the first separator installed in South Korea this year. Pramoninis skraidančio pelenų atskyrimo istorija yra nurodytas lentelėje 1.

Lentelė 3. Examples, mineral separations using triboelectrostatic belt separation

Use of the triboelectrostatic belt separator has been demonstrated to effectively beneficiate many mineral mixtures. Since the separator can process materials with particle sizes from about 300 μm to less than 1 μm, and the triboelectrostatic separation is effective for both insulating and conductive materials, the technology greatly extends the range of applicable material over conventional electrostatic separators. Since the triboelectrostatic process is entirely dry, use of it eliminates the need for material drying and liquid waste handling from flotation processes.

COST OF TRIBOELECTROSTATIC BELT SEPARATION

Comparison to Conventional Flotation for Barite

Lyginamąjį sąnaudų tyrimą užsakė STET ir atliko "Soutex Inc". Soutex yra Kvebeko Kanadoje įsikūrusi inžinerijos įmonė, turinti didelę patirtį tiek šlapio flotacijos, tiek elektrostatinio atskyrimo proceso vertinimo ir projektavimo srityse. The study compared the capital and operating costs of triboelectrostatic belt separation process to conventional froth flotation for the beneficiation of a low‐grade barite ore. Both technologies upgrade the barite by removal of low density solids, mainly quartz, to produce an American Petroleum Institute (API) drilling grade barite with SG greater than 4.2 g/ml. Flotation results were based on pilot plant studies conducted by the Indian National Mettalurgical Laboratory “NML (2004)". Triboelectrostatic belt separation results were based on pilot plant studies using similar feed ores. The comparative economic study included flowsheet development, material and energy balances, major equipment sizing and quotation for both flotation and triboelectrostatic belt separation processes. The basis for both flowsheets is the same, Perdirbimo 200,000 t/y of barite feed with SG 3.78 to produce 148,000 t/y of drilling grade barite product with SG 4.21 g/ml. The flotation process estimate did not include any costs for process water, or water treatment.

Flowsheets were generated by Soutex for the barite flotation process (Paveikslas 6), and triboelectrostatic belt separation process (Paveikslas 7).

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Paveikslas 6 Barite flotation process flowsheet

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Paveikslas 7 Barite triboelectrostatic belt separation process flowsheet

Theses flowsheets do not include a raw ore crushing system, which is common to both technologies. Feed grinding for the flotation case is accomplished using a wet pulp ball mill with cyclone classifier. Feed grinding for the triboelectrostatic belt separation case is accomplished using a dry, vertical roller mill with integral dynamic classifier.

The triboelectrostatic belt separation flowsheet is simpler than flotation. Triboelectostatic belt separation is achieved in a single stage without the addition of any chemical reagents, compared to three‐stage flotation with oleic acid used as a collector for barite and sodium silicate as a depressant for the silica gangue. A flocculant is also added as a reagent for thickening in the barite flotation case. No dewatering and drying equipment is required for triboelectrostatic belt separation, compared to thickeners, filter presses, and rotary dryers required for the barite flotation process.

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NUORODOS

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