Iudlan JODrDalot ChemistryVol. 16A, AUIlDSt 1978, pp. 688·691

Viscometric Studies of Clay-Dye Suspensions: Viscosity Variations ofH-Bentonite-Anionic Dye (Solochrome Fast Navy 2RS &

Solochrome Black WDFA) SuspensionsS. K. SRIVASTAVA* & SATISH KUMAR

Chemistry Department, University of Roorkee, Roorkeeand

PUSHPATI RAZDANSoil Science and Chemistry Department, ·Himachal Pradesh University, Simla

Received 25 April 1977; revised 6 March 1978; accepted 14 April 1978

Viscosity variations of the aqueous suspensions of Hvbentonrte have been measured in thepresence of two anionic dyes, solochrorne fast navy 2RS and solochrome black WDFA. Visco.sity of clay suspension decreases considerably on the addition of solochrome dyes. A sharpfall in the initial stages of the dye addition is followed by a gradual decrease in viscosity whenlarge amounts of the dye are added. The effect is more pronounced in suspensions havinghigher clay concentrations. The results show effectiveness of these dyes as defloccularrt, Visco.metric constants, viz. intrinsic viscosity and interaction index, have been calculated with thehelp of Schulz-Blaschk equation and the axial ratios of the particles have been evaluated usingthe Kuhn equation. A sharp decrease in the intrinsic viscosity and axial ratio in the initialstages of dye addition and subsequently a minute change when more amount of dye is added isdue to the fact that once the system gets deflocculated completely a further addition of the dyewould not produce any change in the dissymmetry of the particles.

EARLIER investigators--P have found closeagreement between the viscometric, sedimen-tation and diffusion, electron microscope

and X-ray methods for evaluating the shape of smallparticles. Intrinsic viscosity has been reportedto be a function of the axial ratios of non-sphericalparticles and is thus an expression of particle shape.Packter-' examined the structure of numerous com-plexes of montmorillonite-carboxymethylcellulose byviscometric measurements and contributed signifi-cantly to this method. Van der Watt+ also utilizedviscometric measurements for the estimation ofthe shape and interactions of montmorillonite-vinylacetate-maleic anhydride complexes.

In an earlier communications, we have reportedthe sorption of two anionic dyes, solochrome blackWDFA and solochrome fast navy 2RS, on clays.In this paper we report the results of investigationson viscosity variations of clay-anionic dye suspen-sions. These investigations were undertaken tohave an idea of the shape of aggregates and theparticle-particle interaction forces existing in thesystem as well as the deflocculating effects of thedye.

Materials and Methods

Bentonite used in these investigations was obtainedfrom Ward's Natural Science Estt., USA. The

*Present address: Indian Cooperation Mission. Kathmandu(Nepal).

688

cation as well as anion exchange capacity of themineral was 95·00 and 5·90 meq(100 g of clay. Themineral was ground (200 mesh) and its surface areawas 234 m2(g. Benter ite was converted to hornoionicform by treating it with Amberlite IR-120 andIR-400 resins. The concentration of homoionic claywas determined by drying the sample in an ovenat 120° for a few hours.

Solochrome fast navv 2RS and solochrome blackWDFA were obtained" from ICI. Bombay. Thesetwo dyes were chosen after making some preliminaryinvestigations on a number of anionic dyes. Al-though the projected area of the dye molecules isnot known they seem to have a suitable moleculardimensions and geometry with respect to the edgesurface of clay particles". Apart from this the dyeswere also quite suitable for polarographic investi-gations", These dyes were recrystallized from 50%aq. ethanol and the resulting product dried oversilica gel and tested for purity by chromatography'.

The method employed for determining viscositywas devised by Scarpa" later modified by Farrow?and further improved by joshi-", The pH adjust-ments were made in a similar way (by mixing HCIor NaOH with clay suspension) as reported by Tali-budeen-! for such systems. All the measurementswere made at 300±0·5°. The following sets werearranged for viscosity measurements:

Varying amounts of solo chrome fast navy 2RS(5,0, 10'0, 15·0, 20'0, 25·0, 30'0, 35'0, 40'0, 45·0,meqj100 g clay) were added to a fixed concentration

SRIVASTAVA et al.: VISCOMETRIC STUDIES OF CLAY-DYE SUSPENSIONS

of clay suspension (0'5 %). Sets with above-men-tioned dye concentration were also prepared with0'7, 0,9 and 1,0% concentrations of clay. Similarsets were made with solochrome black WDFA.Viscosity variations of all the sets were observedat PH 3·0 and 9·0.

A falling head viscometer was used to make certainthat the concentrations of the clay-dye suspensionsmaintained in these studies are in a region ofNewtonian flow.

Results and DiscussionThe viscosities of bentonite suspensions against

concentrations of the two dyes at pH 3-0 and 9-0are plotted in Figs. 1 and 2.

Viscosity of the clay suspension decreases Con-siderably on the addition of solochrome dyes. Itis found that very small quantities of both the dyesde:flocculate the suspension showing that anionrather than cation is the important factor. A sharpfall (Fig. 1) in the viscosity of clay-dye suspensionat pH 3-0 is observed up to a point when 15-0 meq/100 g clay of solochrome fast navy 2RS is added.Thereafter the decrease is gradual. The breaks in the

curve are more sharp in suspensions having higherclay concentration. Similar behaviour is foundwith the other dye solochrome black WDFA. How-ever, with solochrome fast navy 2RS (Fig. lA, PH3-0) the curves have a different shape and exhibitdifferent slopes towards the end, specially whenhigher concentrations of the dye as well as clay areemployed. This is probably due to higher adsor-bability of this dye, with increasing dye con-centration, on the clay surface! as compared to theother one, and the fact that the effectiveness ofdefl.occulants in general is greater, the more con-centrated is the clay suspension.

In initial stages the dye added i!:'taken up at thepositive edge surface of clay particles. On furtheraddition, it seems likely that the polyanions areheld to the surface by physical adsorption in additionto anion exchange, resulting in defiocculation ofthe clay suspension. The zeta-potentials of theclay-dye suspensions are also found to be quite high.Similar behaviour has been reported by Worrall'",who observed the defl.occulating behaviour of sodiumsilicate, Calgon (sodium hexametaphosphate) andDispex (sodium polyacrylate) on clay systems.

A

~.~<:)q,.•..-c: ,~ 4.....•>,.~ t.co 3Q 3~s»~'l>.•..::s- 2()co,Q 2~

me,. of dye Soloch,.ome f(ls/ n(lvy 2RS (ldded/lfJO!clay (pHcs".O)

me,. of dye Soloch,.ome navy 2RS added /1009clay (pH-S.D)

l'ig_ 1- Plots ot absolute viscosity versus meq of solochrome fast navy 2RS added per 100 g of clay [Clay conc.: (1) 0·5;(2) 0·7; (3) 0·9; (4) 1-0%]

689

INDIAN J. CHEM.• VOL. 16A. AUGl.l'ST 1978

es

4

3

22

10.9

meq.of dye solocbrome block WJ)FAodtJed/lddJ mefl·of dye Solochrome hlack J¥/)FA (Jaded/100!clay (pll-=.3.0) clay (pH=9.0)

Fig. 2 - Plots of absolute viscosity versus meq of solochrome black WDFA added per 100 g of clay [Clay conc.: (1) 0·5;(2) 0·7; (3) 0·9; (4) 1-O%J

These compounds are found to be quite effectiveat low concentrations, even when there are notenough sodium ions present to replace the existingions on the clay surface.

These findings are also supported by the X-raymeasurements of the clay-dye complexes, reportedearlier by USI3, wherein a distinct increase in edgesurface spacing has been noted. By the additionof 20 meq/l00/g clay of the two dyes an expansionequivalent to 0·042 A for case of solochrome fastnavy 2RS and 0·049 A for solochrome blackWDFA in the edge surface of bentonite is observed-",

There is a considerable change in viscosity evenat pH 9,0 (Figs. 1B and 2B) by the addition of thesedyes, but the overall decrease in viscosity at thisPH is lesser as compared to PH 3·0. The numberof positive adsorption sites at the edge would beless at PH 9·0 (ref. 14) and so the small amount ofdye added is quite sufficient to neutralize the charge,thus creating the conditions of deflocculation andreducing the viscosity of the suspension to a largeextent. The large amount of the dye added

690

probably gets physically adsorbed without causinga further significant change in viscosity.

The viscosity of a dilute suspension during New-tonian flow depends on the shape, orientation, inter-action and hydrodynamics of the particles.

Schulze-Blaschke equation (1) has been used to

"f)'P/c = K["f)J"fJsp+ ["f)] .,. (1)determine the interaction index and intrinsic viscosityof the clay suspension. A plot of viscosity number('f)sP/c) versus specific viscosity ('f)ep) should be linearwith a slope equal to the product of interactionindex (K) and intrinsic viscosity ('f)) and an interceptequal to intrinsic viscosity ('f)). The values of thetwo viscometric constants calculated on the basisof these plots (not shown here) are given in Table 1.A decrease in intrinsic viscosity with a simultaneousincrease in interaction index (K) is observed withincreasing amount of dyes in clay suspensions. Theaddition of the dye results in an increase in eitheror both, the hydrodynamic and electrical inter-actions between the suspended units.

SRIVASTAVA et al.: VISCOMETRIC STUDIES OF CLAY-DYE SUSPENSIONS

diameter to the platelet lattice thickness's. Sincethe expression developed by Simha involves a com-plicated function, the axial ratio of the suspendedparticles were calculated by Kuhn's-? equation (2),"fJspfc = 2·5+U2jI6) ... (2)which expresses a much simpler functionaldependence between the specific viscosity andaxial ratios. The values of the axial ratio (j)calculated by Eq. (2) are given in Table 1. The Kuhnequation states that specific viscosity is constanttimes the concentration c, and so it can only be validfor clay-water system at infinite dilution and theaxial ratio calculated are those in which theviscosity number has been replaced by intrinsicviscosity. These axial ratios (Table 1) henceapply only to infinite dilution of the system anda decreasing order with increasing dye concentrationshows a decrease in the anisometry of the particlesor an approach to sphericity. A sharp decreasein the intrinsic viscosity and axial ratio in theinitial stages of dye addition and subsequently aminute change when more amount is added is dueto the fact that once the system gets deflocculatedcompletely a further addition of the dye would notproduce any more change in the dissymmetry ofthe particles.

References

TABLE 1 - VISCOMETRICCONSTANTSOF BENTONITE-SOLOCHROMEFAST NAVy 2RS, SOLOCHROMEBLACK WDFA

SUSPENSIONSAT DIFFERENT pH VALUES

Amount pH 3·0 pH 9·0of dye

K ]added TJsp K ] TJsp(meqfl00 g

clay)

BENTONITE-SOLOCHROMEFAST NAVy 2RS SUSPENSIONS

0 49·6 1-03 27'4 44-8 1-19 26·65 43'5 1·26 25·6 34·4 1'66 22·5

10 41'0 1·29 24'8 32'4 1'81 21·715 39·2 1·33 24·2 30·8 1'86 21·220 37·0 1'40 23-5 30·0 1·90 20'925 35'5 1'46 22·9 28·8 1'87 20·530 33·6 1-56 22·3 28·0 1·92 20·135 32·0 1'58 21·7 27'4 1·98 19·840 30·5 1·66 21·1 26·8 2·06 19·645 28'5 1·70 20·8 26·0 2·03 19'4

BENTONITE-SOLOCHROMEBLACK\VDFA SUSPENSIONS

0 49·6 1·02 27'4 42·0 1·37 25·05 32·0 1·77 21'5 29'6 1·96 20·8

10 27·2 2'10 19·8 28'4 HI 20·315 24·8 2·23 18'8 27'6 2'20 19'820 23·2 2·41 18·1 26·6 2·23 19·525 22-8 2·45 18·0 25'8 2·29 19·330 22·4 2·50 17·8 25·2 2·33 18·935 21-6 2·55 17·4 24·8 2-35 18·740 20'8 2·59 17-1 24·4 2·41 18·545 20·0 2·62 16·8 24·0 2·46 18·3

Considering that the edge double layer of the clayparticle is positive, the results can be explainedin terms of particle interaction forces and modesof particle association. In the presence of dyes,both the double layers are affected in a way thatthe positive edge to negative face attraction iseliminated, and a strong edge to edge and edge toface repulsion is created. Apparently the repulsiveforces dominate the forces of attraction in the cardhouse structure or double T arrangement of particlesand the floes become disengaged. Thus with theaddition of the dye the card house structure of theparticles in clay suspension breaks down to smallerunits of reduced dissymmetry.

According to Simha's-" the axial ratio of clayparticles is the ratio of their average surface

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