Izvēlieties valodu:
Lucas Rojas Mendoza, ST aprīkojums & Tehnoloģija, ASV
lrojasmendoza@steqtech.com
Frank Hrach, ST aprīkojums & Tehnoloģija, ASV
Kyle Flynn, ST aprīkojums & Tehnoloģija, ASV
Abhishek Gupta, ST aprīkojums & Tehnoloģija, ASV
ST aprīkojums & Tehnoloģiju LLC (STET) has developed a novel processing system based on tribo-electrostatic belt separation that provides the mineral processing industry a means to beneficiate fine materials with an energy-efficient and entirely dry technology. In contrast to other electrostatic separation processes that are typically limited to particles >75μm izmērs, the STET triboelectric belt separator is suited for separation of very fine (<1µm) līdz vidēji rupjai (500µm) Daļiņas, ar ļoti augstu caurlaidspēju. The STET tribo-electrostatic technology has been used to process and commercially separate a wide range of industrial minerals and other dry granular powders. šeit, bench-scale results are presented on the beneficiation of low-grade Fe ore fines using STET belt separation process. Bench-scale testing demonstrated the capability of the STET technology to simultaneously recover Fe and reject SiO2 from itabirite ore with a D50 of 60µm and ultrafine Fe ore tailings with a D50 of 20µm. The STET technology is presented as an alternative to beneficiate Fe ore fines that could not be successfully treated via traditional flowsheet circuits due to their granulometry and mineralogy.
Dzelzsrūda ir ceturtais visizplatītākais zemes garozas elements [1]. Dzelzs ir būtisks tērauda ražošanā, un tāpēc tas ir būtisks materiāls pasaules ekonomikas attīstībai [1-2]. Dzelzs tiek plaši izmantots arī būvniecībā un transportlīdzekļu ražošanā [3]. Lielāko daļu dzelzsrūdas resursu veido metamorfizēti dzelzs veidojumi (BIF) kurā dzelzs parasti atrodams oksīdu veidā, hidroksīdi un mazākā mērā karbonāti [4-5]. A particular type of iron formations with higher carbonate contents are dolomitic itabirites which are a product of the dolomitization and metamorphism of BIF deposits [6]. The largest iron ore deposits in the world can be found in Australia, Ķīna, Kanāda, Ukraina, India and Brazil [5].
Dzelzsrūdu ķīmiskajam sastāvam ir acīmredzami plašs ķīmiskā sastāva diapazons, jo īpaši Fe saturam un ar to saistītajiem gangu minerāliem [1]. Galvenie dzelzs minerāli, kas saistīti ar lielāko daļu dzelzsrūdu, ir hematīts, goetīts, limonīts un magnetīts [1,5]. Galvenie piesārņotāji dzelzsrūdās ir SiO2 un Al2O3 [1,5,7]. Tipiskie silīcija dioksīda un alumīnija oksīdu saturošie minerāli, kas atrodas dzelzs rūdās, ir kvarcs, kaolinīts, gibbsite, diaspora un korunds. Of these it is often observed that quartz is the mean silica bearing mineral and kaolinite and gibbsite are the two-main alumina bearing minerals [7].
Dzelzsrūdas ieguve galvenokārt tiek veikta, veicot atklātas raktuvju ieguves darbības, rezultātā rodas ievērojama sārņu veidošanās [2]. Dzelzsrūdas ražošanas sistēma parasti ietver trīs posmus: Ieguves, apstrādes un granulēšanas darbības. No tiem, apstrāde nodrošina, ka pirms granulēšanas posma tiek sasniegta atbilstoša dzelzs pakāpe un ķīmija. Apstrāde ietver saspiešanu, klasifikācija, milling and concentration aiming at increasing the iron content while reducing the amount of gangue minerals [1-2]. Katrai minerālu atradnei ir savas unikālas īpašības attiecībā uz dzelzi un gangu saturošiem minerāliem, un tāpēc tam ir nepieciešama cita koncentrācijas tehnika [7].
Magnetic separation is typically used in the beneficiation of high grade iron ores where the dominant iron minerals are ferro and paramagnetic [1,5]. Mitra un sausa zemas intensitātes magnētiskā atdalīšana (LIMS) metodes tiek izmantotas, lai apstrādātu rūdas ar spēcīgām magnētiskām īpašībām, piemēram, magnetītu, savukārt mitru augstas intensitātes magnētisko atdalīšanu izmanto, lai atdalītu Fe saturošus minerālus ar vājām magnētiskām īpašībām, piemēram, hematītu no ganga minerāliem. Dzelzs rūdas, piemēram, getīts un limonīts, parasti sastopamas sārņos un ne ar vienu vai otru paņēmienu ļoti labi neatdalās; [1,5]. Magnetic methods present challenges in terms of their low capacities and in terms of the requirement for the iron ore to be susceptible to magnetic fields [5].
Flotation, on the other hand, is used to reduce the content of impurities in low-grade iron ores [1-2,5]. Dzelzs rūdas var koncentrēt vai nu ar tiešu dzelzs oksīdu anjonu flotāciju, vai ar silīcija dioksīda reverso katjonu flotāciju, tomēr apgrieztā katjonu flotācija joprojām ir populārākais flotācijas ceļš, ko izmanto dzelzs rūpniecībā [5,7]. Flotācijas izmantošana ir ierobežota ar reaģentu izmaksām, silīcija dioksīda un alumīnija oksīda bagātu gļotu klātbūtne un karbonātu minerālu klātbūtne [7-8]. Turklāt, flotācijai nepieciešama notekūdeņu attīrīšana un lejteces atūdeņošanas izmantošana sausai galīgai izmantošanai [1].
Flotācijas izmantošana dzelzs koncentrācijai ietver arī novājēšanu, jo peldēšana naudas sodu klātbūtnē samazina efektivitāti un rada augstas reaģentu izmaksas [5,7]. Denovēšana ir īpaši kritiska alumīnija oksīda noņemšanai, jo gibsīta atdalīšana no hematīta vai getīta ar jebkādām virsmaktīvajām vielām ir diezgan sarežģīta [7]. Lielākā daļa alumīnija oksīdu saturošo minerālu rodas smalkākā izmēru diapazonā (<20Um) ļaujot to noņemt, izmantojot novājēšanu. Vispārējo, augsta naudas sodu koncentrācija (<20Um) un alumīnija oksīds palielina nepieciešamo katjonu kolektora devu un dramatiski samazina selektivitāti [5,7].
Turklāt, the presence of carbonate minerals – such as in dolomitic itabirites- can also deteriorate flotation selectivity between iron minerals and quartz as iron ores containing carbonates such as dolomite do not float very selectively. Dissolved carbonates species adsorb on the quartz surfaces harming the selectivity of flotation [8]. Flotation can be reasonably effective in upgrading low-grade iron ores, but it is strongly dependent on the ore mineralogy [1-3,5]. Flotation of iron ores containing high alumina content will be possible via desliming at the expense of the overall iron recovery [7], while flotation of iron ores containing carbonate minerals will be challenging and possibly not feasible [8].
Modern processing circuits of Fe-bearing minerals may include both flotation and magnetic concentration steps [1,5]. For instance, magnetic concentration can be used on the fines stream from the desliming stage prior to flotation and on the flotation rejects. The incorporation of low and high intensity magnetic concentrators allows for an increase in the overall iron recovery in the processing circuit by recovering a fraction of the ferro and paramagnetic iron minerals such as magnetite and hematite [1]. Goethite is typically the main component of many iron plant reject streams due to its weak magnetic properties [9]. In the absence of further downstream processing for the reject streams from magnetic concentration and flotation, the fine rejects will end up disposed in a tailings dam [2]. Tailings disposal and processing have become crucial for environmental preservation and recovery of iron valuables, attiecīgi, and therefore the processing of iron ore tailings in the mining industry has grown in importance [10].
Clearly, the processing of tailings from traditional iron beneficiation circuits and the processing of dolomitic itabirite is challenging via traditional desliming-flotation-magnetic concentration flowsheets due to their mineralogy and granulometry, and therefore alternative beneficiation technologies such as tribo-electrostatic separation which is less restrictive in terms of the ore mineralogy and that allows for the processing of fines may be of interest.
Triboelektrostatiskā atdalīšana izmanto elektrisko lādiņu atšķirības starp materiāliem, kas radušies virsmas saskares vai triboelektriskās uzlādes procesā. Vienkāršotā veidā, , kad divi materiāli ir saskarē, the material with a higher affinity for electron gains electrons thus charges negative, bet materiāls ar zemāku elektronu afinitāti uzlādē pozitīvus. In principle, low-grade iron ore fines and dolomitic itabirites that are not processable by means of conventional flotation and/or magnetic separation could be upgraded by exploiting the differential charging property of their minerals [11].
Here we present STET tribo-electrostatic belt separation as a possible beneficiation route to concentrate ultrafine iron ore tailings and to beneficiate dolomitic itabirite mineral. The STET process provides the mineral processing industry with a unique water-free capability to process dry feed. The environmentally friendly process can eliminate the need for wet processing, downstream waste water treatment and required drying of final material. turklāt, 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.
Materiāli
Two fine low-grade iron ores were used in this series of tests. The first ore consisted of an ultrafine Fe ore tailings sample with a D50 of 20 µm and the second sample of an itabirite iron ore sample with a D50 of 60 µm. Both samples present challenges during their beneficiation and cannot be efficiently processed through traditional desliming-flotation-magnetic concentration circuits due to their granulometry and mineralogy. Both samples were obtained from mining operations in Brazil.
The first sample was obtained from an existing desliming-flotation-magnetic concentration circuit. The sample was collected from a tailings dam, then dried, homogenized and packed. The second sample is from an itabirite iron formation in Brazil. The sample was crushed and sorted by size and the fine fraction obtained from the classification stage later underwent several stages of desliming until a D98 of 150 µm was achieved. The sample was then dried, homogenized and packed.
Particle size distributions (PSD) were determined using a laser diffraction particle size analyzer, a Malvern’s Mastersizer 3000 E. Abiem paraugiem tika arī raksturo zaudējumi uz aizdedzes(LOI), XRF un XRD. Zudums, karsējot (LOI) tika noteikts, novietojot 4 gramiem parauga 1000 Ēc krāsns 60 minūtes un ziņošanas LOI kārtā kā saņemto. Ķīmiskā sastāva analīze tika aizpildītas viļņu dispersīvs x-ray Fluorescence (WD-XRF) instrumentu un galveno kristālisko fāžu izpētījis XRD tehnika.
Ķīmiskais sastāvs un LOI sārņu paraugu (Smagās frakcijas), un itabirite dzelzs veidošanās paraugu (Itabirite), tiek parādīts tabulā 1 and particle size distributions for both samples are shown in Fig 1. For the tailings sample the main Fe recoverable phases are goethite and hematite, and the main gangue mineral is quartz (Vīģes 4). For the itabirite sample the main Fe recoverable phases are hematite, and the main gangue minerals are quartz and dolomite (Vīģes 4).
Tabula 1. Result of chemical analysis for major elements in tailings and Itabirite samples.
| Sample | Grade (wt%) | |||||||
|---|---|---|---|---|---|---|---|---|
| Fe | SiO2 SiO2 | Al2O3 Al2O3 | MnO | Mgo | Cao | LOI** | Others | |
| Smagās frakcijas | 30.3 | 47.4 | 4.3 | 1.0 | * | * | 3.4 | 13.4 |
| Itabirite | 47.6 | 23.0 | 0.7 | 0.2 | 1.5 | 2.2 | 4.0 | 21.0 |
Particle Size Distributions
Metodes
A series of experiments were designed to investigate the effect of different parameters on iron movement in both iron samples using STET proprietary tribo-electrostatic belt separator technology. Eksperimenti tika veikti, izmantojot stenda mēroga triboelektrostatisko jostas atdalītāju, turpmāk "stenda atdalītājs". Stenda mēroga testēšana ir trīsfāžu tehnoloģiju ieviešanas procesa pirmais posms (Skatīt tabulu 2) tostarp sola novērtējums, izmēģinājuma mēroga testēšana un komerciāla mēroga īstenošana. Stenda separatoru izmanto triboelektrostatiskās uzlādes pierādījumu skrīningam un lai noteiktu, vai materiāls ir labs kandidāts elektrostatiskajam labumam. Galvenās atšķirības starp katru iekārtu ir norādītas tabulā 2. Lai gan katrā posmā izmantotais aprīkojums atšķiras pēc izmēra, darbības princips būtībā ir viens un tas pats.
Tabula 2. Trīsfāžu ieviešanas process, izmantojot STET triboelektrostatisko jostas atdalītāja tehnoloģiju
| Fāze | Izmanto: | Elektrods Dimensions (W x L) cm | Type of Process/ |
|---|---|---|---|
| Stenda skala Novērtēšanas | Kvalitatīvu Novērtēšanas | 5*250 | Partijas |
| Pilota mērogs Testēšana | Kvantitatīvs Novērtēšanas | 15*610 | Partijas |
| Komerciālo Mērogs Implementation | Komerciālo Ražošana | 107 *610 | Nepārtrauktu |
STET Operation Principle
The operation principle of the separator relies on tribo-electrostatic charging. Triboelektrostatiskās jostas atdalītājā (Skaitļi 2 un 3), material is fed into the narrow gap 0.9 - 1.5 cm starp diviem paralēliem planārajiem elektrodiem. Daļiņas ir triboelektriski uzlādētas, saskaroties ar starpdaļiņām. The positively charged mineral(s) and the negatively charged mineral(s) pievelkas iepretim elektrodi. Inside the separator particles are swept up by a continuous moving open-mesh belt and conveyed in opposite directions. Drošības jostas ir izgatavota no plastmasas materiāla un blakus katra elektroda pie pretējās galus atdalītāju daļiņas kustas. Letes straumju plūsmas dalāmo daļiņu un nemitīgu triboelectric tarifikācijas, daļiņu daļiņu sadursmes paredz daudzpakāpju atdalīšana un rada lielisku tīrību un atgūšanas iet vienā vienībā. Triboelectric jostas atdalītāju tehnoloģija ir lietots, lai atdalītu plašu materiālu, to skaitā maisījumos, stiklveida aluminosilicates/oglekļa (vieglie pelni), Kalcīts/kvarcs, talks/magnezāts, un barīts/kvarcs.
Vispārējo, the separator design is relatively simple with the belt and associated rollers as the only moving parts. Elektrodi ir nekustīgi un sastāv no atbilstoši izturīga materiāla. Separatora elektroda garums ir aptuveni 6 metru (20 ft.) un platums 1.25 metru (4 ft.) pilna izmēra komerciālām vienībām. The high belt speed enables very high throughputs, līdz 40 tons per hour for full size commercial units. Enerģijas patēriņš ir mazāks par 2 kilowatt-hours per ton of material processed with most of the power consumed by two motors driving the belt.
Triboelektrisko jostu atdalītāja shēma
Atdalīšanas zonas detaļas
Kā redzams tabulā 2, galvenā atšķirība starp stenda separatoru un pilota mēroga un komerciālā mēroga separatoriem ir tāda, ka stenda separatora garums ir aptuveni 0.4 kas ir reizes garāks par pilota mēroga un komerciāla mēroga vienībām. Tā kā separatora efektivitāte ir elektroda garuma funkcija, stenda mēroga testēšanu nevar izmantot kā pilota mēroga testēšanas aizstājēju. Izmēģinājuma mēroga testēšana ir nepieciešama, lai noteiktu, cik lielā mērā STET process var sasniegt, un noteikt, vai STET process var sasniegt produktu mērķus saskaņā ar likmi, kas noteikta. Vietā, stenda separatoru izmanto, lai izslēgtu kandidātmateriālus, kas, visticamāk, nepierādīs būtisku atdalīšanu pilota skalas līmenī.. Rezultāti, kas iegūti stenda mērogā, netiks optimizēti, un novērotā nošķiršana ir mazāka par to, kas būtu novērojama komerciāla izmēra STET separatorā.
Testēšana pilotiepludējumos ir nepieciešama pirms komerciāla mēroga ieviešanas, Tomēr, tiek veicināta testēšana stenda mērogā kā īstenošanas procesa pirmais posms attiecībā uz jebkuru konkrētu materiālu,. Turklāt, gadījumos, kad materiālu pieejamība ir ierobežota, stenda atdalītājs ir noderīgs instruments potenciālo veiksmīgo projektu pārbaudei (t.i., projekti, kuros var sasniegt klientu un nozares kvalitātes mērķus, izmantojot STET tehnoloģiju).
Stenda mēroga testēšana
Standard process trials were performed around the specific goal to increase Fe concentration and to reduce the concentration of gangue minerals. Different variables were explored to maximize iron movement and to determine the direction of movement of different minerals. The direction of movement observed during benchtop testing is indicative of the direction of movement at the pilot plant and commercial scale.
The variables investigated included relative humidity (RH), temperatūra, electrode polarity, belt speed and applied voltage. No tiem, RH and temperature alone can have a large effect on differential tribo-charging and therefore on separation results. Tādējādi, optimum RH and temperature conditions were determined before investigating the effect of the remaining variables. Tika pētītas divas polaritātes līmeņi: es) Tops elektrodu polaritāti pozitīvo un ii) negatīva augšējā elektrodu polaritātes. Par STET atdalītāju, saskaņā ar vienošanos par konkrētu polaritāti un optimālu RH un temperatūras apstākļos, lentes ātrums ir galvenais kontroles tura pilnveidot produktu pakāpes un masveida atkopšanas. Sola atdalītāju palīdz šķūnī gaismu uz noteiktiem ekspluatācijas mainīgajiem ietekmi uz tribo elektrostatisko maksas konkrētā minerālu paraugu testēšana, un tāpēc var izmantot iegūtos rezultātus un tendences, to certain degree, to narrow down the number of variables and experiments to be performed at the pilot plant scale. Tabula 3 lists the range of separation conditions used as part of phase 1 evaluation process for the tailings and itabirite samples.
Tabula 3 lists the range of separation conditions
| Parameter | Units | Range of Values | |
|---|---|---|---|
| Smagās frakcijas | Itabirite | ||
| Top Electrode Polarity | - | Positive- Negative | Positive- Negative |
| Electrode Voltage | -kV/+kV | 4-5 | 4-5 |
| Feed Relative Humidity (RH) | % | 1-30.7 | 2-39.6 |
| Feed Temperature | °F (° C) | 71-90 (21.7-32.2) | 70-87 (21.1-30.6) |
| Belt Speed | Fps (m/s) | 10-45 (3.0-13.7) | 10-45 (3.0-13.7) |
| Electrode Gap | Inches (mm) | 0.400 (10.2 mm) | 0.400 (10.2 mm) |
Tika veikti testi stenda separatoram partijas apstākļos, with feed samples of 1.5 lbs. per test. A flush run using 1 lb. of material was introduced in between tests to ensure that any possible carryover effect from the previous condition was not considered. Before testing was started material was homogenized and sample bags containing both run and flush material were prepared. At the beginning of each experiment the temperature and relative humidity (RH) was measured using a Vaisala HM41 hand-held Humidity and Temperature probe. The range of temperature and RH across all experiments was 70-90 °F (21.1-32.2 (° C) un 1-39.6%, attiecīgi. To test a lower RH and/or higher temperature, feed and flush samples were kept in a drying oven at 100 °C for times between 30-60 Minūtes. Turpretī, higher RH values were attained by adding small amounts of waters to the material, followed by homogenization. After RH and temperature was measured on each feed sample, the next step was to set electrode polarity, belt speed and voltage to the desired level. Gap values were kept constant at 0.4 collas (10.2 mm) during the testing campaigns for the tailings and itabirite samples.
Pirms katra testa, a small feed sub-sample containing approximately 20g was collected (apzīmēts kā "Feed"). Iestatot visus darbības mainīgos, materiāls tika ievadīts sola separatorā, izmantojot elektrisko vibrācijas padevēju caur stenda separatora centru. Katra eksperimenta beigās tika savākti paraugi un produkta gala svars 1 (apzīmēts kā "E1") un produkta beigas 2 (apzīmēts kā "E2") tika noteiktas , izmantojot likumīgu tirdzniecības skaitīšanas skalu. Following each test, small sub-samples containing approximately 20 g of E1 and E2 were also collected. Mass yields to E1 and E2 are described by:
KurYE1 un YE2 are the mass yields to E1 and E2, attiecīgi; and are the sample weights collected to the separator products E1 and E2, attiecīgi. For both samples, Fe concentration was increased to product E2.
Katram apakšparaugu kopumam (t.i., Feed, E1 un E2) LOI and main oxides composition by XRF was determined. Fe2 O3 contents were determined from the values. For the tailings sample LOI will directly relate to the content of goethite in the sample as the functional hydroxyl groups in goethite will oxidize into H2 Og [10]. Gluži pretēji, for the itabirite sample LOI will directly relate to the contain of carbonates in the sample, as calcium and magnesium carbonates will decompose into their main oxides resulting in the release of CO2g and sub sequential sample loss weight. XRF beads were prepared by mixing 0.6 grams of mineral sample with 5.4 grams of lithium tetraborate, kas tika izvēlēta sakarā ar sārņus gan itabirite paraugi ķīmisko sastāvu. XRF analīze tika normalizēti, LOI.
Beidzot, FE atkopšanas EFe produkta (E2) un SiO2 noraidījums QSI tika aprēķināts. EFe ir Fe procentu atgūst sākotnējo barības parauga koncentrāts un QSiO2 procentuāli aizvāc no sākotnējā parauga plūsmu. EFe un QSI ir aprakstīts:
Kur Ces,(barība,E1, E2) tiek normalizēti koncentrācijā procenti apakš parauga i komponents (EG., Fe, SIO2)
Mineraloģija paraugi
The XRD pattern showing major mineral phases for the tailings and itabirite samples are shown in Fig 4. For the tailings sample the main Fe recoverable phases are goethite, hematite and magnetite, and the main gangue mineral is quartz (Vīģes 4). For the itabirite sample the main Fe recoverable phases are hematite and magnetite and the main gangue minerals are quartz and dolomite. Magnetite appears in trace concentrations in both samples. Pure hematite, goetīts, and magnetite contain 69.94%, 62.85%, 72.36% Fe, attiecīgi.
D patterns. A – Tailings sample, B – Itabirite sample
Stenda mēroga eksperimenti
A series of test runs were performed on each mineral sample aimed at maximizing Fe and decreasing SiO2 content. Species concentrating to E1 will be indicative of a negative charging behavior while species concentration to E2 to a positive charging behavior. Higher belt speeds were favorable to the processing of the tailings sample; Tomēr, the effect of this variable alone was found to be less significant for the itabirite sample.
Average results for the tailings and itabirite samples are presented in Fig 5, which were calculated from 6 un 4 experiments, attiecīgi. Vīģes 5 presents average mass yield and chemistry for feed and products E1 and E2. turklāt, each plot presents the improvement or decrease in concentration (E2- Feed) for each sample component e.g., Fe, SiO2 Positive values are associated to an increase in concentration to E2, while negative values are associated to a decrease in concentration to E2.
Fig.5. Average mass yields and chemistry for Feed, E1 and E2 products. Error bars represent 95% confidence intervals.
For the tailings sample Fe content was increased from 29.89% lai 53.75%, on average, at a mass yield YE2 – or global mass recovery – no 23.30%. This corresponds to Fe recovery ( and silica rejection (QE2 ) values of 44.17% un 95.44%, attiecīgi. The LOI content was increased from 3.66% lai 5.62% which indicates that the increase in Fe content is related to an increase in goethite content (Vīģes 5).
For the itabirite sample Fe content was increased from 47.68% lai 57.62%, on average, at a mass yield YE2 -no 65.0%. This corresponds to Fe recovery EFe( and silica rejection (QSiO2) values of 82.95% un 86.53%, attiecīgi. The LOI, MgO and CaO contents were increased from 4.06% lai 5.72%, 1.46 lai 1.87% and from 2.21 lai 3.16%, attiecīgi, which indicates that dolomite is moving in the same direction as Fe-bearing minerals (Vīģes 5).
For both samples,AL2 O3 , MnO and P seem to be charging in the same direction as Fe-bearing minerals (Vīģes 5). While it is desired to decrease the concentration of these three species, the combined concentration of SiO2, AL2 , O3 , YE2 MnO and P is decreasing for both samples, and therefore the total effect achieved using the benchtop separator is an enhancement in the product Fe grade and a decrease in the contaminants concentration.
Vispārējo, benchtop testing demonstrated evidence of effective charging and separation of iron and silica particles. The promising laboratory scale results suggest that pilot scale tests including first and second passes should be performed.
Diskusija
The experimental data suggests that the STET separator resulted in an important increase in Fe content while simultaneously reducing SiO2 content.
Having demonstrated that triboelectrostatic separation can result in a significant increase in Fe content, a discussion on the significance of the results, on the maximum achievable Fe contents and on the feed requirements of the technology is needed.
To start, it is important to discuss the apparent charging behavior of mineral species in both samples. For the tailings sample the main components were Fe oxides and quartz and experimental results demonstrated that Fe oxides concentrated to E2 while quartz concentrated to E1. Vienkāršotā veidā, it could be said that Fe oxide particles acquired a positive charge and that quartz particles acquired a negative charge. This behavior is consistent with the triboelectrostatic nature of both minerals as shown by Ferguson (2010) [12]. Tabula 4 shows the apparent triboelectric series for selected minerals based on inductive separation, and it shows that quartz is located at the bottom of the charging series while goethite, magnetite and hematite are located higher up in the series. Minerals at the top of the series will tend to charge positive, while minerals at the bottom will tend to acquire a negative charge.
On the other hand, for the itabirite sample the main components were hematite, quartz and dolomite and experimental results indicated that Fe oxides and dolomite concentrated to E2 while quartz concentrated to E1. This indicates that hematite particles and dolomite acquired a positive charge while quartz particles acquired a negative charge. Kā redzams tabulā 4, carbonates are located at the top of the tribo-electrostatic series, which indicates that carbonate particles tend to acquire a positive charge, and in consequence to be concentrated to E2. Both dolomite and hematite were concentrated in the same direction, indicating that the overall effect for hematite particles in the presence of quartz and dolomite was to acquire a positive charge.
The direction of movement of the mineralogical species in each sample is of paramount interest, as it will determine the maximum achievable Fe grade that can be obtained by means of a single pass using the tribo-electrostatic belt separator technology.
For the tailings and itabirite samples the maximum achievable Fe content will be determined by three factors: es) The amount of Fe in Fe-bearing minerals; ii) the minimum quartz (SiO2 ) content that can be achieved and; iii) The number of contaminants moving in the same direction as Fe-bearing minerals. For the tailings sample the main contaminants moving in the same direction of Fe-bearing minerals are Al2 O3 MnO bearing minerals, while for the itabirite sample the main contaminants are Cao Mgo Al2 O3 bearing minerals.
| Mineral Name | Charge acquired (apparent) |
|---|---|
| Apatite | +++++++ |
| Carbonates | ++++ |
| Monazite | ++++ |
| Titanomagnetite | . |
| Ilmenite | . |
| Rutile | . |
| Leucoxene | . |
| Magnetite/hematite | . |
| Spinels | . |
| Garnet | . |
| Staurolite | - |
| Altered ilmenite | - |
| Goethite | - |
| Zircon | -- |
| Epidote | -- |
| Tremolite | -- |
| Hydrous silicates | -- |
| Aluminosilicates | -- |
| Tourmaline | -- |
| Actinolite | -- |
| Pyroxene | --- |
| Titanite | ---- |
| Laukšpats | ---- |
| Kvarcs | ------- |
Tabula 4. Apparent triboelectric series for selected minerals based on inductive separation. Modified from D.N Ferguson (2010) [12].
For the tailings sample, the Fe content was measured at 29.89%. XRD data indicates that the predominant phase is goethite, followed by hematite, and therefore the maximum achievable Fe content if a clean separation was possible would be between 62.85% un 69.94% (which are the Fe contents of pure goethite and hematite, attiecīgi). Now, a clean separation is not possible as Al2, O3 MnO and P-bearing minerals are moving in the same direction as the Fe-bearing minerals, and therefore any increase in Fe content will also result in an increase of these contaminants. Then, to increase the Fe content, the amount of quartz to E2 will need to be significantly decreased to the point it offsets the movement of , MnO and P to product (E2). As shown in Table 4, quartz has a strong tendency to acquire a negative charge, and therefore in the absence of other minerals having an apparent negative charging behavior it will be possible to considerably decrease its content to product (E2) by means of a first pass using the triboelectrostatic belt separator technology.
For instance, if we assume that all the Fe content in the tailings sample is associated to goethite (FeO(AK)), and that the only gangue oxides are SiO2, Al2O3 un MnO, then Fe content to product would be given by:
Fe(%)=(100-SiO2 – (Al2 O3 + MnO*0.6285
Kur, 0.6285 is the percentage of Fe in pure goethite. Eq.4 depicts the competing mechanism that takes place to concentrate Fe as AL2O3 + MnO increases while SiO2 decreases.
For the itabirite sample the Fe content was measured at 47.68%. XRD data indicates that the predominant phase is hematite and therefore the maximum achievable Fe content if a clean separation was possible would be close to 69.94% (which is the Fe content of pure hematite). As it was discussed for the tailings sample a clean separation won’t be possible as CaO, Mgo, Al2 O3 bearing minerals are moving in the same direction as hematite, and therefore to increase Fe content SiO2 content must be reduced. Assuming that the entirety of the Fe content in this sample is associated to hematite (Fe2O3) and that the only oxides contained in gangue minerals are SiO2, Cao, Mgo, Al2O3 un MnO; then Fe content in the product would be given by:
Fe(%)=(100-SiO2-CaO+MgO+Al2O3+MnO+LOI*0.6994
Kur, 0.6994 is the percentage of Fe in pure hematite. It must be noticed that Eq.5 includes LOI, while Eq.4 does not. For the itabirite sample, the LOI is associated to the presence of carbonates while for the tailings sample it is associated to Fe-bearing minerals.
Evidently, for both tailings and itabirite samples it is possible to significantly increase the Fe content by reducing the content of SiO2; Tomēr, as shown in Eq.4 and Eq.5, the maximum achievable Fe content will be limited by the direction of movement and the concentration of oxides associated to gangue minerals.
In principle, the concentration of Fe in both samples could be further increased by means of a second pass on the STET separator in which Cao,Mgo Al2 O3 un MnObearing minerals could be separated from Fe-bearing minerals. Such separation would be possible if most of quartz in the sample was removed during a first pass. In the absence of quartz, some of the remaining gangue minerals should in theory charge in the opposite direction of goethite, hematite and magnetite, which would result in increased Fe content. For instance, for the itabirite sample and based in the location of dolomite and hematite in the triboelectrostatic series (Skatīt tabulu 4), dolomite/hematite separation should be possible as dolomite has a strong tendency to charge positive in relation to hematite.
Having discussed on the maximum achievable Fe contents a discussion on the feed requirements for the technology is needed. The STET tribo-electrostatic belt separator requires the feed material to be dry and finely ground. Very small amounts of moisture can have a large effect on differential tribo-charging and therefore the feed moisture should be decreased to <0.5 wt.%. turklāt, the feed material should be ground sufficiently fine to liberate gangue materials and should be at least 100% passing mesh 30 (600 Um). At least for the tailings sample, the material would have to be dewatered followed by a thermal drying stage, while for the itabirite sample grinding coupled with, or follow by, thermal drying would be necessary prior to beneficiation with the STET separator.
The tailings sample was obtained from an existing desliming-flotation-magnetic concentration circuit and collected directly from a tailings dam. Typical paste moistures from tailings should be around 20-30% and therefore the tailings would need to be dried by means of liquid-solid separation (dewatering) followed by thermal drying and deagglomeration. The use of mechanical dewatering prior to drying is encouraged as mechanical methods have relative low energy consumption per unit of liquid removed in comparison to thermal methods. About 9.05 Btu are required per pound of water eliminated by means of filtration while thermal drying, on the other hand, requires around 1800 Btu per pound of water evaporated [13]. The costs associated with the processing of iron tailings will ultimately depend on the minimum achievable moisture during dewatering and on the energetic costs associated with drying.
The itabirite sample was obtained directly from an itabirite iron formation and therefore to process this sample the material would need to undergo crushing and milling followed by thermal drying and deagglomeration. One possible option is the use of hot air swept roller mills, in which dual grinding and drying could be achieved in a single step. The costs associated with the processing of itabirite ore will depend on the feed moisture, feed granulometry and on the energetic costs associated to milling and drying.
For both samples deagglomeration is necessary after the material have been dried to ensure particles are liberated from one another. Deagglomeration can be performed in conjunction to the thermal drying stage, allowing for efficient heat transfer and energy savings.
The bench-scale results presented here demonstrates strong evidence of charging and separation of Fe-bearing minerals from quartz using triboelectrostatic belt separation.
For the tailings sample Fe content was increased from 29.89% lai 53.75%, on average, at a mass yield of 23.30%, which corresponds to Fe recovery and silica rejection values of 44.17% un 95.44%, attiecīgi. For the itabirite sample Fe content was increased from 47.68 % lai 57.62%, on average, at a mass yield of 65.0%, which corresponds to Fe recovery and silica rejection values of 82.95% un 86.53%, attiecīgi. These results were completed on a separator that is smaller and less efficient than the STET commercial separator.
Experimental findings indicate that for both tailings and itabirite samples the maximum achievable Fe content will depend on the minimum achievable quartz content. turklāt, achieving higher Fe grades may be possible by means of a second pass on the STET belt separator.
Šī pētījuma rezultāti parādīja, ka zemas kvalitātes dzelzsrūdas smalkumus var uzlabot, izmantojot STET tribo-elektrostatisko jostas separatoru. Further work at the pilot plant scale is recommended to determine the iron concentrate grade and recovery that can be achieved. Based on experience, produkta reģenerācija un/vai pakāpe ievērojami uzlabosies izmēģinājuma mēroga apstrādē, salīdzinot ar stenda mēroga testa ierīci, ko izmanto šajos dzelzsrūdas izmēģinājumos. The STET tribo-electrostatic separation process may offer significant advantages over conventional processing methods for iron ore fines.
