The present paper describes typical case studies of improved gravity separation of slimes in relation to (a) the separation of synthetic mixture of blue dust and kynite (concentration criterion 2) in advanced gravity separation equipment, and (b) preparation of  bauxite feed following stage-grinding and size classification for enhanced separation following WHIMS.  

  

A sort of size classification has been achieved over the deck of belt concentrator which necessitates need  to treat the slimes in a narrow size range,  especially when the concentration criterion is less.  A significant better yield  and better grade of the products has been observed while following an improved method of feed preparation (stage grinding and size classification) vis-à-vis those following conventional one (grinding and de-sliming) for their separation

Bhagat, R P

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POG (AGS-SOUVENIR) 2007 = 1511ST PROOF (CHAP-23)151ISBN : 81-87053-54-7Advanced Gravity SeparationEds. : R. Singh, A. Das and N. G. Goswami NML, Jamshedpur-831 007, India, 2007, pp. 151-160IMPROVED GRAVITY SEPARATION :TYPICAL CASE STUDIES IN RELATION TO SLIMESRam Pravesh  BhagatMineral Processing DivisionNational Metallurgical Laboratory, Jamshedpur 831 007The present paper describes typical case studies of improvedgravity separation of slimes in relation to (a) the separation ofsynthetic mixture of blue dust and kynite (concentrationcriterion 2) in advanced gravity separation equipment, and (b)preparation of  bauxite feed following stage-grinding and sizeclassification for enhanced separation following WHIMS.A sort of size classification has been achieved over the deck ofbelt concentrator which necessitates need  to treat the slimesin a narrow size range,  especially when the concentrationcriterion is less.  A significant better yield  and better grade ofthe products has been observed while following an improvedmethod of feed preparation (stage grinding and sizeclassification) vis-à-vis those following conventional one(grinding and de-sliming) for their separation.Keywords : Gravity separation, Slimes, Bautixe, Bartles MozleySeparator, Cross belt concentrator.INTRODUCTIONWhile treating finely disseminated lean grade or complex oresthrough wet processing the generation of slimes and tailingsis substantial and if not recovered, causes a heavy materialloss besides, loss of process water. This necessitates treatmentof these products through the process routes incorporatingadvanced gravity separation.Bartles Mozley Separator and Cross Belt ConcentratorSome gravity separators such as Bartles Mozley Separator(BMS) as a rougher devise  in tandem with Bartles cross beltconcentrator (CBC) as a cleaner have made a major advance inslime gravity concentration. These equipment are ideally suitedfor treating lean grade ores  constituting   of minerals with highconcentration criterion, such as, lean grade tungsten oresconstituting of wolfamite mineral and quartz. These equipmentPOG (AGS-SOUVENIR) 2007 = 1521ST PROOF (CHAP-23)152have also application in the sub-sieve range of the mineralslike, tin, gold, silver, platinum etc. Keeping the versatile utilityin view, these have been added to the NML' facilities as regardsto gravity separation.The Fig. 1 shows the BMS consisting of four decks under tiltposition (washing cycle) when heavies are collected and theFig. 2 shows the separation of minerals over the deck of CBC [1].RAM  PRAVESH  BHAGATFig. 2 : Separation of minerals over duel cross belt concentrator.Fig. 1 : Bouttes Mozley Separator.Orbital motion is imparted to the whole assembly driven anout of balance weight which is powered by an electric motor.Slurry is distributed to each of the four decks by a system offeed pipes. The heavy minerals settle on the decks during thePOG (AGS-SOUVENIR) 2007 = 1531ST PROOF (CHAP-23)153orbital motion while tailings being continuously dischargedinto a launder. The heavy mineral is periodically removed fromthe decks by an automatic pneumatically operated liftingdevice in tilt position when wash water is introduced in placeof slurry. After washing the deck the assembly is returned tothe normal operating position and slurry is re-introduced.The BMS,  used in the present study, consists of a 2.4 m wideendless variable speed synthetic polymer belt, the surface ofwhich is inclined transversely from a central longitudinal ridgeto both sides of the belt. The belt assembly is hung from afree standing main frame by four suspension wire. Like, BMSa variable orbital shear motion is imparted to the belt byrotating a out of balance weight.RESULTS AND DISCUSSIONThe efficacy of BMS and CBC was established by carrying outseparation of a synthetic mix at 10 % pulp density consistingof 15% blue dust and remaining kyanite ground to -106 micronsize. The concentration criterion in this case was 2 [(5.1-1.08)/(3.1-1.08)]. The concentrate from the BMS was re-pulped to10% solid in a conditioner and pumped to the feed end of theCBC. The concentrate and tailings produced from the CBCwere separately collected. Table shows the results in terms ofmass balance, Fe2O3 in  the products and size analysis.Table 1 : Results on separation a synthetic mixture of blue dustand KyniteFeed/ Product/ Process Solid flow rate Fe2O3 flow rate % Fe2O3 Mean diam.Feed to the BMS 100 kg/h 12.62 kg/h 12.62Tailings from the BMS  42 kg/h 2.40 kg/h  5.71Concentrate from the BMS  58 kg/h 10.22 kg/h 17.62(Feed to the CBC)  58 kg/h 10.22 kg/h 17.62 27.1 mTailings from the CBC  40.2 kg/h  4.97 kg/h 12.38 13.9 mConcentrate from the CBC  17.8 kg/h  5.25 kg/h 29.51 50.6 mIt is evident from the Table 1 that separation on the deck ofthe CBC has not only upgraded the Fe2O3 content the heavies,but a sort of size classification was also achieved in theirsub-sieve range, possibly due to the difference in terminalIMPROVED GRAVITY SEPARATION : TYPICAL CASE STUDIES...POG (AGS-SOUVENIR) 2007 = 1541ST PROOF (CHAP-23)154velocities of the smaller and larger particles vis-à-vis thoseof heavy (hematite) and lighter (kyanite) minerals underhindered settling condition. The observation indicated thatthe need to treat the slimes in a narrow size to affect betterseparation in terms of grade even though these equipmentare meant for the size range in between 150 and 5 micron.This is important when the minerals with high specific gravityare brittle and therefore selectively and preferentially groundto a much finer size. Tungsten bearing mineral  could beone of the possible examples [2].Size Classification before SeparationPreparation of the feed sample before separation plays a crucialrole in the overall process of beneficiation. A case study inrelation to the beneficiation of the bauxite sample fromMaharashtra State, India is presented here [3]. The objectivewas to remove Fe2O3 and TiO2 from the sample  followinggravity and magnetic separation techniques so that theproduct meets the refractory specification.The material was stage- crushed to 100% -2 mm size fraction.Table 2 shows the size distribution and chemical analysis ofthe (crushed) sample. It is apparent from the table 2 that graterquantities of impurities reported to the finer fractions, whichindicates that the gangue minerals are finely disseminated.The sample was predominantly gibbisitic in nature withtitanium and iron bearing minerals (hematite, goethite,magnetite, rutile and anatase) as major impurities [4].Table 2 : Sieve size distribution and chemical analysis of -2 mmcrushed bauxite sampleSize fraction, mm Wt., % Al2O3 , % Fe2O3 ,% TiO2, % -2000 + 650 34.0 59.55 3.10 4.14  -650  + 320 15.2 58.81 3.34 3.97  -320  + 150 14.5 58.76 3.47 4.28            -150 36.3 54.26 4.78 8.42   Total 100.0 57.40 3.80 5.69RAM  PRAVESH  BHAGATPOG (AGS-SOUVENIR) 2007 = 1551ST PROOF (CHAP-23)155De-slimed Feed (Process `A')One kg of -2 mm crushed bauxite sample was wet ground ina rod mill to 87 wt.% passing a 150 m screen aperture. Theground sample was de-slimed to separate sand and slime.Both sand and slime fractions were separately subjected tothe wet high intensity magnetic separation (WHIMS) at 1.25T. Table 3 shows the results of separation.Table  3 : Results of WHIMS (1.25 T) of crushed andde-slimed bauxite feedProduct Wt. , % Al2O3, % Fe2O3 , % TiO2, %Magnetic fraction of sand 15.3 54.07 7.17 7.49Non-magnetic fraction of sand 27.5 62.26 1.91 1.43Sand total 42.8 59.33 3.79 3.60Magnetic fraction of  slime 11.2 46.76 13.65 9.05Non-magnetic fraction of slime 46.0 57.07 3.50 5.41Slime total 57.2 55.05 5.49 6.12Magnetic total 26.5 50.98 9.91 8.15Non-magnetic total 73.5 59.01 2.90 3.92Feed 100 56.88 4.76 5.05Stage Ground and Size Classified (Process `B')One kg of -2 mm crushed bauxite sample was scrubbed andde-slimed. The sand fraction was wet ground in a rod-mill forsix minutes. The ground sample, which had the sizedistribution 6.0% +212 m, 35.5%-212+150 m and 58.5% -150m, was separated into coarse and fine fractions and treatedseparately following  wet high intensity magnetic separation(WHIMS) at 1.25 T. Table  4 shows the results of separation.Table 5 compares the chemical assays of the products followingthe two processes of feed preparation as mentioned above (Tables3 and 4). The assays of the magnetic & non-magnetic productsof the de-slimed feed have been normalized keeping the assay ofthe stage ground and size classified feed (Al2O3, % = 57.98, Fe2O3,% = 3.81, TiO2,%= 5.34) in view.IMPROVED GRAVITY SEPARATION : TYPICAL CASE STUDIES...POG (AGS-SOUVENIR) 2007 = 1561ST PROOF (CHAP-23)156Table 4 : Results of WHIMS (1.25 T)  of stage ground &size-classified bauxite feedProduct Wt., % Al2O3, % Fe2O3,  % TiO2,  %Magnetic fraction of  coarse  7.3 51.16 9.97 10.28Non-magnetic fraction of coarse 36.7 63.67 1.25 1.26Coarse total 44.0 61.59 2.70 2.76Magnetic fraction of fine  5.6 52.80 8.40 7.46Non-magnetic fraction of fine 16.4 60.42 3.20 3.17Fine total 22.0 58.48 4.52 4.26Magnetic fraction of slime  4.5 39.33 12.44 18.83Non-magnetic fraction of slime  29.5 55.05 3.65 7.96Slime total 34.0 52.97 4.81 9.40Magnetic total 17.4 48.63 10.10 11.58Non-magnetic total 82.6 59.95 2.49 4.03Feed 100 57.98 3.81 5.34Table 5 : Results of the magnetic separation of the bauxitesamples following two different routes of feed preparation (de-sliming and stage grinding & size classification)Product  (process) Wt.,% Al2O3,% Fe2O3, % TiO2,%Non-mag (de-slimed feed) 73.5 60.15 2.32 4.15Non-mag (Stage ground & size classified) 82.6 59.95 2.49 4.03Mag (de-slimed feed) 26.5 51.97 7.93 8.61Mag (stage ground & size classified ) 17.4 48.63 10.10 11.58It is interesting to note that 9.1% (in absolute term) materialrecovery of the non-magnetic fraction has been accomplished(82.6% vis-à-vis 73.5%) when the feed (for the magneticseparation) has been prepared following the Process `B' asmentioned above compared to that following the Process `A',while the quality (chemical analysis) of the products remainsapproximately the same. It is also apparent from Table 5 thequantity of reject, that is,  the  magnetic fraction (17.4 wt. %)when the  stage grinding and size classification was followed(Process `B') was lesser than that (26.5 wt. %) in when thesample was de-slimed and treated (Process `A'). Besides,quality of the reject was also poorer (alumina content wasless; Fe2O3  and  TiO2 were higher) in case when the ProcessRAM  PRAVESH  BHAGATPOG (AGS-SOUVENIR) 2007 = 1571ST PROOF (CHAP-23)157IMPROVED GRAVITY SEPARATION : TYPICAL CASE STUDIES...`B'  for the feed preparation was followed compared to thosein case of Process `A'.The gangue minerals (Fe2O3 and TiO2) in bauxite ore samplehad been finely disseminated; more of which reported to thefiner fraction on grinding (Table 2). Excessive grinding (of thewhole sample) when the Process `A' was followed resulted inthe significantly higher generation of slimes (57.2 weight %)which had difficult separation characteristics because of itsunfavourable granulometry: the feed to the magnetic separatorwas extremely fine which did affect the separation. The slimegenerated in case of  Process `B' was only 34% of the totalfeed and when treated separately resulted in more cleanlinessof the products (magnetic and non- magnetic fractions) asshown in Table 4. This is expected since the finer faction wasnot mixed with the slime.The above explanation could be substantiated from the resultsof gravity separation of the bauxite sample. Table 6 showsresults of tabling of the feed at two different mesh of grind.Table 6 : Results of Tabling of the bauxite  ores at -35 meshand -65 mesh of grindProduct Feed size : -35 mesh of grind Feed size : -65 mesh of grindWt. % Al2O3,% Fe2O3, % TiO2,% Wt. % Al2O3,% Fe2O3, % TiO2,%Heavy 18.10 57.53 4.54 5.58   4.00 49.49 11.94 7.92Middling 26.90 60.69 2.27 3.03 22.50 61.55 2.34 3.17Light 55.00 56.82 4.31 6.35 73.50 57.30 2.84 5.85Head 100.0 57.95 3.81 5.32 100.0 57.95 3.81 5.32It is apparent from the Table that more of light fraction (andless of heavy fraction) were generated with decrease in feedsize from -35 mesh of grind to -65 mesh of grind. Besides,alumina constituent was enriched while Fe2O3 and TiO2 werereduced only in the middling fraction of the feed. That is, betterseparation was achieved only in the middling portion of thesample. When the feed size was coarser (-35 mesh of grind)the generation of middling fraction was higher (26.90 wt. %)compared to that (22.50 wt. %) when the feed size was lesser(-65 mesh of grind)[3].POG (AGS-SOUVENIR) 2007 = 1581ST PROOF (CHAP-23)158A separate investigation on the gravity separation of bauxitesample Panchpatmali mines of M/s NALCO, Bhubaneswarhas shown the effect of feed preparation on the beneficiationefficiency in relation to Tabling. Grinding of the sample wascarried out in stages with de-sliming at every stage.The sample was ground to -10 mesh (-0.2 mm) size andscrubbed for 2 minutes to remove slimes (a). De-slimedproduct was ground for 4 minutes to 75% passing through -48 mesh (-0.295 mm) size. The ground sample was again de-slimed to remove slimes (b). The slimes thus generated weremixed together, as slimes (a+b). The two products namely,sand and slimes were separately treated in a concentratingtables fitted with sand and slimes decks  respectively. Resultsof the Tabling are shown in Table 7[5].Table 7 : Results of tabling tests of Panchpatmali bauxite ore(sand and slime fractions)Feed Product Wt. % Al2O3,% Fe2O3, % TiO2,% SiO2, %Sand Head 45.96 39.19 31.85 3.61 1.28Heavy 11.96 23.53 50.31 7.05 1.41Middling 5.00 37.13 34.29 4.06 1.29Light 29.00 46.00 23.81 2.11 1.22Slime Head 54.04 37.48 28.86 2.27 2.29Heavy 1.24 32.50 38.03 4.85 1.87Middling 0.91 34.60 36.71 3.55 1.91Light 51.89 37.65 28.50 2.19 2.31Feed 100.00 38.26 30.23 2.88 1.82It is apparent from Table 6 that the sand fraction of the bauxitesample had undergone a substantial enrichment followinggravity separation. The content of alumina increased from 39.2wt. % in the feed to 46.0 wt. % in the light fraction. The contentof Fe2O3  and  TiO2 decreased from 31.85 wt. % and 3.6 wt. %in the feed to 23.8 wt. %  2.3 wt. % respectively in theconcentrate. Table 6 further shows that  the process of  Tablingwas not effective in case of slimes as the quantity of  generatedRAM  PRAVESH  BHAGATPOG (AGS-SOUVENIR) 2007 = 1591ST PROOF (CHAP-23)159middling and heavy products was meager. The poor separationefficiency in case of slimes may be attributed to the hetero-coagulation of the particles and possibly, the application ofdispersant in order to maintain the stability of the dispersedsuspension phase and reduce hetero-coagulation may behelpful. Besides, the of treating the slime fraction in advancedgravity separation units such as, Bartles- Mozley separatorand cross belt concentrator could be looked into.CONCLUSION(a) A sort of size classification of the materials is observedover the deck of cross belt concentrator while treatingslimes with low concentration criterion (around 2). Thissuggests that it is necessary to size classify the feedmaterial for treating these over the deck. In case of placerdeposits, such as tin gold etc. with high concentrationcriterion this may not be required.(b) The preparation of feed is crucial in affecting theseparation of minerals from ores/ slime. A typical casestudy of the beneficiation of bauxite ore  for the removalof iron and titanium bearing minerals has beenpresented. A significantly higher recovery of  the valuablematerial has been observed when the feed to the wethigh intensity magnetic separator was prepared  followinggrinding the bauxite ore in stages and size classificationcompared to that when the whole bauxite ore was groundand de-slimed.(c) Alumina content is enriched while Fe2O3 and TiO2 arereduced only in the middling fraction of the  bauxitefeed during the Tabling of the sample with feed size -35mesh and -65 mesh. Besides, more of light fraction isgenerated with decrease in feed size from -35 mesh ofgrind to -65 mesh of grind.(d) The efficacy of separation during the Tabling of  the sandportion of bauxite ore is higher than that in case of slimefraction. The content of alumina increased  by around 7wt. % (in absolute term) in the light fraction of TablingIMPROVED GRAVITY SEPARATION : TYPICAL CASE STUDIES...POG (AGS-SOUVENIR) 2007 = 1601ST PROOF (CHAP-23)160the sand. The slime portion of the bauxite sampleresponds very poorly during the process of Tabling asthe quantity of middling and heavy products generatedwas meager.ACKNOWLEDGEMENTThe author expresses his sincere gratitude to the co- workersof the projects whose names  are  mentioned under thereferences 2, 3 and 5. He would like to thank M/s. INDAL forsponsoring the bauxite project and the Director, NML forproviding the laboratory and infra-structural facilities.REFERENCES1. Bhagat R.P., Sarkhel B.R., Saha P., et al. (1991), Installation& Commissioning of Pilot Scale Fine Particle ProcessingEquipment, Investigation Report, NML, Jamshedpur.2. Bhagat R.P., Saha P., Sarkhel B.R., Srivastava J.P., GaneshR., Pathak P.N. and Chakravorty N. (1992), Salient Results onGravity Separation of Wloframite using Bartles MozleySeparator and Cross Belt Concentrator. Proc. National Seminaron Research & Process Development in Mineral Preparation,Org. by IIME and NML Jamshedpur, April 14-15, pp. 250-254.3. Bhagat R.P., Kunwar R.K, Banerjee B., Dey S., Mukherjee B.C.,Choudhury V.N. (1996), Development of Flow-Sheet usingGravity and Magnetic Separators for Quality Production ofBauxite for Refractory Purpose. (Report No. IR 12326089),March.4. Bhagat R.P., Banerjee B., Kunwar R.K. and Dey S. (2001),Trans. IMM Section C (Mineral Processing and ExtractiveMetallurgy), Vol. 110, pp. C165-C168.5. Bhagat R.P., Dey S., Rao D.S., Choudhary V.N. (2000),Exploratory Study on Beneficiation of Bauxite Sample fromPanchpatmali Mines of M/s. NALCO, Bhubaneswar (aninhouse), October.RAM  PRAVESH  BHAGAT

Improved gravity separation : typical case studies in relation to slimes

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Improved gravity separation : typical case studies in relation to slimes

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