An overview of the Namakwa Sands ilmenite smelting operations

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1 An oveview of the Nmkw Snds ilmenite smelting opetions by M. Gous* J o u n l Synopsis Nmkw Snds is hevy minels mining nd beneficition business in the Anglo Bse Metls Division, nd opetes long the West Cost of South Afic. The business encompsses mining, minel concenttion, seption, nd smelting opetions. The smelting pocess compises the cbonceous eduction of ilmenite to poduce titni slg with TiO 2 content of 86%, nd ion with cbon content of 2.5%. The Nmkw Snds smelte, situted ne the Sldnh By hbou, commenced smelting opetions in 1994, when 25 MW DC-c funce ws commissioned. The smelting opetions wee expnded in 1999, with the commissioning of second 35 MW DC-c funce. Despite the fct tht ilmenite smelting poses technicl chllenge in tems of the high tempetues equied, the physicl chcteistics of the slg, the constints plced on the feedstock, nd the tight poduct specifictions, Nmkw Snds hs continully incesed slg poduction since High funce feed-on utiliztion nd funce stbility, complemented by continuous impovement dives, will be the vehicle to dive pefomnce in the shot-tem, with longe-tem pefomnce enhncements due to sttegic pocess development. Keywods: Pyometllugy, Nmkw Snds, ilmenite, DC-c funce, titni slg, pig ion Intoduction Nmkw Snds is hevy minels mining nd beneficition business tht opetes long the West Cost of South Afic, nd is the only hevy minels opetion within Anglo Ameicn plc. The compny flls unde the Anglo Bse Division of the London-bsed Anglo Ameicn plc. The business consists of mining, minel seption, nd smelting opetions, s shown in Figue 1. The mine is situted t Bnd-se-Bi, 385 km noth of Cpe Town, nd is divided into n est nd west section whee opencst stipmining ctivities occu, togethe with pimy nd secondy concenttion of hevy minel snds contining zicon, utile, nd ilmenite. The non-mgnetic (zicon nd utile) nd mgnetic (ilmenite) concenttes e tnspoted septely to the minel seption plnt, ppoximtely 60 km south of the mine, ne Koekenp. At the minel seption plnt, electosttic, dy mgnetic, nd gvity methods futhe septe ilmenite, utile, nd zicon. The thee poducts e disptched by il, vi the Sishen-Sldnh line to the smelte. The smelte is locted ne Sldnh By. Zicon nd utile e stoed hee, pio to bulk shipping to pedominntly oveses mkets vi the Sldnh hbou. Ilmenite is smelted to poduce two gdes of sleble titni slg, nd sevel gdes of pig ion, nd is lso shipped vi the Sldnh hbou to oveses mkets. The poject ws initited in two phses, t totl cost of R2.1 billion. At full cpcity, 18 million metic tons pe nnum of oe is mined to poduce tons of titni slg, tons of high-puity pig ion, tons of utile poducts, nd tons of zicon. Pocess flow The Nmkw Snds pocess flow is indicted in Figue 2. The smelte pocesses The DC-c ilmenite-smelting technology ws developed nd tested to pilot scle, in conjunction with Mintek, between 1992 nd The fist funce, 25 MW diectcuent funce, ws commissioned in June 1995, nd second funce, 35 MW diectcuent funce, ws bought on line in Febuy The smelting pocess compises the cbonceous eduction of ilmenite to poduce titni slg with TiO 2 content of 86%, nd ion with cbon content of 2.5%. The min ection in the funce cn be summized s: * Nmkw Snds, Vedenbug, South Afic. The South Aficn Institute of Mining nd Metllugy, SA ISSN X/ This ppe ws fist published t the SAIMM Confeence, Southen Aficn Pyometllugy 2006, 5 8 Mch P p e The Jounl of The South Aficn Institute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER JUNE

2 An oveview of the Nmkw Snds ilmenite smelting opetions Bndd-se-Bi Mine Site Pimy & Secondy Minel Concenttion Plnt Seption Plnt Koekenp Lutzville Vedenbdl Vedenbug Sldnh Smelte A T L A N T I C O C E A N Cpe Town Cpe Town Intentionl Figue 1 Mp of Nmkw Snds opetions Esten Oebody Westen Oebody Est Pimy Concenttion Mine Site Hevy Minel Concentte West Pimy Concenttion Secondy Concenttion Secondy Concenttion Smelte Smelte (Stoge nd Expot) Non-mgnetic Concentte Minel Seption Mgnetic Concentte Ilenite Smelte (Smelting Pocess) TiO 2 Slg Ion Zicon Rutile Slg Milling Ion Tetment Chloide Slg Sulphte Slg Pig Ion Figue 2 Nmkw Snds flowsheet 380 JUNE 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The South Aficn Institute of Mining nd Metllugy

3 An oveview of the Nmkw Snds ilmenite smelting opetions [1] Ilmenite nd nthcite e fed vi hollow electode into the funce whee the endothemic eduction of ilmenite occus. The contol vibles fo slg chemisty e: Rtio of ilmenite to powe Rtio of nthcite to ilmenite Ac length Slg nd ion inventoy. The mount of eduction, nd enegy vilbility, e the spill points ound which the funce chemisty hs to be opeted. Ove- o unde-eduction situtions cn led to tpping poblems, efctoy we, nd euptions. A schemtic of the funce is shown in Figue 3. The funce is efctoy-lined with MgO efctoies. The oof pnels nd off-gs ducting, s well s the oute shell, e wte cooled, while the heth is i cooled. The conductive funce heth consists of efctoy bicks cld with stinless steel, lye of high cbon efctoy, nd coppe bse plte. Most of the enegy is geneted in the c between the electode nd the sufce of the bth, poviding the enegy necessy fo the smelting nd eduction of the ilmenite nd nthcite feed chge. By feeding ilmenite nd nthcite though the hollow electode, the feed is plced diectly into the plsm c ttchment zone, theeby mking efficient use of the enegy of the c. Slg nd ion e tpped fom the funce t 1750 C nd 1450 C espectively. The cicul funce hs two slg tpholes nd two ion tpholes. Two cly-gun units otte ound the tphole e of the funce, nd cn be used to dill nd plug ll fou tpholes. The thee poducts fom the funce follow diffeent pocessing outes: Gs FeTiO3 + C TiO2( slg)+ Fe( metl)+ CO( gs) The CO gs poduced by the funces psses though the gs-clening plnts (shown in Figue 4), whee the gs is cooled, scubbed, nd wshed, to emove entined dust fom the funce. The clened gs cn be outed to the gsholde fo use in the peheting of ilmenite nd the dying of nthcite. Excess gs is fled to the tmosphee. When the gs plnts e down, the gs is fled to the tmosphee vi the w-gs stcks. A potion of the ilmenite feed cn be peheted in the pehetes, theeby loweing the specific enegy equiement of the pocess, nd consequently incesing thoughput. The CO gs is then bunt with oxygen in the gs bune of the pehete, nd povides enough enegy to pehet the ilmenite to 880 C. Both pehet plnts wee shut down in June 2003, due to the sevee destbilizing effects they hd on the funces. The incesed feed-on utiliztion of the funces hve subsequently compensted fo the fct tht the pehetes e not opetionl. WATER COOLED ROOF REFRACTORY LINING CONDUCTIVE HEART (node) GRAPHITE ELECTRODE (cthode) ARC SLAG IRON Figue 3 Schemtic of DC-c funce OFF-GAS (to gs plnt) TAPHOLES J o u n l P p e Figue 4 Gs clening plnt The Jounl of The South Aficn Institute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER JUNE

4 An oveview of the Nmkw Snds ilmenite smelting opetions Slg Slg is tpped into slg pots, 25 tons t time. Afte tpping, the slg pots e llowed to i cool fo ppoximtely fou hous. Theefte, they e tken to pimy cooling (shown in Figue 5), whee wte is spyed onto the sides of the pots. Afte two dys in pimy cooling, the pots e tken to secondy cooling (shown in Figue 6), whee the slg buttons e tipped out into the secondy cooling bys. Wte is spyed onto the buttons to educe decepittion of slg. Cooled slg is boken down to 300 mm, in peption fo cushing. The slg is cushed in jw cushe to less thn 50 mm. The cushed slg is then died, nd sceened vi Humme sceen nd thee Rotex sceens. The ovesize mteil is sent to Loesche mill, which hs otting tble nd two sttic olles (shown in Figue 7). The slg flls onto the cente of the tble, nd the centifugl foce moves the slg undeneth the olles cusing the ginding ction. The milled slg is conveyed bck to the Rotex sceens. The Rotex sceen undesize is fed into the clssifie units tht clssify the slg into chloide slg ( µm) nd sulphte slg ( µm). The slg plnt ws hot commissioned in Septembe Thoughput though the clssifiction section, t cceptble split vlues, poved to be the bottleneck nd this led to doubling-up in clssifiction cpcity s pt of the Phse 2 extensions in Excess Phse 2 pneumtic tnsfe cpcity could be utilized to tnspot mteil diectly to sulphte slg poduct since the beginning of Ion Molten ion is tpped, 32 tons t time, fom the funces, into efctoy-lined ldles, nd tnspoted to the injection sttion to be ecbuized nd desulphuized. At the injection sttion, cbon is injected to incese the cbon content of the metl fom ppoximtely 2.5% to 4.1%. Clcium cbide is injected to decese the sulphu content to below 0.012%. Feosilicon is lso dded to the molten ion, to incese the silicon content. The mount of feosilicon equied depends on whethe high- o low-silicon pig ion poducts e being poduced. Figue 7 The Loesche mill olles Figue 5 Pimy cooling Figue 6 Secondy cooling Figue 8 Pig csting 382 JUNE 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The South Aficn Institute of Mining nd Metllugy

5 An oveview of the Nmkw Snds ilmenite smelting opetions Afte injection, the ldle is tken to the pig-csting mchine (shown in Figue 8), whee the molten ion is poued into moulds to fom 8 kg pigs. Mould wsh is spyed onto the moulds, nd peheted befoe the csting pocess commences, theeby peventing the pigs fom sticking to the moulds. Afte the csting pocess hs been completed, the pigs e tken to dity by fo cooling. Theefte, the pigs e sceened ove 35 mm vibting sceen, septing ion chips fom the pigs. The pigs e then stoed in the designted clen by befoe being shipped to the client. The ion plnt ws commissioned in 1995, nd becme fully opetionl in August A second pig-csting mchine ws dded to ccommodte the incese in poduction with the constuction of the second funce in Poduction The slg nd ion poduced fom the funces hve been stedily incesing ove the pst ten yes, with mked impovements since 2002 minly due to: Impoved chemisty contol Incesed efctoy life fom the funce lining, due to less side-wll nd heth MgO excusions Impoved tphole mngement with egd to opetion, mintennce, nd efctoy type Impoved cente-oof design. The slg nd ion poduction histoy is indicted in Figue 9. The mjo detimentl events influencing the slg poduction ove the smelte lifespn hve been: 1997 Euption on Funce Funce 2 commissioned 2001 Funce 1 eline (Octobe 2001 to Jnuy 2002) 2003 Smlle funce euption events on both Funce 1 nd Tphole ebuild ( V-down ) on Funce Funce 2 eline (June to July 2005) Mjo impovements hve, howeve, been mde to decese the fequency nd dution of the funce elines. The dution of the eline (including efctoy cuing) of Funce 2 in 2005 ws 52 dys, with etun to noml slg tpping opetion fou dys lte. It is estimted tht the totl slg tpped, if nomlized to exclude the eline, would hve been in excess of t fo Sfety nd envionment Sfety All thee opetions hve been gded in the NOSA Integted SHE System, nd hold the NOSA Pltinum 5 St sttus. The Nmkw Snds behvioul sfety pocess, implemented in 2003, lso plys mjo ole in the pevention of ccidents nd injuies. The behvioul sfety pogmme is nmed the MEERKAT Pocess Mking the Effective Elimintion of t-risk Behviou Key Attitude Togethe. The Anglo Ameicn policy of Zeo Tolence, Tget Zeo (OTTO) is pctised, nd hs been implemented though to ll levels of opetion vi the NOSA, the Behvioul Sfety MEERKAT Pocess, Visible Felt ledeship, nd isk ssessment pocesses. Focusing on the smelte opetions, the histoicl sfety pefomnce ove the life of the smelte is indicted in Figue 10. Notwithstnding the 5 lost-time injuies t the smelte duing 2005 (compising 3 lost-shift injuies nd 2 esticted-wok cses), the smelte hs shown mked ovell impovement in sfety pefomnce. This is pticully evident in the significnt eduction in the totl numbe of injuies, fom 107 in 2003, to 94 in 2004, nd 68 in Envionmentl ISO cetifiction ws obtined in The min envionmentl issues t the smelte e: Enegy consumption, s Anglo Ameicn hs committed Nmkw Snds to educe enegy consumption by 15% ove the next 10 yes. Wte usge, due to the opetions being situted in the id west cost egion. Ai emissions, s the smelte site is the only diect emitte of cbon dioxide to the tmosphee. The envionmentl pefomnce of the smelte is tbled in Tble I: J o u n l P p e Figue 9 Poduction histoy of titni slg nd pig ion Figue 10 Histoicl LTIFR (lost tme injuy fequency te) The Jounl of The South Aficn Institute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER JUNE

6 An oveview of the Nmkw Snds ilmenite smelting opetions Tble I Envionmentl pefomnce Pmete Wte [m3/t] Enegy [GJ/t] CO 2 [t/t] The smelte implemented poject in 2004, which hs been esponsible fo lge eduction in potble wte consumption. Sluied effluents geneted on the plnt e sent though thickene nd pumped to esidue dm wee solid mteil settles out. Insted of losing tht wte to evpotion, it is now etuned s cooling wte to the two lgest wte consumes: pimy nd secondy cooling. Impovements wee lso mde to the i emissions fom the smelte, fte modifictions to the gs-clening plnt sequences wee mde. The modifictions included: Pevention of gs-clening plnt stoppges duing shot funce outges, less thn 1 minute, pending tht the funce did not tip out due to high hydogen o oxygen levels in the clen-gs system, Elimintion of nitogen puging if the clen-gs plnt hs been off fo less thn 5 minutes, pending the funce o gs plnt did not tip due to high hydogen o oxygen levels in the clen-gs system. Enegy eduction inititives e bsed on decesed enegy equiements pe ton of poduct deliveed by the funces, nd e dependent minly on impovements plnned with egd to the feed egimes to the funces, nd the eduction of unwnted downtime nd subsequent hetup peiods. Poduct specifictions The ISO qulity mngement system hs been implemented t Nmkw Snds, nd ll nlyses of finl poducts e pefomed ccoding to the ISO ccedited methods. Typicl smelte poduct nlyses e indicted in Tbles II nd III. Futue pojects nd development The min focus t the funces will emin on stble opetions, with incesed funce utiliztion nd poduction thoughput. The following pojects will focus on incesed funce utiliztion: Optimiztion of feed system nd feed egimes to the funce, to educe specific enegy equiements, nd optimize utiliztion Optimiztion of the type, size, nd chemicl composition of the nthcite eductnt Impoved scheduling nd mintennce egimes on tpholes, to incese ovell funce efctoy-lining lifespn Incesed life of cente oofs, electode sels, nd oof pnels Tble II Typicl chemicl nd size nlyses of slg poducts Chemicl nlysis Chloide slg Sulphte slg Totl Ti s TiO % 82.0% Ti 2 O % 20.0% Totl Fe s FeO 10.0% 10.5% Metllic Fe 0.20% 0.10% Al 2 O % 1.40% SiO % 3.20% CO 0.16% 0.30% MgO 0.68% 0.65% MnO 1.85% 1.90% Size nlysis +850 µm 10% µm - 20% -106µm 5% 80% -75µm 2% 55% Tble III Typicl chemicl nlyses of ion poducts Mjo elements C 4.0% S 0.005% P 0.035% Mn 0.05% Silicon High Si Gde 1.00% Low Si Gde 0.25% Instlltion of utomted pessue pot clening devices Instlltion of mechnicl electode toquing equipment to pevent stub losses nd impove electode consumption. Subsequent impovements will lso be investigted nd implemented t the ion plnt: The eplcement of feosilicon (FeSi) dditives with silicon cbide (SiC) Impoved ldle life Impoved ion scp ecycling Altentive desulphuistion methods, due to the high sfety isks ssocited with the clcium cbide cuently used. Due to the diffeence in poduct pice of chloide nd sulphte slg, the min focus t the slg plnt is the optimiztion of the poduct split to chloide slg vi: Impoved slg-cooling egimes t pimy nd secondy cooling Recovey of entined chloide slg fom the sulphte slg poduct Optimized milling egimes, to pevent ove eduction in size of ne-size mteil fed to the mill. Refeences 1. Nmkw Snds Footpints, ISSUE III, Febuy JUNE 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The South Aficn Institute of Mining nd Metllugy