India is gifted by nature by way of large quantities of high grade nonferrous mineral    resources   like barite containing more than 90% barium sulphate. The processing of barite to win   chemicals   from   it    requires its

carbotherrnic reduction at high temperatures being carried out in rotary furnaces. The powdered charge   containing barium sulfide is prone to get   damaged   due to reverse reaction caused by   infiltered    oxygen   at the end of

reduction state. This hampers the yield of water soluble barium sulfide.The paper discusses     about the means of achieving favourbale kinetics and high recovery of water soluble barium sulphide in the carbothermic   reduction of barite at high temperatures. The reaction rate of reduction

step was enhanced many folds by using       briquetting technique. Even with barite containing large amnount of harmful impurites, the yield of barium was      improved considerably on pilot plant scale, thus achieving better

utilisation of natural resoures such as barite and coke

Gokarn, A N

Kale, B B

Kulkarni, S S

English

eprints@NML

Environmental and Waste Management (ISSN: 0971-9407)Eds. - A. Bandopadliyay. N.G. Goswami and PR. RaoNML..lamshedpur - 831 007, 1998, pp. 137-142Conversion of natural resources throughwaste reduction at the processing stepby briquetting techniqueB.B. KALE, S.S. KULKARNI and A.N. GOKARNNational Chemical Laboratory , Pune 411 008ABSTRACTIndia is gifted by nature by way of large quantities of high grade nonfer-rous mineral resources like barite containing more than 90% bariumsulphate. The processing of barite to win chemicals from it requires itscarbotherrnic reduction at high temperatures being carried out in rotaryfurnaces. The powdered charge containing barium sulfide is prone to getdamaged due to reverse reaction caused by infiltered oxygen at the end ofreduction state. This hampers the yield of water soluble barium sulfide.The paper discusses about the means of achieving favourbale kineticsand high recovery of water soluble barium sulphide in the carbothermicreduction of barite at high temperatures. The reaction rate of reductionstep was enhanced many folds by using briquetting technique. Even withbarite containing large amnount of harmful impurites, the yield of bariumwas improved considerably on pilot plant scale, thus achieving betterutilisation of natural resoures such as barite and coke.Keywords : Barite reduction, Briquettes, Rate enhancement.INTRODUCTIONBlack ash process for barite ore (BaSO4) reduction by carbon is the key stepin processing of the mineral for winning various barium chemicals. The reduc-tion is generally carried out in oil-fired rotary kilns which is operated at hightemperatures of the order of 1100°-1250°C. Longer exposure of reduced bariteviz., BaS, to high temperatures makes it water insoluble, thus hampering theyield of barium 1'1. Besides, impurities such as iron oxide, alumina and silicapresent in barite form complexes and the barium losses as water insoluble com-plex accounts to the tune of 1 to 10 times of impurities present 121.137B.B. KALE, et_ al.Prevention of barium losses and for that matter the reduction in losses is thefirst goal of any barium chemical specialist. Towards this end Jagtap et. al. t3lattempted to bring about reduction in the temperature of black ash process byincorporating gasification catalysts in the carbon matrix. Nishev et. al. Hot sug-gested the treatment of barite with lime particles which keeps the barite contentsafe by preferably forming calcium silicates and ferrates. Another methodologyto tackle the problem of low yield is the use of calcium carbide as reducingagent 1st. Here the briquettes were made by using the industrial waste as binderand the cylindrical briquettes retained this shape even after exposure to hightemperatures. Lowering of the specific area of the reduced barite (BaS) to theharmful oxygen environment and proximity of both the solid reactants ensuredbetter reduction rate and higher content of water soluble barium sulfide in theblack ash. The aim of the present work has been to study the kinetics of thebriquetted charge for the carbothermic reduction of barite in laboratroy scaleand also to show with examples how the data can be incorporated on industrialscale.EXPERIMENTALBarite sample used in all the kinetic experiments was obtained from MIsKores (India) Ltd., Mumbai. The sample containing 96.0% BaSO4, 0.5% Fe,O2.0% SiO2 was sized into less than 250 um. As a reducing agent, industrial cokeof 353 p.m size supplied by the same firm was used.For laboratory experiments a tubular furnace made of 450 mm long and 75mm diameter mullite tube covered with kanthal winding was mounted verti-cally. The temperature of the furnace could be controlled by using chromel-alumel thermocouple sensor and a good temperature controller. For kinetic runs,tubular silica reactor made after fusing two tubes of 500 mm long and 15 mmdiameter and 500 mm long and 40 mm diameter was used. The reactor had a 15mm diameter quartz sintered disc at the central part. The reactor was placed inthe furnace in such a way that sintered disc portion was in the hot uniform tem-perature zone. A standard hydraulic press was used for pelletizing the powderedreaction mixture using a die-punch of 20 mm diameter.About 9.78 gm barite powder and 2.10 gm industrial coke which is about62% of standard stoichiometric amount for the system BaSO4+4C, along with abinder were mixed thoroughly and soaked with 4 to 5 drops of water. The reac-tion mixture was taken into the die-punch carefully. By applying a load of ltonne, 20 mm diameter pellets were prepared. Then the pellets were dried in ovenfor 3 hours at 120°C. The dried pellets were cooled and then used for reaction.138'PIRlq^l^^lri l iI ,It1^P^^^^l I'I'! F ^I fd1 I 1^I^M^' lll^'. ^BII'^1"III IIR^^111f11^I AliR^ ^l^^ r1111 , 111JillCONVERSION OF NATURAL RESOURCES THROUGH WASTE REDUCTION......Precisely weighed sample was placed in a silica sample holder [25 mm dia.and 17 mm height] and then introduced in a preheat zone of tubular reactormounted in the vertical furnace. After preheating to the desired temperature thesample pan was introduced in a central hot zone maintained at the desired tem-perature and zero time was noted. After stipulated time interval the reactioncould be stopped by removing the sample pan from the hot zone. The cooledsample was weighed, mixed properly and analysed for water soluble bariumsulfide (BaS) iodometrically. Runs were taken for powdered charge as well asbriquitted charge in the temperature range of 920° to 1000°C.RESULTS AND DISCUSSIONThe kinetic runs were carried out at temperatures 920°C, 960°C and 1000°Cusing barite ore both in powder as well as pellet form. The conversion time plotsfor powder form and pellet form are shown in Fig. 1(a) and Fig. l (b) respec-tively. The sigmoidal behaviour of the plots indicate the slow initial rate fol-lowed by accelerated rate and ending with deceleration. This kind of behaviouris generally observed in the reaction involving decomposition of solids and mostlygasification reactions. This typical trend can be attributed to the rate of CO gen-eration contributing mainly to the reaction rate. This fact is also clear from theobserved linear relationship between the fractional conversion of barium to bariumsulfide and weight of the reduced mass.To obtain the kinetic parameters, modified volume reaction model (MVR)developed by Kasaoka et. al. has been applied to the conversion. time data E63.The linearised equation for the MVR model can be written as,In [-In (1-x)] = In a+ b In 0 ... (1)where x is the fractional conversion, 0 is the time in minutes and a, b are modelparameters. For given x (fraction conversion), model plots were drawn as shownin Fig. 2(a) and Fig. 2(b) for powder and pellete forms respectively. Rate con-stants K were calculated and tabulated in Table 1. Here for conversion x,k(x) = a"h b[-In (1-x)] h-`mand for x;-- 0.5, Kavg = K a"' b(-In 2)h-lm(2)(3)From Table I it is observed that when the reaction mixture is in the pelletform the value of K are higher then in case of powder form. The reaction rate incase of pellet is higher because of the easy heat transferred in the pellet form anddue to perfect solid-solid contact between the reactants f". This helps in the en-hanced direct reduction between the carbon particles and sulphate although the139B.B. KALE, et, al.Table 1 : Kinetic runs of reduction of barite by industrial cokeTemperature Rate constant , k (sec-')cc Powder 20 mm dia pellet (load : I tonne)920 2.6532 x 10' 1.0098 x 10-3960 4.1478 x 10' 1.508 x 10.31000 5.2682 x 101 2.333 x 10-3major portion of the reaction is due to Bourdouard reaction. The CO, generatedgets reduced by carbon in the viscinity to from carbon monoxide which is re-sponsible for enhanced rate of reduction. The compact form of briquettes alsosupport the endothermic reduction reaction system by ensuring better heat transfer.Moreover, due to endothermic nature of reduction reaction, the temperature inbriquette never exceeds outside temperature and hot spot generation is preventedeven in the plant scale. The pellets were found to retain their shape and size evenafter reduction. This helps in protecting the inner portion of the reduced sampleTable 2 : Laboratory experiements with Barite briquettes.Charge composition (kg) : Barite-2400, Lecofines-250,LTC sludge-276, and binders : Briquette size = 25 nim dia.Run Wt. of Wt. of Time BaS BaS in BaCO3 Barite/No. charge product (hrs) Content product expected tonne(g) (g) ( %) (g) in product BaCO3(g) (kg.)1000 657.4 3 59.75 392.7 457.8 17472 1000 656.2 3 57.98 380.5 443.5 18043 1000 648.2 2 64.30 417.2 486.3 16454 1000 663 1.5 57.03 378.1 440.8 18155 1000 658.3 2 64.88 427.1 497.9 16096 3000 1969 2 62.48 1230.2 1434.1 16747 3000 2165 2 58.48 1266.1 1475.8 16268 61.1 40.4 2 63.67 25.72 29.99 16309 64.6 42.7 2 61.45 26.24 30.59 168910 54.3 36.2 2 59.03 21.37 24.91 174411* 3000 1960 2 54.35 1065.8 1241.9 193312** 686 468 2 48.65 227.6 265.3 2120Nitrogen flow absent** Powder charge1111RIN loll!1Fl9!^!I¶1 ! F^ ^ "1^4"I" ^'^IT3R^N1 PR I' r ur rfl lll^l mfrnjp^niq^I MR ARIIF^P IIRII1fIf11^ + M'AN+^IIIRAFIIF9N11 iCONVERSION OF NATURAL RESOURCES THROUGH WASTE REDUCTION......10080200 n0o) POWDER FORMTEMP.0 1000,CA 950 'C• 920 'C20 40 60T I ME,1(min)60 100 20 40 60TI ME, t (min)Fig . I : Conyercion-tune plots for reduction ofbarite b1• inudstr'ial carbon (62% stoichiometric).100.110TIME,e(min) 100 10TIME,6(min)Fig. 2: Model plots for reduction of bcn itc by industrial carbon (62% sroichioiiretric)_containing barium sulfide from the attack of oxygen infiltered into the system.This helps to arrest reverse reaction resulting in loss of barium sulfide. Thusenhanced rate of reaction observed in the particular system using briquettes hasbeen responsible in achieving higher extent of recovery of barium using samplefrom industries . Table 2 gives a comparative data of conversion efficiency of141B.B. KALE, et. al.powder and pellet form of reduction charge in the laboratory 111. Here lowergrade barite containing more impurities (SiO44.0%, Fe,O1 1.5% andBaSO4 93.00%)was employed. The briquettes were made by using a special binder system. Re-duction runs on laboratory scale indicate that with powder charge requirementof barite per tonne of barium carbonate is 2120 kg., while with pellet charge it is1719 kg., which itself shows a reduction of about 19% of barite requirement. Onthe plant scale we have achieved a much higher efficiency in the overall yield ofbarium (more than 25%) using the similar barite sample. As a conservative esti-mate the annual saving of barite will be about 6000 tonnes and also coke savingwill be of the order of 1200 tonnes.CONCLUSIONCarbothermic reduction of barite can be accomplished in a better way usingbriquitted charge. It has been shown that briquette configuration shows betterkinetics and can be applied advantageously on the plant scale also. This fact hasbeen shown clearly with examples in present work.REFERENCES[1] AN. Gokarn, A.R. Pande, S.S. Kulkarni, `Mineral Processing-Recent Advancesand Future Trends', S.P. Mehrotra and R. Kumar, Eds., Allied Publishers, NewDelhi, 1995, pp. 829-833.[2] K. Hargreaves and D.M. Murray, `J. Chemsitry Technology Biotechnology', 45,1989, pp. 319-325.[3] S.B. Jagtap, A.R. Pande and AN. Gokarn, `Ind. Engg. Chem. Res.', 29, 1990, pp.795-799.[4] M. Neshev, M. KheravimovaandT. Peshev, 'Gud. Nauch. Inst. Khim. Prom.', 8,1971,pp. 55-64.[5] M. Starczewski, O.M. Switonska and T. Greywaczwski, Eur. Pat. Appl. EP251,155, 1988.[6] S. Kasaoka, Y. Sakata, S. Kayano and Y. Masuoka, `Internat. Chem. Engg.', 23,1983, pp. 477-485.[7] Y.J. Hao and T. Tanaka, `Canadian Journal of Chem. Engineering', 66, 1988,pp. 761-766-[81 A.N. Gokarn, D.D. Ravetkar and S.S. Kulkarni, `Processing of Fines', P. Bhattacharyya,K.V. Rao and N.G. Goswami, Eds., NML & TIME, Jashedpur, 1997, pp. 266-272.142

Conversion of Natural Resources through

Waste reduction at the Processing Step

by Briquetting Technique

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Conversion of Natural Resources through Waste reduction at the Processing Step by Briquetting Technique

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