To improve its strategic  position in the iron ore fines market, Hamersley Iron Pty. Ltd. investigated a number of options for   improving  quality of fines by reducing the level of gangue. As a result of this a  processing  plant was constructed to deslime  the  fines  product  from its mines at Paraburdoo   in  the  Pilbara  region of Western Australia . Improvements  made  to  both the chemical and physical characteristics of the processed fines were also expected to improve its sintering performance.   classif-ication to remove ultralne material is able to improve the quality of the fines as  the  predominant  gangue mineral, kaolinite, has a finer size   distribution  than the iron bearing minerals, hematite and goethire. Lab    scale and pilot plant studies indicated that 30% of the total alumina

content could be   removed   with  10% weight loss through destiming at 0.01mm.  This  upgradation  would  reduce the alumina content of the Paraburdoo fines from 2.7% to 2. 1 % A1,0j and the final Hamersley blend for shipping from 2. 45% to 2. 2% Al2O3.This paper examines the background to the decisions for installing this plant   as well as disc-ussing the plant circuit and the impact  of the  problems associated with dewatering the cyclone underf ort

Munro, D

Poetschka, N

English

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ISBN : 8I-8705J- 53-4Processing of Fines (2)Eds.: P Blutnaclun• v vii, R. Singly and N. G. Gnsictt,titOr- NML Jamshedpur-831 007, Indur, 2000, ply. 5?-5yClassification of iron ore fines at HamerslevIron's Paraburdoo MineD. MUNRO and N. POETSCHKARio Tinto Iron Ore, AustraliaABSTRACTTo improve its strategic position in the iron ore fines market , HamersleyIron Pty. Ltd. investigated a number of options for improving qualityof fines by reducing the level of gangue. As a result of this a processingplant was constructed to deslime the fines product from its mines atParaburdoo in the Pilbara region of Western Australia . Improvementsmade to both the chemical and physical characteristics of the processedfines were also expected to improve its sintering performance.Classification to remove ultralne material is able to improve the qualityof the fines as the predominant gangue mineral , kaolinite , has a finersize distribution than the iron bearing minerals, hematite and goethire.Lab scale and pilot plant studies indicated that 30% of the total aluminacontent could be removed with 10 % weight loss through destiming at0.01mm . This upgradation would reduce the alumina content of theParaburdoo fines from 2.7% to 2 . 1 % A1,0j and the final Hamersleyblend for shipping from 2. 45% to 2 . 2% Al2O3.This paper examines the background to the decisions for installing thisplant as well as discussing the plant circuit and the impact of theproblems associated with dewatering the cyclone underf ort.Key words : Classification, Iron ore fines , Dewatering screen,HYdrocycloningINTRODUCTIONHamersley Iron Pty.Ltd, an Australian company wholly owned by Rio Tinto,commenced mining iron ore at Mt Tom Price in 1966. From its modest start withone mine and one port and a capacity of 5 Mt/a, Hamersley has grown to itscurrent position as a leading iron ore supplier with a capacity of around52D. MUNRO and N. POFTSCHKA65 Mtfa. It is currently operating six mines (Mt Tom Price, Paraburdoo, Channar,Brockman/Nammuldi, Marandoo and Yandicoogina) with 2 shiploading berths atDampier. Crushed ore from the Channar mine is conveyed to Paraburdoo andcombined with crushed Paraburdoo ore for further processing. The location ofthese operations is shown in Fig. 1.A Aline• PortI ' RailwayConveyorYandicooginaAQ 50 700KibmetresFig. I : Location of Hamnersley's ,nines, railways and PoriHamersley Iron currently produces three products : a blended lump (-30+6nom), a blended fines (- 6 mm) and , commencing in 1999, a discrete limoniticpisolite fines (- 10 mm) from Yandicoogina.Prior to 1995, in terns of quality, the blended fines product was at the lowerend of the scale in relation to its major competitors , particularly in terms ofalumina content (Fig. 2).531). MUNRC) and N. POETSCT-IKA0 0.5Robe RiverHIMt. N ewmanBaiiadilaYar.di ( ex BHP)liabiraCaraiasMBAK udrem ukh%A1203 in Fines1.5 2 2.5 3Fig. 2 - A/,O, content crf tradedl iron ore fines circa 1993To improve its strategic position in this market Hamersley investigated waysof reducing gangue levels whilst minimising iron losses. Routine testing of prod-ucts from the individual mines provided` information on their amenability toupgradin,,,. Size analysis showed that the predominant gangue mineral, kaolinite,had a finer site distribution than the iron bearing minerals, hematite and goethitewith a high percentage reporting to the ultrafine fractions (see Fig. 3). A classi-fication process to remove the ultrafines would he suitable for achieving therequired grade improvements.FT-1M r r• d N26 63 125 25U 300 1000 2000 4000Particle Size (Microns)30 iE0 14 13 ?8 53 125 250 5J.3 '400 2000 4'5..-Particle sae ( Microns )Fig. 3 : Fe and AI,O, distrihuuion in parahurdoo trne.r4D. MUNRO and N. POETSCHKABecause of the tonnage of fines produced and the level of upgrading possiblewith classification, Paraburdoo Fines was selected as the appropriate stream totreat (Fig. 4)_MARANDOQ23°l°MTP-HG23%PARR + , MTP-WCHANNAR 7%47%Fig. 4 : Contribution of Mt.TornPrice, Paraburdoo+ Channar andMarandoo Mine to ,41 ,4; content of Hamersley fines (pre-1996)A test work program was instigated in 1993 and following favourable resultsa plant to treat 13 Mt/a was designed and constructed.The plant circuit consists of 4 modules, each containing a wet screen fol-lowed by a 2-stage hydrocyclone circuit consisting of 100 mm dia. cyclones:Cyclone underfiow is dewatered on vibrating screens and recombined with wetscreen oversize to form the washed fines product. Cyclone overflow is com-bined, thickened and pumped to a tailings dam. Each module was- designed totreat up to 700 t/hr of -6 mm feed. Construction commenced in 1994 and theplant was commissioned in October 1995.TEST WORKTest work was carried out in three separate areas.1. Shift composites of fines product were collected over a six monthperiod and subjected to grade by size analysis to examine the grade /recovery relationship of size classification and its variability. Lump/fines recovery data was also examined over the same period to deter-mine the fluctuations in fines tonnages.55HNIiY^11^MIMMYW ^I^NFia W^^IMW iWrirl^Wtli^.+.4 ♦biY+tYxWWdiIWW^MIr i*s-r 1,^.xxlx^le^xWY^4,x r..^nwlrlirlWuYe^11MmNWY^W1^^$i-D. WUIVRO and N. POETSCHKA2. A 20 t/ hr pilot plant was installed to wet screen fines at 0 . 5/1 mm anddeslime the screen undersize using hydrocyclones. Feed was providedfrom discrete pits to test variability, and hulk samples were providedto customers for measuring the impact on downstream processes suchas sintering . A portion of the tailings stream was fed to a pilot thick-ener to obtain information and samples for design of the thickener.tailings disposal system and dam storage requirements . Results indi-cated:2-stage cycloning gave substantially more efficient separation than asingle stage.50 mrn dia. cyclones were unsuccessful due to blockages from elon-(Tated particles passing to screen undersize.A1,O, levels could he reduced from 2.7r- to 2.1% at a yield of 9W-,cusing 2 stages of 100 mm dia, cyclones. This was achieved at a cutpoint (d50) of approx. 10 microns.3. Handling trials were carried out at Hamersley's existing heneficiationplant at Tom Price to test the impact of stockpiling, railing and dump-ing high moisture material. The results of these trials were used togenerate computer models to predict moistures and drainage character-istics for the proposed product at Paraburdoo. Results indicated thatprojected product moisture at Paraburdoo would reduce from 121.% toaround 81% with adequate time for stockpile drainage.PLANT DESIGNThe plant flowsheet is shown schematically in Fig. 5. It consists of 4 identicalmodules, each designed to treat 700 Vhr.From each of the four feed bins, a variable speed belt feeder discharges theunprocessed fines onto a feed preparation screen, where initial size separation at0.6 mm is effected by wet screening involving water sprays located above eachscreen. Oversize (+0.6 mm) is discharged in a dewatered state from the feedpreparation screens onto the product conveyor.The feed preparation screen undersize (-0.6 mm) is processed via a two stagehydrocyclone circuit to separate the -0.01 mm particles- Primary cyclone underftowgravitates to the secondary cyclone feed sumps and overflow from hot Ii stagesgravitates to the thickener via their respective feed sumps where a recycle strewn(Fig. 5) allows these sumps to maintain it steady head. Each module Contains 4clusters of 25 x 100 mm dia. primary cyclones and 4 clusters of 25 \ 1 00 mntdia. secondary cyclones.56D. MUNRO and N. POETSCHKAFROM DRY .......ISCREENING PLANT mommiiiiBINTO SAMPLEPLANTTO BLENDINGSTOCKPILESVARIABLE SPEEDBELT FEEDERS- FEED PREPARATIONSCREENSPRIMARY CONSTANTVOLUME SUMPSPRIMARY CYCLONEFEED PUMPSFig. 5 : Schematic of paraburdoo fines processing plantSecondary cyclone underflow (-0.6+0.01 mm) is dewatered on dewateringscreens before discharge to the product conveyor where it joins the -6+0.6 mmproduct. Dewatering screen. undersize is recycled to the secondary cyclones. Thecombined product passes through a new sampling station before joining thepreviously existing conveyor system to the fines blending stockpiles.The base of each of the two 200 kt capacity fines stockpiles was modified toinclude an underdrainage system to recover water from the stockpiled materialprior to trainloading_ Contained water drains through the filter blankets to theoutside edges of the stockpile where it- is collected in slotted concrete pipeswhich run the full length of the stockpiles to a collection sump from where it ispumped back to the process plant.The tailings fraction is flocculated and thickened in a 75 m diameter Caissonthickener. Thickener underflow is pumped to a tailings dam approximately 4 kmfrom the plant and overflow water is recycled. An aerial view of the ParaburdooFines Processing Plant is shown in Fig. 6.PLANT PERFORMANCESince commissioning in 1995 some operating problems have occurred thathave led to variation from design projections. The major problem has been thatthe dcwatering screens do not operate in steady state until a high circulating load(- 450%r.) has been established.TO SAMPLE PLANTCV1257r^rL+r•^rrMuYYiaWiirY^^^r^... ^w. J. L L. .. ,,, ,_,.,.J ...i.Y1 .1i^iY .. ^,MW ^.drY^YrrtlYi^ dYWh ul^^r«1). MUNROJ and \'. POETSCIIKARio Tinto Iron OreFig. 6 : Pcrruhrcrzlcro Frrres Prot res.cing PlcurrThis has led to high secondary cyclone feed densities I>35r( solids) that hayeresulted in reduced recoveries (84 ) and reduced capacit' (600 t/hr/modUIC). Anincrease in the cyclone d50 cut point to -- 25microns has led to an increased rejec-tion of the lows density gangue that has intproved product alumina -!Iardes hewnnilexpectation. This is illustrated in Fig. 7 which shomo product AI,O. grades decrc:r.ing lrom2.817 to 2.01/( A1,O, following ttte installation of the plant.Reduced recoveries have led to it significant increase in tailings tonnages- thethickener anti t iilirigs pumps have coped with this increase but extra expenditure ha'been required to increase tailings darn capacity. The high circulating load front thedewatering screens wwas evident in pilot plant test work but wva thought to he due tothe pilot screen not producing adequate bed depth as a result of the screen deck con-tai ningover-3O times the required screen area for the tonnage being treated. (Thepilorckru crrel-ill" s, rrrrr ti cr.% in viallecl to tctcilirctte ccurrlr/c irair/hu, rat/tee than ro he rr.wrc/tort/e,vi^rr luulrose.^l. The actual reasons for the high circulating loads compared toother Rio Tinto operations appear to be:- different dewwatering characteristic, between Parahtudoo/Chattnar ore (_'()-t0 ccoelhite) artd other ores (Mt "lout price - <iI)' goethite) with wwhichHantcr,Icy had previous dewatering experience:- finer material than [hat w ith which design engineers had prow ic^u ; dcwwa[er-iris experience.SyD. MUNRO and N. POETSC.'HKA%A1203 in Paraburdoo Fines Product1.81985 1987 1989 1991 1993 1995 1997 1999 2001YearFig. 7 : Reduction in AI,O, after installation of Fines Processing PlantAnother issue that has caused concern is that of product moisture. Productdrainage has also been less effective than projected (-10% final moisture com-pared to 8%) for similar reasons to the differences in dewatering screen responsementioned above.POTENTIAL PROCESS CHANGES _A number of studies have been carried out to improve the performance of thedewatering screens and to reduce the moisture level of the product. The use ofbelt filters was considered but could not be justified unless an increase in pro-duction tonnage was required.Larger cyclones (250 mm and 600 mm diameter) are also being consideredfor trials. Their use would reduce the amount of ultrafines in the screen feed andthereby assist the dewatering screens to lower the circulating load as well asmoisture levels. 4CONCLUSIONTo achieve the objective of improving the fines quality some operating prob-lems have occurred. It has been found that the dewatering screens selected do notoperate in steady state until a high circulating load is established which has ledto cyclone feed densities being, higher than design. As a result the cyclone cutpoint operates at 0.025 nom causing the mass recovery to reduce to 84% andgangue rejection to increase. The preferential separation of lower density miner-als to cyclone overflow in the -0.06+0.01 n1171 size fraction has had a positiveeffect on the final product grade, reducing the alumina content to around 2.0%.S9

Classification of Iron ore Fines at Hamerslev

Iron's Paraburdoo Mine

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Classification of Iron ore Fines at Hamerslev Iron's Paraburdoo Mine

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