A Strategy For Utilisation Of Low Grade High Phosphorus .
t6A Strategy for utilisation of low gradehigh phosphorus manganese ores in theproduction of high carbon ferro mangahege,1 M. Subramanian0. SeetharamayyaC. N. Harman*ABSTRACTA two step process is outlined to utilise low grade high phosphorus ores containingMn 31-35%, Fe 11-13%, S102 8-10%, P 0.35% to 0.5%, whereby in the first step, smelting iscarried out in an Electric furnace to produce High MnO containing slag with equivalent Mn 45 to50% which can be used as synthetic high grade ore and is almost free from phosphorus and iron.The metal obtained is "Spiegeleisen" containing 14 to 18% Mn and 1.5 - 2.0% phosphorus.In the second step the high manganese slag from the first step is blended with additionalquantities of low and medium grade manganese ores and smelled to produce high gradeHigh carbon ferro manganese and a discard slag containing about 16.0% Mn. The smelting trialscarried out at FACOR is briefly mentioned.IntroductionGradual depletion of High grade Manganeseores has taken place in India due to export ofHigh grade ores during earlier years of miningactivities in India and subsequently domestic utilisation of high grade ores only in the production of High carbon ferro manganese during thelast two decades. Considerable difficulties arebeing faced by Ferro manganese producers inprocuring requisite quantities of High grademanganese ores for feeding existing furnacesand this difficulty will increase further as moreand more ferro manganese plants are establishedto meet the growing demand with expansion insteel making capacity. The demand of Highcarbon ferro manganese by 1990 is estimated as3,80,000 tonnes including an export of 100,000tonnes. With 90% capacity utilisation of thefurnaces the production capacity for high carbonferro manganese should be 4,20,000 tonnes.The present installed capacity and production ofhigh carbon ferro manganese in India is indicated in Table - 1.For the production of high carbon fern)manganese, the manganese content of the oreshould be 45.0% minimum, with a minimumMn/Fe ratio of 6.0 and phosphorus 0.16% max,taking into consideration that the carbon reduc-* The authors are with M/s Ferro Alloy Corporation Ltd., Shreeramnagar.187
TABLE-1Installed capacity of high carbon ferro manganese plants in IndiaTransformerrating ofsmelting furnaces (KVA)Production Capacity per annum.(tonnes)Name of the ferro alloy producerNumberoffurnaces1Tata Iron Er Steel Co Joda (Orissa)29000 (each)30,0002Jeypore Sugar Co. Ltd.,Rayagada (Orissa)113600?750024,0003Universal Ferro Alloys EtAllied Chemicals Ltd ,Tumsar (Maharashtra)229000 (each)16500 (each)36,00060,0004Khandelwal Ferro Alloys Ltd.,Kanhan (Maharashtra)29000 (each)36,0005Maharashtra Electro-smeltChandrapur (Maharashtra)16Electro Metallurgical Works (P) Ltd.,Dandeli (Karnataka)11460011200)7Visvesvaraya Iron Et Steel Ltd.,Bhadravati (Karnataka)21500 (each)2,8008Ferro Alloys Corporation Ltd.,Shreeramnagar (Andhra Pradesh)37500 (each)45,000SI.No.3300048.00016,000Additional licensed capacitiesgranted by Government960,000M, 0. I. L. Balaghat,3,57,800TOTALtants namely steel plant cokes contain P to anquantities of high grade ores from single sourceextent of 0.16 to 0.18%. Also physical characterThe size ofof lumpiness is to be ensuredare not available to meet the requirements ofhigh carbon ferro manganese production, severalmanganese ores should be hard and lumpy with— 50 -1- 6 mm, For the production of 4,20,000and low P, low Mn/Fe ratio with low phospho-tonnes of high carbon ferro manganese, therus, high silica ores and low silica ores areore types containing high Mn/Fe ratio with highrequirement of manganese ores of the requisiteblended to obtain an average composition re-grade would amount to 1.05 million tonnes perquired for feeding to high carbon ferro manga-annum.nese furnaces.The total estimated reserves in India in 1971Apart from the chemical composition, it iswas about 108 million tonnes of which aboutknown that for each tonne of manganese ore60% are of medium and low grade oresmined an equal quantity of ore fines are gene-Table - 2. Also more than about 50% of man-rated at the mine head. Also due to friableganese ores are of high phosphorus content.nature of many manganese ores especially inMost of the ores cannot meet the phosphorusEastern Region considerable amount of fineslimit of 0.16% max required for high carbonare generated during mining, transport andferro manganese production.handling of manganese ore. Since the fines as188Since enough
TABLE-22.Ore reserves in millions of tonnesFerruginous ore types : These can be upgraded by magnetising reduction roast follow-Block-1 Block-2 Block-3 TotalMadhya- Orissa Karnapradesh Andhra- takaMahapradeshrashtraGujarated by magnetic separation. Most of theferruginous ores of Orissa are amenable tothis treatment.3.Garnetiferous ore types : These types ofores are amenable for treatment by 18 21108.36static separators or flotation.4.Complex ore types : These ores require combination of two or three treatment methodsdepending on the gangue minerals present.High GRLow GR36.009.006.7738.381.8212.4144.5963.79Though the physical beneficiation methodsenumerated above have shown that several lowsuch cannot be utilised in the electric furnacesgrade manganese ores can be upgraded to im-these are required to be beneficiated and agglo-prove the manganese to iron ratio, the phos-merated into lumpy form as briquettes, sintersphorus content in most of the ores could not beor pellets for their use in the production of highbrought down. Till this date, no solution hascarbon ferro manganese.been found for removal of phos by mineralbeneficiation techniques. It has been shownBeneficiation Studies on Mn Ores :by investigations at National Metallurgical Laboratory and Indian Bureau of Mines that if phos-Voluminous investigations on several man-phorus is present as apatite mineral, this couldganese ores have been undertaken during thebe separated. However, in most of the ores,last two decades to drive home the importanceof mineral beneficiation by various researchphosphorus is present intimately in the manganese oxide crystal lattice and therefore, bycentres like National Metallurgical Laboratory2,employing ore dressing methods phosphorusJamshedpur, Indian Bureau of Mines3, Nagpur,Regional Research Laboratory, Bhubaneswarand other places. Very useful flow sheets havecould not be brought down. FACOR too oncehad set up facilities for beneficiation of lowbeen evolved for several type of manganeseDistrict, Andhra Pradesh. The beneficiationores.plant consisted of crushing, sizing, washingThe salient features of such investigationsare enumerated hereunder :grade manganese ores available in Srikakulamjigging, grinding, tabling, magnetic separationand flotation units.The plant was operatedfor a period of five years and the observationsThe low grade manganese ores from differ-were as follows : (1) To achieve requiredent parts of India could be broadly classifiedinto four groups for the purpose of mineralthe recovery of the mineral was too low, (2)beneficiation.manganese to iron ratio in ores it was found thatEven after flotation the phosphorus contentcould not be brought down below 0.19%, (3)1. Simple Ore Types : These ores are amenable to concentration by simple ore dressingit was found that operation of the plant forbeneficiation was uneconomical, consideringmethods such as gravity, high intensitythat the fine concentrates obtained requiredmagnetic separation or flotation processes.further agglomeration steps.189
Hydrometallurgical method :the object of making synthetic manganese oreSeveral investigations have been done atRegional Research Laboratory, Bhubaneswar'eliminating the iron and phosphorus through theto decrease phosphorus content in manganesemolten spiegel. The slag contains high man-ores by hydro-metallurgical method.ganese oxide with 55 to 70% with very littleThigh Mn0 slag) by preferentially reducing andiron and very low phosphorus of less thanThese studies show that the phosphorus0.03%. This high Mn0 slag can be used eithercontent of some high phosphorus manganesein the production of silico manganese or highores of Southern Orissa and Andhra Pradeshcarbon ferro manganese. Typical examples ofcan be decreased by alkali-roast at 800 -850 Csuch pyro metallurgical method are the Newand subsequent leaching with water at 80 -Castle two stage process is' 18 and Strategic90 C. Phosphorus in manganese ore samplesUDY process".from Madhya Pradesh and Maharashtra regionThe New Castle or Broken Hill process con-could be brought down by leaching in dilutemineral acids6 like H2 SO4, HCL or HNO3. Itsists of two stages in which open hearth slagmay be noted that though several investigationscontaining 10-25% Mn and 1.5% P wasreduced under acid conditions in the first stageas cited above have shown encouraging resultsin certain types of ores on laboratory scale, thein an electric furnace, such that manganese andalkali consumption is high.manganese and the extent of phosphorus remo-silica in the charge were retained in the slagwhile the iron and phosphorus were reducedval are low and the feasibility and economicinto the metal. The initial smelting operationTherecovery ofviability of the process on Pilot plant has notwas usually carried out within a temperaturebeen established.range of 1100 - 1500 C. Hosking and Gregoryreported an optimum temperature of 1430 CMoreover, any method adopted to upgradewith a base/acid ratio of 1 04. In the secondmanganese ores by physical beneficiation andstage, the synthetic ore of first stage was smel-chemical leaching methods requires crushingted with coke and limestone to produce highand grinding the ores to a fine size of minus100 mesh and therefore the beneficiated andcarbon ferro manganese containing upto 7070Mn at a temperature of 1600 - 1650 C with aupgraded ores cannot be directly fed to ElectricSmelting Furnaces and requires agglomerationslag base to acid ratio exceeding 1.5%.by briquetting sintering or pelletising and suchIn the strategic UDY process, ferruginoussteps as crushing, grinding, to a fine particlemanganese ores and low grade ore concentratessize and adoption of physical and hydro-metacontaining manganese between 10 to 15 perIlurgical beneficiation methods would add appreciably to the capital cost and operating cost. Incent were utilised. In the first step, ore wasmixed with coke and flux, preheated and prac-most of the ore types techno-economic viabilitytically reduced at 1100 - 1200 C prior to smelting. Smelting was carried out at 1300-1600 Cof the processes are yet to be established.to reduce iron and P leaving a high Mn0 conPyrometallurgical treatmenttaining slag. The phosphorus alloyed with ironPyrometallurgical method of beneficiationwas oxidised in a succeeding smelting operationwhereby the high iron and phosphorus contentto produce low phosphorus pig iron. Theof low grade ores are selectively reduced withsynthetic slag of the first step was used for thecarbon at high temperatures either in Rotaryproduction of silico manganese and high carbonFurnaces or Electric Furnace is considered asferro manganese. The two step smelting pro-another approach to utilise high phosphorus lowcess was also attempted for utilising Sandurgrade manganese ores. Numerous investigations13 withferruginous manganese ores with low phos-have been reported in the literature 7 190phorus content in pilot plant scale at Electro-
misk A/S, Oslo, at the instance of Mks. SandurTo establish the feasibility of the process, amanganese and Iron Ores Pvt. Ltd., India. Infew years back, smelting campaigns were under-the first stage low grade ferruginous ore withtaken at FACOR to produce spiegeleisenMn 28-35%, Fe 21-23%, SiO 2 1.2%, A13036-8% and 0.03 - 0.05% P was smelted in amethod on industrial production scale in one of2000 kv furnace to produce a high Mn0 slagtheir furnaces producing high carbon ferro man-with 54% Mn and spiegelelsen with 12% Mnganese.and synthetic manganese ore by two stepand 0.2% P. In the second stage, high Mn slagfrom stage one together with additional lowThe furnace shell is 7050 mm dia and isgrade ore was smelted to produce standard ferro-lined with high duty fireclay, silicon carbide andmanganese with 76 0% Mn and 0.10% P.carbon tamping paste. Furnace hearth dia andheight are 5080 mm and 2185 mm respectively.The selective reduction of iron has been theThree soderberg self baking type electrodes withaim of these investigations to utilise ferruginousdiameter of 1050 mm are located on the apexeslow grade manganese ores having low Mn toof an equilateral triangle. The distance bet-iron ratio. However, FACOR proposes to adoptween the centre of electrodes is 2670 mm Thethis method for the utilisation of high phos-electrodes have pneumatic slipping devices tophorus containing low grade manganese ores,provide electrode slipping of maximum 100 mm.available in Srikakulam-Vizag districts and lowgrade ore from Orissa, taking advantage ofThe charge comprising of low grade highselective reduction of phosphorus also alongphosphorus maganese ores, iron ore or mill scalewith iron during smelting.or steel scrap and coke, was smelted, by the heatsupplied through the three self baking electro-Two step process for producingdes and the products were tapped, throughhigh carbon ferro manganese :tapholes at bottom of the furnace at regularintervals.The metal, spiegeleisen and highIn principle, in the first step, low grade highmanganese siege were tapped together and sep-P manganese ore is smelted in an electricarated suitably by collecting into pans whichsubmerged arc furnace under acid conditionswere arranged in cascades. When solidified, thewith carbon as reducing agent to produce spie-metal and slag were lifted from the pans bygeleisen which will contain 14 to 20% Mn,means of a 10/3 ton. E. 0. T. Crane. Metal and1.0% silicon, 6-7% carbon and 1.0 to 2.0% P.slag were sized and weighed. Very valuableThe slag will contain most of the manganese asdata were collected during the campaign formanganese silicates with 45 to 55.0% Mn, 14-smelting of low grade high phosphorus manga-18% SiO 2 , 1.0% Fe and P 0.03% max.nese ores and the process was found suitable forIn the second stage the high manganesecontaining slag which can now be called syn thetic manganese ore will be blended withfurther quantities of low grade high P manganese ores and other manganese ores andsmelted in another electric submerged arc furnace to produce high carbon ferro manganese.Since Si02 content of this blend will be high,due to high silica content in the first step slagadoption on large scale. The salient data arepresented in Table-3. In the second step , Highmanganese slag or Synthetic manganese oresblended with low grade high phos manganeseore and low grade ores were smelted alongwithreductants and flux in the same submerged electric arc furnace for production of High carbonferro manganese.Discussion of resultsthe low Mn0 slag practice will be adoptedwhereby standard high carbon ferro manganese1. Low grade ores were found quite satisfacto-and a discard slag containing about 15% Mnry for production of spiegeleisen and highwill be produced.manganese slag. However depending on191
TABLE-3Data on production of high manganese slag and spiegeleisen in 7.5 MVA furnace at FACORCampaign - IITEMA.1. Low grade Mn Ore (i)Mn 35.5%, Fe 12.8%, Si% 9.5%,P.O. 28%, A1103 7.0%, Ca0 1.5%Mg0 3.5% BaO 3.8%2. Low grade ore (ii)Mn 40%, Fe 12%, Si% 6%,P. 0. 3%, A1803 5.6%, Ca0 2.0%Mg0 3.0%, BaO 3.0%.3.CokeF. C.Ash4. Quartz.SiO.100 kgsFe, 97%P 0.03%7. Electrode paste8. Quantity of speiegel produced9. Quantity of High Mn slag150 kgs350 kgs1400 kwh1500 kwh10 kgs10 kgs400 kgs600 kgs1000 kgs1000 kgs20.00.940.196.50.00418.00.60.26.50.0153.3 (41.29)3.617.212.71.865.405.900.0755.0 (42.60)2.4520.810.03.05.05.00.05SPIEGEL ANALYSIS IN PRECENTMnPSiCSSLAG ANALYSIS IN PERCENTMn0 (Mn)Fe0Si%Al.%Ca0Mg0Be()Pchemical composition of low grade oresavailable, it was necessiated to use millscale or steel scrap to obtain desired Mn andP contents in spiegeleisen2. The slag volume per tonne of spiegeleisenwas about 2.5 tons. Due to this high volumeand high Mn0 content carbon lining of the192250 kgsP. 0.16%6. Electric power/tonne of slagC.1500 kgs98%5. Steel scrapB.1600 kg220 kgs70%28.0%Campaign - IIfurnace corroded severely. It is essential totap the slag at frequent intervals to avoidsevere erosion of refractory lining.3. Slag composition was adjusted to have goodfluidity for better/slag metal separation. TheSi% content should be kept 18,0%minimum.
4. Smelting trails for production of High carbonferro manganese using high manganese slagwere quite satisfactory. The power consumption was 3700 KWH due to increase inslag volume per tonne of High carbon ferromanganese. It is found that 75 kwh extrapower is required for every 100 kg increasein slag volume per tonne of metal.of Mines have been reported by M. B. Royerand R. C. Buehl'5. In their experiments theymade use of spiegeleisen produced by smeltinglow grade manganese ore and open hearth flushslags in an experimental blast furnace". Thespiegeleisen contained on an average Mn 15 23%, Si 1 - 3% P 2 - 5%, C 2.4 - 3.5% andbalance iron.5. The production of high Mn containing slagby selective reduction of Iron and P wasfound feasible on industrial smeltingtrails.The experiments were done in a basic converter of 227 kg capacity. The metal was blownwith air through a 1.5" diameter tuyere arrangedto impinge the blast tangentialy on to the vesselbottom. The air blowing rate was 250-300 Ft'/minute at 3-5 lbsfinz. The converter waspreheated to about 1480 C before molten spiegeleisen was taken into it. The initial series ofthirty blows indicated that if the Mn contentwas odixised to less than 4% in the metal, therequired grade of the high Mn slag with Mn/Pand Mn/Fe ratio of 300 : 1 and 8 : 1 could notbe achieved. Therefore. they adopted the cyclicprocess in which the high Mn slag of the firstblow was refined by further treatment withfresh spiegeleisen. The procedure consisted firstto oxidise the Mn to approximate 1% residualMn in the metal, tap the metal and retain theslag in the vessel.6. In order to bring down the cost of this synthetic Mn ore, it is necessary to make use ofspiegeleisen obtained which amounts to 0.4tonnes per each tonne of Synthetic ore. Saleof by-product spiegeleisen is essential inorder to make the Pyrometallurgical processeconomical.Uses of spiegeleisen :Since spiegeleisen contains 14 to 20% Mn.6 to 7% carbon Si-1 % max it could find use assource of Mn for alloying purposes as well as fordeoxidation. Prior to the advent of L. D. andother B. 0. F. Processes of steel making, it wasextensively used in open hearth furnaces forblocking the heats.However with the modern steel makingprocess, such early blocking steps for workingout the heats are not required and moreoverhigh P input will not be permissible. Now itsuses are limited to foundries only.Moreover, the spiegeleisen produced bytwo step process making use of low grade highphosphorus ores contains 1.5 to 2.0% P andtherefore it cannot be used and therefore recourse has to be made to convert it into saleable by products like alloy steel/special steels.It is proposed that the spiegeleisen can beselectively oxidised with air or oxygen to recovermanganese as high manganese slag, and thebalance metal blown to produce steel. In thisregard Pilot plant investigations at U. S. BureauTo the retained slag in the vessel, containing 10% Fe and 1.0% P, fresh spiegeleisen wasadded and blowing was done which reducediron and P to a low value. This procedureenabled to produce a fluid slag with very littleentrapped metal and high Mn/Fe ratios and highMn/P ratio. In order to make the slag fluid itwas necessary to add quartz, ferro silicon oralumina. The slag was then discharged and the
into four groups for the purpose of mineral beneficiation. 1. Simple Ore Types : These ores are amena-ble to concentration by simple ore dressing methods such as gravity, high intensity magnetic separation or flotation processes. 2. Ferruginous ore types : These can be upgra-ded by magn
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