The present production of refractories in India is of the order of 0.75 million tons. These comprise  fireclay, alumino silixates, high alumina and  basic  refractories 

and refractory cements, mortars,  mortars,  plastics and castables. Besides these, large  tonnages  of dead burnt dolomite are produced in many steel plants  for fettling and repair of open-hearth and electric arc  furnaces or lining L-D vessels. Of the total  production  of refrac-tories, steel plants consume almost 80%.By and large the refractory manufactures were coping up with  the  requi-rements of user industries except for the demand of some speciality refractories. However with the changing techn-ology, particularly in steel making, and greater emphasis on purity of refractories the  refractory  manufacturers find it  exceedingly  difficult  to  meet  the stringent specifications laid down by the users

Mathur, N N

Rao, M R K

Sen, P C

English

eprints@NML

Beneficiation and utilisation of low grade refractory materials * N. N. Mathur, * P. C. Sen and * M. R. K. Rao Introduction : The present production of refractories in India is of the order of 0.75 million tons. These comprise fireclay, alumino silicates, high alumina and basic refractories and refractory cements, mortars, plastics and castables. Besides these, large tonnages of dead burnt dolomite are pro-duced in many steel plants for fettling and repair of open-hearth and electric arc furnaces or lining L-D vessels. Of the total production of refracto-ries, steel plants consume almost 80%. By and large the refractory manufacturers were coping up with the requirements of user industries ex-cept for the demand of some speciality refracto-ries. However with the changing technology, particularly in steel making, and greater empha-sis on purity of refractories the refractory manu-facturers find it exceedingly difficult to meet the stringent specifications laid down by the users. Although at present low grade refractory materials are available in huge quantities to last a few more decades, the resources for high grade materials are limited or not upto the required quality. Further due to ever increasing demand of the industry in terms of quantity and quality of refractory minerals, mechanised mining is adopted. This results in the production of poor quality of R.O.M. ore and a sizeable quantity of fines which go on stock-piling as waste dumps at the mine heads. In order to make good use of the existing refractory mineral deposits and meet quality spe-cifications it becomes imperative to upgrade the  low grade materials as well as the huge quantity of waste materials by suitable beneficiation process. However, beneficiation has some disad-vantage so far as the refractory minerals are concerned. The product of beneficiation is generally a fine material, which generally can-not be used directly in refractory industry unless it is processed to yield a dense, coarse grog acceptable to the refractory manufacturers. Considerable amount of work has been done in NML on beneficiation of low grade refractory minerals both on bench scale as well as pilot plant scale and industrial flow-sheets have been worked out. A summary of results of some of these studies conducted in the Ore Dressing Division are reported in this paper. Further, attempts are being made in the Refractories Division of NML for utilisation of these beneficiated fines for the production of refractories. Studies are underway to study and establish various process parameters and the economic viability of using such fine materials. Some of these test results have also been included. Magnesite : All India production of magnesite in 1981 was around 463000 tonnes of which roughly76% came from Tamilnadu and 21% from U.P. and the rest from Karnataka and Rajasthan. Of the total production of magnesite nearly 63% was consumed by the refractory industry. The raw material Sub-committee of the Development Panel on Refractories (DGTD) in * Scientist, National Metallurgical Laboratory, Jamshedpur-831007. its interim report had worked out a demand of 590,000 tonnes of magnesite by 1990. The mineral is mostly used for the produc-tion of magnesite and chrome-magnesite bricks. The Indian standard specifications for dead burnt magnesite stipulates 5.5% Si02 and 2.5% Ca0 which means that in the raw state the lime and silica should be about half of these limits. Such low silica and lime magnesites are now scarce. (Table - ) In most of the advanced countries very pure quality sea-water magnesia is used for the manu-facture of basic bricks for L-D and EAF (Table-2) but in India where this material is not available indigenously resort has to be taken to imports and considerable quantity of sea water magnesia is being imported. Under the circumstances bene-ficiation of natural magnesites to low Si02 and Ca0 levels is all the more important. Further the beneficiation of the natural magnesite will have the added advantage of low B2 03 , which is a most deleterious impurity in sea water magnesia. Beneficiation studies on a number of Salem and Almora magnesite samples were conducted at NML. A summary of the results is shown in Table-3. The chief problem with the two main magnesite deposits of the country, that is Salem and Almora, is the reduction of Si02 in the for-mer and Ca0 in the latter to acceptable limits. Silica and lime occur as finely disseminated inclusions, veins or stringers; any beneficiation process aimed at reducing these impurities necessarily involves fine grinding and flotation is the only suitable method for beneficiation. Flotation test on Salem rnagnesite assay-ing 7.0% Si02 showed that the concentrate after three cleanings represented 19.4% of the feed and contained 1.18% Si02 . 	 But the concentrate after two cleanings assayed 2.21 % Si02 with a 34.1% yield. A 2.2% Si02 magnesite would be a good material for the production of refractories. Studies are under way to evaluate its refractory properties. Preliminary results show that the fines could be utilised to produce a dense grog. Table-4 gives the grain densities of magnesia fired at 1650°C after different agglomeration techniques and Fig. — 1 their microstructures. Pellets gave a sinter of highest density and lowest porosity. It may be mentioned here that grain density of sinter is important as higher den-sities reduce slag attack and increase service life of refractory. The Refractories division of N. M. L. has successfully developed a process for the reduc-tion of lime cotent in Almora magnesite by a patented process. The lime content in the dead burnt magnesite could be reduced from 7 % to below 2%, with 85% wt. recovery. The bricks produced from the concentrates meet the re-quired specification. Kyanite / Sillimanite : Kyanite and sillimanite are important re-fractory minerals used for the manufacture of high alumina bricks besides refractory grade bauxites or diaspores. The refractory industry requires bauxites/diaspores of low Fee 03 and TiO2 contents (Total 3-5% max) and 56-60% Al2 03 but such deposits are scarce. 	 Both kyanite and sillimanite have the same chemical composition ( Al2 03.Si02) and both transform to mullite on heating but in kyanite this trans-formation is accompanied by a large volume expansion (16% approx). Kyanite Lapsaburu deposits of Singhbhum district, Bihar which were once the world's best deposits are now getting depleted and the production has been falling. Other known occurences are in Bhandara district in Maharashtra, Chickmagalur, Mandya, Shimoga and South Kanara districts of Karnataka and Udaipur district of Rajasthan. Large reserves of low grade kyanite have been disco-vered in Khammarn and Prakasam districts of Andhra Pradesh, Singhbhurn in Bihar and Puru-lia in West Bengal. 307 The total reserves of refractory grade kyanite containing 55 	 Al2 03 ( min ) are estimated to be 956.000 tonnes of which 90,000 tonnes are under the measured category. The cumulative resource of low grade deposits is placed at over 147 million tonnes. Sillimanite Massive sillimanite occurs in Meghalaya, Maharashtra, Madhya Pradesh and Karnataka. The famous Khasi sillimanite deposit of Megh-alaya is diminishing in productivity. Small depo-sits occur in Tiruchirapalli district of Tamil Nadu. Of recent interest are the secondary sillimanite of Kerala, Tamil Nadu and Orissa beach sands con-taining 5 — 10 % sillimanite. The total reserves of sillimanite are of the order of 11.6 million tonnes of which 68,000 tonnes are of massive variety. The total consumption of kyanite and sillimanite was about 49,200 tonnes in 1981 and the demand by such industries as iron and steel, copper, refractory, cement, lead and zinc and aluminium alone is expected to be 84.600 tonnes by 1990. Kyanite and sillimanite even in their purest state contain 62.9 % Al2 03 and as such cannot be used for the production of high alumina bricks containing more than 60% Al2 03 . As such the refractory industry needs the purest varieties containing more than 60% Al2 03 . However for medium range refractory products a 55-60% Al2 03 material is adequate. There is therefore a need to beneficiate this second grade kyanitei sillimanite. NML has been seized with the pro-blem and conducted beneficiation studies on a number of kyanite samples. A summary of these tests is given in Table – 5. Studies have also been done towards ultilisation of these fines. Laboratory scale studies done on a kyanite sample assaying 34.6% Al2 03 in R.O.M. gave encouraging results. This sample was beneficiated by flotation and the concentrate which was ---72 mesh B.S.S. assayed 60% Al2 03 . The concen- trate was compacted and fired to 1550 and 1650°C. The properties of the fired compacts are shown in Table-6, It is evident from the table that the con-centrated fines can be successfully used for the production of a dense sinter which can subse-quently be used for the manufacture of high alumina bricks, Laboratory scale work has also been done on Kerala beach sands and refractory bricks were made. These bricks compared well with the bricks made from lumpy ores. The properties of bricks are given in Table-7. Graphite : Graphite is used for the manufacture of crucibles for melting metals and alloys and sto-pper heads for teeming ladles. Of late another class of graphite based refractories, containing graphite and refractory oxides like MgO, Al2 0 3 etc. has come up which finds increasing appli-cation in steel making furnaces. Some of these applications call for coarse flaky graphite having high resistance to oxidation and low ash content. Indian graphites in general have high ash con-tents and need beneficiation for such applications, Flaky crystalline graphite ( +65 mesh ) is generally used for crucible making and refractory purposes. Natural graphite deposits in India are located in Orissa, Gujarat, Kerala, Tamilnadu, Andhra Pradesh, Rajasthan, Bihar, and Jammu and Kashmir, The estimated total reserve is about 7.8 million tonnes of all grades. Table-8 gives the summary of beneficiation studies on some Indian graphites. Graphite is used for refractory industry, foundry, lubricant, paint and various other industries for which specification are available. The quality requirement of natural graphite for use in the refractory crucible industries is given in Table-9. The oxidation study of a sample of Kerala graphite beneficiated in the laboratory in comparison with Madagaskar graphite is shown in Table - 10, which showed that the 308 sample is at par with imported flaky graphite. The concentrates were sent for trial production of graphite crucibles at Rajahmundry. They were found to be eminently suitable for cru-cible manufacture. Conclusions In view of the depleting resources of high grade refractory raw materials the problem Indian refractory industry is presently confron-ted with is two-fold. Firstly to get consistent supplies of raw materials such as magnesite, kyanite, sillimanite, graphite etc. conforming to the stringent specifications, leaves no alter-native other than beneficiation by suitable me-thods. Secondly beneficiation would result in the generation of concentrates which are of fine size, usually below 100 mesh. The proP- lem then arises as to its utilisation because this fine material cannot be used as such. Therefore, even if the industry gets the concentrate of requisite quality it will not be able to take up the whole of the concentrate for brick making un-lessiit is suitably processed to yield a dense grog. This requires tailored processes suitable for each concentrate so that it is accepted by the refractory industry for brick making. 	 The technical parameters and economics of such process have to be worked out and work is being done in NML to this end. Acknowledgement : The authors are thankful to Prof. V. A. Altekar, Director, National Metallurgical Labora-tory for his kind permission to present this paper. (A) 	 (B) Fig. — 1 Microstructure of 1650°C fired brick (A) and pellets (B) 309 Table — 1 	 All India reserves of magnesite as on 1A-1980 (in tonnes) State 	 Measured 	 Indicated 	 Inferred 	Total I Reserves of magnesite with Silica upto 3.25% Karnataka 	 4,500 	 4,500 Rajasthan 	 23,600 	12,000 	35,600 Tamil Nadu 1/ 	141,224 	141,224 Total : 	 23.600 	 157,724 	181,324 II Reserves of magnesite with Silica 0.50% to 10% Karnataka 	 436,000 	428,380 	 134,000 	 998,380 Kerala 	 15,000 	15,000 Tamil Nadu 1/ 	 4,638,797 	 4,635,863 	3,369,019 	 12,643,679 Total : 	 5,074,797 	5,079,243 	 3.503,019 	 13,657,059 Uttar Pradesh Uttar Pradesh Uttar Pradesh 111 Reserves of magnesite with CaO upto 2.5% 	331,330 	 7,722,700 	 20,550,000 	 28.604,030 IV Reserves of magnesite with CaO 2.5% to 8% 	4,000,000 	 11,390,000 	 2,810,000 	 18,200,000 V Reserves of magnesite with CaO 0.00% to 9.30% 	2,451,632 112,465,438 	 13,716 114,930,786 Himachal Pradesh Rajasthan Tamil Nadu 1/ Uttar Pradesh VI Reserves of magnesite of Unclassified type 87,620 228,792 	1,002,800 	93,01 9 	 21,644,857 	731,049 	 941,115 	18,071,549  87,620 228,792 22,740,676 19 743,713 Total : 	 1,733,849 1,262,926 	 39,804,026 	 42,800,801     All India Total : 	 13,591,608 137,943,907 	 66,838,485 218,374,000 1/ According to M/s. Dalmia Magnesite Corporation, the insitu inferred reserves in their leasehold are around 20 million tonnes. Table -- 3 	 Summary of beneficiation results of some magnesites of Indian origin Sample State and Locality R.O.M. Assay%  MgO% 	 S102% Beneficiation Method Concentrate Wt. % Assay% SiO2 Tamil Nadu Salem 	 44.51 	 2.85 	 Heavy Media separation at 	 73.5 	1.48 - 3/4" -I- 10 mesh Salem Salem Salem Salem (Dead- Burned) 	45.9 	 3.0 	44.9 	 1.1 	45.86 	 3.9 	85.7 	 8.6 Flotation and cleaning Crushing, sizing at -12 mm + 65 mesh (only screening) Flotation and cleanings Heavy Media Separation/ Magnetic separation 70.0 82,0 77.6 0.9 2.2 1.05 6.18 7.63 Salem 	 42.2 	 7.0 	 (i) HMS of -25 -- 6.33 mm at 2.8 13.2 	 2.20 (ii) Flotation (93% -200 mesh) 	 52.4 	2.26 with cleanings (iii) Flotation with reground midd- 	 54.8 	1.87 ling recirculation Salem 	 42.2 	 7.0 	 Flotation (93% -200 mesh) and 	 53,1 	 2.30 Middlings reground (98% -200 mesh and recirculation Karnataka Kadakala 	 38.4 	14.7 	 Flotation and cleanings 	 48.2 	1.73 U. P. Pithoragarh (I) 	 43.65 	 0.99 	 CaO Flotation and cleaning with 	 67.8 	 0.35 3.01 Katha for lime removal. Pithoragarh (II) 	 42.21 	 1.31 	 4.04 	 -Do-- 	 0.70 Rajasthan Ajmeer 	 41.6 	 9.8 	 Flotation and cleanings 	 37.6 	 1.63 311 312 Table - 2 : Chemical Analyses of some magnesites used abroad vis-a-vis Indian magnesites Source Si02 Al2 03 Fee 03 Ca0 Mg0 B2 03 Indian : Salem Natural 5.5 - 7.0 1 0 - 1.5 0.5 - 0.1 1.4 - 2.5 89 - 90 Almora Natural 4 - 6 1.0 - 1.5 3.0 - 5.5 17.0 85 - 92 Foreign : Greece Natural 0.8 0.20 0.2 1.60 94.87 0.01 Turkey Natural 1.16 0.04 0.61 2.28 95.88 0.01 Austria Natural 0.86 0.56 3.91 2.75 91.82 0.08 USSR Natural 2.4 2.6 1.70 92.40 Pelletised magnesia A Sea water 0.8 0.4 1.50 1.8 95.5 0.03 B Sea water 0.8 0.2 0.15 2.0 96.8 0.03 C Sea water 0.5 0.2 0.15 2.0 97.1 0.04 Table - 4 	 : 	 Grain 	 density 	 of 	 different compacts 	 made 	 from 	 salami magnesite concentrate and fired at 1650°C Table - 5 : 	 Summary 	 of 	 beneficiation studies on Kyanite State 8- 	 Assay% ROM Yield% Assay °,; Locality 	 Al2 03 	 Si02 Conc. Al2 03 Method of compaction Grain density, gm/cc Andhra Pradesh : Khamam 	 25.4 	 62.7 Bihar : Badia 	 45.3 Singhpura 	 51.2 Rajkharswan 	 54.9 Amba-lapso 	 38.2 21.6 59.0 69.3 71.7 30.9 60.0 60.2 61.1 60.4 60.4 50 x 50 mm cylindrical specimen Bricks (Screw press) Pellets 3.30 3.27 3.37 Sirbali 	 46.8 45.1 60.1 Lapsa-buru 	 34.6 22.8 60.0 Table - 7 : Properties of sillimanite bricks - dO - 	 35.4 18.4 57.0 made from Kerala Beach sands Orissa : Meganmohan 	 51.6 57.1 60.8 Mines, Pallaharu A12 03 60 % Si02 36 % Maharashtra : P. C. E. Cone 38 (Orton), 1850°C Dahagaon Sample - 1 	 401 10.1 57.5 App. Porosity 21-25`)/, - do - R.U.L. Ta 1640-1650°C Sample - 2 	 38.4 27.4 59.6 Te 1655-1675°C - do - C.C.S. 13000-17900 P.S.I. Sample - 3 	49.0 54.4 61.1 Thermal -!-• 	 32 Karnataka : spalling (BRRA) Mavinkere 	 64.1 72,5 72.8 Table 6 : Properties of the sintered compacts of kyanite concentrates. Sample composition and size 	 1550°C firing 	1650°C firing No. -60 mesh 	K yanite 	 China clay 	 Porosity 	 B.D. 	 Porosity -150 	 -300 	 addition% 	 gm/cc 	 0/0  mesh 	 mesh B. D. gm/cc 1.  100 - 	 nil 	 48.6 	 1.64 	 46.10 1.74 2.  100 5 	 51.6 	 1.76 	 34.60 1.97 3.  100 	 - 	 nil 	 41,2 	 1.67 	 35.09 2.02 4, 100 	 5 	 39.6 	 1.74 	 30°35 2.06 5.  100 	 nil 	 32.7 	 2.06 	 10.30 2.46 6.  100 	 5 	 33.8 	 2.06 	 15.20 2.40 Table-8. Summary of the beneficiation studies on some low grade of Indian origin as done in N. M . L. graphite Locality Process Original analysis Concentrate 	 Recovery analysis Sitampalli, 	 A. P. Flotation 17% FC 82% 	 F. C. 	 91.5 55% - 200 mesh 79% Ash Khepchisbi Hill Flotation 10.66% F. C. 63.4% F. C. 	 78 Bhutan 86,4% Ash Palamau, Bihar Flotation 15.5% F. C. 88% F. C. 	 90 79.4% -200 mesh 76.5% Ash Doomara, Ajmer Flotation 8.19% F. C. intimately 	 mixed 	 with - 200 mesh 84.37% Ash mica and not amenable to flotation. Chammuda Flotation 4.86% F. C. Not amenable to benehi- Sidhi, M. P. 87.34% Ash ciation. Panchmahal, Gujrat Flotation 7.1% F. C. 80% Ash 41.65 F. C. 	 76.6 Khammam Flotation 10.4-64 F. C. 69.5-87.4 F.C. 87-88 A. P. 81.7-31.6 Ash 313 Table —9. Specifications of graphite used in crucible industries Table-10 : Oxidation loss of two varie-ties of graphite flakes (-14 +72 B: S. S.) British* 	 U.S.A.** 	 India*** (ISI draft) 1. Chemical analysis Carbon content 85% 85-90% 	 90%+ Fee 03 	 1.2% Max TiO2 	0.5% Max Ca0 	 0.02% Max 0.5% Max Volatile 	 1.5% Max Temp °C Madagascar graphite Kerala State graphite 800 900 1000 5.5% 17% 73% 6% 22% 75% 2. Sieve analysis Retained on 8 TSS 20 28 	20% 35 42 	80% 48 60 	95% Passing 	 60 	5% 3. Flakiness index 	 129 	 -- 	 Graphite m1/100 gm 	 should be crystalline flaky. 4. Physical require- 	 Graphite ment 	 should be reasonably free from mica. The oxidation temperature should be approx 750"C * British crucible makers specification ** National stockpile specification U. S. A. p- 22A, 1-14-1947 *** A minimum 80% carbon is acceptable if the balance of impurities is aluminous or silli-manite. References 1. Beneficiation of industrial minerals for the basic refrac- tories. 	 — P. D. Prasada Rao 	 A. Peravadhanulu, N. Chakravorty, S. K. Banerjee and G. P. Mathur. 	 Paper presented at the seminar on basic refractories for Steel making organised by the Indian Ceramic Society, Jam-shedpur chapter and National Metallurgical Laboratory on 23-1-1982 and 24-1-1982 at Jamshedpur. 2. NML's experience in the field of mineral beneficiation and conservation. — B. L. Sengupta, G. P. Mathur and V. A. Altekar. Paper presented at "National Mineral Convention" held at New Delhi on 16-18th February, 1981. 3. An appraisal of occurrence and requirements OT kyanite in India and a preliminary investigation on the refractory properties and processing of beneficiated kyanite concen-trates. — M. R. K. Rao, N. B. Sarkar, P. C. Sen and R. V. Hargave. I. R. No. 914/77 February, 1977. 4. Raw materials for refractories for iron making. — P. C. Sen and M. R. K. Rao. Paper presented at the Seminar on 'Refractories for iron making' organised by the Indian Ceramic Society, Damodar Valley Chapter, at Bokaro on 8th and 9th January, 1983. 1% 8% 34% 75% 95% 97% 3% Particle size between-14 mesh BS to 90 mes h BS 314 

Beneficiation and Utilisation of Low Grade Refractory Materials

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Beneficiation and Utilisation of Low Grade Refractory Materials

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