Steimour Rate of sedimentation concentrated flocculated suspensions of powders.pdf

8/13/2019 Steimour Rate of sedimentation concentrated flocculated suspensions of powders.pdf

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RATE OF SEDIMENTATIONConcentrated Flocculated Suspensions of Powders

HAROLD H . STEINOURPortland C emen t kssoc iation , Ch icago, 111.

Hates of sedimentation are reported for concerlIrateclflocculated suspensions of various finely divided solids,iucluding microscopic glass spheres. Most of these solidswere tested at more tha n one fineness. Each powder em -braced a wide range of partirle sizes and was tested at a

N THE second articlt. of this series I S ) 13quatiori 3 for rateof Sedimentation was shown to be applicable to concen-tra ted, flocculated suspensions of emery particles of prac ti-

cally uniform size. In the present article this rate equation isapplied to flocculated suspensions of powders which containedparticles of m any sizes, and were in this respect, more typ iral ofsuspensions in general.

IThe ra te equation is

(Eq. 3, 13)

This equation may b e re~ardc t l s a modification of one appliedby Powers (9) to the sedimentation of portland cement pastes.In the present studies it was developed first for nonflocculatedsuspensions, in which uniform-size particles were used in order toobtain uniform settlement. In : ac h suspensions of emery parti-cles, empirical constant wi s needed apparent ly because of liquidwhich remains with the particles during their fall; during sedi-ment,ation the main mass of liquid moves relative t o the parti-cles, but a quan tity of liquid equal to w/ 1 - wi) er uni t volumeof solid appears not to tak e part in this flow but to remain stag-nant a t th e surfaces of the angular particles. In the first articleof this series 12) wi as shown to be zero for nonflocculated sus-pensions of spheres; evidently the rounded surfaces did not keepan y of th e liquid ou t of the flow.

When concentrated suspensions of th e emery particles wereflocculated, Equation 3 13) was still found t o apply, but with ahigher value of ini. Apparently the conditions that control thera te of settl ement remained much the same as before; indeed,experiments indicated that the initial resistance to settlementremained wholly of viscous origin, an d th e appearance of the sus-pensions was con. tent wi th the assumption th at th e displacedliquid still flowed past th e individual particles. Th at is, there ap-peared to be no opportuni ty, such as occurs at ow concentrations,for the flow-to by-pass groups of particles.

To apply Equation 3 13) to powders containing particlcs ofmany sizes, V , s formulated as follows:

where u = specific surface value, sq. cm./cc calculated as ifeach particle were a sphere ha g same densityas particle and same rat e of fall when alone in alarge volume of viscous li uid. For uniform-sizeparticles it is equal to 3 7 ~ , here T is radius ofequal-set tling sphere. Numerical value of u isobtained from sedimentation analysis of a verydilute, nonflocculated suspension.

With V , calculated as in Equation 1 the application of Equa-tion 3 13) to flocculated mixtures of particles of various sizes

series of concentrations. A rate equat ion previously foundapplicable to flocculated suspensions of approximatelyuniform-size emery particles was, in general, supportedby the new data. The equation is shown to be compatiblewith Powers equa tion for portland cem ent pastes.

involves the assumption that the particles can be treated theSame as uniform-size particles having thc same value of u .

DESCRIPTION OF LOWDERS

Tu make the testing of Equation 3 (23) fairly thorough, pow-ders were used which differed in chemical composition, in fineness,an d in characteristic particle shape. These powders comprisedfive finenesses of ground glalis, two of microscopic glassspheres, three of burned shale, one of silica, an d two of lime-stone. The glass and burnet1 shale were ground in a laboratoryball mill. The spheres were made by feeding some of the groundglass into a blast lamp 10, 11). The silica and limestone werepurchased already ground. To obtain different finenesses, air-separat ion and mixing were employed in some cases. Micro-scopic examination 12 ) showed tha t the preparations of spherescontained relatively few particles tha t were not well shaped. Th eparticles of burned shal e werc shown t,o havc a comparativelyrough surface texture.

The values of u , th e specific surfaces of equivalent spheres,were determined from sedimentation analyses, essentially by theWagner turbidimeter method 1 4 ) , using the equipment specifiedfor testing cement (A.S.T.M. standard test (3115-42). All tur-bidimeter tt:sts were made in water, using a little sodium hexx-metaphosphate as dispersant. The size analyses were commonlycarried down only to a particle diameter of 5 microns, but thecontribution of the finer sizes to the value of u was estimated bya method devised by Dah1 5) . By this method a cubic equationis assumed to fit the size-distribution.curve below 10 microns.

Since u enters Equation 3 13) as a part of V,, its determina-tion by sedimentation analysis is wholly in accord with the theoryof th e equation. However, since th e sedimentation of a concen-ha te d suspension is in some respects similar to flow through a bedof partic les, specific surface values determined by the air per-meability method of Lea and Nurse (7) were obtained for com-parison with the u values. Indeed, since the glass spheres usedin this investigation varied somewhat in density because of en-closed gas, th e specific surfaces of both prepara tions were de-termined solely by this air permeability method; the methoddoes not require th at th e particles have the same density, and itseems to give th e ac tual specific surface of spheres (6, 12).

Table I shows the specific surface values obtained by each ofthe two methods, sedimentat ion and air permeability. Valuescalculated from air permeability tests (by the Lea and Nurseformula) are identified bysymbol So. ,411 values, whether of Soor u, are averages from two or more tests, except u for burnedshale 1 which is a selected result (4 above th e average) believedto represent the best-dispersed sample. Table I gives some ofthe data from the turbidimeter size analyses and values of wi

901


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902 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 36, No. 10

TABLE . PHYSICAL ROPERTIES F MATERIALSND VALUESOF w OBTAINEDNSEDIMENTATIONESTS

Particle Si zea, Cumulativeup to Particle Diam. of: Sp. Surface, w i in Sedi-

Grams/ 5 10 25 60 _ _ _ _ _q. Cm./Co. mentationDens-

itj,, -

Powder Cc. microns microns microns microns u SO* SO/U TestsGround glass 1 2 . 5 0 2 . 3 6 . 9 24 .0 80 .5 2615 3,290 1.25 0.170Ground glass 2 2. 50 2 . 4 8 . 7 27. 1 79. 2 2720 3,570 1. 31 0.195Ground glass 3 2 . 5 0 5 . 2 11.8 31 .6 83 .0 3610 4,040 1.12 0.175Ground glass 4 2 . 5 0 6 . 7 18.1 40.2 84 .9 4220 5,240 1. 24 0.190

Ground glaC 5 2.5 0 1 2 . 8 2 9 . 2 5 9 . 5 8 7 . 6 6700 7,500 1.16 0.185

Reading3 were taken with a mi-crometer microscope sighted on adisk float which rode a t t he sur-face of the suspension (9, I S )Flocculants were chosen accord-ing to the requirements of th eseveral powders and are given inTable 11. Waterwas thesuspen-

sion medium. The conditions ofGlass spheres 1 2 .35 . , , , . . . . . . . . . . . . . . . _ 2,980 (1.00) 0.100 sedimentation ensured laminarflow of the displaced water in a l llass spheres 2 2.32 , , . . . . . . . . . . . . . . . . 3,990 (1.00) 0.095cases as judged by comparisonurned shale 1 2.57 7.4 19.7 47.7 7 9.8 4710 9,130 1.94 0.315Burned shale 2 2.5 7 (11.3) (26. 6j (60.5) (89. 0) (6320) (11,160) (1.76) 0.31 2

Burne dshal e3 2.57 15.2 33.6 73.4 98.2 7940 13,200 1.66 0.315 with the work of Carman 4) n

The curves of height of susperi-Limestone 1 2.7 8 11.7 19. 0 36. 2 63. 2 6650 6,050 LO7 . . . ., Limestone 2 2.78 18.0 29. 4 54.6 82.9 8320 9,980 1.2 0 . . . . . . . sion against time were similar to

those obtained in the previousstudies of sized particles in t hatthe y exhibited a n initial straight-line portion followed by somerounding off, The coarser the

Silica 1 2. 65 1 2 . 7 22.1 44.9 8 2 . 9 5850 8,500 1. 45 0 .20 3 (lime) flow through granular beds.0.165 (dye)

Parentheses enclose values not obt ained by direct experiment. Burned shale 2 was a mixture of I and, 3.Glass spheres were not analyzed for size distribution, but microscopic inspections showed that particles variedwidely in sine.

Mean porositieswere: ground glass, ,0.49, except 0.52 for No. 5 ; spheres 1 and 2, 0.47 and 0.45, respectively; burn ed shale ,0.47; eillca, 0.49; limestones 1 and 2, 0.45 and 0.51, respectively.

* Porosity of tes t bed was sometimes varied in check tests, results of which were averaged.

which will receive attent ion la ter . All powders of a given ma-terial or ty pe are numbered in t he order of increasing fineness.

SEDIMENTATION TESTS

In t he sedimentation tests on the flocculated suspensions themixtures were stirred with an electrical mixer for at least 2 min-utes and were tested in a cylindrical jar 100 mm. in diameter,using dep ths of sample between about 30 and 60 mm. Previouswork had indicated th at wall effects do not significantly influencethe settlement a t the center of the vessel under these conditions.

100

90

8 0

-E 70

2

al---

60-c-? 50P

69S 40

8

5 30PB

v,

v

20

10

0

0 10 20 30 40 50

Time, (unitschoren to give same i n i t i a ls lope)

Figure 1. Sedimentation Curves for GroundGlass Powders 1 and 5 i n 0.25 Zinc Sulfate

Solution at B = 0.60

powder, the more dominant wasthe straig ht portion of t he curve. This is illustrated by Figure 1in which coarse and fine glass powders are compared by plottingso that the initial slopes of the curves are the same. In mostcases the curves ended rather abruptly, but a somewhat pro-longed slow final set tlement was characteristic of the silica powder(Figure 2 ) . Limestone 2 showed peculiar behavior; it s finenesswas about t he same as that of burned shale 3, but t he settlementwas much slower a t he same dilutions and continued for a long timeat a ra te tha t remained a large fraction of the initial rate (Figure3). The greater the dilution of suspensions of limestone 2, themore the curves tended to round over and to fail to show a longinitial straight-line portion, th e opposite of the usual tendency.

Rates of sedimentation calculated for the initial constant-rate periods are given in Table I1 together with the porositiesof the sediments and supplementary data .

RATES OF SEDIMENTATION

Figure 4 hows th e degree of conformity between Equati on 3of the second article 15) and the rate data from Table 11. Ifthe equation is applicable, the data for a set of tests in whirh

20 40 60 100 120

Time, minutes

Figure 2 Sedimentation Curve for Silica Powderin One-Sixth Sa turated Lime Water at e = 0.62

(Height of suspension, 57 Mm.)


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October, 1944 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 903

TARI,ET. SEDIMENTATIONF FLOCCULATED USPENSIONS T VARIOUSDECREES F DILUTIONFluidCon-tent, Settling%in Ra teTotal Cm.8'Vol. See.,

( x 102) x 108

Poros-i ty ofSedi-ment,

ofSettled

VOl.

Fluid Poros-Con- ity of

Test tent, Settling Settle- Sedi-NO. in Rate &, ment, ment,

(Chrq- Initial Total Cm./ of ofnologi- Height, Vol. Sec., Initial Settled

cal) Mm. 6 X 109 X 108 Height Vol.

Settle-ment,

InitialHeight

oTestNo.

(Chrynologi-

ta l)

51230478

81234567

123

54

179238456

101112

110

234

11135

614

78

129

10111213

234516789

781293456 '

7645819

1023

IiiitinlHeight,

Mm.Flocculant,of Water Wt.

Lime water,S H t d .

Flocculant,r i f Water Wt.

Zinc sulfat,e,0.26

Zinc sulfate,0 .25

Z i n c sulfate,0 .25

Zinc sulfate,11.25

Burned Shale 2, 26.0' C.

39.1 57.5 125 4.243.7 60.0 155 6 .04 5 . 1 02.5 193 7.8

40.2 07.5 351 11.840.3 70.0 445 15.540 .4 72 .5 579 20.246 .1 75.0 744b 25 .7

45.0 65.0 258 9.7

Burn ed Shale 3, 25.7' C.

Ground Glass 1 26.6' C.55.657.459.361.263.164 .565.566.4

56.456.658.560.662 .463.266.365.265 .865.867.6

53 .054.354.556.057.057.858.4

48.450.050.051.852.453.253.5

48.251.053.154.2

52.3

54.556.458.660.062.064.164.2

. .

. .

. .

. .

. .

12345078

3102I456789

11

1234507

1234507

2314

4

3125678

13456a

43.843.840.349.049.052.050.059 .0

52.55 2 . 555.05 7 . 557.500 .002 .505.0

8 . 49 . 1

11 .914.213 .717 .120.022.7

48.147 .848.950.550 .851 .852 .854.7

48.248.149.45 1 . 453 .154 .85 0 . 167 .9

47.949 .550.851 .401 . B

47.547.947.948.950 .851.052 .153 .555.055 .554.95 7 . 3

48.448 .150.452.05 4 . 355.0

54 .855.058 .35 8 . 759 .36 0 . 101 .201 0

33.236.236.737.940 .941.041.242.044.442.343.040.04 5 , 9

38 .138 .039 .740 .840.041.342 .342.042 .3

55 .556 .558.658.260 .059.900 .861.701.762 .3

(;ro und Glass 2, 20.1' C. 39.23 9 . 84 2 . 042.243.744 .444 .145.546.246.445.7

49.052.054.058.000 .504.068 .0

48.549.054.057 .061.064.567.0

46.245.046.047.0

57.5 70 2 . 457.5 78 2 . 060 .0 92 3 . 60 2 . 5 f 2 8 4 . 805 .0 150 0 .907.5 208 11.570 .0 281 11.170 .0 272 14.072 .5 370 19.775.0 507 26.975 .0 485 22.9

Lime s a t e r .satd.3.8

43.840 .349 .052.056.659.004 .0

52.552.5

5 7 . 500.002 .565.007.5

55 .0

680637843

10881360181023202930

8 . 38 . 0

11.112.014 .817 .120 .322.7

(;round Glass 3, 25.2' C.37 .4 52 .3 426 8 .43 9 . 4 54.7 527 10.341.4 56.9 689 12.3

41.4 50.9 030 1 1 . 444.0 59.4 906 15.6

Silica 1 24.0' C.

50 .0 199 6.458.0 254 7.900 .0 318 12.062.0 370 13.764 .0 470 10.36 0 . 0 576 19.568.0 701 23.0

Silica 1 24.0' C.

Lime water,satd.

Grou nd Glass 4, 25.7' C.

36.736.736.73 8 . 73 9 . 539 .543.240.049.0

02 .550.6

29.0

4 .74 . 14 . 07 . 08 . 58 .0

11.213.816.615 .822.423.9

ss 5, 24.6' C.

103 3.090 3 .8

113 4.3138 6.2154 7.0202 5.6

194 6 . 0242 11.2300 9.9310 9.3392 14.0533 18.4506 16.1679 23.2

56.0 228 14.858.0 258 16..100 .0 338 19.062 .0 422 21.204 .0 554 24.406.0 683 27.468.0 913b 31.1

Lime wnter,sat,d.

Silica 1 24.0' C.Ground Gla Gentian 0.01

violet 0.040.010.02

57.5 281 17.957.5 296 13.205.0 616 25.46 5 . 0 600 23.0

30 .7 50 .043.2 50.038 .8 52 .540.7 55.043.3 57.539 .7 57 .5

39.5 57.546.0 60.049.0 62.540 .3 02 .552.4 65.050.6 67.553 .9 67 .561.2 70.0

%tic sulfate,0 .25

Limestone 1, 25.2" C.

30 .4 55.0 112 5 . 5

30.2 57. 5 153 6.631.1 60.0 190 8.231.9 62.5 208 9.232.7 65.0 273 12.433.3 07.5 304 14.534 .1 70 .0 467 16.434.2 72.5 910 23 .0

Lime water,satd.

Limesto ne 2, 25.8' C.

38.2 05.0 35 . .31.7 05.0 33 . .32.5 67.5 54 . .33.0 70.0 50 . .34 .0 72 .5 90 . .46 .1 75.0 169 . .

Glass Spheres 1, 24.6O C.Lime water,

satd.inc sulfate,0 .25

I

231301391358486651797

10251074142118652550

6 . 55 . 99 . 2

11.56.9

11.014 .918.119 .122.024.725 .13 0 . 8

0 Sedimentation curve for thi s highly conce ntrated suspension was ex-ce tional in t hat the constant rate established initially changed abruptly toa her one. Channel ing was not observed and was im robable because ofthe %igh concentration. The curve was somewhat like tto se previously oh-tained with nonflocculated emery at high concentratio ns 1.3).

b Channeling observed.

Glass Spheres 2, 25.7' C.

25.625.026.020.027.829.230.632.234.0

40.04 0 . 042.545 .045.047.550.052.555.0

3 . 13 .34.67 . 07 .4

10.013.218 .122.2

only e has been varied should fall on a strai ght line for which

where the value of w ives the intercept of the line on t he -axis.The solid lines drawn through the dat a points in Figure 4 havethese theoretical slopes.

The graphs for ground glass and glass spheres (Figure 4) howgood agreement between the data points and the theoreticallines, except for glass spheres 1 a t high values of e. The lack ofagreement in t ha t case is similar to what was observed previously

13) a t high dilutions of emery powder. The exceptionally highpoints can be attributed to flow of liquid through fine channels

Burned Shale 1, 25.5' C.38.9 58.3 205 6.343.4 6 0 . 0 243 7.946 .0 62 .5 354 9 .944 .4 02 .5 333 10.344.9 65.3 442 13.347.1 65.3 447 13.545.2 07.5 593 17.045.6 70 .0 720 21.747 1 70.0 782 21.047 1 70 787 20.4

J,iine water,3atd.


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904 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 36, No. 10

developed in the floc structure because of the relatively low con-centrations of solid.

Fair agreement with the rate equation is shown by the graphfo; burned shale. At the lowest values of E the points are a littlehigh, but otherwise agreement is good.

6.4

5.6

4 8

e

A.oE

d 3.2a

VI*

2.4

xB2 1.6

0.8

a0 20 40 60 80 100 120 140

Time, minutes

Figure 3. Sedinientation Curve (Incomplete) forLimestone 2 in Tap Water at E = 0.125

(Height of auspension, 3 4 m m .

The tests on silica (Figure 4) agree in part with the theory.

However, the high point at B = 0.68 for a test in saturated limewater and most of the point>s or tests in one-sixth saturated limewater are not represented by the theoretical line. These excep-tions, like those for glass spheres 1, can he attributed to breaksin th e floc structure. If this is the correct explanation, the breaksevidently occur a t much lower values of B in one-sixth saturatedthan in saturated lime water, an indication that the particles cfsilica have less cohesion in the weaker solution.

The breaks in floc struc ture assumed here were not, in general,actual ly seen. Only in the tests in one-sixth saturat ed lime watera t E = 0.68 (and in a test on burned shale 2 a t E = 0.75) were dis-tinct channels detected. In contrast, Powers (9) nearly alwaysfound channels and boils in tests, on cement pastes when therates of sed imenta tion were too high to agree with his equation.This has also been the writers experience in testing cement

pastes. In suspensions in which channels are suspected but n otseen, the cohesion between particles may be weaker and mayresult in m any breaks but smaller, shifting ones.

At low fluid contents the rates of sedimentation of the silicawere nearly equal in the two different lime solutions, eventhough the differences in total settlement were pronounced(Table 11). Results of thi s kind had previously been obtainedby Powers 9). The floc structure is evidently weaker in thelower concentrations of flocculant, bu t this weakness does notappear to affect the rate significantly unless actual breaks de-velop in the structure.

It is not clear from Figure 4 whether the suspensions of lime-stone 2 are exceptions to th e theory, but obviously those forlime-stone 1 fail to conform. Apparent ly the nature of the floc struc-ture is not the same in all suspensions, a fact that has beenindicated also by tests with organic liquids which in some in-

stances have given unusual results 9) . Some suspensions seemt.o be too strongly flocculated for Equation 8 I S ) t o apply; insuch cases structural resistance may sometimes be involved.Certain other suspensions are apparently too weakly flocculateti-for example, the less concentrated suspensions of silica in onesixth saturated lime water. However, the fact that so many ofthe powders that have been investigated have settled in approxi-mate conformity to Equation 3 ( I indicates that the equationhas a considerable range of application (although only at concen-trations great enough to avoid channeling and t o permit of B con-t,inuous floc structure) .

EFFECT OF SPECIFIC SURFACE

Since u was varied widely, conformity of the experimentaldata t o Equation 3 of the second article 13) (with V 8 ormulatedas in Equation 1 of thi s paper) is support for the assumption tha tu has the effect indicated by the equation. To show more di-rectly th e degree of this support , straigh t lines representing thedata were first drawn on plots of [ (1 - e ) ] 3 us E without re-course to the theory. If these lines had conformed strictly to thet)heory, their slopes would have been given by Equation 2 which,b-ith V expanded, is:

Solved for u this becomes

(3)

if _ _ y(p - ) is designated by F. To show the degrcv~ ( 1 ~i)~(slope)3

to which the data conform to Equation 4, he experimental valuesof u are plotted in Figure 5 against F 1 / z calculated from thc:slopes and wi values found empirically from the plots of

[ (1 - ] 1 / 3 us e-1 oint for limestone 2 is not shown because its location was toouncertain. The single point for silica represents the tes ts insaturated lime water; the dat a for emery were obtained in p r pvious work I S ) . The solid line has the slope 0.35 required t)yEquation 4.

As was to be expected, the point for limestone is distant fromthe rest. Otherwise, the points are represented rather well bythe theoretical line. Thus, the use made of u in determinirip thorate of sedimentation seems justified.

The specific surfaces determined by the Lea and Kurse airpermeability method (designated XO s in Table I) are almplotted in Figure 5. Since tho points are widely scattered ant1cannot well be represented by any straight line through t heorigin, it is evident that So is, in general, unsuitable for use iiplace of u in Equation 3 I S ) . Whether this situation may bvaltered by recently suggested modifications 3, 6) of the Lea aridNurse method is not apparent from this study.

FACTORS AFFECTING w i

I n the formula for rate of sedimentation, as given by Equatioii3 (IS), the wi term differs from the others in not being determin-able at present except by actual sediment,ation tests on concen-tr at ed suspensions. The problem of prediction is complicated 1 )the increase in w caused by flocculation. When a powder is rv-active chemically, like portland cement, there are further com-plications. However, some qualitative inferences from presriit.dat a are possible.

From Table I, w for inert powders seems to show no pro-nounced change as the fineness is changed. -4lthough W i increasedwith the fineness of flocculated emery powders of practically uni-form particle size I S ) , inert powders that are not closely sizcdmay ordinarily show no such effect. Aqueous pastes of portlandcement show a consistent increase in the value of V i with in-rrease in fineness (Q), hut it nwms J)rObahl(~ hat this is rausctl


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October, 1944 I N D U S T R I A L

0.10

0.0s

0.ot

0 07

0.oc- , m

z

W

5 0 0:

0.01

0 0:

0 0:

0.01

0.K

0 07

0 06

0.05

0.04

0.03

0 02

0.01

?oo

R N D E N G I N E E R I N G C H E M I S T R Y 905

E

E E

Figure 4. [ Q l - e ) ] /a wvs e for Various PowdersThe solid lines conform to Equation 3 of the second article 1 3 ) .

F.l 0.2 0.3 0 4 0 5 0 6 0.7f

1)) u layer of hydrate formed over the grains when they are firstnuxed with water. An added layer should have the same elTecton w, s stagnant liquid; the greater the quantity per unit volumeof solid, th e greate r would be the value of w,. Hence, since thequantity would probably be approximately proportional to theq)ecific surface, w, ould increase with iacrease in fineness.

It is noteworthy that fair-sized values of wt were found neces-+iry in the rate equations for the flocculated glass spheres.Siiice the value of w, or nonflocculated spheres has been shownt o be zero l a ) , he d ata support th e previous evidence from testso i l emery (IS) that flocculation increases w,.

That the nature of the floccrilant r an affect the value of ID

in a flocculated suspension is evident from the fact that, for thesilica powder, the value was less when the flocculant was thedye than when it was saturated lime water.

COMPARISON WITH POWERS' EQUATION

This series of studies, f rom which Equation 3 IS) was de-veloped, was undertaken to help explain the sedimentation ofportland cement pastes, especially the significance of the w, erm

which Powers (9) found to be necessary in his rate equation forthe sedimentation of such pastes. The significance of wi waRgiven detailed consideration in the second article of the series(IS), and views advanced there have now received furthersupport. However, Equation 3 I S ) which embodies thoseideas differs somewhat from the Powers equation and, indeed,differs with respect t o t he use th at is made of wi. If wi actuallyhas the same significance for the cement pastes that it has beenconcluded to have for the other systems, then Equation 3 (IS)may be expected to be practically equivalent to the Powersequation within the range of conditions tha t prevail in the pastesThat there is approximate equivalence can be shown as followt::Powers' equation is.

(5)0.2 d P s - P / ) ( e - w d 3n u 2 ? 1 -


6/7

906

12

10

8

b

4

2

I

Vol, 36. No. 10N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

I I I

10 20 30

F T

20

18

16

14

12*

X

yo 10

8

6

4

2

20 300

F ?

Figure 5 . Respective 3Ierits of Specific: Surface Values, u and So, as Factorb i n the Rate EquationTo conform to the theory, the points should fall on one straight line through the origin (Equation 4) .

* Ground glass A Silica 0 Burned shaleGlass spheres A Limestone 0 Emery

where uu. = specific surface value, sq. cnl./cc., calculated asif the particles were spheres of the same densityas the particles and the same rates of fall atinfinite dilution except that particles smallerin dianieter than 7.5 microns are assumed tohave t,he average diameter of 3.75 microns(A.S.T.31. method C115-42). Ttic, :issumptionregarding the particles smaller in diameterthan 7.5 microns distinguishes u from the udefined previously; u is assumed to representthe equivalent-sphere surface rathcir closely.

In contrast with P o w r s equation, F:qnation 3 I S ) with V,expanded is:

Equating the two formulations of Q and solving for u u,, gives

u 1.109u w 1 - wz

~ E

The magnitude of t he ratio u/u, can be e\tablished a5 follow?Lea and Nurse (7) found that So/u averaged 1.22 for cement\They also found that So/u, ranged between 1.6 and 1.8. How-ever, in other investigations the ranges in So/u, have been 1.77-1.92, 1.70-1.99, and 1.70-2.00 1, 2 , 8). From these data antimuch additional unpublished work, a value of 1.85 appear3 to bereasonably representative of Sg,uwfor American cements. Com-hining the ratio of SO o uu with the ratio of SO o u, gives.

u / u U = 1.52 8 )

Equation 7 can then be solved for u nd the result is 0.27For cements, ut generally lie5 between 0.24 and 0.32, and the aver-

age is close t o 0.27; evidently Equat ion 6 is approximately v ah iunder average conditions. In general, however, the slopes ofthe data lines in plots of [ ( I - < ) ] 1 3 us. E should be in -pendent of the value of w if Equation 5 is correct, but shouldvary about 4 from the mean if Equation 6 is correct. SinwEquation 5 has been found applicable to cements, this mightbe thought t o rule out Eyuation 6, but the data for cement pare not sufficiently precise to justify such a conclusion. I t is be-lieved, therefore, that the ideas regardirig the nature of 713; I N Ithe effect of specific surface embodied in Equation 6, and itrequivalent, Equatio n 3 of the serond article I S ) , are appliczat~lto cmicnt pastes.

COh c 1.u SIOYS

The initial rates of sedimentation of highly concentrateil YIIS-1)ensions of th e materials investixat,cd, except, the limestonc:, :iprt:ofairly well with Equation 6 .

Comparison of specific surface values determined b y thtz :tirI)ermeabi lity method of Lea arid Nurse ( 7 ) with u values. n . ) i i t , l l: rehe specific surfaces of equivalent spheres as determined I J iedimentat,ion analysis, indicates th at the former arc di9tinc.tl (w suitable for use in the r a t e equation.

Comparison of Equation G with the equation developccl 11)Iowers (9) from studies on portland cement, indicates thitt t I ivt,wo should give approximately t he same rrsults for r x n ~ e i i tp:istes.

ACKNOW LEDGMEKT

Tlie writer was assisted a t different timeb by Lynn I 3mii?r,Richard G. Brusch, and Herbert IT. Schultz in t he expvrimcmt:ilwork reported in this article.


7/7

October, 1944 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 907

F

g =Q =

r =

Sa=

v, =

w i =9 =

E

P I =Pa =u =

YOMEhCLATURE_____g p s - ) cni.-2, in which wi and the slope are

q ( l - wi)Z(slope)3'determined experimentally from a plot of IQ 1 - )]* av s

acceleration of gravity, cm./sec.Qinitial rate of settlement of top surface of suspension, cm./

radius of a sphere, em.

specific surface of a powder as determined by air perme-

2g(p,- ), cm./sec. (velocity given by Stokes' law for a

dimensionless constaiit, experimentally determinedcoefficient of viscosity of a fluid, grams/(cm. X sec.), or

proportion of total volume of a sus ension occupied by

density of a fluid, grams/cc.density of a solid, rams/cc.specific surface va ue , sq. cm./cc., calculated as if each

particle were a sphere having same density as particleand same ra te of fall when alone in a large volume of vis-cous liquid; for uniform-size particles it, is equal to 3 / r

sec.

ability method of Lea and Nurse T), q. cm./cc.

162single particlr)

po1ses

liquid, analogous to porosity in bels of particles

vqD = specific surface value, sq. cm./cc., calculated the same asu except that particles smaller in diameter than 7.5microns are assumed t o have the average diameter of3.75 microns

LITEHA L I RE CI rEI)

(1) Bates, P. H., Proc. Am. Soc. T estCag,Mate~iuls, 1, 224-34 (194 1).(2) Blaine, R. L., A.S.T.M. Bull. 108, 17-20 (Jan., 1941).

(3) Blainc,R. L., in Rept. of Working Comm. on Fineness of A.S.T.M.Comm. C-1 on Cement: ASTM Bull . , 118, 31-6 (Oct. , 1942).(4) Carman, P. C., J SOC. hem. I d . , 57, 225-34T (1938).(5) Dahl, L. A., Portland Cement Bssoc. , unpublished work.(6) Keyes, W. F., to be published.(7) Lea, F. M., and Nurse, R . W., I Soc. Chem. l ,nd.+58, 277-83T

(8) Meyers, S. L., Rock: Products, 44 (l a) , 56-9 (1941).(9) Powers, T. C., Research Lab., Portland Cement Assoc., Bull. 2

(10) Sklarew, Samuel, IND. ENG. CHEM., N ~ L .D., 6, 152-3 (1934).(11) Sollner, K., Ibid., 11, 48-9 (1939).(12) Steinour, H . H., IND.ENG. HEM. ,6, 618-24 (1944).

14) Wagner, L. A., Proc. . 4 w SOC. Te s t i n g Materials, 33, Part 2,

(1939).

(1939).

(13) Ib id . , 36,840-7 (1944).

553-70 (1933).

Chemical Nature of RedwoodTannin and Phlobaphene

M. . BUCHANAN,H. . LEWIS,A N D E. F. K U RT H

The Znstitute of Paper Chemistry, A p p l e t o n , W i s .

HE wood of the redwood tree Sequoia eernperuirens) coii-tains a relatively high proportion of extractives, consisting

chiefly of tannin and a water- and ether-insoluble materialcalled phlobaphene. These extractives represent a potentialsource of valuable by-products and as such should be removedfrom the wood before it is converted into pulp or is used as astarting material for alcohol by the Scholler process. Certainother uses of redwood (Le., the manufacture of a plastic pulp)depend upon th e presence of these same materials. Therefore, aknowledge of the nature of these extractives is important in aprogram involving the utilization of redwood.

Redwood tannin is one of the many natural products whichhas the property of converting animal hides into leather. Thesetannins from various sources have different compositions. Then:ttural tannins may be classified as hydrolyzable tannins andphlohatannins 2, 4 , 6). Tannic acid is a well-known exampleof t h e first class; on hydrolysis with enzymes or mineral acids,

Tit yields glucose and gallic acid. The phlobatannins, in compari-son, when heated with dilute mineral acids, form insoluble con-

densation products which are called phlobaphenes. The phloba-tannins are built on the catechin model and, on alkaline fusion,yield a phenol and phenolic acid, or two different phenols.Thus, phlobatannins from several sources yield phloroglucinoland protocatechuic acid on alkaline fusion. Although thenatural tannins differ in composition, they all appear to containseveral phenolic hydroxyl groups. These groups are responsiblefor the solubility of the tannin in water and for the leather-mak-ing properties. Water-insoluble materia ls called phlobaphenesnormally occur in the wood Yith the phlobatannins. Little isknown concerning the true nature of these materials, but th ey aregenerally considered to be condensation products derived fromthe corresponding tannins by the elimination of water. Thenaturally orcurring phlobaphenes differ somewhat from those

_ _ ~ ~

Tannin an d phlobap hene have been isolated from redwood(Sequoia sempervirens), and their chemical nature hanbeen investigated. Both tannin and phlobaphene can beacetylated and methylated. The purified tann in contains2.8 methoxyl, 63.6 carbon, 5.6 hydrogen, 15.4phenolic groups, and 20.3 total hydroxyl groups; itstill contains 24 of material which is not adsorbed byhide powder but which contains approximately the samemethoxyl and total hydroxyl groups as the total fraction.Classification reactions show t hat the product is a phloba-tannin. The phlobaphene contains 6.9 methoxyl.66.8 carbon, 5.9 hydrogen, 10.1 phenolic groups,

and 13.7 total hydroxyl groups. The high methoxylcontent indicates that this fraction may contain some ace-tone-soluble lignin. Alkali fusion of both the tan nin andphlobaphen e yields only protocatechuic acid and catechol;the corresponding meth ylated prod ucts yield only veratricacid. Destructive distillation of phlobaphene yieldsCatechol and small amo un ts of phenol. Ultraviolet ab-sorption spectra for both tannin and phlobaphene aresimilar to those for mimosa tannin and alcohol-solublespruce lignin. Methylation with diazomethane does notcause any significant change in the ultraviolet absorptionspectra.

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