Sukinda-Nausahi belt of Orissa, represent about 90% of the Indian Chromite ore reserves. These ores are later-itic type in nature resulted by weathering  of  ultrabasic rocks, Metallurgical industries consume  maximum  chromite ores- around 50% followed by refractory and  chemical indu-stries which consume about 35% and 15%  respectively.  The utility pattern  of  chromite  in  industries  is  varying greatly. The variation in the demand could be due to  lim-ited market for medium and low grade chromite. Hence it is necessary to improve the chromium content for better util-isation and conservation of available resources

Bhima Rao, R

Charan, T G

Sastri, S R S

English

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Characterisation and response to beneficiation of ferruginous chromite ores ** R. Bhima Rao, * T. G. Charan and ** S. R. S. Sastri INTRODUCTION Sukinda-Nausahi belt of Orissa, represent about 90% of the Indian chromite ore reserves. These ores are lateritic type in nature resulted by weathering of ultrabasic rocks. Metallurgical industries consume maximum chromite ores—around 50% followed by refractory and chemical industries which consume about 35% and 15% respectively. The utility pattern of chromite in industries is varying greatly. The variation in the demand could be due to limited market for medium and low grade chromite. Hence it is necessary to improve the chromium content for better utilisation and conservation of available resources, Raw Materials Two different chromite ore dump samples of Kaliapani 1 Et 2 and other dumps under the lease of M/s. Orissa Mining Corporation Ltd. and one medium grade chromite ore sample from M/s. Misrilal Mines Pvt. Ltd. have been received to assess the amenability for beneficiation. Liberation Studies : The liberation size and the possible grade recoverable from the ore are determined from (1) the texture of the mineralogical constituents pre-sent in the ore and (2) the assay value of each closely sized fraction of the ore or the products obtained from sink-float or magnetic separation of each closely sized fractions of different mill products. Mineralogical studies were carried on the samples to find out the different constituents present and their liberation size. Physical and chemical characteristics of the samples as received were determined. All the ROM samples were size analysed and each fraction was analy-sed for chromium and iron. Based on these results, representative samples were stage crushed to pass through 1.5 mm open rolls. Each crushed product was further size analysed. 	 Separate sink-float and magnetic separation tests were carried out on each of the closely sized fractions to assess the liberation and the type of concen-trate recoverable either by gravity or magnetic separation (Fig. 1). An organic liquid of 2.83 specific gravity was used for sink-float studies. Each crushed product was subsequently ground for different time intervals in a batch ball mill of 1200 X 1200 mm in size with 25% ball charge. Each mill product was further size analysed to determine chemical constituents in each fraction and degree of liberation. Following the liberation studies bench scale beneficiation studies were carried out with or without combination of screen, hydro-cyclone, Diester table and Bartles-Moziey separator for enrichment of chromium content. BENEFIClATION STUDIES Samples—Di and D2 A representative sample was ground to optimum size as indicated in Fig. 2. A sample of 5 kg material was taken for each experiment and subjected to tabling with or without ** Regional Research Laboratory (Council of Scientific & Industrial Research) Bhubaneswar - 751 013, Orissa. M. A. Sc., Mineral Processing, Gulbarga University. desliming by hydro-cyclone or pre-concentration on Bartles-Mozley separator. Experiments were also carried out on a deslimed product using a Bartles-Mozley separator. Representative samples of concentrates, middlings and tailings of each experiments were collected for chemical analysis. The optimum results obtained from different experiments are tabulated in Tables 2 Et 3. Sample-C1 : A representative sample was washed and sized. Each size fraction was analysed for metal content. Based on the results, two tonnes of sample was washed over a double deck screen of 25 and 8 mm aperture and the washings as well as the fines below 8 mm were deslimed in a spiral classifier (225 mm dia X 1800 mm long) at a rate of about 75 kg/hr with 250 litihr water. The results are tabulated Table in 4. Results and discussions : Characteristics of the chromite ore sam-ples are shown in Table-1. Sink-float separa-tion and effect of particle size on crushed products related to liberation size are shown in Table-5 and Fig. 1. The results obtained from detailed beneficiation studies under optimum conditions are tabulated in 2a, 2b and 2c for sample D-1 and Table 3 and 4 are for sample D-2 and C-1 respectively. Schematic flow-sheets for the above ores are shown in Fig. 2 and 3. It is observed from Fig. 1, the assay values of closely sized fractions of the samples, the libera-tion size is around 100 and 250 microns for sample D-1 and D-2 and Table-2 indicates, the sample C- -1 is as such liberated. Based on these results, detailed investigations were carried out both on laboratory and large scale. A product is obtained from a feed sample D-1 on Diester table analysing 41% Cr203 with 72% metal recovery. But by desliming/pre-concentrating the feed sample D 1, by using hydro-cyclone/ Bartles-Mozley separator a better product is obtained, which analyses 43% Cr203 with 70% metal recovery. These results indicate that desliming or preconcentrating the feed prior to tabling, help in getting a better product and reduce the feed load and water requirements for tables. Sample D-2 yielded a product after desliming analysed 40% Cr203 with 78% metal recovery. The product obtained from slimes on Bartles-Mozley separator is recirculated to the process. A common flow-sheet is obtained for sample D-1 and D---2. shown in Fig. 2. From Table-5 and Fig. 3, the sample C-1 yielded a product of 55% Cr2O3 with 94% metal recovery by desliming with spiral classifier. Conclusions : The possible libreration size of the dump samples D-1 and D-2 is around 100 and 250 microns and the possible grade recoverable from the ores is around 43% Cr2O3 is determined from the assay values of each closely sized frac-tions obtained from size analysis of the ore. A product assaying 43% and 40% Cr2 O3 with 70% and 78% metal recovery is obtained from these samples on Diester table after desliming the feed. Sample C-1 is, as such liberated and a product containing 55% Cr203 with 94% metal recovery is obtained after desliming the feed using a spiral classifier. Accordingly suitable flow sheets have been suggested. it is concluded that these samples are amenable to gravity separation and the products are suitable for industries after suitable blending and agglo-meration. Acknowledgements The authors express their sincere thanks to Prof. P. K. Jena, Director of the Laboratory for his keen interest and encouragement in the work and for permitting to present this paper at "National Seminar on Mineral Processing", Jamshedpur. The authors also wish to thank Sri M. I. Ansari, Project Co-ordinator for his constant encouragement. Thanks are due to Dr. B. S. Acharya for X-ray diffraction studies and others involved in this project. 142 Table-1 : Characteristics of chromite ore samples SI. No. Area/Mine Nature of sample Sample code Cr2 O3 % feed Major mineralogical constituents 1. M/s. OMC Ltd. Dump--1 Lumpy, 	 friable, ferruginous 	 low grade ores. D-1 29.9 Mg 2 Cr204 	 Hematite go- ethite, 	 magnetite, 	 quartz, serpentine and nickel oxide minerals. 2. M„is OMC Ltd. Dump-2 Lumpy, friable ferruginous low grade ores, D-2 26.5 Chromite, 	 goethite, 	 hem- atite, 	 megnetite, 	 quartz, serpentine and 	 nickel 	 oxi- de minerals. 3. M/s. Misrilal Mines Pvt. Ltd, Chromite ore. Lumpy, friable, ferruginous me- dium grade ore. C-1 49.4 FeO (Cr, Al)2 03  Mg-Cr-Al-Silicate- hydroxide, 	 goethite. Table-2 	 Sink-float separation on crushed product related to liberation Sample No. C-1, Feed Cr2O3 % 49.4 SI. No, Size 	 in microns Feed Wt. % Heavies Wt. % Feed Cr2 O3 % Heavies Cr2O3 % 1.  1000 38.9 37.8 51.4 53.0 2.  350 18.8 13.5 54.0 54.0 3.  150 21.8 21.6 57.9 57.3 4,  53 10.8 10.6 57.5 57,7 5,  B 53 14.7 27.8 - Head 100.0 83.5 50.4 54.9 Table-3 (A) Results obtained from Diester table on D-1 sample SI No. 	 Sample 	Weight, °Z) 	 cY0 of Cr2O3  Grade Recovery  1.  Concentrate 53.84 41.59 72.0 2.  Middlings 23.08 23.71 18.0 3.  Tailings 23.08 14.87 10.0 Head 1 00 .00 31.29 100.0 143 Table - 3 (5) : Results obtained from cyclone and Bartles-Mozley separator on D-1 sample SI. No. Sample Weight °/,, % of Cr203 Grade Recovery Desliming by Concentrate 64.0 37.79 81,0 hydro-cyclone Tailings 36.0 15.27 19.0 Head 100.0 29.69 100.0 II Pre-concentrate by Concentrate 70.97 35.70 85.0 Bartles-Moziey separator. Tailings 29.03 15.53 15.0 Head 100.00 31.29 100.0 Table-3 (C) : Optimum results obtained on sample D-1 SI. No. Sample Weight % % of Cr203  Grade Recovery I Desliming Concentrate 64.0 37.8 81.0 Tailings 36.0 15.3 19.0 ll Head 100.0 29.7 100.0 Diester Concentrate 49,0 43.05 71,0 table Middlings 10.0 24.37 8.0 Tailings 5.0 13.20 2.0 Tailings 36.0 15,27 19.0 (deslimed) Head 	 100.0 	 29.69 	 100.0 144 Table-4 : Results obtained on sample D-2 Sample Weight % % of Cr203  Grade Recovery Coarse 4.39 20.26 3.0 Concentrate 53.82 40.30 78.0 Tailings 13.46 13.85 7.0 Concentrate 7.08 21.56 6.0 Tailings 21.25 7.82 6.0 Head 100.00 26.63 100.0 SI. No. I Screen ( 1.5 mm. open ) II Diester table on deslimed product III Bartles-Mozley on slimes. Table-5 : Results obtained on sample C-1 SI. No. Unit size (mm) Feed % Product % Recovery Weight Cr203  Weight Cr20 3  1.  Screen +25 4.6 48.9 4.2 52.9 4.0 2.  Screen + 8 18.1 51.5 16.9 51.5 17.0 3.  Spiral -- 	 8 77.3 50.7 64.4 55.5 71.0 4.  Spiral slimes - - 14.5 25.7 8.0 Head 100.0 50.7 100.0 50.4 100.0 145 .11 90 cr 70 co 50 X 0 30 40 30 20 10 I  100 	 300 I 	 ' 	 500 	 700 I 9 0 SIZE IN MICRONS 100 300 500 700 900 SIZE IN MICRONS % CHROMIUM % RETAINED 10 40 30 20 10 (0) s/ 	 • (W) 	 (WI 2 do 	 ►  • Rp a WEIGHT % o Cr2 03% 	 0 Cr2 03 % IN HEAVIES 	 • CHROMITE % FIG 1  LIBERATION SIZE BY DIFFERENT METHODS. .  (0) ORE (W) WATER (P.) PRODUCTIR) REJECTS 1. JAW CRUSHER 2. ROLL CRUSHER 3 BALL MILL 4. HYDROCYCLONE 5. BARTLES-MOZL EY 6. TABL E FIG .2 SCHEMATIC FLOW SHEET FOR BENEFICIATION OF SAMPLE D1 & D2 - 146 (0) (W) (0) ORE (W) WATER- (PI & P2 ) PRODUCTS (R) REJECTS 1. SCREEN (VIBRATORY WITH 8mm OPENING) 2.. SPIRAL CLASSIFIER FIG.3 SCHEMATIC FLOW SHEET FOR BENE FICIATION OF SAMPLE - Ci 147 

Characterisation and Response to Beneficiation of Ferruginous Chromite Ores

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Characterisation and Response to Beneficiation of Ferruginous Chromite Ores

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