Indian Journal of Chemical Technology Vol. 5, July 1998, pp. 199-208

Effect of preparation conditions of Raney on its catalytic properties for slurry phase of o-nitrophenol to o-aminophenol

V R Choudhary'& M G Sane Chemical Engineering Division, National Chemical Laboratory, Pune 411 008, India Received 5 November 1997; accepted 10 June 1998

Influence of leaching conditions of Ni-Al alloy (50% AI) on the catalytic activity of Raney Nt (m the hydrogenation of o-nitrophenol at 308 K and H2-pressure of 1508 kPa) has been studied and optimum conditions for the preparation of Raney-Ni catalyst for the hydrogenation process have been obtained. The hydrogenation activity of Raney-Ni is found to be strongly influenced by its preparation conditions.

Catalytic slurry phase hydrogenation of 0• nitrotoluene over Raney-Ni prepared under nitrophenol using Raney Ni catalyst is an different conditions4 has indicated a strong important commercial process for the production influence of leaching conditions of Ni-Al (50%, AI) of o-aminophenol, an important intermediate for alloy (viz. type of alkali, concentration of alkali, drugs, dyes and pesticides. Nickel alloy temperature and duration of leaching, and the is commonly used for the preparation of Raney• washing agent (viz. tap water, distilled water, nickel. The alloy contains NiAI3, Ni2A13, and Ni3AI deionised distilled water, 50% ethanol and 95% phases 1.2 and the composition of these phases ethanol) used in the washing of the leached alloy depends on the alloy composition. The non• on the content and hydrogenation catalytic part of the alloy (i.e. AI) can be leached activity of Raney-Ni. out by hydrolysis with water, alkali or acid. The present investigation was undertaken to However, the leaching IS most commonly done by study systemati cally the effect of various alkali treatment. The catalytic activity of Raney preparation conditions of Raney nickel on the nickel is found to be strongly affected by leaching catalytic activity in the liquid phase hydrogenation conditions, viz. type of alkali used3.4, alkali of o-nitrophenol (ONP) to o-aminophenol (OAP) concentration4 , temperature4.5, duration of using methanol as a reaction media and arn ve at leaching4.6 and washing agent4. the optimum conditions for the preparation of The physico-chemical and surface properties of Raney-nickel catalyst giving maximum activity for Raney Ni, such as lattice parameters1, distributIon the hydrogenation process. This study was of hydrogen on the surfaceS, surface area4.9 crystal undertaken as a part of the development of Raney• size4, residual aluminium and hydrogen content4,9 Ni catalyst for the above process. are also strongly influenced by the conditions of Raney Ni preparation. It has been shown that Experimental Procedure Raney-Ni catalyst having its maximum activity for Preparation of Raney-Nickel Catalyst the hydrogenation of a substance has a definite The experimental setup for the preparation of crystal size characteristic of a substance, and hence Raney nickel is shown in Fig.I. It consisted of a it is impossible to prepare Raney nickel catalyst stirred jacketed reactor (made of stamless steel 15 which exhibits its highest activity to every cm diameter and 35 cm height), provided with a substance to. The effect of crystal size on catalytic cooling coil, a thermometer, H2 inlet tube and activity indicated that the activity is strongly provision for addition of the alloy. A known affected by the geometrical factors of the catalyst. volume of aqueous alkali solution (2000 cm\) was Earlier studies on the hydrogenation of p- taken in the reactor and maintained at the desired

* For correspondence temperature by circulating water having constant 200 INDIAN 1. CHEM. TECHNOL., JULY 1998

Type of alkali used :NaOH and KOH Concentration of alkali (NaOH) :1.25-20.00 mol dm-3 Leaching temperature :283-358 K Leaching time :1-12h Washing agents :tap water, distilled water, r deionised distilled water, CHILLED .ATER 50% ethanol and 95% ethanol. WATER JACKET

The temperature of the leaching could be ALKALI SOLUTION controlled within ±l dc. COOLIN8 COIL A number of Raney nickel catalysts were prepared by systematically varying one FLAT BLADE DISC TURBINE STIRRER preparation condition at a time while keeping all the other conditions the same. The catalyst prepared under different controlled conditions are listed in Table 1.

L WATER FROM CONSTANT TEMP. BATH Measurement of Properties of Raney Nickel Fig. I-Experimental set-up for preparation of Raney nickel. Residual aluminium in the catalyst -I

The residual aluminium in the Raney nickel temperature through the reactor jacket. The catalyst was determined by the method similar 'to solution was stirred at 1200 rpm and hydrogen gas that used by Schnyderl1• A known amount of (20-30 cm3 min-I) bubbled through it in order to catalyst about 3.0 g based on the weight was remove the dissolved oxygen. The hydrogen flow warmed with 10 cc of dilute hydrochloric acid was continued throughout the leaching period. (3M). After the complete dissolution of the When the temperature of the alkali solution catalyst, dilute ammonium hydroxide was added reached the desired value, a known amount of until the turbidity cleared and 1 or 2 drops of the Raney alloy (50 g, particle size: 30-60 1-1) was acid were added in excess. To the solution, 100 added to it in small portions in a period of 10 min. cm3 of 6% succinic acid solution, 10 g ammonium The reaction temperature was maintained by chloride and 4 g urea were added successively. The removing the exothermic heat of reaction by resulting solution was made upto about 400 cm3 adjusting the flow of the chilled water through the with distilled water. It was then boiled for 2 hand cooling coil. cooled to room temperature. The precipitate After the alloy was added for the period, the formed was filtered and washed with a 1% stirring was stopped and the catalyst particles were succinic acid solution neutralised by ammonium allowed to settle. The supernatant solution was hydroxide. The precipitate along with the filter removed by suction and the catalyst particles were paper was ignited at 1473 K in a platinum crucible washed with the desired washing agent and the residual alumina (AI203) was estimated (presaturated with hydrogen) at 303-308 K till free gravimetrically. The weight percent of the residual from alkali (as shown by litmus paper test). The aluminium in the catalyst was obtained as, duration of washing was 20-25 min. The catalyst was then stored under hydrogen atmosphere in the same liquid medium as that used for the washing. 26.97 x w x 100 The catalyst was subjected to the activity test Residual Al (wt %) = 101.04 X (w3 - w4) after the storage period of 45-50 h. The leaching and washing variables were, where, w is the amount of A1203 (g), W3 is the

'I ,. III I CHOUDHARY & SANE: EFFECT OF PREPARATION CONDITIONS OF RANEY-Ni ON ITS PROPERTIES 201

Table 1- Preparation conditions of Raney Nicke] catalysts

Volume of alkali solution - 2000 cm3, Composition of Raney Nickel alloy - Ni (50 wt %) - Al (50 wt %), Particle size of alloy (av) - 30-60 f.l, Amount of Raney alloy - 50 g, Stirring speed - 1200 rpm

Catalyst Concentration Temperature Time of Washing Storage of NaOH of Leaching Leaching agent Conditions mol dm-3 K h " """" " " Effect of alkali95%50%distilledHzDistilledDistilledwaterFilteredHzFiltereddeioniseddistilled313298328343358under1250%95%4268Stored atat 13136DeionisedStoredin2836Deionised ethanol room room Hz water tapin water temp.at deionised temp. under water room under under20.0010.0012.503.756.252.501.25 RN2 AllEffectRN21RN catalysts 222010 of alkali were concentration stored for 45-50RNEffect 151816 17h beforeof washing measuringEffectRN agent 1213]1 oftheir leaching catalyticEffectRN6RN7RN8RN periodRN4 activity. 5 of Temperaturetapdistilledethanolwater water roomtemperatureunderRNRN9 31914I temp. Hz at

weight of the wet catalyst, and W4 is the weight of Solid phase density (Ps)-The Raney nickel, water contained in the wet catalyst as determined along with methanol, was introduced in to the by the Karl Fisher method. The residual alumilJ.ium catalyst bulb by removing the cap of the Rotaflow was determined in the catalyst Rn-l, 14, 17 and 18 stopcock. The cap was replaced and the methanol prepared at different leaching periods. in the catalyst bulb was evaporated very carefully at room temperature by applying suction to the Solid phase and particle density and porosity of bulb. The Rotaflow stopcock was closed and the the catalyst apparatus weighed. This procedure was repeated These properties of the catalyst were determined till a constant weight was obtained. The graduated using the apparatus shown in Fig.2. tube was filled with up to the level 202 INDIAN J CHEM. TECHNOL, JULY 1998 marked A (Fig.2) and the reading A noted. Gas TO ATMOSPHERE bubbles, [1' any present in the liquid column, were t removed by applying a slight suction. The system was connected to atmosphere by the two way -- TO VACUUM stopcock. The liquid was introduced in the evacuakd catalyst bulb, the rota flow stopcock TWO WAY STOPCOCK closed and the reading of the liquid level B in the graduated tube noted. A similar experiment was performed without the catalyst. The \ olume of the solid phase of the catalyst could be obtamed as the difference between (A-B) withoUi catalyst and (A -B) with catalyst from whIch the solid phase density (pJ could be calculated (p, = weight of the catalyst/volume of s(,!;d phase of the catalyst). l'article density - For determining the particle B density, mercury was used instead of cyclohexane as it does not penetrate the pores at atmospheric pressure. In thIs case the difference between (A -B) without catalyst and (A -B) with catalyst gave the ioltlmc of the particles of the catalyst. The particle .Jemity could be calculated from thc catalyst weIght and the volume of its particles. Porosity- -It was obtained from the particle CATALYST BULB density and the solid phase density of the catalyst,

Fig.2~Apparatus for mcasuring solid phase and particle Purosl ty (£) = I-(p/ Ps) densitics of Raney Nickcl

Bulf.: density ---The bulk density of the catalyst \V.1> determllled by measuring the loss in 'Weight X-ray diffraction line broadening method due to evaporation of methanol under vacuum at described elsewhere 11. The values of surface area l\\UlI temperature. The evaporation was contmued and Gorystallitesize of the catalysts are included in t i1: a constant weight was obtained. Table 2. The results mdicate that the size of the Raney-Ni crystallite ll1crease very significantly with the increase in the leaching temperature and period. However, the surface area of the catalyst is affected by the change in the leaching parameters \VhU2, H'j IS weight of catalyst covered \vlth to a relatively small extent. The increase in the size I11clL.mol(g), W2 is weight of methanol (i.e. loss 1Il of nickel crystallites with no significant decrease \\ cighl due to evaporation, g) and Vb IS the volume in their surface area may be because of the 0111< catalyst in methanol (cm3). formation of cracks and/ or crystal defects. The morphology of the particles of the Raney-Ni Surface area and clystallite size catalysts was studied with a Cambridge steoscan

J le;,udace area of the catalyst was detem1ll1cd 150 model Scanning Electron Microscope. The us ng the method described by Smith Fuze k ;, nickel particles have rod-like shape and their size w!."h i.' based on the monomolecular adSOf\,I()'1 mcreases with the mcrease in the alkali of Jaunc acid from its solution I ;\c L'oncentration, temperature and period of leaching crystaline sIze of the catalysts was obtamed b\ f;:c in the catalyst preparation.

'1 I iii I CHOUDHARY & SANE: EFFECf OF PREPARATION CONDITIONS OF RANEY-Ni ON ITS PROPERTIES 203

Table 2-Properties of Raney Nickel catalysts prepared at different conditions

Catalyst" Concentration Leaching Leaching Surface Crystallite of NaOH tell)perature period area size mol dm-3 K h m2g-1 Dx108, cm

Effect of al/cali 313631331366 10.003136 20.003136 12.503136 10.006.252.503136 3.751.25313 (KOH) EffectRN2RN6RNRN7RN4RN5 8 of al/cali concentration RNRN3 I 600

61 127 58 134 65 109 70 83

Effect of leaching temperature RN 9 10.00 283 6 RN 10 10.00 298 6 64 104 RN 11 10.00 328 6 63 133 RN 12 10.00 343 6 59 171 RN 13 10.00 358 6 56 180 Effect of leaching period RN 14 10.00 313 I 61 114 RN 15 10.00 313 2 67 132 RN 16 10.00 313 4 66 RN 18 10.00 313 12 57 156

Catalyst washed with deionised water saturated with hydrogen and stored in deionised water under H2 atmosphere at room temperature

Measurement of Catalytic Activity the hydrogenation process was determined in an A number of Raney nickel catalysts were agitated three phase high pressure reactor (Parr prepared by substantially varying one preparation autoclave), using methanol as the reaction condition at a time while keeping all the other medium. The reactor (capacity : 2000 cm3, inside conditions same. The catalyst prepared under diameter: 10 cm and inside depth : 26.7 cm) was different controlled conditions are listed in Table made up of SS 316. It was provided with a gas 1. The catalyst was always kept under the liquid as inlet tube, a cooling coil, a stirrer, a thermowell, a it is extremely pyrophoric. For measuring the pressure gauge and a safety valve. The reactor can catalyst volume the required volume of catalyst be heated externally to a desired temperature by an was removed from the catalyst container and electrically heated oven. The exothermic heat of transferred to a 10 cm3 measuring cylinder. The the reaction could be removed by passing cooling catalyst was then washed with methanol till it was water through the internal cooling coil. Stirring is free from the liquid in which it was stored and achieved by a three blade stirrer situated at a allowed to settle. The measuring cylinder was distance of2.8 cm from the bottom of the reactor. tapped from time to time. The time allowed for A known amount of Raney catalyst (about 1.0 settling (20 min) and the tapping procedure were cm3 in methanol) was introduced in the reactor, exactly the same for all the catalysts. All the along with 200 cm3 of methanol. A solution of results are based on the dry weight of the catalysts, GNP (50 g in 800 cm3 of methanol) was then obtained from the knowledge of bulk density and transferred to the reactor. The reactor was then the volume of the catalyst used. closed by tightening the side flanges and was put The catalytic activity of Raney nickel catalyst in ,in the electrical oven. Nitrogen gas (free of 204 INDIAN 1. CHEM. TECHNOL., mLY 1998

0·7 Table 3- Initial hydrogen rate data for the catalysts prepared by leaching with aqueous alkali of different concentrations

0,6 Leaching conditions: Leaching temperature - 313 K, Leaching period - 6 h, Washing solvent - Deionised distilled water, Storage condition - Stored in deionised distilled water under Hz for 45-50 h. Catalyst Concentration of Initial reaction alkali rate mol dm-3 KOH (10 ••••.•• -~ (lit" I) roxl03, min-I RN 1 10.00 (NaOH) 7.33 RN2 10.00 (KOH) 3.80 RN 3 20.00 (NaOH) 1.84 0·1 RN4 12.50 (NaOH) 2.95 RN 5 6.25 (NaOH) 5.71 40 60 eo 100 '20 140 '60 180 RN 6 3.75 (NaOH) 9.80 TIME, min RN 7 2.50 (NaOH) 7.09 RN 8 1.25 (NaOH) 8.33 Fig.3- The activity curves (x versus t) for the catalysts prepared using different alkalies was initiated. The liquid samples were taken from ',0 time to time, while maintaining the H2 - pressure in the reactor constant. All the Raney-Ni catalysts were tested for their 0·, hydrogenation capacity under following . experimental conditions: Volume of reaction :1000 cm3 !•• 0·, a: ... mixture

U~ Initial concentration of ..J •• Z o-nitrophenol :0.36 mmol cm-3 o i= 0-4 ~ Catalyst loading :(1.03 + 0.62)xlO-3 g cm-3 f Reaction temperature :308 K H2 pressure :1508 kPa 0·2 Stirring speed :980 rpm Reaction time :3 h

140 Results and Discussion TIME. Mle, Effect of Type of alkali-The experimental data

Fig.4-- The activity curves (x versus t) for the Raney Nickel on hydrogenation with catalysts RNI and RN2 catalysts prepared using aq. NaOH of different concentration prepared by leaching the Raney alloy with aqueous (M = mol.dm-3) NaOH (10 M) and with aqueous KOH (10 M), respectively are plotted in Fig. 3. The values of the oxygen) was then passed through the reactor to initial reaction rates (ra) for these catalysts are remove the air from the reaction medium and from given in Table 3. The results (Table 3) indicate that the free space in the autoclave. After driving out the catalyst RNl (prepared by leaching with air from the reactor, hydrogen gas (>99.99%) was NaOH) has higher activity than the one prepared introduced in the reactor at atmospheric pressure by leaching with KOH. Fig. 4 shows that NaOH is and the reactor was flushed with H2• As soon as the superior to KOH for preparing active Raney nickel temperature of the reaction mixture attained a catalyst by the alkali leaching process. This desirable value (i.e. 308 K), the reactor was observation is constant with those of Csuros and pressured to 1508 kPa of hydrogen and the stirring Petr03 and Choudhary et at. 4.

II I II ~ Iii 1"ifl~1 II 'I I" I I I CHOUDHARY & SANE: EFFECT OF PREPARAnON CONDITIONS OF RANEY-Ni ON ITS PROPERTIES 205

Table 4- Initial hydrogenation rate data ofthe catalysts prepared by leaching at different temperatures Leaching conditions: Concentration ofNaOH - 10.0 mol dm-3, Leaching period - 6 h, Washing solvent - Deionised distilled water, Storage conditibn - Stored In deionised distilled water under H2 for 45-50 h. Catalyst Leaching Initial reaction Temperature rate K ro x103, min-I RN9 288 3.78 5 S 7 • fl tS tS .? 1_ RN 10 298 7.14 COlICDITIlA~ lII' _ , _ .• -, RN I 313 7.33 Fig.5-Dependence of the initial rate (r.) for the RN II 328 3.78 hydrogenation of o-Nitrophenol on the concentration of alkali RN 12 343 9.13 (NaOH) used in the preparation of Raney-Nickel catalyst. RN13 358 12.70

',0, Table 5-lnitial hydrogenation rate and residual aluminium content of the catalysts prepared by leaching for different periods Leaching conditions: Concentration ofNaOH - 10.00 0,' mol.cm-3, Leaching temperature - 313 K, Washing solvent • Deionised distilled water, Storage condition - Stored in deionised distilled water under H2 for 45-50 h. . Catalyst Leaching Residual Initial reaction rate § 0,6 period aluminium roxl03, min-I " content >•• ~u wt% c-' ~ RNI4 63.487.33123.267.2012.703.4043.734.0583.36 I4.73 ~ 0·4 ~ RNRN 171618 I "..

of catalytic activity with alkali concentration employed in the catalyst preparation seems to be quite complex. Results indicate that the catalyst with maximum activity for hydrogenation is Fig.6- The activity curves (x versus t) for the Raney nickel obtained by using 3.75 M aqueous NaOH in the catalyst prepared at different leaching temperatures. leaching process. At lower catalyst concentration (1.25 M NaOH) Effect of Alkali Concentration-The the catalyst produced did not settle immediately, hydrogenation activity curves (xvst) for the hence washing became difficult and the catalysts prepared by leaching with aqueous NaOH supernatant liquid was blackish. of different concentrations (1.25-20.00 M) are Effect of leaching temperature -The x vs t presented in Fig.4. The values of initial reaction curves for the catalysts prepared at different rates are included in Table 3. The results clearly leaching temperatures (288-358 K) are presented indicate a strong dependence of catalytic activity in Fig.6 and the values of the initial reaction rates of Raney Ni on the concentration ofNaOH used in are presented in Table 4. The variation of the its preparation. initial reaction rate with leaching 'temperature Fig.5 shows that the catalytic activity passes employed in the catalyst preparation is shown in through a maxima (at 3.75 M NaOH) and then Fig. 7. It may be noted from Fig. 7 that the initial decreases with concentrations of NaOH..Variation reaction rate passes through a maximum (at 308 K) 206 INDIAN 1. CHEM. TECHNOL., JULY 1998

14 12

12 '-0 '0 •.. III .•. ~ ~ I 10 ~ Ii c •.... 'c: u o E ZI :; 41 ••~ 8 )• -~. III o 4-0 Z .. C 4 o II: ~ 6 ! C 2 273 293 313 333 ~ 4 :)c LEACHING TEMPERATURE, K Q iii III II: (r 2 ],0 Fig.7-Dependence of the initial rate J for the o 2 4 6 8 '0 12 hydrogenation of -o-nitrophenol on the leaching temperature LEACHING PERIOD, II employed in the preparation of Raney nickel catalyst. Fig.9-Dependence of the initial rate a (ro) for the 0,' hydrogenation of o-Nitrophenol and the residual aluminium in the catalyst on the leaching period employed in the catalyst preparation.

O'T leaching for different durations are presented in Fig. 8. The values of initial reaction rate and residual aluminium content for the catalysts are given in Table 5. It may be seen that the amount of residual aluminium in the catalyst decreases with the increase in the leaching period. Dependence of the initial reaction rate for hydrogenation and residual aluminium in catalyst on the leaching period is shown in Fig. 9. On enhancing the duration of leaching from 1-12 h, the catalytic activity passes through a maximum

60 100 140 160 for leaching period of 8 h. It has also been TIME ••••••• observed earlier6 that prolonged leaching leads to less effective catalysts. Crystal size of the catalyst Fig.8- The activity curves (x versus t) for the Raney nickel increases 10 with leaching time, and this trend is catalysts at different leaching periods. accelerated when the temperature is increased. Effect of washing agent-Activity curves (x and a minimum (at 328 K) with increase in the versus t) for the catalysts prepared at the same leaching temperature from 288 to 358K. The leaching conditions but washed with different catalyst prepared at leaching temperature of 358 K washing agents after leaching are presented in showed maximum activity during hydrogenation. Fig.10. The values of the initial reaction rate for The catalyst prepared at lower leaching the catalyst washed with different solvents and temperature (288 K) does not settle immediately stored in respective solvents for 45-50 h under H2 and hence washing is difficult. However, the atmospnere are presented in Table 6. catalyst prepared at higher leaching temperature (> Results indicate that the activity of the Raney 358 K) were found to be agglomerised to a large nickel catalysts (prepared at the same leaching extent. conditions) depends strongly on the kind of solvent Effect of leaching period-The activity curves (x used for its washing. Washing with deionised versus t) for the catalyst prepared by carrying out distilled water leads to the catalyst with the

iii I CHOUDHARY & SANE: EFFECT OF PREPARATION CONDITIONS OF RANEY-Ni ON ITS PROPERTIES 207

Table 6--Initial hydrogenation rate data for the catalysts washed by different solvents after their preparation by leaching

Leaching conditions:_Concentration of NaOH - 10.0 mol dm-3, Leaching temperature - 313 K, Leaching period - 6 h.

Catalyst Washing agent Catalyst storage Initial reaction rate conditions roxlO3, min-I RN I Deionised distilled Deionised distilled 7.33

water water under H2 RN 9 Filtered tap water Filtered tap water under H2 1.40 RN 20 Distilled water Distilled water under H2 6.00

RN 21 50% Ethanol 50% Ethanol under H2 1.70 RN 22 95% Ethanol 95% Ethanol under H2 1.9 (i) Catalysts stored for 45-50 h, (ii) The pH of the distilled water and the 'deionised distilled water was 5.5 and 6.7 respectively. The dilution of ethanol was done by the deionised distilled water.

Duration ofleaching :8 h 0,7 Washing agent :deionised distilled water 0·, DIIONIIED WATER .RII t I The optimum conditions for preparation of the catalyst are expected to vary depending upon the organic compound to be hydrogenated, as the catalyst has definite crystal size that is characteristic of the substance. In case of hydrogenation of p-nitro toluene with a Raney nickel catalyst the optimum preparation conditions for the catalyst giving maximum activity were found to be quite different. Properties of the Raney-Nickel catalyst prepared under the aforesaid optimum conditions are,

40 10 .0 tOO \10 140 110 TlIII, ••• Solid phase density (Ps) :8.10 g cm-3 Particle density (Pp) :332 g cm-3 Fig.1 {}-Activity curves (x versus t) for the Raney nickel Porosity (c) :0.59 catalyst with different washing agents after leaching at the same conditions. Bulk density (A) :1.04 g cm-3

The initial hydrogenation rate for the catalyst maximum activity. The activity of the catalysts prepared under the optimum conditions was found obtained by using different washing agents is of to be 18.5xl0-3 min-I• the order : Deionised distilled water > distilled water> 95% ethanol>j 50% ethanol> filtered tap water. References Optimum Conditions for preparation of the I Taylor, A & Weiss,J, Nature. 141 (1938) 1055. catalyst for the hydrogenation of ONP to OAP• 2 Freel, J, Pieters, W J M & Anderson, R B, J Catal, 16 (1970) 281. Based on the above study the optimum conditions 3 Csuros, Z & Petro J, Acta Chem Acad Sci (Hung), 17 for preparation of the catalyst with maximum (1758) 289 (English). activity (from the Raney alloy containing Ni 50 4 Choudhary, V R, Chaudhari, S K & Sane M G, Advances (wt %) - Al 50 (wt %) for the hydrogenation in Catalyst-Science and Technology, edited by Prasada processes were found to be, Rao T S R, (Wiley Eastern Ltd., New Delhi), 1985, 171. 5 Kagan, A S, Kagan, N M, UI'yomov, G D & Mirnov, L G (USSR) Zh Fiz Khim, 47(7) (1973) 1729. Concentration of alkali :3.75 M NaOH 6 Petrov, B F & Fasman, A B, Zh Prikl Khim 47(4) (1974) Leaching temperature :358 K 496 (Russ). 208 INDIAN J. CHEM. TECHNOL., JULY 1998

7 Davtyan, 0 K, Misyuk, E G & Makordei, R I, 11 Schnyder, A, Diss£rtation (Polytechnique Institute of Electrokhimiya, 7 (11) (1971) 1595 (Russ). Brooklyn) 1962. 8 Yakubunok, E F, Podvyazhin;Yu A & Yuekelison,I I, Zn 12 Smith, H A & Fuzek, J E, JAm Chem Soc, 68 (1946) 229. Prikl Khim 42(11) (1969) 2605 (Russ). 13 Klug, H P & Alexander, L E, in X,ray diffraction 9 Ishikawa, J, Nippon Kagaku Zasshi, 81 (1960) 1629. procedure for polycrystalline and amorphous materials 10 Ishikawa, J, Nippon Kagaku Zasshi, 82 (1961) 135. (John Wiley and Sons, Inc, London) 1954,491.

III I , 'I